DEMONSTRATION OF STORAGE AND RELEASE OF GONADOTROPIN BY THE ANTERIOR PITUITARY OF THE MOUSE DURING GESTATION1,2

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Abstract
Pituitary glands obtained from pregnant mice during 5 stages of gestation were assayed for gonadotropic potency by inducing ovulation in recipient pregnant mice. By this procedure gonadotropic potency was found to be max. at 12.5 and 15.5 days of pregnancy, intermediate at 6.5 days, and min. at 9.5 and 18.5 days, suggesting a cycle fluctuation in gonadotropic content of the pituitary during pregnancy. Analysis of responsiveness of assay animals during 4 stages of pregnancy indicates that an increased rate of release of gonadotropic hormone occurs as pregnancy progresses. The gonadotropin which appears to be released from the pituitary at an augmented rate during the last half of pregnancy is considered to be LH. Statistical analysis of the gonadotropic potency of the donor pituitaries as related to the responsiveness of recipient animals to gonadotropin demonstrates that a fluctuation of 10% in gonadotropic content can effect a variation of 82% in responsiveness of assay animals. The wt. of the pituitary gland increases significantly during pregnancy. Histologic observations of the cell types of the anterior pituitaries of pregnant mice were made after staining with a modified trichrome technique. With this method, the variations in the percentages of cell frequencies at different stages of pregnancy were shown not be be statistically significant. It seems possible however, that the transformation of acidophiles from a fully-granulated to a sparsely-granulated condition may be associated with the postulated release of LH from the pituitary during the last half of pregnancy.