A significant increase in the weights of testes and accessory reproductive glands was observed with the highest dose injected (500 µg per rat per day) as follows: testes, 583 ± 21 (SEM) versus 448 ± 38 mg (P < 0.05); prostate, 80.0 ± 4.0 versus 64.7 ± 3.1 mg (P < 0.05); epididymis, 72.1 ± 5.0 versus 58.2 ± 4.0 mg (P < 0.05).

Serum levels of LH were significantly higher in prolactin-treated animals. Maximal values of serum LH were attained with the dose of 50 µg (99.0 ± 11.2 versus 32.0 ± 4.6 ng/ml; P < 0.05).

Increasing doses of prolactin produced a concomitant rise in serum 3-androstanediol (2.21 ± 0.45 versus 6.63 ± 0.42 ng/ml in the group treated with 50 µg), whereas testosterone plus dihydrotestosterone levels remained unchanged.

A decrease in the concentration of exchangeable cytosolic androgen binding sites in the prostate (fmoles/mg protein) was observed in prolactin injected animals (88.2 ± 0.8 in the control group versus 80.6 ± 0.3 and 74.9 ± 0.3 for doses of 5 and 50 µg, respectively; P < 0.05). No changes in androgen binding sites were detected in the group treated with 500 µg per rat per day. On the other hand, prolactin treatment did not alter the number of available androgen binding sites in the prostate gland. Increasing doses of prolactin induced a dose-related increase in the total number of nuclear KCl-extractable receptors, expressed per mg DNA or per organ. In addition, the total content of androgen receptors (cytosolic plus nuclear binding sites) was significantly higher in animals treated with 500 µg of prolactin (385 ± 34 versus 228 ± 37 fmoles per organ; P < 0.05).

These results suggest that, in addition to the previously described effects of prolactin on Leydig cell responsiveness to LH and on androgen metabolism, this hormone could also modify peripheral LH and androgen levels as well as the androgen receptor content in the rat prostate gland.