Hypothalamo-pituitary-interrenal responses to opioid substances in the trout. I. Effects of morphine on the release in vitro of corticotrophin-releasing activity from the hypothalamus and corticotrophin from the pituitary gland.
The effects of morphine and naloxone on the secretion in vitro of corticotrophin (ACTH) and and corticotrophin-releasing factor (CRF) by the pars distalis and hypothalamus, respectively, have been studied in the trout. The spontaneous in vitro secretion of corticotrophin by the pars distalis is depressed significantly by the addition of high concentrations of morphine (10(-6)-10(-7) mol/litre) to the incubation medium. The effect is naloxone reversible. Morphine does not influence the response of the pituitary tissue to exogenous CRF41, suggesting that the inhibitory influence of the opiate is exerted primarily on the CRF nerve terminals within the pars distalis and not on the corticotrophs. At considerably lower concentrations (10(-10)-10(-8) mol/litre) morphine stimulates the release of CRF from the isolated trout hypothalamus in vitro. Its effects are dose-dependent and antagonized by naloxone. The results suggest that two anatomically and pharmacologically distinct populations of opioid receptors mediate opposing actions of morphine on the hypothalamo-pituitary-corticotrophic system in the trout.
Bird
D J
DJ
School of Biological Sciences, Bath University, England.
Buckingham
J C
JC
Baker
B I
BI
Mukherjee
S
S
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000375:Aging; D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism; D012487:Salmonidae / Q000502:physiology*; D014337:Trout / Q000502:physiology*
D009270:Naloxone; D009020:Morphine; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone