Release of somatostatin-like immunoreactivity from the perfused canine thyroid. Selective stimulatory effect of calcium ions.

It is well accepted that the C cells of the thyroid contain somatostatin, but the role in local endocrine function has not yet been firmly established in this organ, and it has not been proved that thyroidal somatostatin is released into the circulation. We have measured the contents of somatostatin-like immunoreactivity in the effluent of canine thyroid glands perfused without recirculation with a synthetic buffer medium. During basal conditions a definite release was consistently found in the order of 10 pg/ml corresponding to 12 pg/min. The somatostatin-like immunoreactivity was studied in dilution experiments and by gel-filtration chromatography, and found to have properties identical to those of synthetic cyclic somatostatin, which was also recovered quantitatively when added to sampling tubes. Various compounds were infused in concentrations that are highly active in pancreas perfusion experiments. 14-min infusion of arginine, 5 and 11.5 mmol/liter; isoproterenol, 10 and 23.7 nmol/liter and 68.7 mumol/liter; acetylcholine, 5 mumol/liter, carbamylcholine, 10 and 100 mumol/liter; glucagon, 1 and 30 nmol/liter; and porcine calcitonin, 1 and 100 ng/ml did not affect the basal release of somatostatin-like immunoreactivity significantly. Neither did an increase from the control level of 4 mmol/liter glucose of 10 or 20 mmol/liter, nor an increase in the control level of 4.4 mmol/liter K+ to 7.5 or 14.4 mmol/liter. Each of these compounds were tested in three or four dogs. The effect of an increase in Ca++ from the control level of 1.5 mmol/liter to 2.25, 3.0, and 4.5 mmol/liter was tested in random order in five thyroid lobes. All three doses elicited an immediate increase in effluent somatostatin-like immunoreactivity. In most experiments the response was biphasic with an early spike, followed by a stable level that was maintained during prolonged Ca++ infusion. The secretory response was not diminished through a series of repeated short pulses of calcium infusion. The response to 3.0 mmol/liter Ca++ (control period 8.4 +/- 1.5, test period 337 +/- 110 pg/ml, mean +/- SE) and 4.5 mmol/liter Ca++ (control period 9.5 +/- 1.4, test period 386 +/- 125) were significantly higher than 2.25 mmol/liter Ca++ (control period 7.2 +/- 1.0 test period 140 +/- 39), while there was no significant difference between responses to the two high doses. Infusion of salmon calcitonin, 10 ng/ml and 1 microgram/ml; or porcine calcitonin, 1 microgram/ml during calcium stimulation (2.25 mmol/liter of Ca++) did not induce alterations in the release of somatostatin-like immunoreactivity. The results demonstrate that thyroidal somatostatin is mobilizable, and it appears to be selectively sensitive to calcium stimulation, indicating a possible role in calcitonin release control.

The relationship between endogenous serum insulin concentration and glucose uptake in the forearm muscles of nondiabetics.

IN A SERIES OF EXPERIMENTS ON THE HUMAN FOREARM, PREPARATION DESIGNED TO EXAMINE THE EFFECTS OF VARIATIONS IN IMMUNOLOGICALLY DETERMINED ENDOGENOUS SERUM INSULIN LEVELS AND OF BLOOD GLUCOSE CONCENTRATIONS ON MUSCULAR GLUCOSE UPTAKE, THE FOLLOWING RESULTS WERE OBTAINED: (a) A highly significant correlation between muscular glucose uptake and simultaneous arterial serum insulin concentration. (b) No correlation between glucose uptake and simultaneous arterial blood glucose concentration during hyperglycemia. (c) A maximal insulin effect on muscular glucose uptake at arterial serum insulin concentrations at about 200 muU/ml. This observation is, however, based on only a few experiments.

Cubilin is an albumin binding protein important for renal tubular albumin reabsorption.

Using affinity chromatography and surface plasmon resonance analysis, we have identified cubilin, a 460-kDa receptor heavily expressed in kidney proximal tubule epithelial cells, as an albumin binding protein. Dogs with a functional defect in cubilin excrete large amounts of albumin in combination with virtually abolished proximal tubule reabsorption, showing the critical role for cubilin in the uptake of albumin by the proximal tubule. Also, by immunoblotting and immunocytochemistry we show that previously identified low-molecular-weight renal albumin binding proteins are fragments of cubilin. In addition, we find that mice lacking the endocytic receptor megalin show altered urinary excretion, and reduced tubular reabsorption, of albumin. Because cubilin has been shown to colocalize and interact with megalin, we propose a mechanism of albumin reabsorption mediated by both of these proteins. This process may prove important for understanding interstitial renal inflammation and fibrosis caused by proximal tubule uptake of an increased load of filtered albumin.

Concomitant, specific determination of growth hormone and pegvisomant in human serum.

Growth hormone (GH) and the GH receptor blocker, pegvisomant are usually circulating in high concentration in pegvisomant treated acromegalic patients. This and the close similarity between the peptides make determination of either difficult. In the present methodological study, endogenous GH in serum is initially isolated and determined in a slightly modified commercial immunometric assay, whereafter the now GH free medium allows measurement of pegvisomant. Inter-individual steady state levels of serum pegvisomant vary remarkably in both acromegalic patients and healthy controls, while the intra-individual variations are negligible.

Insulin-like growth factor (IGF) I, -II, and IGF binding protein-3 and risk of ischemic stroke.

BACKGROUND: Low IGF-I levels may be associated with the development of stroke; however, prospective data appear to be unavailable. METHODS: This was a nested case-control study within a Danish follow-up study, including 57,053 men and women. Baseline data included circulating IGF-I, IGF-II, and IGF binding protein (IGFBP)-3 concentrations as well as lifestyle factors and medical history. We identified 254 cases with incident ischemic stroke and 254 gender- and age-matched controls. RESULTS: Participants in the bottom quartiles of IGF-I and IGFBP-3 levels (median concentrations, 72 and 2937 ng/ml, respectively) were at increased risk of ischemic stroke, e.g. adjusted odds ratios (ORs) of 2.06 [95% confidence interval (CI), 1.05-4.03] and 2.29 (95% CI, 1.17-4.49), respectively, when compared with participants in the top quartiles (median concentrations, 125 and 4835 ng/ml, respectively). A negative, although weaker, association was also found for IGF-II (adjusted OR 1.44, 95% CI 0.79-2.64) when comparing the bottom quartile with the top quartile. No substantial associations were seen for IGF-I and IGF-II when also adjusting for IGFBP-3; adjusting IGFBP-3 for IGF-I and -II had only a minor impact on the risk estimates. CONCLUSION: These findings give some support to the hypothesis that the IGF axis is involved in the pathogenesis of ischemic stroke.

Reversal of D- and A-cell insensitivity to glucose in alloxan-diabetic dogs by treatment with the artificial beta cell (Biostator).

Insulin-deficient diabetes in man as well as in experimental diabetes is associated with islet cell insensitivity to glucose. The present study was designed to determine whether this abnormality could be counteracted either by increasing the intraislet insulin level or by normalizing the diabetic state by a glucose-controlled insulin infusion system (GCIIS: Biostator, Life Science Instruments, Elkhart, Indiana). Using the isolated, perfused pancreas of dogs with moderate, untreated alloxan diabetes of 4 days duration, we found that 5 mM arginine (N = 4) and 5 mM calcium (N = 4) stimulated D- and A-cell secretion, whereas an increment in glucose from 1.3 to 11 mM (N = 4) had no effect on islet hormone secretion. In the pancreas from untreated alloxan-diabetic dogs, acute infusion of large amounts of insulin (25 mU/ml) in vitro simultaneously with an elevation of perfusate glucose from 1.3 to 11 mM failed to restore the glucose from 1.3 to 11 mM failed to restore the glucose sensitivity. In contrast, treatment of alloxan-diabetic dogs (N = 3) by a GCIIS for 24 h revived some responsiveness of the glucagon, insulin, and somatostatin to glucose (1.3-11 mM) of the subsequently perfused pancreas. It is concluded that the insensitivity to glucose of islet cells in insulin-deficient diabetes is not ascribed to an intra-islet insulin deficiency per se but rather to an abnormal metabolic state secondary to insulin deficiency. The results also indicate that the glucose receptor dysfunction is not due to a direct lesion by the diabetogenic drug.

Synthetic pancreatic growth hormone-releasing factor (GRF-40) stimulates the secretion of the endocrine pancreas.

The effects on islet hormone secretion of the synthetic replicates of two peptides with potent GH-releasing activity isolated from human pancreatic islet cell tumors (GRF-40 and GRF-44) were studied using the isolated, perfused dog pancreas. GRF-40 produced a dose-dependent stimulation of insulin, glucagon, and somatostatin secretion. The responses to GRF-40 were modified by the prevailing glucose level: higher insulin and somatostatin and lower glucagon responses were obtained at high rather than low glucose. In contrast, GRF-44 did not produce any stimulation of the endocrine pancreas. In vivo GRF-40 and GRF-44 elicited identical pronounced growth hormone responses in the rat. The findings reported here provide support that pancreatic insulin and glucagon are modulated by GRF-40 with somatostatin as its inhibitory counterpart. The question, whether GRF-40 is of physiologic relevance in the regulation of the endocrine pancreas, must await evidence that it is present and releasable from the pancreas.

Similar insulin sensitivity in NIDDM patients with normo- and microalbuminuria.

OBJECTIVE: To investigate whether insulin resistance and microalbuminuria are associated in non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS: Insulin sensitivity was assessed using a hyperinsulinemic euglycemic clamp in 11 normoalbuminuric and 9 microalbuminuric NIDDM patients matched for sex, age, body composition, glycemic control, diabetes duration, and therapy. RESULTS: Isotopically determined glucose disposal was similar in normo- and microalbuminuric patients in the basal state (mean +/- SD; 3.30 +/- 1.01 vs. 3.46 +/- 0.82 mg.kg lean body mass [LBM]-1.min-1; NS) and during hyperinsulinemia (7.16 +/- 2.65 vs. 6.63 +/- 2.88 mg.kg LBM-1.min-1;NS). No difference was observed in nonoxidative glucose disposal or lipid oxidation. Endogenous glucose production was equally suppressed by insulin (-0.08 +/- 0.99 vs. 0.30 +/- 1.12 mg.kg-1 LBM.min-1; NS). Glucose oxidation tended to be lower in the normoalbuminuric patients in the basal state (1.16 +/- 0.37 vs. 1.41 +/- 0.36 mg.kg LBM-1.min-1) and during hyperinsulinemia (2.35 +/- 0.72 vs. 2.90 +/- 0.77 mg.kg LBM-1.min-1; both P < 0.15). Urinary albumin excretion rate correlated with the insulin-stimulated glucose oxidation rate (r = 0.59, P = 0.0064), and a similar trend was seen in the basal state (r = 0.42, P = 0.063). Protein oxidation was higher in normoalbuminuric patients (1.6 +/- 0.5 vs. 1.0 +/- 0.4 mg.kg LBM-1.min-1; P = 0.017) and correlated inversely with albuminuria (r = -0.70, P = 0.0007). Serum growth hormone increased during insulin infusion; however, the increase was significantly greater in microalbuminuric patients. Plasma lipoproteins, maximal aerobic capacity, and 24-h ambulatory blood pressure were similar in the two groups. CONCLUSIONS: Basal and insulin-stimulated glucose uptakes are comparable in carefully matched normo- and microalbuminuric NIDDM patients, and glucose oxidation may be positively related to albuminuria. The inverse relation between protein oxidation and albuminuria may be due to higher growth hormone levels during daily life perturbations in glucose in microalbuminuric patients.

Insulin action in insulin-dependent diabetics after short-term thiazide therapy.

The influence of short-term thiazide treatment on peripheral tissue and liver sensitivity to insulin in insulin-dependent diabetes mellitus was determined by the euglycemic insulin clamp technique. A sequential three-step hyperinsulinemic clamp was performed in six insulin-dependent diabetics before and after 2 wk of hydroflumethiazide (HFT) administration in a daily dose of 75 mg. Insulin was infused at rates of 0.5, 2.0, and 4.0 mU X kg-1 X min-1, and each dose was given for at least 120 min. Glucose uptake during the last 30 min of each step was almost identical in the two situations (2.7 +/- 0.6 vs. 2.4 +/- 0.5 mg X kg-1 X min-1, 9.6 +/- 0.9 vs. 9.7 +/- 1.2 mg X kg-1 X min-1, and 12.0 +/- 1.3 vs. 12.6 +/- 1.5 mg X kg-1 X min-1). Serum insulin levels were also similar, and blood glucose was kept at 100 +/- 3, 99 +/- 4, and 97 +/- 3 mg/dl before thiazides and at 93 +/- 6, 93 +/- 6, and 94 +/- 6 mg/dl after thiazides. Another five insulin-dependent diabetics were infused with tritiated glucose followed by insulin infusion at two rates: 0.45 and 1.0 mU X kg-1 X min-1. Basal glucose output was comparable before and after thiazides (3.63 +/- 0.24 vs. 2.97 +/- 0.26 mg X kg-1 X min-1), as was the liver response to increasing insulin concentrations. The metabolic state as assessed by HbA1c and fasting blood glucose did not differ in the two experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone stimulates bone formation and strength of cortical bone in aged rats.

The influence of growth hormone on bone formation, mechanical strength, and composition has been investigated in femur middiaphyseal cortical bone from 2-year-old male rats. The rats were given biosynthetic human growth hormone (bhGH) at 2.7 mg/kg/day in two daily injections for 20, 40, or 80 days, and all animals were killed 80 days after the start of bhGH administration. Control animals were given saline. All animals were labeled with tetracycline on days 41 and 69. Only in the bhGH-80-day group was subperiosteal tetracycline double labeling seen all around the femur diaphysis, and this pattern was found in all animals of the group. Double labeling subperiosteally at the posteromedial aspect was found in all animals of the experiment, but compared with the control group, a 400% and an 800% increase in mineral apposition rate was seen in the bhGH-40-day and bhGH-80-day groups, respectively. Light microscopy and polarization microscopy showed that this newly deposited bone was organized in the same concentric lammellae and had the same direction of the collagen fibers when compared with the surrounding bone formed before the start of bhGH injections. The cortical bone cross-sectional area was increased in the bhGH-40-day and bhGH-80-day groups. At the endosteum, scattered labeling was found in animals from all groups, and no differences in medullary cross-sectional areas were seen. The mechanical analysis revealed an increased mechanical strength of the whole diaphyseal bone after bhGH administration. When the data were corrected for dimensions of the diaphyseal bone, no differences in intrinsic mechanical properties of the bone tissue were found. No differences in apparent density of dry defatted bone, ash, and collagen were seen, whereas apparent density of dry defatted bone minus ash was decreased in all groups given bhGH. Correspondingly, a slight increase in ash concentrations of the bhGH-injected animals was seen. bhGH administration also increased the body weight, muscle mass, and total serum IGF-I and thyroxine concentrations.

Growth hormone and mild exercise in combination markedly enhance cortical bone formation and strength in old rats.

The effects of a combination of mild exercise and GH injections on bone were studied in old female rats. Biosynthetic human GH, 2.7 mg/kg/day, was injected s.c. for 73 days. Exercised rats ran 8 m/min on a treadmill for 1 h/day. All rats (age 21 months old) were labeled with a tetracycline injection 56 days and a calcein injection 11 days before killing. The GH injections resulted in an 11-fold increase in femoral middiaphyseal bone formation rate and a 12% increase in cross-sectional area compared with the saline-injected group. The mild exercise doubled the mineralizing surface but did not influence the bone formation rate significantly. The combination of GH injections plus exercise, however, resulted in a further increase of 39% in bone formation rate, primarily at the anterolateral aspects, and an increase of 5% in cross-sectional area compared with the group injected with GH only. The femur ultimate breaking load was increased by 37% and the stiffness by 42% in the group injected with GH compared with the saline-injected group. Exercise alone did not influence the femur mechanical properties. The combination of GH injections plus exercise induced a 4% further increase in ultimate breaking load and 7% further increase in stiffness compared with the group injected with GH alone. The GH injections induced a 117% increase in serum insulin-like growth factor I. The GH-insulin-like growth factor I axis stimulates recruitment of osteoblast precursor cells, resulting in increased bone formation at the periosteal surface. GH injections and mild excercise in combination modulate and increase further the formation and strength of cortical bone in old female rats.

Developmental changes in serum levels of free and total insulin-like growth factor I (IGF-I), IGF-binding protein-1 and -3, and the acid-labile subunit in rats.

We have recently described a competitive binding assay for rat insulin-like growth factor-binding protein-3 (IGFBP-3) based on the ability of IGFBP-3 to form a ternary complex with the acid-labile subunit (ALS) in the presence of IGF-I. Using this assay we studied groups of male (n = 6) and female rats (n = 6) at 20, 30, 40, 50, 60, 80, and 130 days of age. Nonfasting serum levels of IGFBP-3 were compared with those of total (extractable) IGF-I (tIGF-I) and ALS as well as IGFBP-3 determined by ligand blotting. Additionally, we studied the relationship between ultrafiltered free IGF-I (fIGF-I) and immunoassayable IGFBP-1. IGFBP-3 was dependent on age only (P < 0.0001), but tended to be higher in males than in females (P = 0.06); between 20-130 days levels increased from 6.5 +/- 1.7 to 73.6 +/- 7.2 nmol/liter in males and from 5.4 +/- 1.6 to 51.3 +/- 8.0 nmol/liter in females. IGFBP-3 correlated positively with tIGF-I (r = 0.90; P < 0.0001), ALS (r = 0.92; P < 0.0001), and IGFBP-3, as determined by ligand blotting (r = 0.88; P < 0.0001). The molar ratio of IGFBP-3 to tIGF-I increased from 0.23 +/- 0.04 to 0.76 +/- 0.04 (P < 0.0001) without any sex dependence. An age- and sex-dependent decrease in IGFBP-1 was observed (P < 0.0001), from 10.9 +/- 2.5 to 1.2 +/- 0.2 nmol/liter in females and from 8.9 +/- 0.7 to 0.2 +/- 0.04 nmol/liter in males. Free IGF-I (fIGF-I) increased with age (from 0.7 +/- 0.2 to 7.1 +/- 0.5 nmol/liter; P < 0.0001), and levels were inversely correlated with IGFBP-1 (r = -0.80; P < 0.0001). In young rats, IGFBP-1 circulated in a 10-fold molar excess over the level of fIGF-I, whereas in older rats, fIGF-I exceeded IGFBP-1 by an average of 9-fold in females and by up to almost 60-fold in males. We conclude that in rats 1) IGFBP-3 and fIGF-I are strongly age dependent; 2) IGFBP-3 correlates positively with ALS and tIGF-I; and 3) fIGF-I and IGFBP-1 are inversely correlated. This is in accordance with clinical findings. However, in humans the adult level of fIGF-I rarely exceeds 0.3 nmol/liter, and IGFBP-1 usually circulates in excess of fIGF-I. Thus, our results also imply species differences in the IGF systems of humans and rats.

Greater in vivo than in vitro pulsatility of insulin secretion with synchronized insulin and somatostatin secretory pulses.

To examine the control of pulsatile insulin secretion by an intrapancreatic pacemaker, samples at minute intervals were taken from the portal vein in dogs in vivo and from an isolated perfused pancreas preparation in vitro. Anesthetized dogs had high amplitude pulsatile insulin secretion which was not consistently regular. Fourier transform analysis showed dominant 20- and 10-min periods of spectral power (P less than 0.01). After vagotomy, the relative oscillatory power was reduced from 83% to 42%, about a lower mean concentration with abolition of the 20-min oscillations. The isolated perfused dog pancreas also had oscillatory insulin secretion with oscillatory power of 12%. Autocorrelation showed regularity of in vitro insulin secretion with a period of 10-11 min (P less than 0.0001). In addition, somatostatin was secreted from the in vitro pancreas in pulses in phase with insulin (cross-correlation P less than 0.0001). These data are in accord with the theory that the pancreas has an internal pacemaker which controls insulin secretion, and that the amplitude of the oscillations is modulated by vagal control. The pacing of the islets may be coordinated by a neural network, whereas coincident pulsatile somatostatin release may temporarily suppress islet secretion and help to synchronize hormonal oscillations.

The effect of oral glucose on serum free insulin-like growth factor-I and -II in health adults.

Insulin-like growth factor (IGF) binding protein-I (IGFBP-1) has been suggested to regulate the availability of free IGF and the glucose lowering activity of the IGF-system in relation to fuel supply. Our recent observations of significant inverse correlations between free IGF-I and IGFBP-1 in cross-sectionally collected fasting serum samples support a possible physiological association between the peptides. To further study the impact of IGFBP-1 on free IGF levels and the possible participation of the IGF-system in glucose homeostasis, we studied the time course of changes in IGFBP-1 and free IGFs in 13 healthy subjects undergoing an oral glucose tolerance test (OGTT). Serum was collected every 30 min for 330 min. Glucose, insulin, and GH followed the expected patterns and had regained baseline levels at 270 min. Total IGF-I and free and total IGF-II remained unaltered. IGFBP-1 decreased significantly by 37-52% (P < 0.05) from 150 to 210 min, whereafter the concentration gradually increased by 75% to a level that tended to be above baseline (P = 0.052). Free IGF-I decreased by 29-38% (P < 0.05) at the end of the study (270-330 min). IGFBP-1 was inversely correlated to free IGF-I at baseline (r = -0.57; P < 0.05), as well as during the OGTT (r = 0.66; P < 0.0001). In contrast, free IGF-II was not correlated to IGFBP-1. Insulin, but not free IGF-I, correlated significantly with serum glucose (P < 0.05). These results extend our previous findings of an inverse correlation between free IGF-I and IGFBP-1 in cross-sectional studies to include longitudinal observations, and thus further substantiates the hypothesis that IGFBP-1 is an important determinant of free IGF-I in vivo. Significant changes in free IGF-I were observed only in the late postprandial phase, when glucose and insulin were fully normalized, demonstrating that free IGFs probably do not participate in glucoregulation to any significant degree during an oral glucose load in healthy subjects.

Effect of sex hormone replacement on the insulin-like growth factor system and bone mineral: a cross-sectional and longitudinal study in 595 perimenopausal women participating in the Danish Osteoporosis Prevention Study.

This study used a cross-sectional design to investigate relationships among serum insulin-like growth factor (IGF) parameters (total serum IGF-I, IGF-II, and IGF-binding protein-3), serum estradiol, and bone mineral density (BMD) stratified for potential confounders, and a longitudinal design to investigate the effects of hormonal replacement therapy (HRT) on IGFs and BMD. Five hundred and ninety-five perimenopausal women (median age, 50.0 yr; range, 45-56 yr) participating in the Danish Osteoporosis Prevention Study were investigated in a cross-sectional study, and a randomly selected subgroup of 110 was followed after 5 yr in a longitudinal study for changes in serum IGFs and BMD of lumbar spine, femoral neck, and ultradistal forearm during (n = 46) or without HRT (n = 64). In the cross-sectional study, serum IGF-I correlated positively to distal forearm BMD and spine BMD, but not to femoral neck BMD, after stratification for age, body mass index, and other variables. In the follow-up study, HRT decreased IGF-I and IGF-II, but did not influence the age-related decline in IGF-binding protein-3 significantly. Serum alkaline phosphatase and urinary hydroxyproline/creatinine ratio both decreased during HRT, whereas BMD increased compared to control values. After adjustment for age, body mass index, treatment, and other factors, IGF-I correlated positively to changes in forearm and femoral neck BMD, but not to changes in spine BMD. We conclude that serum IGF-I was positively associated to bone mineral density. Oral HRT decreases IGF-I and IGF-II.

In vivo insulin action in type 1 (insulin-dependent) diabetic pregnant women as assessed by the insulin clamp technique.

To determine the influence of pregnancy on insulin sensitivity in patients with type 1 diabetes mellitus in more detail, a hyperinsulinemic euglycemic clamp study was performed in six pregnant type 1 diabetic women and eight nonpregnant women with type 1 diabetes mellitus. All of the pregnant women were studied three times: in early pregnancy (mean, week 13), late pregnancy (mean, week 34), and within a week after delivery. Insulin was infused in a constant rate of 1.0 mU/kg X min, which resulted in steady state serum free insulin levels (I) of 44 +/- 3 (+/- SEM), 56.6 +/- 6, and 55 +/- 8 microU/ml in the pregnant diabetic women and 52 +/- 4 microU/ml in the nonpregnant women. Mean glucose disposal (M) was 5.6 +/- 0.3 mg/kg X min early in pregnancy and 3.4 +/- 0.5 mg/kg X min late in pregnancy (P less than 0.02). However, in the early postpartum period, M was again higher (7.2 +/- 0.7 mg/kg X min; P less than 0.02) and similar to values in early pregnancy and nonpregnant diabetic women (7.2 +/- 0.6 mg/kg X min). When tissue sensitivity to insulin was expressed as the M to I ratio, similar results were obtained (nonpregnant women, early stage of gestation, and postpartum vs. late stage of gestation: 0.13 +/- 0.01, 0.13 +/- 0.01, and 0.15 +/- 0.03 mg/kg X min per microU/ml vs. 0.06 +/- 0.1 mg/kg X min per microU/ml; P less than 0.03 in all). There tended to be an inverse relationship between serum levels of human placental lactogen and the M to I ratio during pregnancy (r = -0.74; P = 0.09). However, we found no association between changes in the impairment of insulin action and serum estradiol, progesterone, or cortisol levels. In conclusion, pregnant type 1 diabetic women have insulin resistance in peripheral tissues in the late stage of gestation. Insulin sensitivity returns to values found in nonpregnant diabetic women within the first week after delivery.

Somatostatin-stimulated insulin-like growth factor binding protein-1 release is abolished by hyperinsulinemia.

It was demonstrated recently that administration of lanreotide and octreotide, two somatostatin octapeptide analogs, increased circulating insulin-like growth factor binding protein 1 (IGFBP-1) levels. The present study demonstrates that native somatostatin 14 shares this ability and that the increase in abolished by concomitant hyperinsulinemia within the physiological range. Five fasting healthy volunteers underwent a hyperinsulinemic as well as a normo-insulinemic (i.e. basal insulinemic) euglycemic clamp lasting 8 h (serum insulin levels remained constant, about 570 vs. 16 pmol/L). Immediately before the clamps, a somatostatin infusion (500 micrograms/h) was started and continued throughout. During normo-insulinemia, IGFBP-1 levels increased slowly from 6.3 +/- 6.2 to 36.1 +/- 14.8 micrograms/L (P < 0.05) reaching maximum after 7 h constant somatostatin infusion, whereas hyperinsulinemia induced a significant decrease from basal levels (from 4.7 +/- 5.4 to 1.1 +/- 1.5 micrograms/L) after 8 h (mean +/- SD, n = 5). These results may indicate hitherto unnoticed interactions of somatostatin and insulin on IGFBP-1 release with possible impact on IGF-I action at the cellular level.

Dose-dependent stimulation of insulin-like growth factor-binding protein-1 by lanreotide, a somatostatin analog.

It was recently reported that octreotide, besides its many, almost obligatory, inhibitory actions, stimulates the release of insulin-like growth factor-binding protein-1. The present study sought to exclude the possibility that the inescapable preceding somatostatin analog-induced reduction in serum insulin participated in the observed effect. We, therefore, administered sc two clinically relevant doses (5 and 80 micrograms/kg) of lanreotide, another somatostatin octapeptide analog, which induced identical 60% initial suppressions of serum insulin. In spite of this, clear dose-dependent increases in insulin-like growth factor-binding protein-1 were observed, starting between 1-2 h after administration of lanreotide, and levels were still elevated several-fold 5 h after administration of 80 micrograms/kg lanreotide. In addition, we found that infusion of amino acids had no discernible effect on binding protein-1 release. The changes found in immunoreactive binding protein-1 were confirmed employing Western ligand blotting. The data indicate that the lanreotide-induced increase in binding protein-1 levels in serum is not due to the changes in circulating insulin. The magnitude and duration of the increase raise the possibility that the stimulation may have clinically relevant implications in somatostatin analog treatment.

Dose-response studies with biosynthetic human growth hormone (GH) in GH-deficient patients.

Increasing doses of biosynthetic human GH (R-hGH) were given sc to seven GH-deficient patients for three consecutive 14-day periods (2, 4, and 6 IU/day at 2000 h), followed by 14 days of no GH therapy. At the end of each period each patient was hospitalized for frequent blood sampling from 2000 to 1100 h the following day. A dose-dependent increase in serum GH and serum insulin-like growth factor I (IGF-I) levels occurred. However, the time course of the serum IGF-I concentrations was different on the four occasions; there was a significant fall in the evening when no therapy was given (P less than 0.01), a significant increase after injections of 2 IU R-hGH, and constant levels during treatment with 4 and 6 IU R-hGH. Plasma glucose levels were within the normal range, with a significantly lower fasting level (at 0400 h) when no GH was given. Breakfast induced a plasma glucose rise when GH was administered, but no rise without GH, and a postprandial serum insulin response that was GH dose dependent. GH therapy increased serum FFA (P less than 0.05) and blood 3-hydroxybutyrate levels, but had no effect on blood alanine or lactate or serum triglyceride and cholesterol levels. We conclude that the serum IGF-I response to GH is dose dependent, and that a GH replacement dose of 2 IU/day (equalling 1.5 IU/m2.day) is insufficient to maintain normal diurnal serum IGF-I levels. Furthermore, a GH-independent diurnal variation in serum IGF-I in these patients is suggested. This GH preparation also has diabetogenic and lipolytic actions.

Abdominal fat determines growth hormone-binding protein levels in healthy nonobese adults.

The circulating high affinity GH-binding protein (GHBP), which derives from the extracellular domain of the hepatic GH receptor, correlates inversely to GH levels and directly to body mass index (BMI) in healthy adults. As GH secretion and adiposity are also interrelated, we tested the hypothesis that body composition more than GH, determines GHBP levels in healthy adults. Forty-two healthy adults [21 females and 21 males; mean age, 39.4 yr range, 27-59 yr); mean BMI, 23.9 kg/m2 (range, 18.9-34.7 kg/m2)], underwent anthropometric measurements (BMI, W/H ratio, computed tomography scan, dual energy x-ray absortiometry (DEXA) scan, and bioimpedance) in addition to two GH stimulation tests (arginine and clonidine) and a 24-h GH profile. By simple linear regression, serum GHBP correlated positively to several indices of adiposity: intraabdominal fat (r = 0.537; P = 0.001), sc abdominal fat (r = 0.680; P < 0.001), BMI (r = 0.483; P = 0.001), W/H ratio (r = 0.452; P = 0.003), total body fat (DEXA scanning; r = 0.503; P = 0.002), and body fat (bioimpedance; r = 0.354; P = 0.023). Lean body mass estimated by DEXA scan was negatively associated with GHBP (r = 0.541; P < 0.001). GHBP was inversely proportional to arginine-stimulated GH release (r = -0.346; P = 0.027) and negatively associated with several measures of spontaneous GH release as estimated by deconvolution analysis (GH mass, GH production rate, and mean GH; r = -0.371; P = 0.017, r = -0.393; P = 0.011, and r = -0.343; P = 0.028, respectively)). With multiple linear regression analyses, indices of adiposity were significant determinants of GHBP levels, whereas GH status did not contribute independently to the prediction of GHBP. Neither insulin-like growth factor I nor fasting insulin levels correlated to GHBP levels. In conclusion, GHBP levels in normal adults seem to be determined by abdominal fat mass rather than GH secretion.