Hypoinsulinemic and hyperglycemic effects of beta-endorphin in rabbits.
The present study was designed to investigate the in vivo effects of beta-endorphin on plasma levels of glucagon, insulin and glucose in rabbits, and to elucidate some of the mechanisms involved. beta-Endorphin (50 micrograms) injected intravenously into fasted rabbits, decreased plasma levels of insulin (-4.5 +/- 1.3 microU/ml, P less than 0.05) and increased plasma levels of glucose (+2.7 +/- 0.4 mmol/l, P less than 0.05). Similar hypoinsulinemic and hyperglycemic effects were observed for 25 and 2.5 micrograms beta-endorphin in fasted and 50 and 0.5 micrograms beta-endorphin in fed rabbits. beta-Endorphin produced slight and transient increases in plasma levels of glucagon at the highest dose in fed rabbits, only (+80 +/- 9 pg/ml, P less than 0.05). The beta-endorphin-induced hypoinsulinemia was not inhibited by phentolamine, yohimbine, propranolol or atropine, which is in consistency with a direct inhibitory effect of beta-endorphin on the beta-cell in rabbits. The beta-endorphin-induced hyperglycemia was reduced by naloxone (+0.8 +/- 0.1 mmol/l) but not by N-methyl-naloxone (ORG 10908) a peripheral opiate receptor blocking drug (+2.2 +/- 0.2 mmol/l), suggesting a central nervous action on opiate receptors. This central action of beta-endorphin was probably not mediated by catecholamine release or other stimulation of adrenergic or muscarinic receptors, since the beta-endorphin-induced hyperglycemia was not inhibited by phentolamine, yohimbine, propranolol or atropine. These results suggest that the beta-endorphin-induced hyperglycemia was caused, at least in part, by a peripheral inhibition of insulin release and a central stimulation on glucoregulation.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001786:Blood Glucose / Q000378:metabolism; D004723:Endorphins / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D005934:Glucagon / Q000097:blood; D006943:Hyperglycemia / Q000097:blood* / Q000139:chemically induced; D007275:Injections, Intravenous; D007328:Insulin / Q000097:blood*; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds; D011817:Rabbits; D015016:Yohimbine / Q000494:pharmacology; D001615:beta-Endorphin
D001786:Blood Glucose; D004723:Endorphins; D007328:Insulin; D000644:Quaternary Ammonium Compounds; D015016:Yohimbine; D009270:Naloxone; D001615:beta-Endorphin; C041269:N-methylnaloxone; D001285:Atropine; D005934:Glucagon; D011433:Propranolol; D010646:Phentolamine