Studies on hypophyseal isografts in mice. I. Biologic aspects.

Experiments are reported on the induction of mammary carcinoma in intact, mammary tumor agent (MTA)-free female ( 9 020 x a" DBAf)Fi mice by single and multiple (4) prolactinproducing hypophyseal isografts in the kidney. Tumor incidences varying between 67 and 88 % were recorded in the treated groups as against 2% in virgin controls. Identical treatment of intact and castrated males proved totally ineffective. In the female hosts all grafts became extremely enlarged—some weighing up to 2000 mg or even more—whereas in the male animals they seldom exceeded 10 mg. Evidence is put forward which suggests a differ ence in hypothalamic control over the ectopie hypophyses be tween female and male animals due to a basic difference in hypo thalamic prolactin-inhibiting factor (PIF) potency, which is enhanced by the suppression of PIF by estrogens. The neoplastic transformation of the enlarged grafts is questioned.