Stimulatory effect of intracerebroventricular met- and leu-enkephalin on corticosterone secretion in rats.
The significance of enkephalins for the function of the hypothalamic-pituitary-adrenal (HPA) axis, in spite of many efforts, is still elusive. We investigated the effect of leucine- and methionine-enkephalin on the HPA activity in conscious rats. These enkephalins, given intracerebroventricularly (i.c.v.) increased dose-dependently the activity of the HPA axis, measured indirectly through serum corticosterone levels. On a molar basis, leu-enkephalin exerted a stronger effect that met-enkephalin. Naloxone, an opioid receptor antagonist, given i.c.v. prior to enkephalins almost abolished the corticosterone response to met-enkephalin and significantly impaired the response to leu-enkephalin. Prazosin, an alpha 1-adrenergic antagonist, considerably reduced the increase in serum corticosterone levels induced by both enkephalins. Pretreatment of rats with yohimbine, an alpha 2-adrenergic antagonist, also considerably reduced the corticosterone response to met-enkephalin and significantly diminished the response induced by leu-enkephalin. Naloxone and yohimbine inhibited to the same extent the corticosterone response to met- and leu-enkephalin. This suggests an interaction between presynaptic opioid and alpha 2-receptors in regulation of the HPA function. Propranolol, a beta-adrenergic antagonist, given i.c.v. did not alter the corticosterone levels raised by met- and leu-enkephalin. These results indicate that both met- and leu-enkephalin increase the activity of the HPA axis in rats and both central opioid and adrenergic alpha-receptors are involved in this stimulation.
Gadek-Michalska
A
A
Department of Physiology, Polish Academy of Sciences, Cracow, Poland.
Bugajski
J
J
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002552:Cerebral Ventricles / Q000378:metabolism*; D003345:Corticosterone / Q000378:metabolism*; D004743:Enkephalin, Leucine / Q000494:pharmacology / Q000502:physiology*; D004744:Enkephalin, Methionine / Q000494:pharmacology / Q000502:physiology*; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D007276:Injections, Intraventricular; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D009292:Narcotic Antagonists; D011941:Receptors, Adrenergic; D015016:Yohimbine; D009270:Naloxone; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; D003345:Corticosterone