Clonidine effect on insulin secretion and lipolysis in man

Clonidine is a hypotensive drug acting as an alpha-mimetic agent in the central nervous system and causing cardiovascular depression. Clonidine administration in animals and man causes slight hyperglycemia and lipid mobilization, as well as an increase in growth hormone levels. We have studied the effect of a 3-day oral treatment (78 microgram three times daily) upon glucose (5 g i.v.)- and tolbutamide (1 g i.v.)-induced insulin release in subjects without metabolic alterations. Acute insulin response (3 min after IVGTT) and insulin release (area between 0 and 10 min) were significantly reduced after clonidine treatment. Blood glucose levels were not affected by clonidine treatment; the insulinogenic index 3 min after the glucose load was significantly reduced by clonidine administration. There was neither an evident effect on tolbutamide-induced insulin release nor a modification of the hypoglycemic effect of tolbutamide. Clonidine did not affect basal lipolysis, evaluated in vitro as glycerol release from human subcutaneous adipose tissue fragments, while norepinephrine-induced lipolysis was slightly reduced. The results presented are compatible with an alpha-mimetic effect of clonidine on pancreatic and adipose tissue.

Histamine stimulates prolactin release in norman men

Histamine stimulates prolactin (PRL) and growth hormone (GH) release in the experimental animal. In order to evaluate the possible effect of histamine on these hormones in man, in our study, 9 normal volunteers underwent an intravenous histamine infusion (200 microgram in 15 min). Five of them also underwent an intravenous histidine infusion (200 microgram). Histamine induced a significant PRL release in 7 subjects, the maximum level reached being 36.2 +/- 12.09 ng/ml, while GH levels were not affected. Histidine was ineffective on both PRL and GH levels. It is known that histamine, administered peripherally, does not cross the blood brain barrier. This fact suggests that, in man, histamine stimulates PRL release by acting directly on the pituitary. In addition, since stressful situations may elicit both PRL and GH release, the fact that the latter was not affected by histamine, suggests that a mere stress-effect is not responsible for the PRL release observed in our subjects.

Effect of vincristine on glucose-induced insulin secretion in man

60 min after the injection of therapeutic doses of vincristine for cancer chemotherapy, there is a reduction of the total (40%) and of the acute phase (43%) areas of insulin secretion inductedby 5-g i.v glucose load, and the constant of gllcose utilization is reduced by 25%. No differences are observed after 3 5-g i.v. glucose loads given at hourly intervals in control subjects.

In vitro effect of insulin on peripheral T-lymphocyte E-rosette function from normal and diabetic subjects

Juvenile-onset diabetics (JOD) have a significantly low peripheral T-lymphocyte count. In vitro exposure of diabetic lymphocyte cultures to insulin causes a significant T-cells count increase and thereafter no significant difference is detectable among JOD, maturity-onset diabetics (MOD) and normal subjects (NS) T-cells counts. This finding supports the hypothesis that the T-lymphocyte depressed function present in JOD is a secondary phenomenon due to in vivo insulin deficiency. Possible mechanisms of insulin action in restoring E-rosette function are discussed.

Stimulatory effect of the dopa-decarboxylase inhibitor Ro 4-4602 on prolactin release; inhibition by l-dopa, metergoline, methysergide and 2-Br-alpha-ergocryptine

In order to evaluate the role of serotonin (5-HT) in the effect of L-dopa on prolactin (PRL) release, normal subjects received L-dopa alone or L-dopa plus a dopa-decarboxylase inhibitor (Ro 4-4602) in basal conditions and following the repeated administration of metergoline, a specific anti-5-HT agent. The inhibiting effect of L-dopa on PRL levels was enhanced by metergoline. On the contrary, L-dopa plus Ro 4-4602 induced a sharp increase in serum PRL levels. This effect was completely abolished by metergoline, which also significantly reduced fasting PRL levels in all the subjects studied. Ro 4-4602 alone induced a significant increase in serum PRL levels, similar to that commonly observed with chlorpromazine and TRH. The effect was similar in males and in females and was reproducible in experiments performed on different days. The effect of Ro 4-4602 was completely abolished by 2-Br-α-ergocryptine and metergoline, and, to a lesser degree, was reduced by methysergide. These results suggest that Ro 4-4602 is a reliable stimulus to PRL release and show that any stimulus to PRL secretion may be blocked by both dopa-minergic and anti-serotonin agents.

Effect of the antihistaminic agents meclastine and dexchlorpheniramine on the response of human growth hormone to arginine infusion and insulin hypoglycemia

Histamine is found in most tissues including the central nervous system. Here it reaches the highest concentrations in the hypothalamus and in the median eminence. In order to evaluate the possible role of endogenous histamine in the control of human growth hormone (hGH) secretion, we investigated the effect of two anti-histamine drugs, meclastine and dexchlorpheniramine, on the hGH response to arginine infusion and to insulin hypoglycemia in 30 normal subjects. The oral administration of meclastine for three days or the intravenous infusion of dexchlorpheniramine significantly reduced the hGH response to arginine infusion. Neither drug affected the secretion of hGH following insulin hypoglycemia. These results suggest that histamine is involved in the control of hGH release, at least in response to arginine. Our data are consistent with the finding that histamine stimulates GH release in the baboon (Meyer and Knobil, Endocrinology 80: 163, 1967) and with previous results indicating that the release of hGH in response to different stimuli is subject to different regulatory mechanisms.

Inhibitory effect of clofibrate on arginine-induced insulin secretion in chemical diabetes

Clofibrate 3 g/die for 10 consecutive days, significantly reduced arginine-induced IRI release in chemical diabetics and in normal controls, whether of normal body weight or obese. Blood glucose levels were not affected by clofibrate. In agreement with previous findings, it would appear that clofibrate, administered for short periods does not lead to a decrease in glucose tolerance. However, studies relating to the effect of chronic clofibrate administration in chemical diabetes are needed in order to be sure that prolonged inhibition of IRI secretion does not lead to overt diabetes.

Peripheral T-lymphocytes in juvenile-onset diabetics (JOD) and in maternity-onset diabetics (MOD)

The percentage and absolute number per mm.3 of peripheral T-lymphocytes were determined in 11 juvenile-onset diabetics (JOD), in 21 maturity-onset diabetics (MOD), and in 18 normal subjects (NS). The percentage was significantly lower in JOD (38.1) than in MOD (57.2) and NS (56.5). The absolute T-lymphocytes number per mm.3 was significantly lower in JOD (833) than in NS (1,260); this was also true for JOD as against MOD (1,026), even if the difference was not statistically significant. No difference was found between MOD and NS, or between MOD on oral therapy and on insulin treatment. The decrease of peripheral T-lymphocytes in JOD was not related to associated illness or drugs. The data presented suggest the possibility of an altered cell-mediated immunity in juvenile-onset diabetics.

Effect of metergoline, a specific serotonin antagonist, on human growth hormone response to arginine and L-dopa

In seven normal subjects the repeated oral administration of metergoline, a specific antiserotonin agent, has enhanced HGH response to arginine infusion. Following placebo administration, arginine-induced HGH release was slightly but not significantly reduced; similarly, in eight metergoline treated subjects, HGH response to oral L-Dopa was slightly but not significantly reduced. HGH response to i.v. L-Dopa was not modified by the drug. These results suggest that serotonin controls HGH response only in response to arginine, not to L-Dopa.

Effect of metergoline, a powerful and long-acting antiserotoninergic agent, on insulin secretion in normal subjects and in patients with chemical diabetes

The effect of metergoline on insulin secretion has been evaluated in normal subjects and in patients with chemical diabetes. The repeated administration of metergoline, 2 mg at four-hour intervals to give a total of 24 mg, has enhanced insulin secretion in response to i.v. glucose in normal subjects but not in chemical diabetics. No changes in blood glucose pattern were observed. Under similar conditions, metergoline administration caused a slight but significant decrease in arginine-induced insulin release, both in normal subjects and in chemical diabetics. These results support the concept of a serotoninergic control of insulin secretion and suggest that serotonin exerts different effects on insulin release according to the different stimuli.