STUDIES ON THE PATTERN OF CIRCULATING STEROIDS IN THE NORMAL MENSTRUAL CYCLE

Abstract

By the use of a non-thrombogenic pump, blood was withdrawn continuously at a rate of 4.0 ml/h over a period of 48 h from 10 normally menstruating women during various phases of the peri-ovulatory period, and the integrated levels of estradiol, estrone, 17-hydroxyprogesterone, progesterone, 20.alpha.-dihydroprogesterone and biologically active luteinizing hormone (LH) were estimated in 3-hourly plasma collections. The 1st significant change detected 2 days prior to the LH surge (day LH-2) in 1 subject studied during this period was a continuous parallel rise in estradiol and estrone levels, which occurred in the absence of any simultaneous change in LH and 17-hydroxyprogesterone levels. Marked fluctuations followed by a sudden drop in estradiol levels were observed in another woman during the day preceding the LH peak (day LH-1). These changes were not associated with similar alterations in estrone levels. The marked drop in estradiol coincided with the beginning of a simultaneous major rise in LH and 17-hydroxyprogesterone levels followed some 6-9 h later by a small but significant increase in progesterone levels. The period of the LH surge (day LH) was studied in 3 women. This period was characterized by a constant decline in estradiol levels in the presence of unchanged estrone values. The decrease in estradiol levels preceded the LH peak by at least 12 h. The LH peak was biphasic in all subjects; both the ascending and descending limbs of it were significantly correlated to similarly changing levels of 17-hydroxyprogesterone. The increase in these 2 hormones preceded that in progesterone levels, which occurred later, at the time of the steepest rise in LH levels. The findings of the subsequent day (day LH + 1) were characterized in 2 subjects by a parallel decrease in plasma estradiol, LH and 17-hydroxyprogesterone levels, until a plateau was reached. This plateau coincided with a new rise in progesterone and 20.alpha.-dihydroprogesterone levels. The hormonal profile observed 2 days following the LH surge (day LH + 2) in 3 women was similar to that of the preceding day, with the exception of a beginning new rise in 17-hydroxyprogesterone levels by the end of day LH + 2. This 2nd rise in 17-hydroxyprogesterone paralleled that in progesterone and 20.alpha.-dihydroprogesterone levels and occurred in the presence of decreasing levels of LH. Different control mechanisms are probably involved in the regulation of ovarian steroid secretion during the various phases of the peri-ovulatory period.