Functional characteristics of two spontaneous, one radiation-induced, and two estrogen-induced mammo-somatotropic pituitary tumors (MtT) were compared with special reference to their content of adrenotropic hormone (AtH) and adrenotropic action in the host. AtH activity was evidenced by biological assay of the tumor homogenates, the increase in size of the adrenals, and the presence of hypercorticoidism in the host animal. The steroidogenic capacity in vitro of the adrenals of the spontaneous and radiation-induced MtT-bearing rats was as good or better than that of the normal glands, whereas, on the contrary, that of the adrenals of the estrogen-induced MtT hosts was much diminished.

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This investigation was supported by Grants C-3974, C-6215, and contract ph-43-62-106 from the National Cancer Institute, National Institutes of Health, Bethesda, Maryland.

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