Behavior of C-peptide and immunoreactive insulin in essential obesity]

The levels of glucose, immunoreactive insulin and C-peptide were studied in 13 obese patients and 10 control subjects, in basal conditions and after an oral glucose load (OGTT). The IRI and C-peptide levels were higher in the obese patients than in the controls either during fasting or during the OGTT. The C-peptide/IRI ratio decreased after the oral glucose load in both groups studied. However in the obese subjects the values for the C-peptide/IRI ratio were lower than those found in the controls during the same observation period. These results suggest the hypothesis that in the obese patients the high IRI levels which reflect an increased insulin secretion, are, at least in part, due to an early saturation of the hepatic degradation of insulin and/or to a decrease in the specific receptor sites normally present in the cell membranes.     

Plasma glucagon response to intravenous alanine in obese and non-obese subjects

To investigate glucagon (IRG) and insulin (IRI) responses to alanine infusion in obesity and to assess the effect of body weight reduction with respect to hormonal balance, we compared six obese subjects with nine normal weight controls. None of the subjects were diabetic by OGTT criteria. Plasma IRI and IRG were measured following IV alanine at a rate of 0.1 g/kg over a period of 2 min. Our obese subjects had an increase in IRG response to alanine, which was due to decreased suppression of alpha-cell function due to insulin resistance. Weight reduction via calorie restriction reduced insulin demand, resulting in reduced plasma IRI by restoring beta-cell function, and the IRG response was paradoxically decreased as compared with that before weight loss. It is conceivable that improvements in insulin sensitivity after body weight reduction may re-establish the normalization of pancreatic beta-cell function and the insulin-induced inhibition of IRG secretion. Our obese subjects were characterized by decreased IRG secretion which was reflected in a change in body weight reduction.     

Effect of somatostatin suppression of glucagon secretion on glucose production in sheep.

The effect of somatostatin (SRIF) on glucagon and insulin secretion was examined in fed and fasted sheep. This was related to changes in glucose production. Infusion of SRIF at 80 micrograms/h caused a marked reduction in plasma glucagon concentrations. However, the insulin response to SRIF infusion was not consistent; its concentrations decreased occasionally, but often did not change. The depression of glucagon was not associated with a significant reduction in blood glucose concentrations in either fed or fasted sheep, but was associated with a reduction in glucose production by 12--15%. The inhibitory effect of insulin on glucose production was not markedly increased by glucagon deficiency. Infusion of insulin at 1.17 U/h with SRIF decreased glucose production only an additional 10%. Thus, it appears that under basal conditions pancreatic hormonal influences on hepatic glucose production were relatively small in sheep. This implies that under normal conditions in sheep, substrate supply has a much greater impact on hepatic glucogenesis than do hormones.     

Growth hormone, insulin and placental lactogen in the sera of mothers and fetal blood of infants from physiological pregnancy and pregnancy complicated by diabetes mellitus

The study was aimed at investigating the changes in the blood serum concentrations of growth hormone (HGH), insulin and placental lactogen (HPL) in the newborns of diabetic mothers as compared to those born from physiological pregnancies. The concentration of hormones was determined by RIA both in the newborns and in mothers of the two groups. The mean insulin concentration was significantly higher, and that of HGH significantly lower in the newborns of diabetic mothers, as compared to those of healthy mothers. It seems that the occurrence of fetal macrosomy in diabetic pregnancies is associated with high insulin levels.     

Antibodies against calcium-regulating hormones in infectious-allergic forms of bronchial asthma

Antibodies to calcitonin, parathyroid hormone and cortisol are detected in acute stage of infection-caused bronchial asthma. The appearance of antibodies is paralleled by marked hypercalcaemia. The antibodies may bind excessive hormones in the blood, preventing further hormonal imbalance. Ten-day treatment with glucocorticoids decreased the amount of antibodies possibly due to normalization of hormonal secretion and restoration of their balance. As a result, calcium blood levels returned to normal.     

Oral glucose tolerance test in polycystic ovary syndrome

OGTT was used to clarify the problem of hyperinsulinism and insulin resistance previously investigated by us in PCOS, using the tolbutamide test. The results of this latter investigation were in agreement with the previous found by us and with the similar already reported by other Authors. 26 women (7 obese), aged 14-34 years, affected by PCOS, were studied. The diagnosis of PCOS was made using clinical, hormonal, radiologic and echographic criteria. 16 age matched healthy women were used as controls. Glucose and insulin curves, glucose (GA) and insulin (IA) response areas and IA/GA ratio (insulin resistance in dex-IRI-) were studied by OGTT. Blood insulin values of patients resulted significantly more elevated than that of controls at any point of the curve and more significantly elevated were decreasing values. Mean values of insulin peaks, of insulin areas and of IRI resulted more elevated than that of controls. The presence of both an hyperinsulinism and an insulin resistance in PCOS seems therefore evident. A correlation was found between IRI values and plasma testosterone levels in non obese patients with increased urinary 17-ketosteroid output. A relationship between hyperandrogenism on one hand and hyperinsulinism and insulin resistance on the other is suggested.     

Effect of calcitonin and 1,25(OH)2-vitamin D3 on the FSH, LH and testosterone secretion at rest and LHRH stimulated secretion

The calcium signal plays an important role in the control of the secretory process of some adenohypophyseal hormones which responds to the administration of calciotropic substances by a marked change. In the submitted work the effect of calcitonin and 1,25(OH)2-vitamin D3 (1,25(OH)2D3) on FSH, LH and testosterone secretion was investigated. A single dose of 50 U synthetic salmon calcitonin did not influence the FSH, LH and testosterone secretion at rest nor stimulated secretion. 1,25(OH)2D3 administered for four days in amounts of 3 micrograms/day did not affect the LH and testosterone secretion but increased slightly the secretory response of FSH to LHRH, significantly during the 80th minute following administration of the secretagogue (P less than 0.01). The indication of bi-phasic FSH secretion was eliminated by 1,25(OH)2D3. The significant decline of PTH levels following administration of 1,25(OH)2D3 is evidence of a biologically effective level of 1,25(OH)2D3 attained by the administered dose of hormone. As compared with the marked effect of calcitonin and 1,25(OH)2D3 on thyrotropic hormone secretion, it may be concluded that the gonadotropic system is considerably less sensitive to a change of calcium homeostasis induced by calcitonin or 1,25(OH)2D3. Nevertheless a slight increase of the FSH secretion and a change of the dynamics of its secretion suggest a modulating role of 1,25(OH)2D3 in the control of FSH secretion.     

The influence of plasma triglycerides on human growth hormone response to arginine and insulin: a study in hyperlipemics and normal subjects.

Human growth hormone (HGH) response to arginine (25 gm IV in 30 min) and to insulin (0.1 U/kg B.W.) was studied in 12 male patients (mean age 36 +/- 2 years), with normal glucose tolerance and normal body weight, affected with Fredrickson's Type IV primary hyperlipemia. The patients were examined both when plasma triglycerides (TG) were elevated and following clofibrate (2 gm/die for 30-60 days) induced TG reduction. No variations in glucose or FFA behaviour or in body weight were observed after clofibrate. HGH response to arginine was absent, while that to insulin was only inhibited, when plasma TG were elevated. A significant increase in HGH peaks after arginine (from 1.99 +/- 0.59 to 9.34 +/- 1.58 ng/ml) and a slight increment in HGH peaks after insulin (from 23.09 +/- 7.19 to 31.46 +/- 7.95 ng/ml) were observed following reduction in plasma TG. Arginine test was carried out in 7 normal subjects during saline infusion and at the 3rd hour of lipid infusion (Intralipid 20%). HGH response to arginine was absent in all of the subjects during lipid infusion. The HGH response to insulin test, carried out in 9 other normal subjects during saline infusion and at the 3rd hour of lipid infusion (Lipiphysan 15%) was significantly inhibited during lipid infusion. Since lipid infusion provoked an increment, not only in plasma TG but also in FFA, the inhibition of HGH release could be correlated with the elevated plasma levels of both TG and FFA. The results obtained in both spontaneous and experimental hyperlipemia not only confirm the role played by FFA in the regulation of HGH secretion, but also support the hypothesis that elevated TG levels could inhibit HGH response to some stimuli.     

Establishment of a Refined Oral Glucose Tolerance Test in Pigs,and Assessment of Insulin,Glucagon and Glucagon-Like Peptide-1 Responses

Diabetes mellitus is increasing worldwide and reliable animal models are important for progression of the research field. The pig is a commonly used large animal model in diabetes research and the present study aimed to refine a model for oral glucose tolerance test (OGTT) in young growing pigs, as well as describing intravenous glucose tolerance test (IVGTT) in the same age group. The refined porcine OGTT will reflect that used in children and adolescents. Eighteen pigs were obtained one week after weaning and trained for two weeks to bottle-feed glucose solution, mimicking the human OGTT. The pigs subsequently underwent OGTT (1.75 g/kg BW) and IVGTT (0.5 g/kg BW). Blood samples were collected from indwelling vein catheters for measurements of glucose and the diabetes related hormones insulin, glucagon and active glucagon-like peptide-1. The study confirmed that pigs can be trained to bottle-feed glucose dissolved in water and thereby undergo an OGTT more similar to the human standard OGTT than previously described methods in pigs. With the refined method for OGTT, oral intake only consists of glucose and water, which is an advantage over previously described methods in pigs where glucose is given together with feed which will affect glucose absorption. Patterns of hormonal secretion in response to oral and intravenous glucose were similar to those in humans; however, the pigs were more glucose tolerant with lower insulin levels than humans. In translational medicine, this refined OGTT and IVGTT methods provide important tools in diabetes research when pigs are used as models for children and adolescents in diabetes research.     

Effect of insulin administration on water drinking in children

The effect of insulin administration on water intake, was studied in children submitted to standard protocols for stimulation of secretion of hypophyseal hormones by i.v. treatment with several different drugs: insulin, insulin plus TRH and LH-RH; and propranolol, clonidine or LH-RH. Drinking was measured from 0 to 90 min after drug administration; from blood samples taken at 60 min for hypophyseal hormones analysis, microhaematocrit values were measured, as well as plasma renin activity (PRA) and glycaemia. Water intake was significantly higher in both groups of patients receiving insulin than in the control group (no insulin). Haematocrit values did not change after 60 min. There was a significant correlation of glycaemia of individuals from all three groups and water intake at 60 min. PRA was significantly higher in insulin treated individuals.     

Islet-activating protein (IAP)-induced adrenergic modulation of pancreatic A and B cell in dogs

Islet-activating protein (IAP) is a substance purified from the culture medium of Bordetella pertussis, and its main action is characterized by the enhancement of secretory response to glucose and other stimuli in pancreatic islet. In this experiment, the effect of IAP on epinephrine-induced secretion of immunoreactive insulin (IRI) and glucagon (IRG) was investigated in normal dogs. Epinephrine suppressed IRI secretion and it had a little increment to IRG secretion in control group, while IRI and IRG secretions were significantly increased by epinephrine in IAP pretreated group. Using beta-blocker (Propranolol) with epinephrine, these increments of IRI and IRG secretions in IAP pretreated group were abolished. However, using alpha-blocker (Phentolamine) with epinephrine, these secretions of IRI and IRG in IAP pretreated group were much more increased than epinephrine alone induced secretions. Blood glucose levels were lower in IAP pretreated group than in control group throughout the loading tests in all of the experiments. These findings suggest that (1) IAP decreases blood glucose level and (2) IAP enhances epinephrine-induced secretion of insulin and glucagon by acceleration of beta-adrenergic effect and by reduction of alpha-adrenergic suppression in dogs.     

Correlations between human portal and peripheral venous insulin and proinsulin concentrations under glucose infusion]

In 8 female patients carbohydrate tolerance was proved by means of glucose infusion test 3 days after cholecystectomy. Parameters analyzed in portal and peripheral vein blood are compared with that of 47 healthy persons. All patients demonstrate a pathological carbohydrate tolerance after cholecystectomy, further characterized by an increased lipolysis, a paradoxical rise of HGH, a diminished insulin secretion during the early and increased IRI output in the second phase. There is a significant positive correlation between portal and peripheral vein IRI concentration despite the rising portalperipheral venous IRI difference with raised portal venous IRI concentration. Corresponding differences for proinsulin concentrations can be established in the early phase only. Relations existing between blood glucose and IRI are shown by multiple regression analysis. They suggest that the altitude of IRI concentration is determined by previous blood glucose concentration.     

Time-Related Behaviour of Endocrine Secretion: Circannual Variations of FT3, Cortisol,Hgh and Serum Basal Insulin in Healthy Subjects

Four healthy young male volunteers were submitted to the study of circadian and circannual bioperiodicities of several hormones: FT3, FT4, Cortisol, HGH, prolactin, PTh and plasma insulin levels. They were observed for a whole year and their blood samples were collected six times a day, every other month. The results were analyzed by two-way ANOVA macroscopic analysis and Student r-test. Our data registered a circannual variation in the mean circadian plasma levels of the following hormones: Cortisol (peak in December), HGH (peak in April), FT3 (peak in April), insulin (peak in February). FT4, prolactin and PTH showed no cyclic variation during the period of observation.     

Time-Related Behaviour of Endocrine Secretion: Circannual Variations of FT3, Cortisol, Hgh and Serum Basal Insulin in Healthy Subjects

Four healthy young male volunteers were submitted to the study of circadian and circannual bioperiodicities of several hormones: FT3, FT4, Cortisol, HGH, prolactin, PTh and plasma insulin levels. They were observed for a whole year and their blood samples were collected six times a day, every other month. The results were analyzed by two-way ANOVA macroscopic analysis and Student r-test. Our data registered a circannual variation in the mean circadian plasma levels of the following hormones: Cortisol (peak in December), HGH (peak in April), FT3 (peak in April), insulin (peak in February). FT4, prolactin and PTH showed no cyclic variation during the period of observation.     

Effect of somatostatin in the Syrian hamster bearing a transplantable islet-cell tumor.

The influence of somatostatin (SRIF) on blood glucose, plasma insulin and plasma glucagon was studied in hamsters bearing a transplantable islet-cell tumor secreting insulin and glucagon as well as in normal controls. Fed anesthetized animals were infused intraperitoneally either at a dose of 10 microgram in 15 min or of 150 microgram in 30 min, and intravenously at a dose of 250 microgram in 30 min. Blood was withdrawn from the jugular vein before and after infusion. Before the infusions, tumor bearing animals (TB) had lower blood glucose, markedly elevated plasma glucagon and slightly lower plasma insulin by comparison with normal hamsters (N). Both doses of somatostatin infused by the intraperitoneal route produced a slight but significant hypoglycemia in TB hamsters but not in normals. Ten microgram SRIF did not affect insulin and plasma glucagon levels whereas 150 microgram SRIF significantly depressed plasma insulin in both types of hamsters (N and TB). This latter dose of SRIF decreased plasma glucagon in normal but not in tumor-bearing hamsters. Intravenous infusion of 250 microgram SRIF did not reduce the hyperglucagonemia of TB hamsters either. These results indicate that somatostatin does not reduce the hyperglucagonemia due to the transplantable islet-cell tumor but nevertheless decreases blood glucose and plasma insulin.     

Glucagon and insulin relationships in genetically diabetic (db/db) and in streptozotocin-induced diabetic mice.

An inappropriate molar ratio of circulating insulin to glucagon is frequently associated with the metabolic alterations accompanying diabetes mellitus. Plasma immunoreactive insulin (IRI) and immunoreactive glucagon (IRG) levels were determined and the IRG:IRI ratio calculated at various intervals in overt diabetes in genetically diabetic (db/db) and in streptozotocin-treated mice. Plasma IRI levels in genetic mutants are elevated at nine weeks of age, but are comparable to values found in lean littermates by 21 weeks. The presence of a prevailing hyperglucagonemia is established for the first time in the intact db/db mice. Streptozotocin diabetics are found to have characteristically low plasma IRI and high plasma IRG values. The hormonal imbalance present in these two experimental animal models is accentuated when the data are expressed as the IRG:IRI ratio, which is seen to increase with the progression of diabetes.     

Retinol-binding protein 4 (RBP-4) levels do not change after oral glucose tolerance test and after dexamethasone, but correlate with some indices of insulin resistance in humans

Introduction: Secretory products from adipocytes may contribute to deterioration in glycaemic control and increased insulin resistance (IR). Retinol-binding protein 4 (RBP-4) may increase IR in mice, with elevated levels in insulin-resistant mice and humans with obesity and type 2 diabetes. However, the mechanisms regulating RBP-4 synthesis remain not fully understood. It is not clear whether short-term glucose-induced hyperglycaemia and hyperinsulinaemia as well as glucocorticosteroid-induced increase in IR might be reflected in alterations in serum RBP-4 levels in humans. In order to investigate this, we measured serum RBP-4, glucose and insulin concentrations during 75.0 gram oral glucose tolerance test (OGTT) - Study 1, as well as before and after oral administration of dexamethasone - Study 2. Material and methods: Both studies included 35 subjects (8 males), age (mean +/- SD) 39.1 +/- 15.6 years, BMI 35.8 +/- 8.7 kg/m(2). Twenty-four of those subjects (5 males), age 38.7 +/- 15.1 years, BMI 34.4 +/- 8.3 kg/m(2), had 75 gram oral glucose tolerance test (OGTT) - Study 1. Blood samples were taken before (0 minutes), and at 60 and 120 minutes of OGTT. 17 subjects (3 males, 4 subjects with type 2 diabetes), age 43.1 +/- 18.1 years, BMI 36.7 +/- 9.0 kg/m(2) underwent screening for Cushing's disease/syndrome (Study 2). Dexamethasone was administered in a dose of 0.5 mg every 6 hours for 48 hours. Fasting serum concentrations of RBP-4, glucose and insulin were assessed before (D0) and after 48 hours of dexamethasone administration (D2). IR was assessed by HOMA in all non-diabetic subjects and in subjects participating in study 1 also by Insulin Resistance Index (IRI), which takes into account glucose and insulin levels during OGTT. Results: Glucose administration resulted in significant increases in insulin and glucose (p < 0.0001). There was, however, no change in RBP-4 concentrations (124.1 +/- 32 mg/ml at 0 minutes, 123 +/- 35 mg/ml at 60 minutes and 126.5 +/- 37.5 mg/ml at 120 minutes of OGTT, p = ns). All subjects in Study 2 achieved suppression of cortisol below 50 nmo/l. Dexamethasone administration resulted in an increase in fasting insulin (from 11.6 +/- 6.8 to 17.1 +/- 7.2 muU/ml; p = 0.003), and an increase in HOMA (from 2.73 +/- 1.74 to 4.02 +/- 2.27; p = 0.015), although without a significant change in RBP-4 levels (119 +/- 26.8 vs. 117.5 +/- 24.8 mg/ml, p = ns). RBP-4 correlated with fasting insulin (r = 0.40, p = 0.025), fasting glucose (r = 0.41, p = 0.02) and HOMA (r = 0.43, p = 0.015), but not with IRI (r = 0.19, p = 0.31). There was, however, only a moderate correlation between HOMA and IRI (r = 0.49 [r(2) = 0.24]; p = 0.006, Spearman rank correlation), while the best correlation was obtained between the product of glucose and insulin levels at 60 min of OGTT and IRI in a non-linear model (r = 0.94 [r(2) = 0.88]; p<0.00001). In subjects who received dexamethasone, a positive correlation between RBP-4 and HOMA (p = 0.01) was lost after two days of dexamethasone administration (p = 0.61). Conclusions: RBP-4 levels do not change during oral glucose tolerance test or after a dexamethasone-induced increase in insulin resistance. This implies that it is highly unlikely that RBP-4 is involved in short-term regulation of glucose homeostasis in humans and that it responds to short-term changes in insulin resistance. A moderate correlation between RBP-4 and some insulin resistance indices (HOMA) does not exclude the fact that RBP-4 might be one of many factors that can influence insulin sensitivity in humans.     

SSTR2 mediates the somatostatin-induced increase in intracellular Ca(2+) concentration and insulin secretion in the presence of arginine vasopressin in clonal beta-cell HIT-T15

The effects of somatostatin (SRIF) are mediated through the seven transmembrane receptor family that signals via Gi/Go. To date, five distinct SRIF receptors have been characterized and designated SSTR1-5. We have characterized the SRIF receptor that mediates the increase in [Ca(2+)](i) and insulin secretion in HIT-T15 cells (Simian virus 40-transformed Syrian hamster islets) using high affinity, subtype selective agonists for SSTR1 (L-797,591), SSTR2 (L-779,976), SSTR3 (L-796,778), SSTR4 (L-803,087), SSTR5 (L-817,818) and PRL-2903, a specific SSTR2 antagonist. In the presence of arginine vasopressin (AVP), SRIF increased [Ca(2+)](i) and insulin secretion. Treatment with the SSTR2 agonist L-779,976 resulted in similar responses to SRIF. In addition, L-779,976 increased both [Ca(2+)](i) and insulin secretion in a dose-dependent manner. Treatment with L-779,976 alone did not alter [Ca(2+)](i) or basal insulin secretion. In the presence of AVP, all other SRIF receptor agonists failed to increase [Ca(2+)](i) and insulin secretion. The effects of SRIF and L-779,976 were abolished by the SSTR2 antagonist PRL-2903. Our results suggest that the mechanism underlying SRIF-induced insulin secretion in HIT-T15 cells be mediated through the SSTR2.     

Responses of plasma insulin C-peptide and proinsulin-like components to glucose and glucagon in the pig.

This study was undertaken to evaluate the relative contribution of insulin, proinsulin-like components (PLC) and C-peptide toward plasma levels of immuno reactive insulin (IRI) and C-peptide immunoreactivity (CPR) in the pig and to elucidate the mode of secretion of PLC in the early phase of insulin release. Following the intravenous glucose loads, the concomitant secretion of CPR with that of IRI occured rapidly and the maximum plasma level of IRI was observed at an earlier time than that of CPR. Following the intravenous glucagon injection, the maximum plasma levels of IRI and CPR were observed at the same time in the early phase. After the gel filtration of acid alcohol extracts of plasma in a fasted state, a very small amount of PLC and a small amount of C-peptide as well as a small amount of insulin were detected. The results obtained from the gel filtration of extracts revealed that the increased amounts in IRI and CPR after the injection of glucose or glucagon consisted mostly and respectively of insulin and C-peptide in the pig, because the concentration of PLC increased only slightly in the early phase. In fact, plasma levels of CPR and IRI were essentially and respectively paralleled to those of insulin and C-peptide which were assayed after the gel filtration of extracts. In addition, the slight elevation of PLC in the early phase after these stimulations indicated that PLC was elicited into blood circulation at the same time of the secretion of insulin and C-peptide.