The Influence of Fetectomy at Midgestation upon the Serum Concentrations of Progesterone, Estrone, and Estradiol in Baboons

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Abstract
The objective of this study was to determine the influence of fetectomy at midgestation in baboons upon the peripheral serum concentrations of progesterone (P), estrone (E1), and estradiol (E2). Maternal saphenous venous blood was collected at 1- to 4-day intervals between 90 days gestation and the 24-h postpartum period in five baboons in whom the fetus but not the placenta was removed at 100–109 days gestation and in four untreated baboons. Serum P, E1, and E2 concentrations were determined by RIA. Baboons fetectomized at midgestation spontaneously delivered their placentas on day 169 ± 8 (mean ± SE) of gestation. The mean length of gestation for our baboon colony is 184 days. Fetectomy resulted in a marked decline (64–80%; P < 0.001) in serum P concentrations from mean values of 6.9–9.7 ng/ml in the five baboons before fetectomy to 1.7–3.5 ng/ml thereafter. Between 90 days gestation and term the mean (± SE) serum P concentration in untreated baboons was 7.7 ± 0.3 ng/ml, and although P concentrations fluctuated in value, no significant progressive rise or fall in concentrations occurred. Serum E1 and E2 concentrations rapidly decreased from mean values of 0.38–0.75 and 0.8–3.2 ng/ml, respectively, before fetectomy to very low and, in most cases, undetectable levels thereafter. Serum E2 concentrations in untreated baboons increased (P < 0.001) with progressing gestation, attaining maximum values of 6.4–12.8 ng/ml near term. Serum E1 concentrations in untreated animals ranged between 0.20–2.00 ng/ml throughout the study period and no significant progressive rise or fall in these levels occurred. These results suggest that the elevated concentrations of P and the progressive rise in the concentrations of estrogen in the peripheral circulation during mid to late gestation of the baboon are dependent upon the presence of the fetus.