Effects of Increasing Numbers of Pituitary Transplants in Hypophysectomized Rats1

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Abstract
Intrastrain in pituitary transplants in Sprague-Dawley rats were usually free of homograft reaction as observed in serial sections at 10 weeks after transplantation. Transplantation of 1, 3, 10 or 30 such pituitaries in hypophysectomized weanling females produced continuous growth proportional to the logarithm of the number of grafted glands. At 10 weeks hypophysectomized control rats weighed 96 [plus or minus] 5 g, hypophysectomized-grafted with 1 gland 129 [plus or minus] 3, with 3 glands 151 [plus or minus]3, with 10 glands 170 [plus or minus] 3, with 30 glands 189 [plus or minus] 2, and intact controls 239 [plus or minus]5. The morphology and weights of target organs also showed cumulative trophic effects with increasing numbers of grafts. Thus, in the hypophysectomized-grafted rats with 30 pituitaries the mean weights of the thyroid and adrenals were 2 times, the preputial glands 3 times, the uterus 4 times, and the ovaries 6 times greater than those of hypophysectomized controls. In the hypophysectomized rats grafted as weanlings with 30 glands the ovaries contained mature follicles and multiple corpora lutea. The dose-effect relation obtained suggests that each ectopic pituitary secreted a fixed quantity of trophic hormones. This quantity was so low that extrapolation of the data yielded an estimate that many hundreds of transplants would be required to support normal growth in such hypophysectomized rats. But the aggregate output of 10 or 30 such glands brought about somatotropic, gonadotropic and mammotropic changes not previously reported in hypophysectomized female rats bearing ectopic pituitary transplants.