EFFECT OF ESTRADIOL-17-BETA ON BASAL AND HCG STIMULATED PROGESTERONE SECRETION BY PORCINE LUTEAL CELLS ISOLATED IN VARIOUS STAGES OF THE LUTEAL-PHASE

To explore the direct effect of estradiol-17beta on pig luteal cells a nd its ability to counteract a gonadotropic stimulus, luteal cells wer e incubated in vitro in the presence of estradiol alone, human chorion ic gonadotrophin (hCG) alone or estradiol combined with hCG. Luteal ce lls were collected at three different stages of the luteal phase (0-3 days after ovulation, early; 8-10 days after ovulation, mid; and 14-16 days after ovulation, late). Estradiol alone did not exert any effect on progesterone production by any of the 3 types of luteal cells. Pro gesterone production by cells in the mid-luteal phase was enhanced by hCG in a dose dependent manner. High doses of estradiol combined with hCG significantly diminished production of progesterone by cells colle cted during the early luteal phase. The strongest inhibitory effect of estradiol on hCG stimulated progesterone production was observed in c ultures of luteal cells in the midluteal phase. In contrast, 100 ng of estradiol and the 10 and 100 ng/ml concentrations of hCG increased pr ogesterone secretion over basal control values in cultured luteal cell s in the late luteal phase. Differences in the production of progester one in response to estradiol at different stage of the luteal phase su ggest that different cellular mechanisms must be triggered in each lut eal phase investigated. These data support a physiological role for es trogen in the regulation of the pig corpus luteum during its life span in the non-fertile cycle.