Effects of prolactin on LH release in male rats

Normal and castrated male rats were injected subcutaneously (s.c.) with a homologous preparation of prolactin (Prl) for 4 1/2 days, and serum levels of LH and FSH were measured at the end of the treatment. LH was undetectable in normal animals, injected either with Prl or with the vehicle. The treatment produced a significant reduction of the levels of LH in the castrated animals. No effect on FSH levels could be observed in either the normal or the castrated animals. The only relevant autopsy finding was a reduction of pituitary weight in normal animals treated with Prl. No effect on the weight of the testes or of the sex accessories was observed. It is suggested that Prl may directly interfere with the central mechanisms which control LH secretion.