Studies on the pattern of circulating steroids in the normal menstrual cycle. 4. Periovulatory changes in relation to the LH surge.

Abstract

ABSTRACT By the use of a non-thrombogenic pump, blood was withdrawn continuously at a rate of 4.0 ml/h over a period of 48 h from 10 normally menstruating women during various phases of the peri-ovulatory period and the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 oestradiol, oestrone, 17-hydroxyprogesterone, progesterone, 20α-dihydroprogesterone and biologically active luteinizing hormone (LH) were estimated in 3-hourly plasma collections. The first significant change detected two days prior to the LH surge (day LH-2) in one subject studied during this period was a continuous parallel rise in oestradiol and oestrone levels, which occurred in the absence of any simultaneous change in LH and 17-hydroxyprogesterone levels. Marked fluctuations followed by a sudden drop in oestradiol 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 oestrone levels. The marked drop in oestradiol coincided with the beginning of a simultaneous major rise in LH and 17-hydroxyprogesterone levels followed some 6 to 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 characterised by a constant decline in oestradiol levels in the presence of unchanged oestrone values. The decrease in oestradiol 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 two 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 characterised in two subjects by a parallel decrease in plasma oestradiol, LH and 17-hydroxyprogesterone levels, until a plateau was reached. This plateau coincided with a new rise in progesterone and 20α-dihydroprogesterone levels. The hormonal profile observed two 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 second rise in 17-hydroxyprogesterone paralleled that in progesterone and 20α-dihydroprogesterone levels and occurred in the presence of decreasing levels of LH. The data reported strongly suggest that different control mechanisms are involved in the regulation of ovarian steroid secretion during the various phases of the peri-ovulatory period.