Prostaglandin E2 mediates the stimulatory effect of methoxamine on in vivo luteinizing hormone-releasing hormone (LH-RH) release in the ovariectomized female rhesus monkey.

Previously, we found that noradrenergic input through alpha 1-receptors modulates pulsatile release of luteinizing hormone-releasing hormone (LH-RH) in ovariectomized rhesus monkeys in the absence of estrogen. In the present study, the role of prostaglandin E2 (PGE2) in mediating alpha-adrenergic stimulation of LH-RH release is investigated. In the first experiment the effects of the alpha 1-adrenergic agonist methoxamine (MTX) on LH-RH and PGE2 release were examined. Push-pull perfusion of the stalk-median eminence (S-ME) was performed in conscious, ovariectomized monkeys, and perfusate samples were collected on ice. MTX (10(-5) M) was infused into the S-ME through the push cannula for 10 min at 90-min intervals, and LH-RH and PGE2 in aliquots of the same perfusate samples were measured by radioimmunoassay. Infusion of MTX significantly stimulated LH-RH release (n = 12; P less than 0.01) and PGE2 release (P less than 0.05). In the second experiment, the effect of PGE2 infusion on LH-RH release was tested. PGE2 (10(-7) M) was infused using the same protocol as above, and LH-RH was measured in the perfusates. Infusion of PGE2 through the push cannula significantly stimulated LH-RH release (n = 23; P less than 0.05). These results suggest that the stimulatory effect of MTX on LH-RH release is at least partly mediated by PGE2, since MTX stimulated not only LH-RH but also PGE2 release, and since PGE2 itself stimulated LH-RH release. Therefore, PGE2 may be an important endogenous mediator of alpha 1-adrenergic input stimulating pulsatile LH-RH release.(ABSTRACT TRUNCATED AT 250 WORDS)