Contraception
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In six normally menstruating women, ovarian and adrenal steroids and biologically active lutropin (LH) were measured in peripheral plasma samples collected every 3 h. during a period of 39 h. in the early follicular phase, periovulatory period or luteal phase of three consecutive cycles. The purpose of the study was to assess the influence of the phases of the cycle on the diurnal variation in the levels of different steroids and lutropin following the elimination of the between subject variation. Cortisol, 17-hydroxypregnenolone, dehydroepiandrosterone and androstenedione showed a marked circadian rhythm in all three phases of the cycle. ⋯ In none of the phases studied did the levels of progesterone or estradiol show any circadian variation. The data indicate that a circadian rhythm in the peripheral levels of a given steroid mainly depends on the relative contributions of the ovaries and adrenals and that these contributions exhibit major differences at the various phases of the cycles. It is concluded that - in contradistinction to the situation in the human male - in normally menstruating women, the peripheral levels of steroids of predominantly gonadal origin do not exhibit a circadian rhythmicity.