The influence of fetal genome on cortisol biokinetics and gestational duration.

The biokinetics of cortisol metabolism were assessed simultaneously in chronically catheterized pregnant ewes and their fetuses in two breeds of sheep (Finnish Land-race, (Finn) and Rambouillet, (Ra)) with distinctly different gestational durations. The purpose of these studies was to examine the genetic differences in fetal development and its influence in regulating the duration of gestation. Catheterized fetuses were born at 147.5 +/- 0.7 (Ra) and 141.7 +/- 0.9 days (Finn), respectively. Uncatheterized purebred Ra and Finn ewes had gestational periods of 150.7 +/- 1.3 and 145.5 +/- 1.4 days, respectively. Cortisol blood production rates in Finn fetuses at approximately 141 days gestation were 5.71 +/- 1.08 mg/day (mean +/- SD) and comparable to those in Ra fetuses (6.16 +/- 1.32 mg/day) at 146 days gestation. These differences could not be attributed to corresponding changes in maternal cortisol production rates which varied from 11.66 mg/day to 17.91 mg/day in all ewes. This study provides additional data describing fetal cortisol metabolism in utero as well as further describing the role of fetal genome in initiating adrenal metabolic activity and regulating gestational length in sheep.