Inhibition of ovarian aromatase by prolactin in vivo.
Ovarian aromatase activity was inhibited by prolactin treatment in both cycling rats and immature gonadotropin-primed animals. Cycling rats were injected s.c. with prolactin (4 mg/kg BW) beginning on diestrus 1. Aromatase activity in the largest follicles on diestrus 2 and on proestrus was reduced relative to controls. None of the prolactin-treated animals had ovulated when examined on the expected estrus morning. In other experiments, the immature pregnant mare's serum gonadotropin (PMSG)-primed rat was used as a model for the cycling rat. Microsomal aromatase activity but not the activity of the C17-21 lyase was reduced in ovaries of animals injected with prolactin [6 IU (200 micrograms)/rat] 48 h after PMSG administration and sacrificed 4 h later. Furthermore, aromatase activity was significantly increased when endogenous prolactin was inhibited by bromocryptine (CB-154). The effect of LH treatment, on the other hand, was to increase both aromatase and lyase activities. However, prolactin pretreatment did not consistently prevent the LH-induced increase in aromatase activity. The results suggest that inhibition of ovulation by prolactin is mediated, at least in part, by direct inhibition of aromatase activity.
D000818:Animals; D047072:Aromatase Inhibitors; D001971:Bromocriptine / Q000494:pharmacology; D004971:Estrus; D005260:Female; D010053:Ovary / Q000201:enzymology*; D010060:Ovulation / Q000187:drug effects; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D011247:Pregnancy; D011388:Prolactin / Q000494:pharmacology* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012741:Sexual Maturation
D047072:Aromatase Inhibitors; D001971:Bromocriptine; D011388:Prolactin; D010088:Oxidoreductases