Incidence and Character of the Spontaneous Pituitary Tumors in Strain CR and W/Fu Male Rats2

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Abstract
Thirty-eight pituitary tumors and associated changes in 54 rats (50 males and 4 females), exsanguinated in extremis when older than 640 days, were studied. Sera of 25 of these were assayed for prolactin and 12 for growth hormone. Of the male CR and W/Fu rats, 20 had macroscopic tumors and 14 different rats had microscopic tumors. Hyperplasia of the mammary gland and radioimmunoassay indicated that most, if not all, of these tumors were mammotropic. All 4 female CS rats, similarly studied, had mammotropic tumors. The primary tumors were usually multifocal and most appeared to be "chromophobic" adenomas; a few had morphologically distinct carcinomatous foci. Immunohistochemical staining gave strong reaction for growth hormone in the tumor-free areas. The tumors themselves gave very weak or no reaction for prolactin. This is correlated with elevated hormonal levels in sera, suggesting rapid discharge of prolactin from the tumors. Transplantation of 3 pituitary tumors arising in male rats was successful in males of the strain of origin. One multifocal tumor grafted on normal rats gave rise to metastasizing carcinoma. The pathogenesis of mammotropic pituitary tumors in male rats remains to be elucidated. These 54 exsanguinated rats are a sample of 1,040 rats autopsied after natural death in lifespan nutritional studies of H. Kaunitz. His preliminary tabulation agrees with the above findings on the high incidence of pituitary tumors in old male rats.

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