Abstract
Pituitary weight, pituitary mitotic index and pituitary and serum concentrations of growth hormone and prolactin were measured at 14โday intervals in male rats given 10 mg diethylstilboestrol dipropionate SC every 14 days for a total period of 70 days. Mean pituitary weight reached a maximum of 21 mg on day 42 and no pituitary gland became a tumour according to a criterion of weight greater than 30 mg. Mitotic index was greatly increased until day 70 when it diminished significantly. Pituitary concentration of growth hormone decreased to maintain a low constant level from day 28 onwards while pituitary prolactin concentration rose to a maximum on day 42. Serum growth hormone was elevated on day 14 and then gradually diminished, while serum prolactin continued to increase until day 42. Pituitary weight and serum prolactin were significantly correlated and pituitary mitotic index was negatively correlated with pituitary growth hormone concentration. The state of apparent equilibrium in mass reached by the pituitary glands from day 42 until day 70, despite greatly increased secretory and mitotic activity, suggests that further disturbance of pituitary function is necessary to bring about net gain in cell numbers and lead to tumour formation.