Dissociated estradiol (E 2) action on the pituitary-testicular axis in a genetically hypoprolactinemic rat (IPL nude rat)

Abstract

Prolactin (PRL) has been reported to be a possible mediator in the estradiol (E 2)-induced inhibition of the pituitary-testicular axis. In order to better characterize the role of PRL, we studied the action of chronic hypoprolactinemia on this E 2 inhibitory effect, using a genetically hypoprolactinemic rat (IPL nude). Normal and IPL nude adult male rats were injected either with vehicle or with E 2 valerianate (4 mg/rat) once a week for 2 weeks. Rats were decapitated 7 days after the last injection. Results showed that E 2 increased, similarly in both strains, pituitary weight and serum PRL levels. Serum testosterone values were reduced by 96% in both strains. However, testis weight was significantly reduced by 30% in normal rat, while in IPL nude rat, no significant decrease was observed. PRL binding sites, expressed as fmol/mg protein, were reduced in normal rat by 40%. No decrease was found in IPL nude rat. The dissociated E 2 action observed in IPL nude rat suggested that only testicular growth inhibition could be mediated by PRL and confirm that testosterone level decrease could be due to a direct action of E 2 on Leydig cells.