Blockade of LHRH-induced lordosis by alpha- and beta-adrenergic antagonists in ovariectomized, estrogen primed rats.
The participation of a noradrenergic mechanism in the facilitation of lordosis by luteinizing hormone-releasing hormone (LHRH) was studied in two groups of ovariectomized estrogen primed rats, with or without sexual experience. The administration of 5 micrograms estradiol benzoate (EB) alone to sexually inexperienced subjects (Ss) induced weak lordosis behavior in some of them (mean lordosis quotient, LQ = 12 +/- 19). The SC injection of 5 micrograms LHRH significantly increased this response four hours later (LQ = 38 +/- 41), though great variability was observed (59% of Ss showing LQs below 30). The systemic administration of either prazosin, an alpha-adrenergic antagonist (0.2 or 1 mg/kg), or propranolol, a beta-adrenergic antagonist (20 mg/kg), totally suppressed LHRH-induced lordosis in sexually inexperienced Ss (mean LQs = 8 +/- 11; 5 +/- 10; 18 +/- 31, respectively). In sexually experienced Ss (tested on two previous occasions with EB and LHRH) the administration of EB alone on a third test induced significant levels of lordosis (mean LQ = 51 +/- 41). The administration of 5 micrograms LHRH to sexually experienced, estrogen primed Ss induced near maximal levels of lordosis (LQ = 94 +/- 18). In these Ss, prazosin (0.2 and 1 mg/kg) and, to a lesser extent, propranolol (20 mg/kg) significantly depressed lordosis to values that were not significantly different from those obtained after EB alone (mean LQs = 59 +/- 38; 63 +/- 20; 74 +/- 32, respectively). These results indicate that blockade of noradrenergic transmission by either alpha- or beta-antagonists counteracts the stimulatory effect of LHRH on lordosis in ovariectomized estrogen primed rats with or without sexual experience.(ABSTRACT TRUNCATED AT 250 WORDS)
González-Mariscal
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Centro de Investigación en Reproducción Animal CINVESTAV-UAT, Tlaxcala, Mexico.
Beyer
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D000818:Animals; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000008:administration & dosage; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D010052:Ovariectomy; D011187:Posture; D011224:Prazosin / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000502:physiology*; D012726:Sexual Behavior, Animal / Q000187:drug effects*
D011941:Receptors, Adrenergic; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D011433:Propranolol; D011224:Prazosin