EFFECT OF OVARIECTOMY FOLLOWED BY ADMINISTRATION OF OVARIAN-STEROID HORMONES ON THE PIG PINEALOCYTE ULTRASTRUCTURE

The ultrastructure of female pig pinealocytes was studied after ovarie ctomy alone and ovariectomy followed by administration of estradiol, p rogesterone, or both. Administration of estradiol as well as a combina tion of estradiol and progesterone induced qualitative ultrastructural changes in pinealocytes relative to Golgi apparatus and cytoplasmic d ense bodies as well as quantitative ones, such as a decrease in relati ve volume of cytoplasmic dense bodies and lysosomes. Administration of progesterone caused the formation of dense bodies and a decrease in t he relative volume of lysosomes. The results point to a relationship b etween the pineal gland and gonads in the pig and suggest that gonadal steroids, particularly estradiol, could be involved in a feedback mec hanism of the hypothalamic-hypophyseal-gonadal system to the pineal gl and.