Hormone Ontogeny in the Ovine Fetus. VII. Circulating Luteinizing Hormone and Follicle-Stimulating Hormone in Mid- and Late Gestation*

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Abstract
Ovine LH and FSH concentrations in plasma were determined by homologous RIH on 96 samples from 24 chronically catheterized fetuses from 79 days gestation to term (147 days) and in 75 fetal samples obtained intraoperatively between 59–148 days gestation. In both series, FSH and LH were detected in the youngest fetus studied (59-day-old female; 64-day-old male). Similar concentrations were obtained in intraoperative and chronically catheterized fetuses. FSH concentrations in chronically catheterized female fetuses were 5.4 ± 1.2 ng/ml between 71–90 days and fell after 139 days to 2.5 ± 0.4 ng/ml. In the male fetuses, plasma FSH was lower than in the female fetuses before 110 days. Between 71–90 days, plasma FSH was 1.4 ± 0.6 ng/ml, rose to 4.7 ± 0.6 ng/ml between 91–110 days, and then fell to 2.2 ± 0.3 ng/ml after 130 days. The sex difference between 71–90 days was present as well when the data obtained from chronically catheterized and acute operative fetal samples were combined. LH concentrations in female fetuses were 3.2 ± 1.2 ng/ml before 90 days and fell progressively to 0.1 ±0.1 ng/ml after 130 days. In male fetuses, lower concentrations were observed before 110 days. Between 71–90 days, plasma LH was 0.6 ± 0.1 ng/ml, rose to 1.2 ± 0.4 ng/ml between 111–130 days, and fell to 0.2 ± 0.04 ng/ml after 130 days. A similar sex difference was noted between 71–90 days gestation when the values for the chronically catheterized and intraoperative groups were pooled. There is a similarity between the pattern of plasma gonadotropins in ovine and human fetuses. It is postulated that the changing plasma gonadotropin concentrations during fetal life reflect the development and maturation of the hypothalamicpituitary gonadotropin unit. The decrease in circulating gonadotropins in late gestation is likely to be due, at least in part, to the development of the negative feedback system and the rise in circulating fetal estrogen concentrations. (Endocrinology108: 874, 1981)