Four cows were treated on day 260 of pregnancy with 300 mg prednisolone succinate i.m., and four other cows with saline solution. Blood samples were taken 4 times daily during a period of 5 days. The concentrations of cortisol progesterone and estrone sulphate in plasma were determined using radioimmunoassay. After V administration of prednisolone the level of Cortisol was depressed for 3 days and returned to initial values afterwards. The level of progesterone was lowered during this time, but the decrease was not statistically siginificant. The estrone sulphate level was not significantly altered by prednisolone administration. In the control cows receiving saline, the concentration of hormones remained nearly constant. There was no statistical difference in gestation length compared to the control group. The results obtained indicate that the suppression of adrenal cortex function in cows on day 260 of pregnancy had little or no effects on progesterone and estrone sulphate. Thus, it appeared that the adrenal contribution to the peripheral blood plasma level of progesterone is small and the synthesis of estrone sulphate by bovine placenta is probably independent of maternal adrenal precursors.
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