Effect of chronic administration of progesterone on the naloxone-induced LHRH release from hypothalami of ovariectomized, estradiol-primed prepubertal rats.
To test the hypothesis that progesterone (P) administered in a high dose and for a long duration would influence in vitro LHRH release by naloxone, silastic capsules containing P (50 mg/ml) or vehicle were implanted sc in ovariectomized, estradiol-primed (OVX+E) prepubertal rats. Following a 48 hr exposure to P, rats were sacrificed and mediobasal hypothalamic (MBH) fragments were obtained. In addition, in other OVX+E primed rats, a single injection of P (1 mg) was given sc 6 hr prior to decapitation. Naloxone or control medium were infused into superfusion chambers containing MBH fragments derived from these animals for 2 hr following a 1 hr control period. Infusion of naloxone (1 x 10(-4) M) markedly stimulated in vitro LHRH release from MBH from rats pre-exposed to P for 48 hr, whereas it was unable to do so in other groups examined. These data clearly indicate that the ability of naloxone (1 x 10(-4) M) to stimulate LHRH release is dependent on the duration of P administration.
Kim
K
K
Department of Zoology, College of Natural Sciences, Seoul National University, Korea.
Lee
C S
CS
Cho
W K
WK
Ramirez
V D
VD
D000818:Animals; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D009270:Naloxone / Q000494:pharmacology*; D010052:Ovariectomy; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012741:Sexual Maturation
D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D011374:Progesterone; D004958:Estradiol