title: Evidence for involvement of alpha-adrenergic receptors in norepinephrine-induced prostaglandin E2 and luteinizing hormone-releasing hormone release from the median eminence.
abstract: Studies were conducted to determine if the stimulatory effect that norepinephrine (NE) exerts on the release of prostaglandin E2 (PGE2) and LHRH from the median eminence is mediated by alpha- or beta-adrenergic receptors. Incubation of median eminence fragments from adult male rats with different concentrations of phentolamine, an alpha-receptor antagonist, resulted in a dose-related inhibition of the release of both PGE2 and LHRH induced by NE, with an IC50 of 3.5 X 10(-7) and 0.9 X 10(-7) M for PGE2 and LHRH, respectively. Complete suppression of the NE effects was observed with a phentolamine concentration of 5 X 10(-6) M. This dose also reduced basal PGE2 and LHRH release. In contrast to phentolamine, the beta-receptor antagonist propranolol, tested at a concentration of 5 X 10(-6) M, was completely ineffective in altering the stimulatory effect of NE on either PGE2 or LHRH release. Moreover (and as previously observed for LHRH), blockade of dopaminergic receptors with Pimozide (10(-6) M) failed to inhibit the release of PGE2 induced by NE, thus indicating that the stimulatory effect of NE is not mediated by a dopaminergic mechanism. It is concluded that NE stimulates the release of PGE2 and LHRH from nerve terminals of the median eminence by first interacting with an alpha-adrenergic receptor.
mesh_terms: D000818:Animals; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008473:Median Eminence / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D010868:Pimozide / Q000494:pharmacology; D011458:Prostaglandins E / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
chemical_list: D011458:Prostaglandins E; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D010868:Pimozide; D007987:Gonadotropin-Releasing Hormone; D009638:Norepinephrine