Mechanisms controlling corpus luteum function in the rhesus monkey (Macaca mulatta): inhibitory action of hCG on luteolysis induced by PGF2 alpha.

The aim of this study was to determine whether daily increasing doses of hCG could overcome luteal regression induced by PGF2 alpha in rhesus monkeys. Prostaglandin F2 alpha (10 ng microliters-1 h-1) or vehicle (tham buffer; 1 microliter h-1) was infused directly into the corpus luteum for 7 days, beginning 7 days after the preovulatory oestradiol surge. hCG was injected i.m. in increasing doses (15, 30, 60, 90, 180, 360 and 720 iu) for 7 days, starting on the eighth day after the preovulatory oestradiol surge, or 1 day after the initiation of luteal infusion of PGF2 alpha or vehicle. Monkeys receiving vehicle plus hCG on the same days served as controls. Daily progesterone, oestradiol and hCG concentrations were determined from blood drawn from the saphenous or femoral vein, and the duration of the luteal phases were recorded. Where intraluteally infused PGF2 alpha resulted in premature, functional luteolysis, hCG always inhibited the luteolytic effect of PGF2 alpha; the secretory patterns of progesterone and oestradiol were augmented, and peak values were reached in concert with the highest concentration of hCG in the blood, and the luteal phase was significantly increased compared with those of untreated monkeys or with monkeys treated with PGF2 alpha alone or vehicle. Treatment with hCG alone or with PGF2 alpha vehicle also resulted in maintained luteal function and a significantly longer luteal phase, but both progesterone and oestradiol concentrations began to decline before hCG reached peak values in the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)