Testosterone Is Necessary for Sexually Stimulated Luteinizing Hormone and Prolactin Release in the Male Rat*

Abstract

Sexually experienced male rats were castrated and simultaneously implanted sc with Silastic capsules filled with testosterone (T). Three weeks later, the rats were bled via indwelling jugular cannulae before and during exposure to receptive females. Silastic capsules (5–40 mm long) produced doserelated increments in plasma T levels. Basal plasma LH levels increased in untreated castrated rats, and T treatment reduced this increase. Basal plasma PRL levels were not affected by castration or T treatment. Sexual behavior was impaired in untreated castrated rats, but T-treated castrated rats displayed sexual behavior similar to that of intact males. During exposure to females, untreated castrated rats did not release LH or PRL, regardless of whether they mated. Both intact and T-treated castrated rats showed significant increases in plasma LH and PRL levels during mating. LH release was observed only in Ttreated castrated rats which had basal LH levels below the range exhibited by untreated castrated rats. PRL release was observed in all T-treated castrated rats and was related to the dose of T administered; rats treated with 5- to 10-mm capsules showed a 75% increase in PRL levels, while rats treated with 25- to 40-mm capsules showed a 200% increase in PRL levels, comparable to that shown by intact rats. These results suggest that sexually stimulated LH and PRL release depends on the presence of adequate plasma T levels.