ULTRASTRUCTURAL CHANGES IN THE ADENOHYPOPHYSIS OF PREGNANT AND LACTATING RABBITS

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Abstract
SUMMARY: Greatly enhanced secretory activity was observed during pregnancy and during lactation in the adenohypophysis of the rabbit, in cells similar to those designated type 1 in normal animals. These cells, whose granules were up to 550 mμ in diameter, showed, under the electron microscope, a very well developed ergastoplasm, an enlarged Golgi region, frequent nuclear inclusions and, during lactation, extensive degranulation. These observations, taken together with the evidence provided by light microscopy (Allanson, Cameron & Foster, 1966), suggest that the type-1 cells are the producers of prolactin.