Hyperprolactinemia Counteracts the Testosterone-Induced Inhibition of the Preoptic Area Dopamine Turnover

The present study was undertaken to determine the effects of hyperprolactinemia on dopamine (DA) concentrations and turnover rates in the medial basal hypothalamus (MBH) and the preoptic area-suprachiasmatic nucleus region (POA-SCN) in castrated and castrated, testosterone (T) implanted male rats. Subcutaneous implants, which raised serum T levels to those found in intact rats, decreased serum LH to basal levels but did not alter DA turnover in the MBH. Anterior pituitary (AP) transplants under the renal capsule increased serum prolactin to 60–110 ng/ml, and accelerated DA turnover by nearly 2-fold in the MBH of both castrated and castrated, T-implanted rats without influencing serum LH levels. While T implants caused a decrease in the POA-SCN DA turnover, high serum prolactin levels produced by AP implants in castrated rats were ineffective in altering POA-SCN DA turnover. However, in the presence of physiological levels of T, these elevated serum prolactin levels not only blocked the T-induced decrease in POA-SCN DA turnover, but further augmented DA turnover over that observed in the castrated or castrated, T-implanted rats. These results indicate that (i) for acceleration of the MBH DA turnover by prolactin T priming is not essential and it appears to occur at serum prolactin levels which do not depress serum LH levels, and (ii) the stimulatory effects of prolactin on the POA-SCN DA turnover are dependent upon the presence of circulating T. Since these synergistic effects of prolactin and T on the POA-SCN DA turnover are not involved in the regulation of gonadotropin secretion, their participation in attenuation of male sexual behavior associated with hyperprolactinemia is discussed.