Immunocytochemical and ultrastructural identification of mitotic cells in the pituitary gland of ovariectomized rats.

Light microscopic immunocytochemistry was utilized on plastic-embedded, acrolein-fixed pituitary glands from intact rats and rats killed 14 days after ovariectomy to determine which cell types were undergoing cell division. A significant increase in the number of cell divisions in anterior pituitary cells was seen in ovariectomized rats compared to intact controls. Most of the dividing cells in ovariectomized rats were immunocytochemically identified as gonadotrophs, but dividing somatotrophs and non-immunoreactive cells were also found. All of the dividing gonadotrophs stained with both anti-FSH beta and anti-LH beta. These cells were large and ovoid with plentiful vesiculated rough endoplasmic reticulum and a single population of granules with a mean diameter of 200 nm. Many of the dividing cells which were not immunoreactive with any of the antisera employed contained small granules, 100 nm in diameter, but the content of these granules was not determined.