Localization of prolactin binding in prostate and testis: The role of serum prolactin concentration on the testicular LH receptor.

Specific binding sites for prolactin (PRL) and gonadotrophins on ventral and dorsolateral prostate as well as on Leydig cells and tubules of testes of rats at different ages were examined. The binding sites for PRL were found in greatest number in ventral prostate and in Leydig cells. LH binding sites were also more numerous than FSH binding sites in the latter. FSH sites were greater than LH sites in tubular preparations obtained from the testis. Specific binding (SB) of PRL in the Leydig cells reached a maximum at 45 days (4%) and in the case of LH a maximum of 12% was obtained at 70 days. In both preparations SB of FSH exhibited a plateau between 20 and 40 days (11%) followed by a gradual decline to 6% at 100 days. Following 20 dyas of treatment with Bromocriptin beginning at 20 days serum PRL was suppressed and SB of LH to the Leydig cells was significantly decreased, whereas SB of PRL and FSH was unaffected. These studies suggest that despite decreases in serum PRL, the number of PRL and FSH receptors remain unaltered. On the contrary, LH receptors in the rat testis are modulated by changes in serum PRL.