Recovery of rat prolactin cells following cessation of estrogen treatment

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Abstract
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. At five and ten days after the suspension of estrogen treatment, many prolactin cells contained numerous secretory granules of various sizes ranging from 150–500 nm. Only occasional granules in these cells were as large as 750 nm, and only the largest of the granules exhibited the irregular shape which is characteristic of mature granules in normal prolactin cells. Fifteen days after the cessation of estrogen injection most prolactin cells exhibited numerous secondary lysosomes. At this time the mature secretory granules were similar in morphology to those of normal prolactin cells. From the fact that the somatotrophs appeared not to be stimulated by the estrogen treatment we find it difficult to accept the concept that somatotrophs cna undergo transformation into prolactin cells.