REGULATION OF LUTEAL FUNCTION BY LUTEINIZING-HORMONE AND PROLACTIN ATDIFFERENT TIMES OF THE LUTEAL-PHASE

In 54 healthy women luteal function was assessed by sequential withdra wals of blood samples at 10-min internals for 8-10 h. Subgroups of the women were studied during the early and late ovulatory period and dur ing the early, mid- and late luteal phase. Bio- and immunoreactive lut einizing hormone (LH), prolactin, testosterone, estradiol and progeste rone levels were determined in each sample. While the bio- and immunor eactivity of LH pulses correlated fairly well, a number of bio- or imm unoreactive LH pulses were observed that were not detected by the resp ective other method. Responsivity of the corpus luteum to LH episodes developed during the second half of the luteal phase and was most mark ed in cases where LH episodes were accompanied by prolactin episodes. In the absence of prolactin episodes, LH episodes did not stimulate pr ogesterone or estradiol secretion. The highest incidence of coincident LH and prolactin pulses was observed during the mid- and late luteal phase. Serum testosterone levels showed also some fluctuations but the se were independent of immuno- or bioactive LH episodes and therefore most likely not of luteal origin. Prior to menstruation LH episodes we re not any more stimulatory to progesterone secretion, indicating that it is not the withdrawal of LH but, rather, another possibly intraova rian mechanism that results in luteolysis. In a number of women, incre ased estradiol and progesterone secretion was strictly related to the prior occurrence of LH and prolactin pulses. In other subjects, both g onadal steroids fluctuated largely with no discernible correlation to LH fluctuations. This may indicate that in these subjects the corpora lutea have some degree of autonomous regulation.