Reduction in prostatic concentration of endogenous dihydrotestosterone in rats by hyperprolactinemia

Persistently high levels of circulating prolactin can be achieved in male rats when pituitaries from female donors are grafted under the renal capsule. Enhanced growth of the lateral prostate can be accomplished by an apparent synergistic effect of excess prolactin with subphysiologic doses of testosterone. To define this effect we measured the endogenous dihydrotestosterone (DHT) concentrations in rat prostate lobes. Twenty Sprague‐Dawley male rats (250 g) were castrated and given subcutaneous implants of silastic tubing filled with 1 cm of crystalline testosterone. Ten of these rats simultaneously received two pituitary grafts under the renal capsule. The remaining ten rats received intrarenal skeletal muscle grafts as controls. Four weeks later, the weight (mg ± SE) of the ventral and dorsal lobes were not significantly different between the two groups, while the lateral lobe was significantly (P < 0.01) heavier in rats with pituitary grafts (121.4 ± 7.5) than in controls (81.7 ± 10.4). Endogenous DHT in the tissue extracts was determined by radioimmunoassay following KMnO₄ treatment to eliminate testosterone. The concentration of DHT (ng/g tissue ± SE) was significantly (P < 0.01) lower in the lateral prostate of graft‐bearing animals (4.40 ± 0.29) than in the controls (5.98 ± 0.34). These results indicate that, in the rat, hyperprolactinemia induced by pituitary grafts is associated with a heavier lateral prostate and a lower concentration of endogenous DHT in that tissue. These results also suggest that the action of prolactin in the rat prostate is not mediated through the action of androgen.