Testicular hormonal regulation of the renin-angiotensin system in the rat epididymis

Evidence for the existence of an intrinsic angiotensin system based on loca lly formed angiotensinogen as a precursor for angiotensin production has be en demonstrated in the rat epididymis. The data strongly support the presen ce of an epididymal renin-angiotensin system (RAS) which may be important f or epididymal and sperm functions. In the present study, the effects of cas tration and testicular hormonal replacement on the expression of RAS compon ents from the rat epididymis are investigated at the gene and protein level s. Results from northern blot and western blot analyses consistently showed that the expression of angiotensinogen mRNA and protein was apparently abo lished by castration whereas their expression was completely restored to co ntrol levels when the castrated rats were hormonally replaced with either t estosterone alone or with combined testosterone and estradiol. Northern blo t did not detect any signal for angiotensinogen mRNA while western blot cou ld detect a weak signal for angiotensinogen protein when the castrated rats were replaced with estradiol alone. Renin could be detected neither in con trol, castrated nor hormonally replaced rats. Moreover, the expression of a ngiotensin II receptor, type I (AT(1)) was almost abolished by castration a s demonstrated by northern blot and reverse transcription-polymerase chain reaction. These data indicate that the expression of RAS by the rat epididy mis at the levels of its precursor angiotensinogen and its receptor AT(1), is subject to the regulation of testicular hormones and its expression appe ars to be predominantly testosterone-dependent.