Somatic growth in hypophysectomized pituitary-homografted rats is promoted by prolactin.

Hypophysectomized male rats bearing a homograft of two adenopituitaries under the kidney capsule showed a significant increase in b.wt as compared to hypophysectomized non-homografted animals. Radioimmunoassay of growth hormone (GH), ACTH, alpha-MSH, beta-endorphin and prolactin (PRL) revealed that only the latter was highly increased in the plasma of hypophysectomized homografted rats. These animals showed also increased levels of plasma corticosterone. However, daily injection of corticosterone failed to promote somatic growth in hypophysectomized non-homografted rats. These results suggest that PRL, and not other hormonal factors, promotes somatic growth in hypophysectomized homografted rats, and stress the concept that only PRL is secreted in significant amounts by pituitary homografts.