CONCENTRATION OF PROGESTIN IN THE SERUM OF THE NON-PREGNANT, PREGNANT AND POST-PARTUM EWE

Abstract

SUMMARY The Hooker-Forbes assay was employed to determine the concentration of free progestin in the serum of ewes during various stages of the reproductive cycle. During the oestrous cycle, the concentration varied from 0\m=.\3 to 2μg/ml. at oestrus to 6μg in the luteal phase. During pregnancy, the level of progestin rose from 1 to 2 μg/ml. at mating to a peak of 8–12 μg/ml. at parturition. The concentration of progestin showed a plateau at a level of 6–8 μg from the 40th to the 100th day of pregnancy. A second rise occurred at about the 120th day of pregnancy. In all sheep parturition took place prior to the drop in serum progestin. By the 10th day post-partum, however, the concentration of the hormone declined to 1 or 2 μg/ml. and remained at this level throughout lactation. Removal of the ovaries between the 66th and 114th day of gestation had no effect on the level of progestin in the blood of five ewes. The pregnancies remained unaffected, and the concentration of progestin increased in a manner comparable to that seen in pregnant sheep with intact ovaries. It is suggested that the placenta is the major source of progestin during the last two trimesters of pregnancy in the sheep.