Fetectomy alters maternal endocrine and uterine activity rhythms in rhesus macaques during late gestation.

Objective: The current study was designed to test the hypothesis that fetectomy will eliminate or substantially alter rhythms in maternal estradiol concentrations and subsequently reduce or eliminate uterine activity rhythms.

Study Design: Six rhesus macaques underwent surgery for catheter implantation between days 117 and 122 of gestation (term = 167 days). At surgery the fetuses were removed and the membranes and placenta remained intact. Thirteen additional catheterized pregnant animals served as controls. Maternal arterial blood samples were collected for hormone analysis at 3-hour intervals for 24 hours, starting at 9 AM. This sampling protocol was performed four times at weekly intervals until 151 to 157 days' gestation.

Results: A significant rhythm (p < 0.01) in estradiol was determined in the control animals with peak concentrations observed in the morning hours whereas the progesterone peak was observed at night. In the fetectomy group mean plasma estradiol concentrations decreased significantly from 312 +/- 34 to 110 +/- 8 pg/ml throughout the study (p < 0.01). Despite a trend toward elevated morning levels, the estradiol rhythm was ablated. The uterine contractile rhythm observed in the control animals with peak activity between 10 PM and midnight (p < 0.01) was also ablated after fetectomy. Basal concentrations of progesterone were significantly lower than control values.

Conclusions: (1) Fetectomy resulted in the elimination of the maternal estradiol rhythm. (2) The uterine activity rhythm was lost after fetectomy. These data suggest that the fetus, by supplying precursors of estrogen, may play an indirect role in the regulation of maternal estradiol rhythms, which in turn appear to play a key role in regulating uterine activity rhythms.