Effect of ovariectomy followed by administration of ovarian steroid hormones on the pig pinealocyte ultrastructure.

The ultrastructure of female pig pinealocytes was studied after ovariectomy alone and ovariectomy followed by administration of estradiol, progesterone, or both. Administration of estradiol as well as a combination of estradiol and progesterone induced qualitative ultrastructural changes in pinealocytes relative to Golgi apparatus and cytoplasmic dense bodies as well as quantitative ones, such as a decrease in relative volume of cytoplasmic dense bodies and lysosomes. Administration of progesterone caused the formation of dense bodies and a decrease in the relative volume of lysosomes. The results point to a relationship between the pineal gland and gonads in the pig and suggest that gonadal steroids, particularly estradiol, could be involved in a feedback mechanism of the hypothalamic-hypophyseal-gonadal system to the pineal gland.