Cardiac performance: growth hormone enters the race.

It is possible that growth hormone can offer therapeutic benefits for treating some forms of heart failure.

Effects of a nutraceutical combination (berberine, red yeast rice and policosanols) on lipid levels and endothelial function randomized, double-blind, placebo-controlled study.

BACKGROUND AND AIMS: Some nutraceuticals are prescribed as lipid-lowering substances. However, doubts remain about their efficacy. We evaluated the effects of a nutraceutical combination (NC), consisting of 500 mg berberine, 200mg red yeast rice and 10mg policosanols, on cholesterol levels and endothelial function in patients with hypercholesterolemia. METHODS AND RESULTS: In this single centre, randomized, double-blind, placebo-controlled study, 50 hypercholesterolemic patients (26 males and 24 females, mean age 55±7 years, total cholesterol 6.55±0.75 mmol/l, BMI 28±3.5) were randomized to 6 weeks of treatment with a daily oral dose of NC (25 patients) or placebo (25 patients). In a subsequent open-label extension of 4 weeks, the whole sample received NC. The main outcome measure was decrease total cholesterol (C) levels in the NC arm. Secondary outcome measures were decreased low-density lipoprotein cholesterol (LDL-C) and triglyceride levels, and improved endothelial-dependent flow-mediated dilation (FMD) and insulin sensitivity in relation to NC. Evaluation of absolute changes from baseline showed significant reductions in NC versus placebo for C and LDL-C (C: -1.14±0.88 and -0.03±0.78 mmol/l, p<0.001; LDL-C: -1.06±0.75 and -00.4±0.54 mmol/l, p<0.001), and a significant improvement of FMD (3±4% and 0±3% respectively, p<0.05). After the extension phase, triglyceride levels decreased significantly from 1.57±0.77 to 1.26±0.63 mmol/l, p<0.05 and insulin sensitivity improved in a patient subgroup with insulin resistance at baseline (HOMA: from 3.3±0.4 to 2.5±1.3, p<0.05). No adverse effect was reported. CONCLUSIONS: This NC reduces cholesterol levels. The reduction is associated with improved endothelial function and insulin sensitivity.

Growth hormone and the heart.

GH exerts direct effects on myocardial growth and function. Evidence from laboratory models shows that GH (or IGF-I) induces mRNA expression for specific contractile proteins and myocyte hypertrophy. Furthermore, GH increases the force of contraction and determines myosin phenoconversion toward the low ATPase activity V3 isoform. These data provide plausible explanations for the cardiac abnormalities observed in clinical settings of excessive or defective GH production. In acromegaly, the functional consequences of GH excess initially prevail (hyperkinetic syndrome), followed by alterations of cardiac function when myocardial hypertrophy develops. This involves both ventricles and is purposeless because it occurs without increased wall stress. Hypertrophy also entails proliferation of the myocardial fibrous tissue that leads to interstitial remodeling. The functional consequence is an impaired ventricular relaxation that causes a diastolic dysfunction, followed by impairment of systolic function. In untreated disease, cardiac performance slowly but inexorably deteriorates and heart failure eventually develops. Several lines of evidence support the specificity of heart disease in acromegaly. Particularly demonstrative are the recent studies in which GH production was suppressed by octreotide, with a consequent significant regression of hypertrophy and improvement of cardiac dysfunction. It is not yet established whether full recovery of normal cardiac morphology and function is possible after correction of GH excess. The point is not a minor one since the possibility to revert, albeit partially, myocardial fibrosis is of great relevance to the control of cardiac hypertrophy in general. GHD leads to a reduced mass of both ventricles and to impaired cardiac performance with low heart rate (hypokinetic syndrome). These alterations are particularly evident during physical exercise and might provide an important contribution to the reduced exercise capacity of GHD patients, in addition to the reduced muscle mass and strength. The data also support a role of GH in the maintenance of a normal cardiac structure and performance. The hypokinetic syndrome is well documented in young patients in whom GHD began very early in their childhood. In contrast, the data in adult-onset GHD are less consistent. This suggests that the consequences of GHD are more relevant if the disorder starts during early heart development. As observed with other abnormalities associated with GHD, cardiac dysfunction is also susceptible to marked improvement by hrGH. This observation lends further support to the proposal to treat these patients with replacement therapy.

Synergistic interactions of physiologic increments of glucagon, epinephrine, and cortisol in the dog: a model for stress-induced hyperglycemia.

To evaluate the role of anti-insulin hormone actions and interactions in the pathogenesis of stress-induced hyperglycemia, the counterregulatory hormones, glucagon, epinephrine, and cortisol were infused alone as well as in double and triple combinations into normal conscious dogs in doses that were designed to simulate changes observed in severe stress. Infusion of glucagon, epinephrine, or cortisol alone produced only mild or insignificant elevations in plasma glucose concentration. In contrast, the rise in plasma glucose produced by combined infusion of any two counterregulatory hormones was 50-215% greater (P < 0.005-0.001) than the sum of the respective individual infusions. Furthermore, when all three hormones were infused simultaneously, the increment in plasma glucose concentration (144+/-2 mg/dl) was two- to fourfold greater than the sum of the responses to the individual hormone infusions or the sum of any combination of double plus single hormone infusion (P < 0.001). Infusion of glucagon or epinephrine alone resulted in a transient rise in glucose production (as measured by [3-(3)H]glucose). While glucagon infusion was accompanied by a rise in glucose clearance, with epinephrine there was a sustained, 20% fall in glucose clearance. When epinephrine was infused together with glucagon, the rise in glucose production was additive, albeit transient. However, the inhibitory effect of epinephrine on glucose clearance predominated, thereby accounting for the exaggerated glycemic response to combined infusion of glucagon and epinephrine. Although infusion of cortisol alone had no effect on glucose production, the addition of cortisol markedly accentuated hyperglycemia produced by glucagon and(or) epinephrine primarily by sustaining the increases in glucose production produced by these hormones. The combined hormonal infusions had no effect on beta-hydroxybutyrate concentration. It is concluded that (a) physiologic increments in glucagon, epinephrine, and cortisol interact synergistically in the normal dog so as to rapidly produce marked fasting hyperglycemia; (b) in this interaction, epinephrine enhances glucagon-stimulated glucose output and interferes with glucose uptake while cortisol sustains elevations in glucose production produced by epinephrine and glucagon; and (c) these data indicate that changes in glucose metabolism in circumstances in which several counterregulatory hormones are elevated (e.g., "stress hyperglycemia") are a consequence of synergistic interactions among these hormones.

Influence of continuous physiologic hyperinsulinemia on glucose kinetics and counterregulatory hormones in normal and diabetic humans.

The effects of continuous infusions of insulin in physiologic doses on glucose kinetics and circulating counterregulatory hormones (epinephrine, norepinephrine, glucagon, cortisol, and growth hormone) were determined in normal subjects and diabetics. The normals received insulin at two dose levels (0.4 and 0.25 mU/kg per min) and the diabetics received the higher dose (0.4 mU/kg per min) only. In all three groups of studies, continuous infusion of insulin resulted in an initial decline in plasma glucose followed by stabilization after 60-180 min. In the normal subjects, with the higher insulin dose there was a fivefold rise in plasma insulin. Plasma glucose fell at a rate of 0.73+/-0.12 mg/min for 45 min and then stabilized at 55+/-3 mg/dl after 60 min. The initial decline in plasma glucose was a result of a rapid, 27% fall in glucose output and a 33% rise in glucose uptake. Subsequent stabilization was a result of a return of glucose output and uptake to basal levels. The rebound increment in glucose output was significant (P < 0.05) by 30 min after initiation of the insulin infusion and preceded, by 30-45 min, a significant rise in circulating counterregulatory hormones. With the lower insulin infusion dose, plasma insulin rose two- to threefold, plasma glucose initially fell at a rate of 0.37+/-0.04 mg/min for 75 min and stabilized at 67+/-3 mg/dl after 75 min. The changes in plasma glucose were entirely a result of a fall in glucose output and subsequent return to base line, whereas glucose uptake remained unchanged. Plasma levels of counterregulatory hormones showed no change from basal throughout the insulin infusion. In the diabetic group (plasma glucose levels 227+/-7 mg/dl in the basal state), the initial rate of decline in plasma glucose (1.01+/-0.15 mg/dl) and the plateau concentration of plasma glucose (59+/-5 mg/dl) were comparable to controls receiving the same insulin dose. However, the initial fall in plasma glucose was almost entirely a result of suppression of glucose output, which showed a twofold greater decline (60+/-6%) than in controls (27+/-5%, P <0.01) and remained suppressed throughout the insulin infusion. In contrast, the late stabilization in plasma glucose was a result of a fall in glucose uptake to values 50% below basal (P < 0.001) and 39% below that observed in controls at termination of the insulin infusion (P < 0.01). Plasma norepinephrine and glucagon failed to rise during the insulin infusion, whereas plasma epinephrine, cortisol, and growth hormone rose to values comparable to controls receiving the same insulin dose. It is concluded that (a) in normal and diabetic subjects, physiologic hyperinsulinemia results in an initial decline followed by stabilization of plasma glucose despite ongoing infusion of insulin; (b) in the normal subjects, a rebound increase in glucose output is the initial or principal mechanism counteracting the fall in plasma glucose and occurs (with an insulin dose of 0.25 mU/kg per min) in the absence of a rise in circulating counterregulatory hormones; (c) in diabetics, although the changes in plasma glucose are comparable to controls, the initial decline is a result of an exaggerated suppression of glucose output, whereas the stabilization of plasma glucose occurs primarily as a consequence of an exaggerated fall in glucose uptake; and (d) failure of plasma norepinephrine as well as glucagon to rise in the diabetics may contribute to the exaggerated suppression of glucose output.

Differential roles of splanchnic and peripheral tissues in the pathogenesis of impaired glucose tolerance.

To identify the mechanism(s) of the altered glucoregulatory response to a glucose load in subjects with impaired glucose tolerance, we selectively quantitated the components of net splanchnic glucose balance, i.e., splanchnic glucose uptake and hepatic glucose output, as well as peripheral glucose uptake, by combining [3-3H]glucose infusion with hepatic vein catheterization. After intravenous glucose infusion (6 mg X kg-1 X min-1 for 90 min), blood glucose rose to 172 +/- 7 mg/dl in controls and 232 +/- 13 mg/dl in subjects with impaired glucose tolerance (P less than 0.01). The response of plasma insulin did not differ significantly between the two groups (29 +/- 4 vs. 40 +/- 10 microU/ml at 90 min in control and in glucose intolerant subjects, respectively; P = NS). In both groups, glucose infusion caused the net splanchnic glucose balance to switch from the net output of the basal state to a net glucose uptake. However, this effect was more marked in subjects with impaired glucose tolerance than in control subjects (at 90 min: 2.83 +/- 0.53 vs. 1.60 +/- 0.18 mg X kg-1 X min-1, respectively: P less than 0.05). The different pattern of splanchnic glucose balance was entirely accounted for by a greater rise in splanchnic glucose uptake in the group of glucose intolerants , as the suppression of endogenous glucose output by the glucose load was practically complete in both groups. In contrast, glucose uptake by peripheral tissues increased considerably less in subjects with impaired glucose tolerance than in controls (2.2-2.6 vs 3.6-4.1 mg X kg-1 X min-1, respectively, between 60 and 90 min; P less than 0.01-0.001). Furthermore, a net splanchnic lactate uptake was present in the basal state, which was inhibited by the glucose load and switched to a comparable net lactate output in both groups. These results indicate that the mechanism responsible for the altered glucoregulation in subjects with impaired glucose tolerance resides entirely in the peripheral tissues whose ability to dispose of a glucose load is drastically reduced. On the other hand, no defect is detectable in any of the explored mechanisms regulating splanchnic glucose metabolism during the disposal of an exogenous glucose load.

Direct evidence for a stimulatory effect of hyperglycemia per se on peripheral glucose disposal in type II diabetes.

The effect of hyperglycemia per se on glucose uptake by muscle tissue was quantitated in six controls and six type II diabetics by the forearm technique, under conditions of insulin deficiency induced by somatostatin (SRIF) infusion (0.7 mg/h). Blood glucose concentration was clamped at its basal value during the first 60 min of SRIF infusion and then raised to approximately 200 mg/dl by a variable glucose infusion. Plasma insulin levels remained at or below 5 microU/ml during SRIF infusion, including the hyperglycemic period. No appreciable difference between controls and diabetics was present in the basal state as to forearm glucose metabolism. After 60 min of SRIF infusion and euglycemia, forearm glucose uptake fell consistently from 2.1 +/- 0.7 mg X liter-1 X min-1 to 1.0 +/- 0.6 (P less than 0.05) and from 1.7 +/- .2 to 0.4 +/- 0.3 (P less than 0.02) in the control and diabetic groups, respectively. The subsequent induction of hyperglycemia caused a marked increase in both the arterial-deep venous blood glucose difference (P less than 0.02-0.01) and forearm glucose uptake (P less than 0.01-0.005). However, the response in the diabetic group was significantly greater than that observed in controls. The incremental area of forearm glucose uptake was 276 +/- 31 mg X liter-1 X 90 min and 532 +/- 81 in the control and diabetic groups, respectively (P less than 0.02). In the basal state, the forearm released lactate and alanine both in controls and diabetic subjects at comparable rates. No increment was observed after hyperglycemia, despite the elevated rates of glucose uptake. It is concluded that (1) hyperglycemia per se stimulates forearm glucose disposal to a greater extent in type II diabetics than in normal subjects; and (2) the resulting increment of glucose disposal does not accelerate the forearm release of three carbon compounds. The data support the hypothesis that hyperglycemia per se may play a compensatory role for the defective glucose disposal in type II diabetes.

Differential effects of insulin on splanchnic and peripheral glucose disposal after an intravenous glucose load in man.

The present study was designed to investigate the mechanisms by which insulin regulates the disposal of an intravenous glucose load in man. A combined tracer-hepatic vein catheter technique was used to quantitate directly the components of net splanchnic glucose balance (NSGB), i.e., splanchnic glucose uptake and hepatic glucose output, and peripheral (extrasplanchnic) glucose uptake. Four different protocols were performed: (a) intravenous infusion of glucose alone (6.5 mg kg(-1) min(-1)) for 90 min (control group); (b) glucose plus somatostatin (0.6 mg/h) and glucagon (0.8 ng kg(-1) min(-1); (c) glucose plus somatostatin, glucagon, and insulin (0.15 mU kg(-1) min(-1)); and (d) glucose plus somatostatin, glucagon, and insulin (0.4 m U kg(-1) min(-1)). In groups 2-4, arterial blood glucose was raised to comparable levels to those of controls ( approximately 170 mg/dl) by a variable glucose infusion. In the control group, plasma insulin levels reached 40 muU/ml at 90 min. NSGB switched from a net output of 1.71+/-0.13 to a net uptake of 1.5-1.6 mg kg(-1) min(-1) due to a 90-95% suppression of hepatic glucose output (P < 0.01) and a 105-130% elevation of splanchnic glucose uptake (from 0.78+/-0.13 to 1.6-1.8 mg kg(-1) min(-1); P < 0.01). Peripheral glucose uptake rose by 150-160% (P < 0.01). In group 2, plasma insulin fell to <5 muU/ml. Net splanchnic glucose output initially rose twofold but later returned to basal values. This response was entirely accounted for by similar changes in hepatic glucose output since splanchnic glucose uptake remained totally unchanged in spite of hyperglycemia. In contrast, peripheral glucose uptake rose consistently by 100% (P < 0.01) despite insulin deficiency. In an additional group of experiments, glucose metabolism by the forearm muscle tissue was quantitated during identical conditions to those of group 2 (hyperglycemia plus insulin deficiency). Both the arterial-deep venous blood glucose difference and forearm glucose uptake increased markedly by 300-400% (P < 0.05 - <0.01). In group 3, plasma insulin was maintained at near-basal, peripheral levels (12-14 muU/ml). Hepatic glucose output decreased slightly by 35-40% (P < 0.05) while splanchnic glucose uptake remained unchanged. Consequently, the net glucose overproduction seen in group 2 was totally prevented although NSGB still remained as a net output. In group 4, peripheral insulin levels were similar to those of the control group (35-40 muU/ml). The suppression of hepatic glucose output was more pronounced (60-65%) and splanchnic glucose uptake rose consistently by 65% (P < 0.01). Consequently, NSGB did not remain as a net output but eventually switched to a small uptake (0.3 mg kg(-1) min(-1)). Peripheral glucose uptake rose to the same extent as in controls. IT IS CONCLUDED THAT: (a) the suppressive effect of hyperglycemia on hepatic glucose output is strictly dependent on the degree of hepatic insulinization; (b) insulin plays an essential role in promoting splanchnic glucose uptake after an intravenous glucose load whereas hyperglycemia per se is totally unable to activate this process; (c) peripheral glucose uptake is markedly stimulated by hyperglycemia even in the face of insulin deficiency. Direct evidence also demonstrates that the skeletal muscle is involved in this response. Our data, thus, indicate that insulin rather than hyperglycemia regulates splanchnic glucose disposal in man. On the other hand, hyperglycemia per se appears to be an important regulator of glucose disposal by peripheral tissues.

Mechanisms of epinephrine-induced glucose intolerance in normal humans.

To evaluate the role of the splanchnic bed in epinephrine-induced glucose intolerance, we selectively assessed the components of net splanchnic glucose balance, i.e., splanchnic glucose uptake and hepatic glucose production, and peripheral glucose uptake by combining infusion of [3-(3)H]glucose with hepatic vein catheterization. Normal humans received a 90-min infusion of either glucose alone (6.5 mg/kg(-1) per min(-1)) or epinephrine plus glucose at two dose levels: (a) in amounts that simulated the hyperglycemia seen with glucose alone (3.0 mg/kg(-1) per min(-1)); and (b) in amounts identical to the control study. During infusion of glucose alone, blood glucose rose twofold, insulin levels and net posthepatic insulin release increased three- to fourfold, and net splanchnic glucose output switched from a net output (1.65+/-0.12 mg/kg(-1) per min(-1)) to a net uptake (1.56+/-0.18). This was due to a 90-95% fall (P < 0.001) in hepatic glucose production and a 100% rise (P < 0.001) in splanchnic glucose uptake (from 0.86+/-0.14 to 1.71+/-0.12 mg/kg(-1) per min(-1)), which in the basal state amounted to 30-35% of total glucose uptake. Peripheral glucose uptake rose by 170-185% (P < 0.001). When epinephrine was combined with the lower glucose dose, blood glucose, insulin release, and hepatic blood flow were no different from values observed with glucose alone. However, hepatic glucose production fell only 40-45% (P < 0.05 vs. glucose alone) and, most importantly, the rise in splanchnic glucose uptake was totally blocked. As a result, splanchnic glucose clearance fell by 50% (P < 0.05), and net splanchnic glucose uptake did not occur. The rise in peripheral glucose uptake was also reduced by 50-60% (P < 0.001). When epinephrine was added to the same dose of glucose used in the control study, blood glucose rose twofold higher (P < 0.001). The initial rise in splanchnic glucose uptake was totally prevented; however, beyond 30 min, splanchnic glucose uptake increased, reaching levels seen in the control study when severe hyperglycemia occurred. Splanchnic glucose clearance, nevertheless, remained suppressed throughout the entire study (40%-50%, P < 0.01). It is concluded that (a) the splanchnic bed accounts for one-third of total body glucose uptake in the basal state in normal humans; (b) epinephrine markedly inhibits the rise in splanchnic glucose uptake induced by infusion of glucose; and (c) this effect does not require a fall in insulin and is modulated by the level of hyperglycemia. Our data indicate that the splanchnic bed is an important site of glucose uptake in post-absorptive humans and that epinephrine impairs glucose tolerance by suppressing glucose uptake by both splanchnic and peripheral tissues, as well as by its well known stimulatory effect on endogenous glucose production.

Abnormal sympathetic overactivity evoked by insulin in the skeletal muscle of patients with essential hypertension.

The reason why hyperinsulinemia is associated with essential hypertension is not known. To test the hypothesis of a pathophysiologic link mediated by the sympathetic nervous system, we measured the changes in forearm norepinephrine release, by using the forearm perfusion technique in conjunction with the infusion of tritiated NE, in patients with essential hypertension and in normal subjects receiving insulin intravenously (1 mU/kg per min) while maintaining euglycemia. Hyperinsulinemia (50-60 microU/ml in the deep forearm vein) evoked a significant increase in forearm NE release in both groups of subjects. However, the response of hypertensives was threefold greater compared to that of normotensives (2.28 +/- 45 ng.liter-1.min-1 in hypertensives and 0.80 +/- 0.27 ng.liter-1 in normals; P less than 0.01). Forearm glucose uptake rose to 5.1 +/- .7 mg.liter-1.min-1 in response to insulin in hypertensives and to 7.9 +/- 1.3 mg.liter-1.min-1 in normotensives (P less than 0.05). To clarify whether insulin action was due to a direct effect on muscle NE metabolism, in another set of experiments insulin was infused locally into the brachial artery to expose only the forearm tissues to the same insulin levels as in the systemic studies. During local hyperinsulinemia, forearm NE release remained virtually unchanged both in hypertensive and in normal subjects. Furthermore, forearm glucose disposal was activated to a similar extent in both groups (5.0 +/- 0.6 and 5.2 +/- 1.1 mg.liter-1.min-1 in hypertensives and in normals, respectively). These data demonstrate that: (a) insulin evokes an abnormal muscle sympathetic overactivity in essential hypertension which is mediated by mechanisms involving the central nervous system; and (b) insulin resistance associated with hypertension is demonstrable in the skeletal muscle tissue only with systemic insulin administration which produces muscle sympathetic overactivity. The data fit the hypothesis that the sympathetic system mediates the pathophysiologic link between hyperinsulinemia and essential hypertension.

Detection of growth hormone abuse in sport.

OBJECTIVE: To develop a test for GH abuse in sport. DESIGN: A double blind placebo controlled study of one month's GH administration to 102 healthy non-competing but trained subjects. Blood levels of nine markers of GH action were measured throughout the study and for 56 days after cessation of GH administration. Blood samples were also taken from 813 elite athletes both in and out of competition. RESULTS: GH caused a significant change in the nine measured blood markers. Men were more sensitive to the effects of GH than women. IGF-I and N-terminal extension peptide of procollagen type III were selected to construct formulae which gave optimal discrimination between the GH and placebo groups. Adjustments were made to account for the fall in IGF-I and P-III-P with age and the altered distribution seen in elite athletes. Using a cut-off specificity of 1:10,000 these formulae would allow the detection of up to 86% of men and 60% of women abusing GH at the doses used in this study. CONCLUSIONS: We report a methodology that will allow the detection of GH abuse. This will provide the basis of a robust and enforceable test identifying those who are already cheating and provide a deterrent to those who may be tempted to do so.

Impact of hyperthyroidism and its correction on vascular reactivity in humans.

BACKGROUND: Although thyroid hormone (TH) exerts relevant effects on the cardiovascular system, it is unknown whether TH also regulates vascular reactivity in humans. Methods and Results- We studied 8 patients with hyperthyroidism, basally (H) and 6 months after euthyroidism was restored by methimazole (EU). Thirteen healthy subjects served as control subjects (C). We measured forearm blood flow (FBF) by strain-gauge plethysmography during intrabrachial graded infusion of acetylcholine, sodium nitroprusside (SNP), norepinephrine, and L-NMMA (inhibitor of NO synthesis). Basal FBF (in mL. dL(-1). min(-1)) was markedly higher in H than in C (5.8+/-1.2 and 1.9+/-0.1, respectively; P<0.001) and was close to normal in EU (2.6+/-0.3, P<0.01 versus H). During acetylcholine infusion, FBF increased much more in H (+33+/-5) than in C (+14+/-3, P<0.01 versus H) and in EU (+20+/-5, P=0.01 versus H and P=NS versus C). In contrast, the response to SNP infusion was comparable in the patients and control subjects. During norepinephrine infusion, the fall in FBF was much more pronounced in H (-6+/-1) than in C (-0.7+/-0.3, P<0.005 versus H) and in EU (-1.5+/-0.3, P<0.01 versus H). Finally, inhibition of NO synthesis by L-NMMA decreased FBF by 2.8+/-0.6, 0.61+/-0.7, and 1.4+/-0.3 in H, C, and EU, respectively (H versus C and EU, P<0.05). CONCLUSIONS: In hyperthyroidism, (1) the marked basal vasodilation is largely accounted for by excessive endothelial NO production, (2) vascular reactivity is exaggerated because of enhanced sensitivity of the endothelial component, (3) the vasoconstrictory response to norepinephrine is potentiated, and (4) this abnormal vascular profile is corrected when euthyroidism is restored by medical therapy. The data demonstrate that vascular endothelium is a specific target of TH.

Abnormal vascular reactivity in growth hormone deficiency.

BACKGROUND: The reason why patients with growth hormone (GH) deficiency (GHD) are at increased risk for premature cardiovascular death is still unclear. Although a variety of vascular risk factors have been identified in GHD, little is known regarding vascular reactivity and its contribution to premature arteriosclerosis. METHODS AND RESULTS: We assessed vascular function in 7 childhood-onset, GH-deficient nontreated patients (age 22+/-3 years, body mass index [BMI] 25+/-1 kg/m(2)) and 10 healthy subjects (age 24+/-0.4 years, BMI 22+/-1 kg/m(2)) by using strain gauge plethysmography to measure forearm blood flow in response to vasodilatory agents. The increase in forearm blood flow to intrabrachial infusion of the endothelium-dependent vasodilator acetylcholine was significantly lower in GH-deficient nontreated patients than in control subjects (P:<0.05). Likewise, forearm release of nitrite and cGMP during acetylcholine stimulation was reduced in GH-deficient nontreated patients (P:<0.05 and P:<0.002 versus controls). The response to the endothelium-independent vasodilator sodium nitroprusside was also markedly blunted in GH-deficient patients compared with control subjects (P:<0.005). To confirm that abnormal vascular reactivity was due to GHD, we also studied 8 patients with childhood-onset GHD (age 31+/-2 years, BMI 24+/-1 kg/m(2)) who were receiving stable GH replacement therapy. In these patients, the response to both endothelium-dependent and -independent vasodilators, as well as forearm nitrite and cGMP, release was not different from that observed in normal subjects. Peak hyperemic response to 5-minute forearm ischemia was significantly reduced in GH-deficient nontreated patients (17.2+/-2.6 mL x dL(-1) x min(-1), P:<0.01) but not in GH-treated patients (24.8+/-3.3 mL x dL(-1) x min(-1)) compared with normal subjects (29.5+/-3.2 mL x dL(-1) x min(-1)). CONCLUSIONS: The data support the concept that GH plays an important role in the maintenance of a normal vascular function in humans.

Studies on the mechanism underlying the influence of alanine infusion on glucose dynamics in the dog.

These experiments have been designed to study the influence of alanine infusion of glucose dynamics in the dog and to further elucidate the role of pancreatic hormones in the interaction of alanine with glucose homeostasis. The primed constant infusion of glucose-2-t was used in order to quantitate the rates of glucose production by the liver (Ra) and glucose utilization (Rd). In a first group of experiments, the intravenous infusion of alanine at the rate of 2 mg./kg./min. produced a moderate enhancement of plasma insulin (IRI), while pancreatic glucagon (IRG) increased more consistently. This different pattern of IRI and IRG response caused the insulin/glucagon molar ratio to decline progressibely throughout the experiment. Both rates of glucose turnover increased significantly during alanine infusion. Since Ra rose more rapidly thanRd did initially, hyperglycemia developed. Later, glucose production slowly decreased and, in spite of the sustained hyperglucagonemia, reached levels very close to the baseline in the second part of the experiment. A significant direct correlation between Ra and IRG was found, while the changes in Ra correlated inversely with those in I/G molar ratio. In a second group of experiments, alanine was infused at the same dose together with 0.4 microng./kg./min. of cyclic somatostatin. In the first part of the infusion, IRG fell more than IRI did, so that I/G ratio increased. Later, IRI levels maintained at low values while IRG returned slowly to the baseline and consequently I/G ratio significantly decreased. Glucose production fell rapidly soon after the beginning of the infusion, and therefore hypoglycemia developed. Later, Ra increased progressively to levels above baseline and plasma glucose returned to the preinfusion levels. As in the the first group of experiments, a significant direct correlation between Ra and IRG and an inverse correlation between the changes in Ra and I/G ratio were observed. These experiments demonstrate that alanine infusion produces an acceleration of glucose turnover and that a clear interrelationship between the release of glucose by the liver and the mobilization of pancreatic hormones exists. Finally, the experiments with somatostatin indicate that hyperglucagonemia is one of the mechanisms underlying the stimulatory effect of alanine on glucose production.

Blood glucose regulates the effects of insulin and counterregulatory hormones on glucose production in vivo.

Continuous, low dose, insulin infusion in conscious dogs produced moderate hypoglycemia but only a transient fall in glucose production that rose towards preinfusion levels 20 to 30 min before any detectable increase in plasma counterregulatory hormones. Addition of epinephrine or glucagon to the insulin infusion prevented the fall in glucose production throughout the experiment but only partially diminished the hypoglycemic response. When hypoglycemia was prevented by a variable glucose infusion, neither epinephrine nor glucagon was able to counteract the suppressive effect of insulin on glucose output. These findings suggest that a fall in blood glucose per se may reverse insulin-induced inhibition of glucose production independent of a rise in counterregulatory hormones and that the insulin antagonist effect of counter-regulatory hormones is modulated, at least in part, by blood glucose concentration.

Effects of theophylline on glucose kinetics in normal and sympathectomized rats.

The influence of intraperitoneal administration of aminophylline on the rate of hepatic glucose production and peripheral uptake (Ra and Rd) was studied in normal and in adrenodemedullated and reserpinized rats by using the primed constant infusion of Glucose-2-3H. In normal rats, the dose of 100 mg. per kilogram of aminophylline produced a marked increase of Ra and Rd. Since Ra rose more rapidly than Rd did initially, hyperglycemia developed. Thereafter, glucose production and uptake increased to nearly the same extent, and a new steady state was reached at plasma glucose levels almost twice those of the baseline. Smaller and transient modifications were observed after the administration of 20 mg. per kilogram of aminophylline. With the higher dose, insulin levels markedly rose (reaching a tenfold peak above the basal value) while minor increments were observed with the lower dose. In a group of normal rats which were given glucose (10 mg. per kilogram per minute) in order to achieve a degree of hyperglycemia comparable to that brought about by the higher dose of aminophylline, an almost identical enhancement of glucose uptake was recorded. However, insulin levels were much higher in aminophylline-treated rats as compared to normal rats. From these finding it was concluded that aminophylline induces resistance to insulin effect. When aminophylline was injected into demedullated rats pretreated with reserpine, at the dose of 100 mg. per kilogram, a marked enhancement of Ra, and consequently of glycemia, was recorded initially; later, severe hypoglycemia developed depending on both a progressive exhaustion of hepatic glucose production and a marked increase of glucose utilization. Insulin levels dramatically increased in these experiments. These results suggest that aminophylline directly increases glucose production by the liver and insulin secretion. The simultaneous activation of the sympathetic system blunts the insulin response and counteracts the restraining effect of insulin on the liver and the stimulatory effect of insulin on overall glucose uptake as well.

Colchicine and insulin secretion in man.

The present study is aimed at investigating the effect of acute and chronic colchicine administration on insulin secretion in humans. Acute insulin response to glucose (0.33 g/kg) was significantly decreased by colchicine (3 mg i.v.). In fact, this response (mean change 2-10 min insulin) was 44 +/- 8 microunits/ml before and 32 +/- 6 microunits/ml after colchicine administration (P less than 0.01). As a consequence of this, glucose disappearance rates were reduced (P less than 0.05). Infusion of lysine acetylsalicylate (LAS), an inhibitor of endogenous PG synthesis, completely reversed the inhibitory effect of colchicine upon insulin secretion and also augmented acute insulin response to glucose (response before colchicine + LAS = 45 +/- 8 microunits/ml; response after colchicine + LAS = 51 +/- 9 microunits/ml, P less than 0.05). This effect was associated with an increase in glucose disappearance rates (P less than 0.05). The 10-day treatment with colchicine (2 mg daily) caused a significant suppression of insulin secretion induced by oral glucose (100 g) and significantly increased the plasma glucose concentrations following the test (P less than 0.05). These findings demonstrate that (1) both acute and chronic colchicine administration inhibit glucose-induced insulin secretion and deteriorate glucose tolerance in humans, and (2) LAS completely reverses these negative effects of colchicine. An increased synthesis of endogenous PGE, which are known to inhibit insulin secretion in humans, might account for the inhibiting effect of colchicine on insulin secretion.

Splanchnic and leg substrate exchange after ingestion of a natural mixed meal in humans.

The disposal of a mixed meal was examined in 11 male subjects by multiple (splanchnic and femoral) catheterization combined with double-isotope technique (intravenous [2-3H]glucose plus oral U-[14C]starch). Glucose kinetics and organ substrate balance were measured basally and for 5 h after eating pizza (600 kcal) containing carbohydrates 75 g as starch, proteins 37 g, and lipids 17 g. The portal appearance of ingested carbohydrate was maximal (1.0 mmol/min) between 30 and 60 min after the meal and gradually declined thereafter, but was still incomplete at 300 min (0.46+/-0.08 mmol/min). The total amount of glucose absorbed by the gut over the 5 h of the study was 247+/-26 mmol (45+/-6 g), corresponding to 60+/-6% of the ingested starch. Net splanchnic glucose balance (-6.7+/-0.5 micromol x kg(-1) x min(-1), basal) rose by 250-300% between 30 and 60 min and then returned to baseline. Hepatic glucose production (HGP) was suppressed slightly and only tardily in response to meal ingestion (approximately 30% between 120 and 300 min). Splanchnic glucose uptake (3.7+/-0.6 micromol x kg(-1) x min(-1), basal) peaked to 9.8+/-2.0 micromol x kg(-1) x min(-1) (P<0.001) at 120 min and then returned slowly to baseline. Leg glucose uptake (34+/-5 micromol x leg(-1) x min(-1), basal) rose to 151+/-29 micromol x leg(-1) x min(-1) at 30 min (P<0.001) and remained above baseline until the end of the study, despite no increase in leg blood flow. The total amount of glucose taken up by the splanchnic area and total muscle mass was 161+/-16 mmol (29+/-3 g) and 128 mmol (23 g), respectively, which represent 39 and 30% of the ingested starch. Arterial blood lactate increased by 30% after meal ingestion. Net splanchnic lactate balance switched from a basal net uptake (3.2+/-0.6 micromol kg(-1) x min(-1) to a net output between 60 and 120 min and tended to zero thereafter. Leg lactate release (25+/-11 micromol x leg(-1) x min(-1), basal) drastically decreased postprandially. Arterial concentration of both branched-chain amino acids (BCAA) and non-branched-chain amino acids (N-BCAA) increased significantly after meal ingestion (P<0.001). The splanchnic area switched from a basal net amino acid uptake (31+/-16 and 92+/-48 micromol/min for BCAA and N-BCAA, respectively) to a net amino acid release postprandially. The net splanchnic amino acid release over 5 h was 11.3+/-4.2 mmol for BCAA and 37.8+/-9.7 mmol for N-BCAA. Basally, the net leg balance of BCAA was neutral (-3+/-5 micromol x leg(-1) x min(-1)), whereas that of N-BCAA indicated a net release (54+/-14 micromol x leg(-1) x min(-1)). After meal ingestion, there was a net leg uptake of BCAA (20+/-6 micromol x leg(-1) x min(-1)), whereas leg release of N-BCAA decreased by 50%. It is concluded that in human subjects, 1) the absorption of a natural mixed meal is still incomplete at 5 h after ingestion; 2) HGP is only marginally and tardily inhibited; 3) splanchnic and peripheral tissues contribute to the disposal of meal carbohydrate to approximately the same extent; 4) the splanchnic area transfers >30% of the ingested proteins to the systemic circulation; and 5) after meal ingestion, skeletal muscle takes up BCAA to replenish muscle protein stores.

Effects of oral salt loading on beta-adrenergic receptor responsiveness in normal and hypertensive subjects.

The effect of oral salt loading (400 mmol per day of NaCl for 7 days) on cardiac and pancreatic beta-receptor responsiveness has been evaluated in 12 patients with established essential hypertension and in seven age-matched control subjects. Cardiac beta-receptor responsiveness was evaluated by assessing the dose of isoprenaline which increased a stable heart rate by 25% (chronotropic dose 25%, CD 25%). Pancreatic beta-receptor responsiveness was measured by the incremental areas of insulin secretion induced by iv infusion of increasing amounts of isoprenaline. Before salt load, CD 25% was significantly higher in hypertensives compared with controls (7.84 +/- 1.34 micrograms vs 3.9 +/- 0.48 micrograms, P less than 0.05) while there was no difference in the isoprenaline-induced insulin secretion between the two groups of subjects. After salt loading, CD 25% was significantly reduced in hypertensive patients but was not modified in normal subjects. Therefore, the difference in CD 25% was no longer detectable between the two groups (5.5 +/- 1.42 micrograms vs 3.2 +/- 0.48 micrograms in normal subjects and in hypertensives, respectively, NS). Furthermore, salt loading failed to induce any change in isoprenaline-induced insulin secretion in either groups. These results support the existence of a relationship between sodium intake and adrenergic beta-receptor responsiveness in human hypertension.

Baroreflex responsiveness in borderline hypertensives: a study with neostigmine.

The baroreflex response to changes in transmural pressure throughout the arterial tree or limited to the carotid sinus was evaluated in ten borderline hypertensives and compared with that observed in ten normal subjects and in ten established hypertensives. Baroreceptor sensitivity was tested by evaluating both heart rate response to phenylephrine-induced increase in arterial pressure and heart rate and blood pressure changes induced by increased neck tissue pressure by means of a neck chamber. The heart rate response to phenylephrine (evaluated by the regression of the R-R interval versus the systolic blood pressure) was depressed both in borderline and established hypertensives as compared with controls. Similarly, the heart rate and the pressor response to increased neck tissue pressure were depressed in both groups of hypertensives. In borderline, but not in established hypertensives, neostigmine administration improved consistently the pressor baroreflex response to increased neck tissue pressure and the heart rate reflex response to both the employed stimuli. These findings indicate that a reduced parasympathetic activity is one of the components involved in the altered baroreflex sensitivity in borderline hypertensives.