[Estrogen-induced pituitary tumors--in relation to the changes in the pituitary gland after estrogen withdrawal]

Pituitary tumors were induced in female rats of Wistar strain by administration of estradiol valerate (E2) and the effect of estrogen withdrawal on E2-induced tumors were studied to elucidate the nature of the induced tumors. Ten mg of E2 was administered to 100 rats intraperitoneally once every 2 weeks, totally four times. Experimental animals were sacrificed at 1 week before, 2, 6, 10, and 14 weeks after stopping injection of E2. The incidence of pituitary tumor and hyperplasia (Table 1). Pituitary glands in each animals were examined and were classified into three groups, namely pituitary tumor, hyperplasia, and normal gland according to histological findings. The incidence of pituitary tumors was highest in rats sacrificed 6 weeks after E2 withdrawal. Pituitary tumors became less frequent and hyperplasias and normal glands became more frequent in rats sacrificed thereafter. Pituitary weight (Table 2, Fig. 1) Irrespective of timing of sacrifice, the weight of pituitary gland (mean +/- SE) was 134 +/- 70 mg in the group which were judged as having a pituitary tumor, 38 +/- 17 mg in the hyperplasia group, and 17 +/- 5 mg in the normal group, respectively. Pituitary weight of control rats were 12 +/- 3 mg. The tumor group had a significantly heavier pituitary weight than hyperplasia and normal groups (p less than 0.01). In each group, there was no significant difference of pituitary weights between animals sacrificed at different intervals after E2 withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)