Pheochromocytomas of Adrenals in Male Rats Chronically Injected with Pituitary Growth Hormone.

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Abstract
Increased numbers of tumors were observed during the course of chronic injection of normal female rats with pituitary growth hormone. Pulmonary and lymphatic tissues, reproductive organs, pituitary and adrenal glands were involved. Outstanding was the occurrence of adrenal medullary pheochromocytomas. Since none of this work had hitherto been done in male rats, the question arose as to whether males would be equally susceptible to tumor formation, especially as regards reproductive organs and adrenal glands. The long term administration of pituitary growth hormone to adult male rats of the Long-Evans strain resulted in progressive growth in body weight and length. Many neoplasms developed in the rats during this prolonged period, but the incidence in treated rats was not significantly different from that in controls, with the exception of tumors of the adrenal medulla. Pheochromocytomas occurred in 9 of 16 growth hormone injected rats and in none of the controls.