Intact and castrated 25- and 60-day-old male rats were given 200 μg of testosterone propionate (TP) daily for 15 consecutive days. The morphology of the prolactin (PRL) cells was examined by electron microscopy and analyzed by the point counting method of Weibel and Bolender (23). The PRL cells in the controls had long cytoplasmic processes that coursed between adjacent parenchymal cells. The Golgi complex was relatively small in these cells and the area occupied by the secretory granules was, in general, less than in the TP-treated animals. After TP administration, the cells became more ovoid and the Golgi complex enlarged, displaying dilated cisternae and many immature secretory granules. In addition, the diameter of the secretory granules was greater in the animals given the steroid. When the morphology of the PRLcells in the sexually immature control rats was compared to that observed in the older, sexually mature rats, relatively few differences were observed indicating that the response to TP was essentially the same in animals of both age groups. The concentration of PRL was measured in the serum and pituitary gland by radioimmunoassay. There was a significant elevation in PRL in both the serum and pituitary glands of all animals given TP. In contrast, castration led to a fall in PRL levels. From these observations and from the morphological data it can be concluded that TP is capable of stimulating the rate of PRL synthesis and release, and that testosterone may have a regulatoryrole i n PRL biosynthesis and turnover in the male rat.
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