Hepatic and renal metabolism of somatostatin-like immunoreactivity. Simultaneous assessment in the dog.

The hepatic and renal metabolism of somatostatin-like immunoreactivity (SLI) was assessed simultaneously in an in vivo dog model. The hepatic extraction of this peptide was 29.4 +/- 2.3% and was similar for endogenous and infused exogenous SLI. The renal extraction was 62.3 +/- 5%. The renal clearance of SLI was significantly greater than that of inulin indicating that the peptide is handled by peritubular uptake from postglomerular blood in addition to glomerular filtration. In both organs SLI extraction was not saturable even at arterial concentrations in excess of 100 times physiological range. The overall metabolic clearance rate of SLI was 19.7 +/- 1.6 ml/kg per minute of which 32.7 +/- 4.6% was contributed by hepatic and 37 +/- 4.9% by renal uptake mechanisms. The plasma half disappearance time of exogenously infused SLI was 1.9 +/- 0.3 min. The studies indicate that in the dog, the liver and kidney are both major sites of SLI metabolism, together accounting for 70.0 +/- 8.7% of the metabolic clearance of the peptide.

C-peptide and insulin secretion. Relationship between peripheral concentrations of C-peptide and insulin and their secretion rates in the dog.

Estimation of the insulin secretory rate from peripheral C-peptide concentrations depends upon the following characteristics of C-peptide kinetics: (a) equimolar secretion of insulin and C-peptide by pancreatic beta cells; (b) negligible hepatic extraction of C-peptide; (c) constant metabolic clearance rate (MCR) of C-peptide over a physiological and pathophysiological range of plasma levels; and (d) proportional changes in the secretion rate of C-peptide and its peripheral concentrations under varying physiological conditions. In the present experiments, the relationship between a variable intraportal infusion of C-peptide and its concentration in the femoral artery was explored in 12 pancreatectomized dogs. As the infusion of C-peptide was rapidly increased, the magnitude of its peripheral concentration initially increased less than the infusion rate by 20-30%. After an equilibration period of approximately 30 min, however, further increases and decreases in the intraportal infusion were accompanied by nearly proportional changes in its peripheral concentration. Estimates of the amount of C-peptide infused during the experiment based on the steady state C-peptide MCR and its peripheral concentration were within 20% of the amount of C-peptide actually infused. These experiments demonstrate that the portal delivery rate of C-peptide can be calculated from its MCR and peripheral concentration in the dog. They also provide a basis for testing the validity of more complicated models of insulin secretion based on peripheral C-peptide concentrations in the dog as well as other species, including man. Finally, we have shown that the hepatic extraction of endogenously secreted C-peptide is negligible in the basal state (3.1 +/- 6.1%), and does not change after oral glucose ingestion. The MCR of exogenous dog C-peptide was similar whether measured by constant peripheral intravenous infusion (12.3 +/- 0.7 ml/kg per min), constant intraportal infusion (13.4 +/- 0.6 ml/kg per min), or analysis of the decay curve after a bolus injection (13.5 +/- 0.7 ml/kg per min).

Heterogeneity of plasma glucagon. Circulating components in normal subjects and patients with chronic renal failure.

Plasma immunoreactive glucagon (IRG) concentrations were measured in 36 patients with chronic renal failure (CRF) and 32 normal subjects. In addition, the components of circulating IRG were analyzed by gel filtration in the fasting state and after physiological stimuli. Fasting IRG was elevated (P less than 0.001) in CRF patients (534 +/- 32 pg/ml) compared with the levels found in healthy subjects (113 +/- 9 pg/ml). Oral glucose suppressed plasma IRG in CRF patients from a basal level of 568 +/- 52 to a nadir of 354 +/- 57 pg/ml (120 min). This degree of suppression (38%) was comparable to that found in normal subjects (basal = 154 +/- 20 to 100 +/- 23 pg/ml) at 120 min (35%). Intravenous infusion of arginine (250 mg/kg) resulted in a 71% rise in IRG in CRF patients and a 166% increase in normal subjects. Gel filtration of fasting plasma from CRF patients showed three major peaks. The earliest (A) was found in the void volume (mol wt greater than 40,000) and constituted 16.5 +/- 4.7% of the elution profile. The middle peak (B) eluted just beyond the proinsulin marker (approximately 9,000 mol wt) and constituted the largest proportion of the elution profile (56.5 +/- 3.4%). The third peak (C) coincided with the standard glucagon and [125I]glucagon markers (3,485 mol wt) and comprised 27.0 +/- 4% of the IRG profile. In contrast, only peaks A and C were found in fasting plasma of normal subjects (53.6 +/- 10.4% in A and 46.4 +/- 10.4 in C). After oral glucose, glucagon immunoreactivity in the 3,500 mol wt peak (C) was markedly suppressed, while the B peak in patients with CRF declined to a lesser extent. The A peak in both groups was unchanged. After an arginine infusion only the C peak increased in both groups of subjects. Gel filtration of plasma in 3 M acetic acid gave similar profiles to those obtained in glycine albumin buffer. Exposure of serum to trypsin indicated that the B and C peaks were digestible, while the A peak was resistant to the action of the enzyme. In one sample, peak C increased after a 2-h exposure of serum to trypsin. We conclude that circulating IRG in normal subjects and patients with CRF is heterogenous. The hyperglucagonemia of renal failure is largely due to an increase in IRG material of approximately 9,000 mol wt, consistent with proglucagon, although the 3,500 mol wt component is also considerably elevated (threefold). The significance of circulating IRG levels should be interpreted with caution until the relative biological activity of the three components is established.

The role of the liver in glucagon metabolism.

Total plasma immunoreactive pancreatic glucagon (IRG) was measured in samples taken simultaneously from the proximal portal vein and superior vena cava of 26 healthy rats. The portal-peripheral ratio of IRG was 2.80+/-0.25, the portal-peripheral difference (Delta) 124+/-15 pg/ml, and percentage extraction 58+/-3. Gel filtration of paired portal and peripheral vein samples showed that reduction in the 3,500-dalton IRG component (glucagon) in peripheral samples accounted for almost all the differences, there being minimal and inconsistent changes in the high molecular weight (>40,000) fraction. The portal-peripheral ratio of the 3,500-dalton glucagon was 5.24+/-1.10, the portal-peripheral difference 130+/-33 pg/ml, and the percentage extraction 81+/-5. To study the transhepatic differences in the 9,000-dalton "proglucagon-like" material, the experiment was repeated in nine rats 24 h after bilateral nephrectomy, a procedure which increases plasma levels of this fraction. The portal-peripheral ratio for plasma IRG in these rats was 1.48+/-0.12, the portal-peripheral difference 140+/-29 pg/ml, and percentage extraction 28+/-5. Gel filtration revealed no consistent differences between portal and peripheral concentrations of the 9,000- and >40,000-dalton components, which comprised 40 and 13%, respectively, of the mean IRG level of 492+/-35 pg/ml. In contrast, there were marked differences between portal and peripheral levels of the 3,500-dalton component the ratio being 3.42+/-0.63, the portal-peripheral difference 182+/-32 pg/ml, and percentage extraction 64+/-5. Similar studies in a healthy dog, in which species there are significant circulating levels of the 9,000-dalton IRG component, confirmed the selective hepatic extraction of the 3,500-dalton fraction. We conclude that the various IRG fractions are metabolized differently by the liver, and that portal-peripheral ratios based on direct assay of plasma IRG will vary depending on the percentage glucagon immunoreactivity in each fraction; the greater the combined contribution of fractions other than the 3,500-dalton component to total plasma IRG, the lower will be the ratio. Because of the heterogeneity of circulating IRG and significant differences in the metabolism of its various components, gel filtration of plasma samples is necessary for precise quantitation of the hepatic uptake of each particular fraction.

Pathogenesis and characterization of hyperglucagonemia in the uremic rat.

The pathogenesis of hyperglucagonemia and of the alterations in the pattern of circulating immunoreactive glucagon (IRG) associated with renal insufficiency was studied in rats in which a comparable degree of uremia was induced by three different methods, i.e., bilateral nephrectomy, bilateral ureteral ligation, and urine autoinfusion. Nephrectomized and ureteral-ligated rats were markedly hyperglucagonemic (575 +/- 95 pg/ml and 492 +/- 54 pg/ml, respectively), while IRG levels of urine autoinfused animals (208 +/- 35 pg/ml) were similar to those of control rats (180 +/- 26 pg/ml), indicating that uremia per se does not account for the hyperglucagonemia observed in renal failure. Similarly, plasma IRG composition in this group of animals was indistinguishable from that of controls, in which 88.2 +/- 5.9% of total IRG consisted of the 3,500-mol wt fraction. The same component was almost entirely responsible (82.6 +/- 4.1%) for the hyperglucagonemia observed in ligated rats, while it accounted for only 57.6 +/- 5.0% of the circulating IRG in nephrectomized animals. In the latter group, 36.8 +/- 6.6% of total IRG had a mol wt of approximately 9,000, consistent with a glucagon precursor. This peak was present in samples obtained as early as 2 h after renal ablation and its concentration continued to increase with time reaching maximal levels at 24 h. These results confirm that the kidney is a major site of glucagon metabolism and provide evidence that the renal handling of the various circulating IRG components may involve different mechanisms. Thus, the metabolism of the 3,500-mol wt fraction is dependent upon glomerular filtration, while the uptake of the 9,000-mol wt material can proceed in its absence, as long as renal tissue remains adequately perfused. This finding suggests that the 9,000-mol wt component may be handled by peritubular uptake.

Glucagon metabolism in the rat.

The renal handling of the biologically active glucagon component (the 3,500-mol wt fraction of immunoreactive glucagon [IRG]) and the contribution of the kidney to its overall peripheral metabolism were studied in normal and uremic rats. The metabolic clearance rate of glucagon was 31.8 +/- 1.2 ml/min per kg in normal animals and was diminished by approximately one-third in each of three groups of rats with compromized renal function: 22.3+/-1.6 ml/min per kg in partially (70%) nephrectomized; 22.9+/-3.3 ml/min per kg in bilaterally ureteral ligated; and 23.2+/-1.2 ml/min per kg in bilaterally nephrectomized animals. In normal rats the kidney contributed 30% to the overall metabolic clearance of the hormone and the renal extraction of endogenous and exogenous glucagon was similar, averaging 22.9+/-1.6% and was independent of plasma IRG levels over a wide range of arterial concentrations. The remnant kidney of partially (70%) nephrectomized animals continued to extract substantial amounts (16.6+/-4.2%) of the hormone, but accounted for only 8% of the total peripheral catabolism of IRG. In the two groups of animals with filtering kidneys, renal glucagon uptake was linearly related to its filtered load and could be accounted for by glomerular filtration and tubular reabsorption. However, the kidneys of animals with both ureters ligated (renal extraction of inulin = 3.2+/-1.8%) and hence virtual absence of glomerular filtration, continued to extract 11.5+/-1.9% of the renal arterial glucagon, contributing by 9% to its overall metabolic clearance, indicating that IRG uptake occurs also from the post glomerular capillaries.

Glucagon immunoreactivity and chromatographic profiles in pancreatectomized humans. Paradoxical response to oral glucose.

The nature and origin of plasma immunoreactive glucagon (IRG) after pancreatectomy in humans remains controversial. Low plasma IRG levels and heterogeneity hamper accurate assessment. We studied plasma IRG levels and profiles in 12 patients 2-57 mo after a total pancreatectomy (with antrectomy and duodenectomy) for cancer (N = 9) or chronic pancreatitis (N = 3). After oral glucose, plasma IRG (with the COOH-terminal-specific 30K glucagon antibody) rose from 59 +/- 7 to a peak of 113 +/- 17 pg/ml at 60-120 min. Chromatographic profiles revealed four distinct IRG fractions. In every patient a plasma IRG fraction of 9000-15,000 Mr, detectable basally, increased markedly after oral glucose and accounted for the rise in total IRG observed in plasma. Nine of the 12 pancreatectomized subjects had no detectable 3500-Mr glucagon and the remaining 3 had very low levels. For the group as a whole, 3500-Mr IRG comprised 1-2% of the total recovered IRG. Two patients were also studied before pancreatectomy: suppressibility of glucagon (Mr 3500) was evident. After surgery this paradoxical response to oral glucose was demonstrated. Reproducibility of these responses was confirmed in two patients studied twice over 2 yr. Diabetic controls without pancreatectomy did not show this response. The absence or marked reduction of pancreatic glucagon was confirmed in five of the pancreatectomized patients after intravenous arginine or oral protein. Normal basal plasma IRG and profiles, oral glucose suppressibility, and arginine stimulation were present in five control patients with unresectable pancreatic malignancies.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of glucagon response to hypoglycemia in type I diabetics after long-term optimal therapy with a continuous subcutaneous insulin infusion pump.

Counterregulatory hormonal responses were studied in six patients after 4-18 mo treatment with a continuous subcutaneous insulin infusion pump. In response to insulin-induced hypoglycemia, significant increases in epinephrine, norepinephrine, cortisol, and growth hormone were measured in all subjects, while in five of the six patients glucagon levels did not increase at all. The persistence of these abnormal glucagon responses despite long-term optimal glucose control suggests that they are not due to hyperglycemia per se, but are due rather to a specific alpha cell abnormality. The high incidence of asymptomatic hypoglycemia in these patients emphasizes that caution is necessary to avoid serious hypoglycemia when striving for near-normal glucose control with insulin infusion pump therapy.

Insulin secretory profiles and C-peptide clearance kinetics at 6 months and 2 years after kidney-pancreas transplantation.

Glucose, insulin secretion, and insulin secretory pulses were measured by deconvolution of peripheral C-peptide concentrations in 10 IDDM recipients of a combined kidney-pancreas allograft 6 mo post-transplantation and were compared with 10 matched nondiabetic control subjects. Seven of the 10 recipients were restudied 2 yr post-transplantation. To control for immunosuppressive therapy, 6 patients with a kidney allograft also were studied. Pancreatic insulin secretion rates were evaluated over a 24-h period with three mixed meals. Six months post-transplantation, fasting (5.3 +/- 0.1 vs. 5.3 +/- 0.1 mM), average 24-h (6.0 +/- 0.1 vs. 5.7 +/- 0.1 mM), and meal-related (6.1 +/- 0.3 vs. 5.8 +/- 0.2 mM) plasma glucose levels were not different in control subjects and recipients, respectively. Total 24-h insulin secretion rates were similar between the two groups (150 +/- 15 vs. 182 +/- 24 nmol.m-2.24 h-1). However, post-transplantation, the relationship between basal and meal-stimulated insulin secretion was altered with increased basal insulin secretion (52.2 +/- 6.4 vs. 97.4 +/- 12.5 pmol.m-2.min-1, P less than 0.004) and reduced meal-related secretion. The proportion of total 24-h insulin secretion comprised by basal secretion was 44 +/- 4% in the control subjects vs. 73 +/- 5% in recipients. The number of ultradian oscillations of insulin secretion identified in each 24-h period by pulse analysis was similar in control subjects and recipients (11.9 +/- 0.9 vs. 10.4 +/- 0.5 oscillations/24 hr).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of aging on hepatic and peripheral glucose metabolism in humans.

Mechanisms of glucose intolerance with aging were studied by comparing the metabolic response to glucose ingestion in 10 young (20-23 yr) and 10 elderly (73-80 yr) normal men with the simultaneous application of the forearm and double-isotope techniques. The latter technique consisted of a primed-constant infusion of [3-3H]glucose followed by the administration of an oral glucose load (mean +/- SE, 90.7 +/- 0.7 g) containing [1-14C]glucose. Fasting plasma glucose and insulin concentrations were similar in young and elderly subjects, but in the elderly, glucose tolerance was markedly impaired. Although in the elderly the initial rise in insulin levels (delta, i.e., the incremental area under the curve) from 0 to 30 min was delayed (P less than .02), the response from 0 to 45 min, 0 to 60 min, and thereafter equaled that in the young group, and from 90 to 240 min insulin concentrations in the elderly exceeded those in young subjects. Basal hepatic glucose output (HGO) was similar in young and elderly men (2.13 +/- 0.10 and 1.97 +/- 0.14 mg.kg-1.min-1, respectively). Similar proportional reductions in HGO from 0 to 270 min after glucose loading occurred in young (59.7 +/- 10.3%) and elderly (50.3 +/- 4.9%) subjects but was delayed in the elderly. Suppression of HGO was observed in the young 30 min after glucose ingestion (P less than .02), but not before 60 min in the elderly subjects (P less than .05). The systemic appearance of ingested glucose (0-270 min) was slowed with age (80.7 +/- 3.1 and 66.9 +/- 4.3% of the oral load in the young and elderly groups, respectively; P less than .02). Initial increments in both total glucose disappearance (Rd) and forearm glucose uptake (FGU) from 0 to 60 min after glucose loading were decreased in the elderly (Rd, 4.1 +/- 0.7 vs. 11.5 +/- 1.3 g, P less than .001; FGU, 17.2 +/- 1.4 vs. 24.6 +/- 2.5 md/dl forearm, P less than .02). The overall increment (delta, 0-270 min) in Rd was reduced with age (47.2 +/- 2.9 and 34.5 +/- 3.6 g, P less than .02 in the young and elderly, respectively), but the corresponding data for FGU were similar in the two groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatic extraction of plasma immunoreactive glucagon components. Predilection for 3500-dalton glucagon metabolism by the liver.

This study examines quantitatively the extraction of plasma immunoreactive glucagon (IRG) components by the liver. It was shown that the liver has a predilection for removal of the 3500-dalton biologically active IRG component with virtually no extraction of the other IRG fractions. Hepatic extraction of whole plasma IRG was 25.2 +/- 2.5%. Analysis of the hepatic extraction of the four plasma immunoreactive components, separated by gel filtration, revealed variable but quantitatively insignificant extraction of all components other than the 3500-dalton fraction, which was 33.4 +/- 3.2% (P less than 0.001). Hepatic extraction of whole plasma IRG was significantly less than that of the 3500-dalton component during periods of basal glucagon secretion when IRG fractions other than the 3500-dalton fraction contribute substantially to the whole plasma IRG level. However, during periods of stimulation of glucagon secretion by arginine or arginine plus cholecystokinin-pancreozymin, when the 3500-dalton component accounts for virtually all of the whole plasma IRG level, hepatic extraction of whole plasma IRG was similar to that of the 3500-dalton fraction.

Glucose counterregulation in patients after pancreatectomy. Comparison with other clinical forms of diabetes.

Glucose and counterregulatory hormone responses to a high-dose (1.7 mU/kg/min) insulin infusion were studied in 6 patients who had undergone total pancreatectomy, and the results were compared with those of normal controls and patients with other clinical forms of diabetes. The maximum increase in the plasma glucagon concentration during hypoglycemia in the pancreatectomized patients (5 +/- 5.6 pg/ml) was less than in normals (121 +/- 22 pg/ml). Type I diabetic subjects (28 +/- 14 pg/ml), and insulin-treated diabetic subjects of recent onset (36 +/- 12 pg/ml) also had reduced responses, while responses were normal in type II diabetic subjects (102 +/- 26 pg/ml). The epinephrine response to the hypoglycemic stimulus was reduced after pancreatectomy (278 +/- 81 pg/ml) and in type I diabetic subjects (628 +/- 244 pg/ml), but was not different from control (858 +/- 126 pg/ml) in type II and recent-onset diabetic patients. There was considerable overlap in counterregulatory hormone responses in individual patients with and without autonomic neuropathy and with normal or undetectable fasting C-peptide concentrations. While the control subjects all experienced symptoms of hypoglycemia within a narrow range of plasma glucose concentrations (35-46 mg/dl), five of the diabetic subjects experienced symptoms of hypoglycemia at plasma glucose levels of greater than or equal to 55 mg/dl, and five had no subjective awareness of hypoglycemia despite plasma glucose levels less than 30 mg/dl.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between decrements in glucose level and metabolic response to hypoglycemia in absence of counterregulatory hormones in the conscious dog.

To determine the relationship between decreases in glucose and metabolic regulation in the absence of counterregulatory hormones, we infused overnight-fasted, conscious, adrenalectomized dogs (lacking cortisol and EPI) with somatostatin (to eliminate glucagon and growth hormone) and intraportal insulin (30 pmol.kg-1.min-1), creating arterial insulin levels of approximately 2000 pM. Glucose was infused during one 120-min period, two 90-min periods, and one 45-min period to establish levels of 5.9 +/- 0.1, 3.4 +/- 0.1, 2.5 +/- 0.1, and 1.7 +/- 0.1 mM, respectively. NE levels were 1.24 +/- 0.23, 1.85 +/- 0.27, 2.04 +/- 0.26, and 2.50 +/- 0.20 nM, respectively. During the euglycemic control period, the liver took up glucose (7.5 +/- 1.9 mumol.kg-1.min-1), but hypoglycemia triggered successively greater rates of net hepatic glucose output (3.0 +/- 0.7, 4.6 +/- 0.9, and 6.9 +/- 1.4 mumol.kg-1.min-1). Total gluconeogenic precursor uptake by the liver increased with hypoglycemia. Intrahepatic gluconeogenic efficiency rose progressively (by 106 +/- 42, 199 +/- 56, and 268 +/- 55%). Both glycerol and NEFA levels rose, indicating lipolysis was enhanced. Net hepatic NEFA uptake and ketone production increased proportionally, but the ketone level rose only with severe hypoglycemia. In conclusion, despite marked hyperinsulinemia and the absence of glucagon, EPI, and cortisol, we observed that lipolysis and glucose and ketone production increase in response to decreases in glucose. This suggests that neural and/or autoregulatory mechanisms can play a role in combating hypoglycemia.

Role of brain in counterregulation of insulin-induced hypoglycemia in dogs.

The role of the brain in directing counterregulation during hypoglycemia induced by insulin infusion was assessed in overnight-fasted conscious dogs. Concomitant brain and peripheral hypoglycemia was induced in one group of dogs (n = 5) by infusing insulin peripherally at a rate of 3.5 mU.kg-1.min-1. In another group (n = 4), insulin was infused as described above to induce peripheral hypoglycemia, and brain hypoglycemia was minimized by infusing glucose bilaterally into the carotid and vertebral arteries to maintain the brain glucose level at a calculated concentration of 85 mg/dl. Glucose was also infused peripherally as needed so that the peripheral glucose levels in both of the protocols were similar (45 +/- 2 mg/dl with and 48 +/- 3 mg/dl without brain glucose infusion, both P less than .05). The responses (in terms of change of area under the curve) of epinephrine, norepinephrine, cortisol, and pancreatic polypeptide when brain glycemia was controlled during insulin infusion were only 14 +/- 6, 39 +/- 12, 17 +/- 8, and 9 +/- 4%, respectively, of those present during insulin infusion without concomitant brain glucose infusion (all P less than .05). Of particular interest was the glucagon response that occurred when head hypoglycemia was minimized; the glucagon level was only 21 +/- 8% of that present when marked brain hypoglycemia accompanied insulin infusion (P less than .05). During hypoglycemia resulting from insulin infusion, endogenous glucose production (EGP), as assessed with [3-3H]glucose, rose from 2.6 +/- 0.1 to 4.4 +/- 0.5 mg.kg-1.min-1 (P less than .05). In contrast, EGP decreased from 2.7 +/- 0.2 to 2.0 +/- 0.3 mg.kg-1.min-1 when brain hypoglycemia was minimized. In an additional set of studies, when insulin was infused at 3.5 mU.kg-1.min-1 and glucose was infused peripherally to maintain both the head and peripheral glucose concentrations at 88 +/- 6 mg/dl, EGP decreased from 2.6 +/- 0.1 to 1.2 +/- 0.2 mg.kg-1.min-1. These results suggest that under marked hyperinsulinemic conditions the brain is the primary director of glucagon release and that it is responsible for approximately 75% of the life-sustaining glucose production.

Counterregulation during hypoglycemia is directed by widespread brain regions.

Previous studies have demonstrated the importance of the brain in directing counterregulation during insulin-induced hypoglycemia in dogs. The capability of selective carotid or vertebrobasilar hypoglycemia in triggering counterregulation was assessed in this study using overnight-fasted dogs. Insulin (21 pM.kg-1.min-1) was infused for 3 h to create peripheral hypoglycemia in the presence of 1) selective carotid hypoglycemia (vertebral glucose infusion, n = 5), 2) selective vertebrobasilar hypoglycemia (carotid glucose infusion, n = 5), 3) the absence of brain hypoglycemia (carotid and vertebral glucose infusion, n = 4), or 4) total brain hypoglycemia (no head glucose infusion, n = 5). Glucose was infused via a leg vein as needed in each group to minimize the differences in peripheral glucose levels (2.6 +/- 0.1, 3.0 +/- 0.2, 2.7 +/- 0.1, and 2.5 +/- 0.1 mM, respectively). The humoral responses (cortisol, glucagon, catecholamines, and pancreatic polypeptide) to hypoglycemia were minimally attenuated (< 40%) by selective carotid or vertebrobasilar euglycemia. In addition, the increase in hepatic glucose production, as assessed using [3-3H]glucose, was attenuated by only 41 and 34%, respectively, during selective carotid or vertebrobasilar hypoglycemia. These observations offer support for the hypothesis that more than one center is important in hypoglycemic counterregulation in the dog and that they are located in brain regions supplied by the carotid and vertebrobasilar arteries, because significant counterregulation occurred when hypoglycemia developed in either of these circulations. Counterregulation during hypoglycemia, therefore, is probably directed by widespread brain regions that contain glucose-sensitive neurons such that the sensing sites are redundant.

Oscillatory insulin secretion after pancreas transplant.

In vivo studies of beta-cell secretory function have demonstrated the existence of rapid insulin oscillations of small amplitude recurring every 8-15 min in normal subjects. This study evaluated the effects of pancreas transplant on rapid insulin oscillations. Samples for glucose, insulin, and C-peptide were drawn during constant glucose infusion at 2-min intervals for 90 min from six successful Px patients with type I diabetes mellitus, from six normal nondiabetic control subjects, and from three Kx subjects. A computerized algorithm (ULTRA) was used for pulse detection. In the Px group, the average insulin pulse period was significantly shorter than in both the control and Kx groups (Px 8.1 +/- 0.5, control 12.5 +/- 0.7, Kx 12.4 +/- 0.5 min, P < 0.0005). By contrast, the C-peptide pulse periods (Px 16.8 +/- 2.3, control 14.7 +/- 1.2, Kx 15.3 +/- 1.5 min) were similar in the three groups. Spectral analysis confirmed that the frequency of the insulin pulses was increased in the Px group. The absolute amplitude of the insulin pulses was greater in the Px group (P < 0.001) while the amplitude of the C-peptide pulses did not differ between the groups. Cross-correlation analysis demonstrated maximal correlation coefficients at a lag of 0 min between insulin and C-peptide (control r = 0.33, P < 0.0001; Kx r = 0.17, P = 0.06) and between insulin and glucose (control r = 0.21, P < 0.001; Kx r = 0.20, P < 0.02) in the control and Kx groups, respectively, whereas no significant correlations were observed at any lag in the Px group.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of metformin action in non-insulin-dependent diabetes.

The mechanism of action of metformin was studied by comparing glucose turnover before and after a 75-g oral glucose load in 10 nonobese men with non-insulin-dependent diabetes mellitus (NIDDM) during metformin and placebo therapy by the combined application of the forearm and double-isotope techniques. During the study, 9 of the 10 patients were regularly receiving glibenclamide therapy. In 5 of the men, the first study was performed during metformin therapy, and the second study was done during placebo administration; in the other 5 subjects, the order was reversed. The interval between the studies was at least 3 mo. The metformin dosage was 1 g twice daily in 9 of the patients and 850 mg thrice daily in the 10th subject. In the basal state, metformin administration reduced plasma glucose levels from 172 +/- 14 to 103 +/- 9 mg/dl (P less than .005), hepatic glucose output (HGO) from 2.67 +/- 0.15 to 2.20 +/- 0.20 mg X kg-1 X min-1 (P less than .02), and forearm glucose uptake (FGU) from 0.106 +/- 0.18 to 0.039 +/- 0.016 mg X 100 ml-1 forearm X min-1 (P less than .005), whereas insulin (23 +/- 6 microU/ml) and lactate (1.56 +/- 0.18 mM) levels were unchanged. Although the oral glucose tolerance curve (OGTC) was significantly lowered by metformin, the incremental area under the curve and the insulin response were unchanged. The systemic appearance of ingested glucose was unaffected by metformin; 64 +/- 2% of the load was recovered peripherally in 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial mechanics in young adult patients with diabetes mellitus: effects of altered load, inotropic state and dynamic exercise.

The disease entity "diabetic cardiomyopathy" has been extensively described in young patients with diabetes in the absence of ischemic, hypertensive or valvular heart disease. The most convincing data have been a 30% to 40% incidence of decreased radionuclide angiographic left ventricular ejection fraction response to dynamic exercise. In the current study, the hypothesis was tested that this abnormal ejection fraction response was due to alterations in ventricular loading conditions or cardiac autonomic innervation (extrinsic factors), or both, rather than to abnormalities in intrinsic ventricular systolic fiber function (contractility). Twenty normotensive patients with diabetes (mean age 30 +/- 5 years, mean duration 15 +/- 6 years) and 20 age-matched normal subjects were studied. All patients with diabetes had a normal treadmill exercise tolerance test without evidence of myocardial ischemia. By radionuclide angiography, all normal subjects increased ejection fraction with exercise (62 +/- 4% to 69 +/- 6%; p less than 0.001). In contrast, 11 (55%) of 20 patients with diabetes maintained or increased ejection fraction with exercise (group 1; 62 +/- 4% to 69 +/- 6%; p less than 0.001) and 9 (45%) of 20 showed an exercise-induced decrease (group 2; 73 +/- 4% to 66 +/- 6%; p less than 0.001). No difference in the incidence of microangiopathy, as noted by funduscopic examination, was present between the diabetic groups. Despite the abnormal ejection fraction response to exercise in the group 2 patients with diabetes, all patients with diabetes had a normal response to afterload manipulation, normal baseline ventricular contractility as assessed by load- and heart rate-independent end-systolic indexes and normal contractile reserve as assessed with dobutamine challenge. Autonomic dysfunction did not explain the disparate results between the group 2 patients' radionuclide angiographic data and their load-independent tests of ventricular contractility and reserve. In addition, the high ejection fraction at rest in group 2 patients (73 +/- 4% versus 62 +/- 4% for normal subjects; p less than 0.001) was not related to the abnormal tests of autonomic function. Thus, when left ventricular systolic performance was assessed by load- and rate-independent indexes, there was no evidence for cardiomyopathy in young adult patients with diabetes who have normal blood pressure and no ischemic heart disease.

Insulin and glucagon infusion in the treatment of liver failure.

In an attempt to improve liver function and promote hepatic regeneration in a patient with severe liver injury, insulin alone or insulin and glucagon were administered by constant peripheral venous infusion during a 61-day period. The response, as assessed by a broad spectrum of hepato-cellular function tests, including synthetic, detoxification, bile metabolism, and microsomal enzyme function, and also histological evidence, indicated a beneficial effect. Continuous insulin and glucagon infusion merits further evaluation in the treatment of some forms of hepatic failure.

Hyperinsulinism complicating control of diabetes mellitus by an artificial beta-cell.

Serum free insulin concentrations were measured in diabetic subjects given insulin intravenously by a glucose-controlled insulin infusion system ("closed-loop" artificial beta-cell) in two experimental situations: hourly during the day while given their usual diet and at short intervals after administration of a standardized test meal. Three of four subjects showed sustained hyperinsulinism when compared with matched controls during a day on their usual diet. In two of the subjects, the insulin levels also exceeded those seen in those subjects on their usual dose of subcutaneous insulin. The glucose levels were not completely normalized in the three hyperinsulinemic subjects, and the insulin levels were significantly correlated with plasma glucose levels. After the test meal, all six diabetic subjects studied showed a delayed rise in insulin levels, when compared with six normal subjects, followed by an abrupt rise in insulin levels to peak levels more than seven times those seen in normal subjects. We conclude that significant hyperinsulinism may accompany feedback-controlled intravenous insulin administration. This should be considered in interpreting studies done with such systems, and in design of control algorithms for future systems.