Corticosterone response induced by intracerebroventricular administration of met-enkephalin and naloxone in rats under stress.
In rats exposed to a 10 min restraint stress naloxone (0.1-10 micrograms) administered intracerebroventricularly (i.c.v.) did not substantially alter the hypothalamic-pituitary-adrenal (HPA) stress response, measured indirectly through serum corticosterone levels. Met-enkephalin (10-200 micrograms i.c.v.) dose dependently increased the stress-induced corticosterone response. The increase in corticosterone secretion elicited by met-enkephalin was markedly diminished by pretreatment with naloxone. The adrenergic alpha 1- and alpha 2-receptor antagonists, prazosin and yohimbine did not significantly affect the met-enkephalin-induced increase in serum corticosterone levels in stressed rats. Conversely, propranolol, a beta-adrenergic receptor antagonist, abolished the met-enkephalin induced corticosterone response. These results indicate that opioid receptors are not significantly involved in the HPA response to a short restrains stress. In stressed rats met-enkephalin stimulates, by a central mechanism, the hypothalamo-pituitary-adrenocortical activity via opioid- and beta-adrenergic but not alpha-adrenergic receptors.
Gadek-Michalska
A
A
Department of Physiology, Polish Academy of Science, Cracow, Poland.
Cetera
B
B
Bugajski
J
J
D000818:Animals; D003345:Corticosterone / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004744:Enkephalin, Methionine / Q000378:metabolism* / Q000494:pharmacology; D007103:Immobilization / Q000009:adverse effects; D007276:Injections, Intraventricular; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000502:physiology*; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D013312:Stress, Physiological / Q000097:blood* / Q000209:etiology; D015016:Yohimbine / Q000494:pharmacology
D011941:Receptors, Adrenergic; D011957:Receptors, Opioid; D015016:Yohimbine; D009270:Naloxone; D004744:Enkephalin, Methionine; D011433:Propranolol; D003345:Corticosterone; D011224:Prazosin