Metabolism of reproductive steroids during the ovarian cycle in two species of callitrichids, Saguinus oedipus and Callithrix jacchus, and estimation of the ovulatory period from fecal steroids.

Gonadal steroids were measured in daily fecal samples providing comparative data on steroid metabolism in two genera of New World primates. Circulating bioactive LH and progesterone concentrations and fecal progesterone, pregnanediol, estradiol, and estrone concentrations were measured by collecting blood and daily fecal samples from four captive common marmoset females and four cotton-top tamarin females for 30 days. High recoveries (> 80%) of labeled steroids that were added directly to the feces before extraction were recovered from feces of both species. Because of the presence of complex steroid conjugates, only one fifth the amount of estradiol was measured without solvolysis as compared to the amount measured with solvolysis. In tamarins, steroids were metabolized rapidly, with all postovulatory increases occurring within two days after the circulating LH peak (an increase of 2 SD higher than mean follicular levels). In marmosets, steroid excretion was slower; increased steroid levels occurred 2-4 days after the LH peak except in the case of estrone, which did not consistently increase after the LH peak. Circulating estrone and estradiol both contributed to the high excretion of estradiol in the feces from both species. The timing in the delay in excretion of fecal steroids was used to accurately determine the ovulatory period to within a 2-day window. This degree of accuracy is possible when the duration of the delay to the LH peak is known for a given species. Additionally, steroid concentrations were highly correlated between frozen and lyophilized fecal samples (0.81 +/- 0.07 SEM), indicating that fluid removal from the feces did not effectively alter steroid profiles.