Direct action of opioid peptides and naloxone on gonadotropin secretion by cultured rat anterior pituitary cells.
Most current evidence indicates that opiates act via the hypothalamus to influence pituitary function. There are no detailed studies concerning pituitary site of action. Direct action of opioids on gonadotropin secretion was studied using enzymatically dispersed rat pituitary cells maintained in a monolayer culture. A time course study demonstrated that pretreatment with beta h-endorphin (beta h-End) (10(-7) M) initiated an inhibitory effect on LH release at 24 h, and was more evident at 48 h. A dose dependent decrease in LH release by beta h-End in concentrations of 10(-9) M to 10(-7) M was shown, whereas FSH was unchanged. Equimolar concentrations (10(-7)M ) of methionine enkephaline (Met-Enk) and D-ala2-met-enkephalinamide (DALA) produced a significant decrease in LH. Naloxone (NAL) (10(-5)) enhanced the release of both LH and FSH, and also blocked the inhibitory effect of beta h-End on LH release. These results indicated that opioid peptides act directly on anterior pituitary cells, decreasing the release of LH, but not of FSH. NAL also had a direct effect increasing the release of LH and FSH, and blocking the inhibitory action of beta h-End.
D000818:Animals; D002478:Cells, Cultured; D004723:Endorphins / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D007986:Luteinizing Hormone / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D001615:beta-Endorphin
D004723:Endorphins; D009294:Narcotics; D009270:Naloxone; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; C022118:enkephalinamide-Met, Ala(2)-; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone