Evidence that Thyrotropin and Prolactin Are Not Secreted by the Posterior Pituitary of the Rat*

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Abstract
After eutopic hypophysectomy of the host, transplants under the renal capsule of three whole pituitaries or of the adenohypophysis alone were capable of maintaining plasma PRL concentration equal to or greater than that of intact controls. The basal plasma TSH levels in rats with these types of heterotopic pituitaries was below that of intact controls but was significantly increased by TRH or chronic antithyroid treatment. Rats with posterior pituitary (intermediate and neural lobe) heterotopic transplants were incapable, under any conditions tested, of raising the plasma PRL or TSH concentration above that seen in hypophysectomized controls without pituitary transplants. In a further experiment, selective extirpation of the anterior or posterior lobe of the eutopic pituitary was performed. Plasma concentrations of TSH and PRL in rats with anterior lobectomy were not significantly different from those of hypophysectomized controls but were significantly higher than those of hypophysectomized controls in rats with posterior lobectomy. These data indicate that only the adenohypophysis secretes physiologically significant quantities of these two hormones.