Temporal relationships of hormonal variables in the menstrual cycle.

Temporal relationships between blood levels of the separate hormones as determined throughout each menstrual cycle are described. Daily measurements showed characteristic patterns. Luteinizing hormone (LH) seemd to be stored in the pituitary and released periodically while follicle stimulating hormone (FSH) was synthesized and secreted more evenly throughout the cycle. LH accumulated from Day 3 to Days 9-13 and was released on Days 15-17 with depletion of pituitary stores. Another pituitary buildup on Days 18-20 and decline on Days 21-27 followed. Characteristic for the course of LH was the sharp midcycle peak in serum levels which rose three- to tenfold. This peak coincided with the shift in basal body temperature. Characteristic features of the normal FSH curve were high levels at the beginning of the cycle a nadir 1 or 2 days before the LH peak and a peak within 1 day of that of LH. Since radioimmunoassay became available estrogen patterns have been determined. In the early phases 7-10 days when FSH levels were high estrogens remained low. Then estradiol levels increased to a maximum about the time of the LH peak followed by a sharp drop. Estrogens have been shown to fall within 3-4 hours after gonadotropin (human chorionic gonadotropin) administration. A more gradual rise and fall of estrogen over the 2 weeks of the luteal phase occurred. By onset of menses estradiol levels reached the baseline. Progesterone patterns showed low levels during the 2 weeks of follicular development and a gradual elevation and decline with corpus luteum growth and regression. Also 17alpha-hydroxyprogesterone 20alpha-dihydroxyprogesterone and 20beta-dihydroprogesterone have been isolated and their serum levels found with curves nearly parallel to progesterone. Levels of delta-5-pregnenclone and for 17X-hydroxy-deltat-5 pregnenolone have been measured. Both compounds were lower in follicular and higher in the luteal phase. Androgens have been measured in th blood of women but significant changes in the cycle have not been shown. Plasma cortisol and corcicosterone levels will require further study by recently available methods. Aldosterone levels followed a course similar to progesterone. Renin had a midcycle peak and a similar curve to estradiol. Growth hormone and prolactin have shown no characteristic patterns. Composite curves showed typical events but individual cycles often showed marked variations in hormonal patterns. The menstrual cycle appeared to be a sequence of processes undergoing continuous readjustments perhaps to disturbances originating outside the reproductive system.