RECEPTORS FOR GONADOTROPHIN AND PROSTAGLANDIN F2α IN BOVINE CORPORA LUTEA OF EARLY, MID AND LATE LUTEAL PHASE

Abstract

ABSTRACT A total of 15 corpora lutea representing early (day 3), mid (day 13) and late luteal phase (days 20 and 21–24) were obtained by ovariectomy on cycling cows. The luteal weights and peripheral plasma progesterone levels just prior to ovariectomy, were consistent with the above luteal phases. The specific binding of [125I]human chorionic gonadotrophin to membranes prepared from corpora lutea was significantly higher (P < 0.01) for days 13 and 20 than for days 3 and 21–24. The binding in day 21–24 corpora lutea was higher (P < 0.01) than day 3. Although there was no difference either in number or affinity (apparent dissociation constant (Kd) = 0.04 nm) of gonadotrophin receptors in days 13 and 20 corpora lutea, only in the former did the binding correlate well with plasma progesterone levels. The specific binding of [3H]prostaglandin (PG)F2α to the membranes of these same corpora lutea showed a progressive increase (P < 0.01) from day 3, reached the highest value at a time when corpora lutea were actively regressing (day 20) and then declined (P < 0.01) by day 21–24. Although a considerable number of PGF2α receptors existed at day 13, the affinity of these same receptors was 203 times lower (Kd = 3458 nm) than the affinity of receptors in day 20 corpora lutea (Kd = 17 nm). In summary, the above results show that gonadotrophin receptors correlate with luteotrophic, whereas PGF2α receptors correlate with luteolytic phases in bovine corpora lutea.