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MITOTIC ACTIVITY IN THE ADENOHYPOPHYSIS OF PREGNANT AND LACTATING RABBITS

Summary.: The rate of mitosis in the adenohypophysis of colchicinetreated female rabbits has been studied in five unmated, non-parous does (controls), nineteen pregnant primiparae, seventeen suckling and five non-suckling post partum primiparae. Data are presented showing that, although the average mitotic rate was higher in Week 4 of pregnancy (4·1 mitoses/mm²) than in the unmated animals ( 1 ·7 mitoses/mm²), only in Weeks 1 and 2 of lactation (8·5 mitoses/mm² and 12·0 mitoses/ mm², respectively) was the increase in mitotic rate statistically significant.

Five per cent of all the mitotic figures examined occurred in mucoid cells, 23% in non-granular cells, and 72% in acidophil cells (prolactin cells and somatotrophs). The majority of mitoses was found in prolactin cells (74%) during pregnancy and in somatotrophs (64%) in late lactation; in Weeks 1 and 2 of lactation, when cell proliferation was most rapid, most of the dividing cells were unidentifiable owing to lack of granules, so that at this period the mitotic rate of these two acidophil cell types could not be determined.

Fluctuations in the mitotic rate in the epithelial cells of the duodenum of the animals did not appear to be correlated with the stages of pregnancy or of lactation.