Effects of hormones, pregnancy and pseudopregnancy on the mast cell count in the rat uterus

Abstract

Quantitative statistical examination was made of regional distributions of mast cells in the uteri of normally cycling rats, hormone-treated animals, pregnant, pseudopregnant and pseudopregnant animals bearing a deciduoma. In normally cycling animals largest numbers of uterine mast cells were observed during metestrus and significantly decreased toward estrus. Subcutaneous administration of estradiol suppressed myometrial mast cells but did not change the endometrial mast cell counts. Progesterone alone had no significant effect, but when injected concurrently with estrogen, a significant increase of myometrial and endometrial mast cells was observed. Uterine mast cells counts in pregnant rats remained fairly constant during the first half of gestation, and irregularly increased during the later stages of pregnancy. The increase of uterine mast cells became statistically significant three days prior to parturition and was followed by another highly significant increase between days 1 and 5 after parturition. During pseudopregnancy, relatively constant numbers of mast cells persisted throughout the experimental period. Decidualization during pseudopregnancy resulted in a greater number of mast cells in the injured than in the intact horns.