Inhibition o'f insulin release by cyproheptadine: effects on 3',5'-cyclic-AMP-content and 45Ca-accumulation of incubated mouse islets

Effects of amino acids, hormones and drugs on insulin release and 45Ca uptake by transplantable rat insulinoma cells maintained in tissue culture

1. Acute effects of amino acids, hormones and drugs on transplantable rat insulinoma cells were examined after 2-3 days culture in RPMI-1640 (11.1 mM glucose) to eliminate necrotic cells and counter prior hypoglycaemia. 2. At 2.6 mM Ca2+, rat insulinoma cells (greater than 95% viability) released 48-97 ng insulin/10(6) cells during 60 min incubations with uptake of 1.0-1.8 nmol 45Ca/10(6) cells. 3. Insulin release and 45Ca uptake by rat insulinoma cells were not modified by arginine, leucine, 2-ketoisocaproate, tolbutamide, glibenclamide, somatostatin, adrenaline, noradrenaline, diazoxide or cyproheptadiene. 4. Responsiveness to acetylcholine (stimulation of insulin release and 45Ca uptake) and to GIP (stimulation of insulin release) was demonstrated. Thiol reagents (CMBS, CPDS and DTNB) and agents affecting microtubules-microfilaments (colchicine, vinblastine and cytochalasin B) enhanced insulin release. 5. The results suggest that rat insulinoma cells exhibit a generalized defect in the regulation of insulin release by nutrients, hormones and drugs which act in pancreatic B-cells by alteration of cellular Ca2+. Responsiveness to agents affecting insulin release through alternative mechanisms appears to be retained.

The effect of cyproheptadine on insulin biosynthesis

The effect of a potent antiserotonin-antihistaminic compound, cyproheptadine (CPH) on insulin biosynthesis was studied in pancreatic islets isolated from CPH-treated rats. Though insulin content of islets was markedly reduced in CPH-treated rats, the incorporation of radiolabeled leucine into proinsulin and insulin fractions was not affected with respect to the rate and amount. It is concluded that CPH may deplete insulin content of the islets through causing the leakage of insulin.

The effects of cyproheptadine on glucose tolerance and pancreatic islets in rats

The effects of cyprohepatadine (CPH) on plasma levels, of glucose, insulin and glucagon were studied in rats in order to clarify the diabetogenicity of this compound. CPH was given to the rats at a daily dose of 45 mg per kg body weight via gastric intubation for up to 20 days. Glucose intolerance appeared after 5 days of CPH treatment without significant increase in fasting glucose level. Plasma insulin response to glucose loading was depressed in the early phase of the glucose tolerance test in groups treated for 10 and 20 days. In these groups the insulinogenic index was significantly lowered. Pancreatic insulin content decreased rapidly after single dose of CPH. Plasma level and pancreatic content of glucagon were not changed by this compound. These results suggested that chronic treatment with CPH caused glucose intolerance in rats through its direct influence on pancreatic B-cell function.

Inhibition of insulin secretion from the perfused pancreas of the rat by pizotifen

1 In the perfused rat pancreas the effects of pizotifen on insulin release induced by 20 mM glucose were studied. 2 Pizotifen (10 and 100 muM) significantly reduced the insulin release during a 25 min perfusion period to 49% and 7% of the controls. 3 The same concentrations of the structurally related agents cyproheptadine, doxepin, and chlorpromazine produced a comparable inhibition.

Inhibition of insulin and glucagon release from the perfused rat pancreas by cyproheptadine (Periactinol, Nuran)

The tricyclic compound cyproheptadine (Periactinol, Nuran) inhibited glucose-induced insulin release from the perfused rat pancreas. Tolbutamide-stimulated insulin release was significantly reduced in the presence and completely suppressed in the absence of a substimulatory glucose concentration (5 mM). Arginine produced a slow rise of insulin release, which was completely abolished by cyproheptadine. Furthermore the biphasic glucagon release due to the stimulus was inhibited. Oxidation of 14C-glucose in isolated islets was unaltered in the presence of cyproheptadine, and pyruvate added to the perfusion medium failed to reverse the inhibitory effect on glucose induced insulin release, indicating that impaired glucose metabolism is not responsible for the inhibition. In addition, the inhibition remained unchanged when phentolamine was present, suggesting that the effect is not mediated by inhibitory adrenergic alpha receptors. Theophylline, in contrast, partly overcame the inhibition. When the calcium concentration of the medium was enhanced, the inhibitory effect of cyproheptadine was still visible, although the relative inhibition had become smaller. The results suggest that cyproheptadine blocks insulin release by affecting a fundamental step of the stimulus-secretion coupling common to peptide hormones. A participation of a calcium-antagonizing effect in the inhibition is discussed.