Amount of Luteal Tissue Required for the Maintenance of Pregnancy in the Rat. ∗

Abstract

Conclusions

The albino rat of the Holtz-man strain was used to determine the minimum number of corpora lutea required to maintain pregnancy. It was found 2 corpora will maintain pregnancy from the eighth day of gestation, but one corpus will not, nor will one corpus and part of another. In animals where all corpora but one were removed on the 15th day of pregnancy, two-thirds either had litters of normal fetuses or some of the fetuses were normal while others were being resorbed. All of the fetuses of the other one-third of the animals were being resorbed at the time of autopsy. Pregnancy was maintained in a group of animals in which all but 2 corpora were removed on the eighth day and hypophysectomized on the 12th day of pregnancy.

There is no evidence that the placentae are adequate supplementary sources of progesterone in those groups where the corpora were reduced below two at the eighth day, since pregnancy was terminated in all cases. However, when the corpora were reduced to one on the 15th day of pregnancy, pregnancy was terminated in only one-third of the group which may indicate that the placenta is a more effective supplementary source of progesterone in the latter third of pregnancy. Reduction in the number of corpora to two per rat does not cause a hypertrophy of the adrenal glands.