Receptors for gonadotrophin and prostaglandin F2 alpha in bovine corpora lutea of early, mid and late luteal phase.

A total of 15 corpora lutea representing early (day 3), mid (day 13) and late luteal phase (day 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 less than 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 less than 0.01) than day 3. Although there was no different 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]prostaglanding (PG)F2 alpha to the membranes of the same corpora lutea showed a progressive increase (P less than 0.01) from day 3, reached the highest value at a time when corpora lutea were actively regressing (day 20) and the decline (P less than 0.01) by day 21-24. Although a considerable number of PGF2 alpha 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 PGF2 alpha receptors correlate with luteolytic phases in bovine corpora lutea.