The prolactin and growth-hormone producing cells of the guinea-pig pituitary. Electron microscopic study using immunocytochemical means.

Different immunohistochemical techniques were used to identify the prolactin and growth hormone producing cells (STH cells) in the pituitary of normal guinea pigs at the ultrastructural level. Prolactin cells revealed two main aspects: 1. Cells with granules from 2500 to 3500 A in diameter some of which are irregularly shaped. These granulations are scattered throughout the whole cytoplasm. The rough endoplasmic reticulum is well developed and organized in parallel lamellae. 2. In cells of the second type the granules are less numerous and smaller in diameter (1800 to 2500 A) and the rough endoplasmic reticulum is less well developed. The cytoplasm of the STH cells contains many more round granules (generally grouped) which also range from 2500 to 3500 A in diameter. The prolactin molecules and the STH molecules are essentially confined to the granules but with the immunocytochemical technique before embedding a slightly diffuse reaction appeared in the entire cytoplasm. These results are discussed.