Suppression of progesterone-induced gonadotropin surge by adrenergic agonists in estrogen-primed ovariectomized rats.
An involvement of catecholamines in the preovulatory gonadotropin surge has been proposed for many years. Specifically, an alpha-adrenergic mechanism has been implicated in the stimulation of ovulation and LH release. On the other hand, little is known regarding the possible role of adrenergic neurotransmission once a gonadotropin surge has been initiated. In this study, drugs which affect adrenergic receptors were administered centrally to estrogen-primed ovariectomized rats and the effects on serum concentrations of LH and FSH induced by treatment with progesterone at 08:00 h were examined. As expected, the progesterone treatment caused a significant (p less than 0.05) increase in blood LH and FSH levels by 14:00 and 15:00 h, respectively, when compared with those seen at 13:00 h. In control rats that received isotonic saline intraventricularly at 15:00-16:00 h, both LH and FSH levels continued to rise linearly and reached peak levels by 17:00 and 18:00 h. By contrast, intraventricular infusion of norepinephrine at 16:00 h caused a significant decrease (p less than 0.05) in LH levels when compared with the saline-infused control groups. Moreover, rats that received intraventricular infusion of phenylephrine (an alpha 1-adrenergic agonist) at 15:00 h failed to show a significant increase in LH and FSH levels until 19:00 h; this inhibitory effect was mimicked by a relatively more specific alpha 1-adrenergic agonist, methoxamine. Consistent with our previous findings, animals which received intraventricular isoproterenol (a specific beta-adrenergic agonist) at 15:00 h also responded with suppressed serum LH levels at 16:00-19:00 h when compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D007276:Injections, Intraventricular; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D009638:Norepinephrine / Q000008:administration & dosage / Q000494:pharmacology*; D010052:Ovariectomy; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology*; D011374:Progesterone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D010656:Phenylephrine; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D007545:Isoproterenol; D009638:Norepinephrine