HORMONAL CHANGES DURING THE MENSTRUAL CYCLE OF THE BABOON (PAPIO HAMADRYAS)

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Abstract
Eleven unconjugated steroids were measured daily during a complete cycle in the peripheral plasma of 6 normally menstruating baboons (P. hamadryas) by means of a radioimmunoassay procedure, and the levels were compared with those found previously in 17 normally menstruating women. The patterns of progesterone and 20.alpha.-dihydroprogesterone were very similar to those found in women throughout the entire menstrual cycle. The ratio of these steroids differed markedly from that found in women. A great similarity of the follicular phase and the periovulatory period profiles was observed in both species for 17-hydroxyprogesterone, pregnenolone, androstenedione, estradiol and estrone. The pattern of estradiol:estrone ratios was similar in both species. An elevation of the levels of the above 5 steroids, typical for the human luteal phase, was not found in baboons. The increase of testosterone values, seen in women at mid-cycle, was not detected in baboons. The plasma concentrations were lower in baboons than in humans for all the above steroids. Similar to the findings in the human female, no cyclic variation was observed in the plasma levels of 17-hydroxypregnenolone, dehydroepiandrosterone and dihydrotestosterone. The mean concentrations were significantly higher in baboons than in women for these 3 compounds. The plasma concentrations of the sulfates of pregnenolone and dehydroepiandrosterone were also estimated at different phases of the menstrual cycle. These measurements indicated that the concentrations in baboon plasma were considerably lower than in human plasma. LH [luteinizing hormone] levels were measured during the periovulatory period, using an in vitro bioassay. The sharp mid-cycle peak found in baboons exceeded that seen in the human. With the exception of the luteal phase, the circulating steroid pattern in normally menstruating baboons resembles very closely that occurring in women.