Persistence of altered metabolic responses to beta-endorphin after normalization of body weight in human obesity

The responses of plasma glucose, insulin, C-peptide and glucagon to an infusion of human beta-endorphin (0.5 mg/h) were studied in 10 formerly obese subjects who had lost 35 kg by dieting (body mass index less than 25) and compared with those of 10 normal-weight control (body mass index less than 25) and 10 obese (body mass index greater than 30) subjects. The fasting plasma concentrations of beta-endorphin were significantly higher in both the obese and the post-obese group than in the control group. In both obese and post-obese subjects, the infusion of beta-endorphin caused significant increases in peripheral plasma glucose, insulin, C-peptide and glucagon concentrations. In the control group, matched for age, sex and weight with the formerly obese group, there was no appreciable change in plasma insulin and C-peptide concentrations during the infusion of beta-endorphin, but the rise in plasma glucose was more sustained. Thus, 1. the increased plasma beta-endorphin concentrations found in human obesity are not corrected by normalization of body weight; and 2. formerly obese, normal-weight subjects behave as obese subjects in their metabolic and hormonal responses to beta-endorphin infusion. The alteration of the opioid system in human obesity may play some role in the predisposition to weight gain.

Elevated dietary protein intake impairs the renal hemodynamic response to hyperaminoacidemia in patients with primary glomerular diseases

We have evaluated the renal hemodynamic response to a mixed amino acid infusion in 7 control subjects and in 8 patients with primary glomerulonephritis (GN). In order to evaluate the role of dietary protein intake in this response, GN patients were maintained for 3 weeks on two separate dietary regimens providing 130 +/- 5 g of protein/day (study 1) and 60 +/- 3 g of protein/day (study 2), respectively. Normal subjects were studied while consuming a free diet. In GN patients, following the reduction in dietary protein intake basal RPF and GFR decreased from 589 +/- 109 to 422 +/- 81 ml/1.73 m2/min (p less than 0.01, vs. study 1) and from 75 +/- 7 to 70 +/- 8 ml/1.73 m2/min (p = NS). Filtration fraction rose from 0.14 +/- 0.02 to 0.19 +/- 0.03 (p less than 0.05). In study 1, during amino acid infusion GFR and RPF did not change significantly from baseline (75 +/- 7 vs. 66 +/- 8 ml/1.73 m2/min at 180 min and 589 +/- 109 vs. 567 +/- 102 ml/1.73 m2/min, respectively). These results are at variance with data obtained in normal controls in whom both GFR and RPF rose significantly following hyperaminoacidemia. In contrast, when dietary protein intake was reduced, a normal renal hemodynamic response to amino acid infusion was restored (GFR went from 70 +/- 8 to 90 +/- 18 ml/1.73 m2/min and RPF from 422 +/- 81 to 517 +/- 90 ml/1.73 m2/min, both p less than 0.05 vs. basal), both absolute and percentage increases were similar to what was observed in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic effects of pulsatile insulin infusion in the elderly

The present study investigated the metabolic effects of pulsatile insulin delivery at a pulse rate of 2 + 11 and 2 + 18 min in 7 healthy, elderly subjects (71.4 +/- 2.1 years), submitted to 260 min controlled iv glucose infusion via the Biostator. The endogenous secretion of pancreatic hormones was inhibited by somatostain (3 micrograms/min) and glucagon was replaced (67 ng/min) to basal levels. The same total insulin dose was delivered on both occasions. Insulin infusion rate was 1.3 and 2.0 mIU. kg-1. min-1 during switching on/off of 2 + 11 and 2 + 18 min, respectively. Blood glucose levels and glucose infusion rate were monitored continuously by the Biostator; [D-3-3H]glucose infusion allowed determination of glucose turnover. During the last 60 min of the experiment, pulsatile insulin at a pulse rate of 2 + 11 vs 2 + 18 min produced a stronger inhibition of endogenous glucose production, whereas glucose disappearance rate and glucose metabolic clearance rate were similarly affected. Plasma triglycerides, apolipoprotein B, and free fatty acids levels were also more suppressed during insulin delivery at pulse rate of 2 + 11 than at 2 + 18 min.

[Beta-endorphin and obesity. Possible pathogenetic implications]

Several experimental data have documented the ability of both opiates and opioid peptides to stimulate food intake. On the other hand, the plasma beta-endorphin levels found in obese patients are higher than those observed in normal-weight controls, which may have pathogenetic implications. We have investigated the responses of plasma glucose, insulin, C-peptide and glucagon to an infusion of human beta-endorphin in formerly obese subjects who had obtained by dieting the normalization of body weight and in lean controls. The data show that: a) the increased plasma beta-endorphin concentrations found in human obesity are not corrected by normalization of body weight; b) formerly obese subjects behave as obese subjects in their metabolic and hormonal responses to beta-endorphin.

Hyperglycemia may determine fibrinopeptide A plasma level increase in humans

The effects of hyperglycemia on plasma fibrinopeptide A (FPA) levels in normal subjects are reported. An increase of FPA concentration parallel to sustained hyperglycemia was observed; when the glycemia returned to basal values, FPA showed values in normal range. Heparin infusion was able to significantly decrease the hyperglycemia-induced augment of FPA levels. Isovolumic-isotonic NaCl solution infusion produced a slight (NS) increase in FPA levels; however, mild hyperglycemia, achieved by glucagon, was also able to produce a significant increase in FPA concentration. These data demonstrate the direct role of hyperglycemia in conditioning FPA level, and suggest that hyperglycemia, by itself, is a sufficient stimulus to produce thrombin activation in humans.

Beta-endorphin and islet hormone release in humans: evidence for interference with cAMP

The present studies were undertaken to characterize further the influence of synthetic human beta-endorphin (0.5 mg/h) on insulin and glucagon responses to intravenous glucose in humans. Infusion of beta-endorphin in 10 normal volunteers caused a clear-cut inhibition of the overall insulin responses to a glucose pulse (0.33 g/kg iv) with values of glucose disappearance rates in the diabetic range [0.89 +/- 0.09 (P less than 0.01) vs. saline 1.82 +/- 0.15%/min]. Glucose-induced glucagon suppression was significantly lower during beta-endorphin, a fact that could have contributed to the reduced glucose utilization rates. The infusion of theophylline (150 mg + 350 mg/h) to increase the intracellular cAMP activity by inhibiting phosphodiesterase completely reversed the inhibitory effect of beta-endorphin on glucose-induced insulin secretion. As a consequence, glucose disappearance rates rose to 1.77 +/- 0.18%/min. Theophylline did not influence significantly the glucagon-releasing effect of beta-endorphin as well as the reduced glucagon suppression. An infusion of exogenous calcium (100 mg as iv bolus + 5 mg/min) to raise serum calcium in the hypercalcemic range (15 mg/dl) and lysine acetylsalicylate (72 mg/min) to block the synthesis of endogenous prostaglandin E did not interfere with the inhibiting effect of beta-endorphin on insulin secretion. These data confirm that beta-endorphin stimulates glucagon and inhibits basal and glucose-stimulated insulin secretion and suggest that the opioid influences the intraislet adenylate cyclase activity.

Increased alpha 2-macroglobulin in diabetes: a hyperglycemia related phenomenon associated with reduced antithrombin III activity

Increased alpha 2-macroglobulin (alpha 2M) activity and concentration, and decreased antithrombin III (ATIII) plasma concentration are reported in diabetic subjects. In diabetes an inverse correlation between ATIII activity and blood glucose, HbA1, alpha 2M activity and alpha 2M concentration, and a direct correlation between both alpha 2M activity and alpha 2M concentration with blood glucose and HbA1 are found. Moreover, a direct correlation between alpha 2M activity and alpha 2M concentration fails. In both diabetic and normal subjects induced hyperglycemia increases alpha 2M activity and alpha 2M concentration reduces ATIII activity, while ATIII concentration is not affected. These data which show that hyperglycemia may increase alpha 2M molecule levels while altering only the biological function of ATIII, provide evidence that hyperglycemia may decrease, directly, the biological function of some proteins and may condition the levels of some risk factors for the development of diabetic complications such as alpha 2M.

Low protein alimentation normalizes renal haemodynamic response to acute protein ingestion in type 1 diabetic children

The effect of an acute protein load (2 g kg-1 bodyweight [BW]) was studied in nine type 1 diabetic children. Patients were maintained on two different dietary regimens. In study one, patients were on a high protein diet providing from 2.7 to 1.8 g of protein/kg of BW per day. In study two, patients were reevaluated after three weeks of a diet providing from 1.0 to 1.2 g kg-1 of BW per day of protein. In study one (High Protein Diet), we failed to observe any rise in GFR and RPF following the protein meal (137 +/- 21 basal vs. 110 +/- 14 and 472 +/- 93 basal vs. 494 +/- 93 ml/1.73 m2 of SA min-1 at 60 min. This is in contrast with results from seven age matched controls consuming a free diet, which showed a significant rise in both GFR and RPF. In study two (low protein diet), basal GFR was significantly reduced. However after the protein load, both GFR (92 +/- 11 vs. 126 +/- 18 ml/1.73 m2 of SA min-1) and RPF (467 +/- 83 vs. 705 +/- 102 ml/1.73 m2 min-1) rose significantly (P less than 0.05 vs. basal). The data indicate that: 1. short term protein restriction reduces significantly GFR in type 1 diabetic children; 2. diabetic children maintained on an high protein intake show an altered haemodynamic response to protein ingestion; 3. a normal response to protein ingestion can be restored by short term dietary protein restriction.

Impaired insulin-induced erythrocyte magnesium accumulation is correlated to impaired insulin-mediated glucose disposal in type 2 (non-insulin-dependent) diabetic patients

Plasma and erythrocyte magnesium levels were measured by atomic absorption spectrometry in 12 healthy subjects and 12 moderately obese patients with Type 2 (non-insulin-dependent) diabetes mellitus. Basal plasma and erythrocyte magnesium levels were significantly lower in diabetic patients than in control subjects. In vitro incubation in the presence of 100 mU/l insulin significantly increased magnesium erythrocyte levels in both control subjects (p less than 0.001) and patients with diabetes (p less than 0.001). However, even in the presence of 100 mU/l insulin, the erythrocyte magnesium content of patients with Type 2 diabetes was lower than that of control subjects. The in vitro dose-response curve of the effect of insulin on magnesium erythrocyte accumulation was shifted to the right when red cells of diabetic patients were used, with a highly significant reduction of the maximal effect. Such reduction of the maximal effect of insulin suggests that the impairment of insulin-induced erythrocyte magnesium accumulation observed in Type 2 diabetic patients results essentially from a post-receptor defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood glucose may condition factor VII levels in diabetic and normal subjects

Increased factor VII levels have been reported in Type 1 (insulin-dependent) diabetic subjects. A direct correlation between fasting plasma glucose and factor VII level was found to exist in both diabetic and normal subjects. Induced-hyperglycaemia was able to increase factor VII levels in both diabetic patients and normal control subjects while, when euglycaemia was achieved in diabetic patients, factor VII values returned to normal range. This study shows that the level of factor VII may be directly conditioned by circulating blood glucose and, therefore, stresses the role of hyperglycaemia in conditioning coagulation abnormalities in diabetes mellitus.

[Prostaglandins, insulin secretion and diabetes mellitus]

The islets of Langerhans have the enzymatic equipment permitting the synthesis of the metabolites of arachidonic acid: cyclo-oxygenase and lipo-oxygenase. Numerous studies have shown that cyclo-oxygenase derivatives, mainly PGE2, reduce the insulin response to glucose whereas lipo-oxygenase derivatives, mainly 15-HPETE, stimulate insulin secretion. So, for instance, drugs that increase prostaglandins synthesis as colchicine or furosemide inhibit insulin secretion while non steroid anti-inflammator drugs, mainly salicylates, which inhibit cyclo-oxygenase, enhance the insulin response to various stimuli. In type-2 (non insulin-dependent) diabetes, an increased sensitivity to endogenous prostaglandins has been proposed as a possible cause for the insulin secretion defect which characterizes this disease. Play in favor of this hypothesis the fact that the administration of PGE inhibits the insulin response to arginine in type-2 diabetics but not in normal subject and the fact that the administration of salicylates could improve the insulin response to glucose in some of these patients.

Diabetes and hypertension in the elderly

Hypertension combined with diabetes in the elderly is characterized by many important metabolic and cardiovascular changes, among which insulin resistance, hyperinsulinaemia and increased total peripheral resistance appear to be the most relevant. Non-insulin dependent diabetes mellitus is also characterized by insulin resistance and hyperinsulinaemia. Moreover, hyperinsulinaemia itself has been shown to increase total peripheral resistance. Hyperinsulinaemia thus seems to play a key role in the pathophysiology of hypertension in elderly diabetic subjects. Therefore elderly hypertensive diabetic patients should be treated with thiazide diuretics in low doses, calcium channel blockers and alpha-adrenergic blockers.

Beta-endorphin-induced inhibition and stimulation of insulin secretion in normal humans is glucose dependent

This study evaluated the effect of human beta-endorphin on pancreatic hormone levels and their responses to nutrient challenges in normal subjects. Infusion of 0.5 mg/h beta-endorphin caused a significant rise in plasma glucose concentrations preceded by a significant increase in peripheral glucagon levels. No changes occurred in the plasma concentrations of insulin and C-peptide. Acute insulin and C-peptide responses to intravenous pulses of different glucose amounts (0.33 g/kg and 5 g) and arginine (3 g) were significantly reduced by beta-endorphin infusion (P less than .01). This effect was associated with a significant reduction of the glucose disappearance rates, suggesting that the inhibition of insulin was of biological relevance. beta-Endorphin also inhibited glucose suppression of glucagon levels and augmented the glucagon response to arginine. To verify whether the modification of prestimulus glucose level could be important in these hormonal responses to beta-endorphin, basal plasma glucose concentrations were raised by a primed (0.5 g/kg) continuous (20 mg kg-1.min-1) glucose infusion. After stabilization of plasma glucose levels (350 +/- 34 mg/dl, t = 120 min), beta-endorphin infusion caused an immediate and marked increase in plasma insulin level (peak response 61 +/- 9 microU/ml, P less than .01), which remained elevated even after the discontinuation of opioid infusion. Moreover, the acute insulin response to a glucose pulse (0.33 g/kg i.v.) given during beta-endorphin infusion during hyperglycemia was significantly higher than the response obtained during euglycemia (171 +/- 32 vs. 41 +/- 7 microU/ml, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Altered metabolic and hormonal responses to epinephrine and beta-endorphin in human obesity

Catecholamines and endogenous opioid peptides are released in response to stress. Exogenous infusions of epinephrine and beta-endorphin (both in doses of 15, 50, and 80 ng/kg.min sequentially, each dose lasting 30 min) were used to mimic short term stress in both normal weight (body mass index, less than 25 kg/m2) and obese (body mass index, greater than 30 kg/m2) subjects. Fasting plasma insulin, C-peptide, and beta-endorphin concentrations were significantly higher in the obese than in the normal subjects (P less than 0.01-0.005). In lean subjects epinephrine produced significant increases in plasma glucose levels, but no appreciable changes in plasma insulin, C-peptide, or glucagon. Infusion of beta-endorphin in the same subjects caused plasma glucose and glucagon to rise, but insulin and C-peptide levels did not change. The simultaneous infusion of epinephrine and beta-endorphin produced a glycemic response which, although greater, was not significantly different than the sum of the responses to the individual hormone infusions. However, the two hormones had a synergistic interaction on plasma glucagon levels [total glucagon response, 2275 +/- 370 pg/min.mL (ng/min.L); sum of single effects, 750 +/- 152 (+/- SE) pg/min.mL (ng/min.L); P less than 0.01]. The plasma epinephrine [207 +/- 21, 607 +/- 70, and 1205 +/- 134 pg/mL (1130 +/- 115, 3640 +/- 382, and 6577 +/- 691 pmol/L] and beta-endorphin [875 +/- 88, 1250 +/- 137, and 1562 +/- 165 pg/mL (250 +/- 25, 358 +/- 39, and 447 +/- 47 pmol/L] concentrations attained during the infusions of each single hormone were not different from those recorded during the combined hormonal infusion. In obese subjects epinephrine raised plasma glucose levels and caused dose-related increments of plasma glucagon concentrations. Plasma insulin and C-peptide concentrations remained low and rebounded at the end of the infusions. In the same subjects, beta-endorphin produced elevations of plasma glucose, insulin, C-peptide, and glucagon. When the combined hormonal infusion was given to obese subjects, the plasma epinephrine and beta-endorphin concentrations rose to values not significantly different from those in normal weight subjects. However, there was a dramatic increase in plasma glucose exceeding 200 mg/dL (11.1 mmol/L), which remained elevated 30 min after the infusion. The glucagon response was not greater than the sum of the single effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on the mechanism of salicylate-induced increase of insulin secretion in man

Salicylate compounds are known to increase basal and stimulated insulin secretion in man. In our studies, infusion of lysine acetylsalicylate (72 mg/min) increased basal insulin levels and amplified insulin responses to glucose (5 g i.v.), arginine (5 g i.v.) and tolbutamide (1 g i.v.). Verapamil, an organic calcium antagonist, did not modify LAS-induced increase of basal insulin levels, but reduced the effect of LAS on glucose-induced insulin secretion. Calcitonin and somatostatin, two agents that inhibit basal and glucose-stimulated insulin secretion, inhibited the insulin response to glucose in presence of LAS infusion. The ability of salicylate compounds to augment insulin secretion might be due to multiple sites of action in the Beta-cells.

Pulsatile insulin delivery is more efficient than continuous infusion in modulating islet cell function in normal subjects and patients with type 1 diabetes

The respective modulating effects of continuous and intermittent insulin delivery on pancreatic islet cell function were studied in seven normal men and nine insulin-dependent (type 1) diabetic patients. In the normal men, saline or continuous (0.8 mU kg-1 min-1) or pulsatile (5.2 mU kg-1 min-1, with a switching on/off length of 2/11 min) human insulin were delivered on different days and in random order. Despite hyperinsulinemia, blood glucose was kept close to its basal value by the glucose clamp technique. The diabetic patients also were infused in random order and on different days with either saline or a smaller amount of insulin delivered continuously (0.15 mU kg-1 min-1) or in a pulsatile manner (0.97 mU kg-1 min-1 for 2 min, followed by 11 min during which no insulin was infused). In all experiments, 5 g arginine were given iv as a bolus dose 30 min before the end of the study, and plasma C-peptide and glucagon levels were determined to assess islet cell function. In the normal men, insulin administration resulted in a significant decline of basal plasma glucagon and C-peptide levels and in a clear-cut decrease in the arginine-induced glucagon response. These effects of insulin were significantly more marked when insulin was delivered in a pulsatile rather than a continuous manner. In the insulin-dependent diabetic patients, the lower dose of insulin infused continuously did not alter the basal or arginine-stimulated glucagon response. In contrast, when the same amount of insulin was delivered intermittently, arginine-induced glucagon release was greatly reduced. Thus, these data support the concept that insulin per se is a potent physiological modulator of islet A- and B-cell function. Furthermore, they suggest that these effects of insulin are reinforced when the hormone is administered in an intermittent manner in an attempt to reproduce the pulsatile physiological release of insulin.

Theophylline prevents the inhibitory effect of prostaglandin E2 on glucose-induced insulin secretion in man

This study was undertaken to assess the mechanism by which prostaglandins of the E series inhibit glucose-induced insulin secretion in man. Acute insulin response (mean change 3-10 min) to iv glucose (0.33 g/kg) was decreased by 40% during the infusion of prostaglandin E2 (10 micrograms/min) and glucose disappearance rates were reduced (P less than 0.05). Insulin response to arginine (5 g iv) and tolbutamide (1 g iv) were not affected by the same rate of prostaglandin E2 infusion. The inhibitory effect of prostaglandin E2 on glucose-induced insulin secretion was prevented by theophylline (100 mg as a loading dose followed by a 5 mg/min infusion), a drug that increases the intracellular cAMP concentrations by inhibiting phosphodiesterase activity. Our data suggest the involvement of the adenylate cyclase system in the inhibitory action of prostaglandin E2 on glucose-induced insulin secretion in man.

Plasma glucose lowering effect of sparteine sulphate infusion in non-insulin dependent (type 2) diabetic subjects

Sparteine sulphate, given i.v. as a bolus of 15 mg/ml plus 90 mg in 0.9% NaCl 100 ml over 60 min, increases plasma insulin and decreases plasma glucose and adrenaline in non-insulin dependent (Type II) diabetic subjects. The hypoglycaemic effect was also evident in the presence of a high plasma glucose level produced by Biostator changing glucose infusion from 20.2 +/- 2.8 to 26.4 +/- 4.2 mg.kg-1.min-1 (p less than 0.01), and it was potentiated by simultaneous infusion of arginine. No additional effect of sparteine on the peripheral sensitivity to insulin were detected by the euglycaemic, hyperinsulinaemic glucose clamp technique, as the glucose infusion rate (3.1 +/- 0.8 vs 2.6 +/- 1.2 mg.kg-1.min-1) was not statistically significant different in the last 60 min of the experiment. It is concluded that sparteine sulphate enhances beta-cell secretion, causing a fall in the plasma glucose concentration.

Pathophysiological study of the non-insulin-dependent phase of type I diabetes mellitus

The usual practice of considering type I diabetes synonymous with insulin-dependent diabetes has been criticized. Since type I diabetes can have a non-insulin-dependent phase (pre-type I diabetes and/or honeymoon) the differentiation of two main types of diabetes according to insulin-dependency is not absolute. We studied the insulin, C-peptide and glucagon responses to various tests (OGTT, IVGTT, glibenclamide test, mixed meal tolerance test and ITT) performed during the non-insulin-dependent phase of 3 young patients (range 8-18 years) who developed ketosis 12-24 months after the discovery of fasting hyperglycemia, and in 6 patients (age 15-23 years) who presented a remission phase 4-6 months after the sudden clinical onset of type I diabetes. An insignificant insulin and C-peptide increase following i.v. glucose was observed in all patients, whereas the B-cell response to both oral glucose and other secretagogues was preserved, although at a subnormal level. In the three hyperglycemic and preketoacidotic patients the basal levels of glucagon were low and no significant increase after secretagogues was seen. Sensitivity to exogenous insulin in all patients was good. Thus, B-cell response in our patients was reminiscent of the differential responsiveness to various stimulants in the early stage of type II (non-insulin-dependent) diabetes. These results suggest that type I and type II diabetes can be characterized by the same functional B-cell defect during a period of their natural history.

Oxytocin increases arginine-induced A and B cell secretion in normal man and in diabetic subjects

In previous in Vitro and in Vivo studies oxytocin was shown to stimulate A and B cell secretion. In the present study we show that oxytocin is also able to increase arginine-induced glucagon and insulin secretion in healthy human beings. Similar results were obtained in both insulin-dependent (type-1) and non-insulin dependent (type-2) diabetic subjects.

A preliminary note on inhibiting effect of alpha-tocopherol (vit. E) on protein glycation

Human plasma albumin was incubated in 25 mM/l glucose at 37 degrees C for up to sevent days. Aliquots of this mixture were also incubated with alpha-tocopherol (Vitamin E) at 2 mg/dl, 4 mg/dl and 8 mg/dl, respectively. Vitamin E inhibited protein glycation and, furthermore, shows a dose-dependent effect. This report suggests the possibility of using Vitamin E, at therapeutic doses, to obtain the inhibition of non-enzymatic glycation.

Pharmacological doses of oxytocin affect plasma hormone levels modulating glucose homeostasis in normal man

Pharmacological doses of oxytocin administered in basal conditions evoked a rapid surge in plasma glucose and glucagon levels followed by a later increase in plasma insulin and adrenaline levels. The effects of oxytocin on plasma glucagon and adrenaline levels were potentiated by hypoglycemia. When the endogenous pancreas secretion was suppressed by cyclic somatostatin (150 micrograms/h) and exogenous glucagon (3.5 micrograms/h) and insulin (0.2 mU/kg.min) were both replaced, oxytocin (0.2 U/min) evoked a transient but significant increase in plasma glucose levels suppressing the glucose infusion rate (GIR) in the first 60 min. On the contrary at higher insulin infusion rate (0.6 mU/kg.min) plasma glucose levels and GIR remained unaffected throughout the study. Oxytocin seems also to potentiate glucose-induced insulin secretion as evidenced by hyperglycemic glucose clamp. In conclusion, pharmacological doses of oxytocin seem to exert a prevalent hyperglycemic effect by a combined action at the liver site (as glycogenolytic agent) and at the endocrine pancreas (as a stimulatory agent of A cell secretion).