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

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Abstract
The variation of the plasma levels of 11 steroids and LH [luteinizing hormone] was investigated in 6 normally menstruating women during the peri-menstrual period. Blood was withdrawn continously over a period of 42 h at a rate of 4 ml/h by means of a non-thrombogenic pump. The changes in hormone levels were studied during fourteen 3-h sampling periods (42 h) which - with respect to the clock time - were identical in all subjects. Cortisol, 17-hydroxypregnenolone and dehydroepiandrosterone exhibited a marked circadian rhythm with the highest mean levels in the morning between 06.00 and 09.00 h and the lowest mean levels during the night between 21.00 and 03.00 h. The amplitude of the variation was high, the differences between the highest and lowest values being 200, 590 and 150%, respectively. The coincidence of individual peak values with the average peaks was high (mostly in 5 out of 6 cases). The correlation of cortisol levels with those of 17-hydroxypregnenolone and dehydroepiandrosterone was significant (r = 0.79 and 0.59, respectively; P < 0.001). The circadian variation of 17-hydroxyprogesterone, androstenedione and pregnenolone was also significant, but less pronounced, as indicated by lower amplitudes and larger spread of individual peaks around average peaks. The correlation of the levels of these steroids with those of cortisol was significant (r = 0.47: P < 0.001; r = 0.44: P < 0.001 and r = 0.31: P < 0.01, respectively). Progesterone, 20.alpha.-dihydroprogesterone, testosterone and estradiol did not exhibit any circadian variation, but a steady decrease of levels. The levels of the first 2 steroids were significantly correlated (r = 0.81; P < 0.001). The dihydrotestosterone and LH [luteinizing hormone] levels did not show any significant changes during the entire study. If only the 2nd half of the sampling time was statistically analyzed, a significant increase was found in the LH levels. During this time the LH levels were negatively correlated with the decreasing levels of progesterone and 20.alpha.-dihydroprogesterone (r = -0.59 and -0.66, respectively; P < 0.001). A comparison of the data with those of a previous study performed during the peri-ovulatory period suggests that the occurrence, intensity and regularity of the circadian rhythm varies according to different phases of the menstrual cycle. The data also suggest that 17-hydroxypregnenolone in plasma is an excellent indicator of adrenocortical activity.