Recovery of rat prolactin cells following cessation of estrogen treatment.

Estrogen treatment for one month in female rats caused some regression of somatotrophs, but induced an increase in the number of prolactin cells and caused these cells to hypertrophy. These stimulated prolactin cells showed extensive development of the granular endoplasmic reticulum which was often arranged in concentric whorls (Nebenkern). Most of the prolactin cells contained a small number of mature granules which were smaller in size than those of prolactin cells in control animals. These prolactin granules were round in sectioned profile and closely resembled the secretory granules of normal somatotrophs.