LHRH and some of its analogs have been reported to exert inhibitory effects on ovarian function, seemingly following interaction of the neurohormone with specific, high affinity binding sites. The present experiments were undertaken to determine whether LHRH binding sites in the ovary undergo quantitative changes during the onset of puberty in the rat. Changes in LHRH receptor content were assessed by the binding of the stable LHRH analog, [D-Ala, Pro]-LHRH to ovarian membrane preparations. LHRH binding in prepubertal rats (anestrus, A) was 166 ± 11 fmol/mg protein, declined gradually (to 127 ± 14 fmol/mg protein) during the early proestrous (EP) phase of puberty” a time at which intrauterine fluid begins to accumulate and uterine weight increases more rapidly” and became even lower (75 ± 4 fmol/mg protein) by 1300 h of the day of first proestrus (LP), prior to the initiation of the first gonadotropin surge. At the time of the surge (1600 h) binding was 70 ± 3 fmol/mg protein. LHRH binding was minimal on the day of the first estrus (E) and increased slightly on diestrus (D). The results indicate that the ovarian steroidogenic activation that precedes the first surge of gonadotropins in the rat is associated with a marked loss in ovarian LHRH receptor content and suggest that a reduction in LHRH inhibitory function within the ovary may be a contributing factor to the pubertal enhancement in ovarian secretory activity.
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