THE ROLE OF PROLACTIN IN THE REGULATION OF TESTIS FUNCTION: THE EFFECTS OF PROLACTIN AND LUTEINIZING HORMONE ON THE PLASMA LEVELS OF TESTOSTERONE AND ANDROSTENEDIONE IN HYPOPHYSECTOMIZED RATS

SUMMARY Testosterone and androstenedione levels in the plasma of hypophysectomized rats were measured by a protein-binding method (sensitivity 150 pg testosterone; precision, 10%). Testosterone levels in the plasma of saline-treated hypophysectomized rats were undetectable (<0·3 ng/ml). Administration of 200 μg prolactin twice daily s.c. for a period of 3½ days caused a slight rise in testosterone in four rats (0·61 ± 0·35 ng/ml) while 5 μg luteinizing hormone (LH) administered in the same regimen increased testosterone levels to 1·42 ± 0·35 ng/ml (P < 0·05). Administration of prolactin ± LH (same doses) increased testosterone levels to 5·07 ± 0·51 ng/ml which is significantly higher than when LH was given alone and exceeds testosterone levels in intact adult males (4·12 ± 0·60 ng/ml). Androstenedione levels in the plasma of saline-treated hypophysectomized rats were, in contrast to testosterone levels, very high and averaged 3·37 ± 0·60 ng/ml. This level is higher than that in saline-treated intact controls (1·89 ± 0·36 ng/ml). Treatment with prolactin, LH or prolactin + LH induced insignificant changes in androstenedione levels which were 1·80 ± 0·33, 2·02 ± 0·28 and 4·22 ± 0·75 ng/ml, respectively. The ratio testosterone: androstenedione was calculated to be 0·37 ± 0·08 in the prolactin-treated group, 0·76 ± 0·20 in the LH-treated group and 1·47 ± 0·64 in the prolactin + LH-treated group compared with 2·36 ± 0·28 in intact control males.