Effect of perphenazine on growth and zinc‐65 uptake of the rat prostatic adenocarcinoma, R 3327

Prolactin affects the growth and function of both normal and carcinatomous prostate tissue. Therefore, the effect of modifying prolactin secretion on the growth of the adenocarcinoma of the rat prostate (R3327) was studied, utilizing chronic administration of the dopamine antagonist perphenazine. At 4 and 8 weeks after tumor inoculation, perphenazine (0.5 and 1.0 mg per dose) was injected for 12-16 weeks. Tumors weighed at autopsy showed that the 0.5 mg dose resulted in significantly smaller and the 1.0 mg dose, in significantly larger tumors than the controls. Perphenazine at both doses increased serum prolactin, but the increase was greater when 0.5 mg was administered. There was a higher uptake of 65Zn when the tumor growth was inhibited as in the animal receiving 0.5 mg of perphenazine. Several possible explanations are offered for the results, including the fact that prolactin might follow a bell-shaped curve in its effect on the tumor and that perphenazine might have other mechanisms of action besides dopamine antagonism.