The secretion of growth hormone from anterior pituitary transplants under the kidney capsule of gonadectomized and hypophysectomized male rats was investigated with special regard to the importance of the mass of functioning pituitary tissue. Body growth and mammary gland development after testosterone stimulation were studied.
In rats with the pituitary gland autotransplanted to the kidney capsule body growth was markedly reduced. After administration of testosterone a few groups of alveoli only were seen in the mammary glands.
Hypophysectomized rats with four pituitary transplants (an autotransplant and three homotransplants) under the kidney capsule showed slightly better body growth than rats with an autotransplanted hypophysis. When compared with rats with intact pituitary glands body growth was markedly reduced. Mammary gland development after testosterone stimulation was as poor in rats with four pituitary transplants as in rats with an autotransplanted hypophysis.
These results suggest strongly that the normal secretion of growth hormone is regulated by the hypothalamus and that the deficiency of growth hormone in rats with the pituitary gland transplanted remote from the brain is due mainly to a loss of 'specific' stimuli from the hypothalamus and not to a 'non-specific' reduction in the amount of functioning pituitary tissue.