Ultrastructural changes of pituitary gonadotropic cells in estrogen-treated pregnant rats

An ultrastructural study of gonadotropic pituitary cells was performed in estrogen-treated pregnant rats. Estradiol-treatment on Day 10 of pregnancy led to signs of ovulation or luteinization on Day 12 in 50% of the animals. Degranulation was observed in the FSH and LH cells of estrogen-responsive rats, whereas in the unresponsive group, the same cells were intensely granulated. The FSH cells of the control group showed signs of degranulation which could be correlated with follicular development. LH cells were sometimes degranulated. The role played by FSH and LH cells in the triggering of ovulation and luteinization by estrogen in the pregnant rat is discussed in the light of the ultrastructural observations.