Surface pits of typical gonadotrophs and castration cells of the rat anterior pituitary suggestive of exocytosis and micropinocytosis.

For a long time, the occurrence of exocytotic discharge of secretory granules from the typical gonadotrophs (Type 1 gonadotrophs) of the anterior pituitary has been doubted. A simple observation with immunocytochemistry and morphometric examination using transmission electron microscopes indicated an increase in number of surface pits and subsurface vesicles of the typical gonadotrophs after castration, which were confirmed by immunocytochemical reaction with anti-LH beta. Large pits and vesicles were also increased progressively as days after castration advanced. Some large pits contained dense granules or less dense flocculent substance. These findings suggest that the typical gonadotrophs also exert granule discharge by the mechanism of exocytosis and concomitant retrieval of surface plasma membrane by the micropinocytosis.