RESTORATION OF NORMAL ADULT PENILE ERECTILE RESPONSE IN AGED RATS BY LONG-TERM TREATMENT WITH ANDROGENS

In order to determine whether the aging-related impairment of penile e rection can be corrected by exogenous androgens, 20-mo-old (''old'') r ats received implants of Silastic tubing containing either testosteron e (T) or dihydrotestosterone (DHT). Untreated aged-matched rats were u sed as reference controls, and values were compared with those obtaine d previously for 5-mo old (''adult'') rats. After 45 days, groups of s ix rats were submitted to electrical field stimulation of the cavernos al nerve (EFS), and the intracavernosal pressure and mean arterial pre ssure (MAP) were recorded. Compared to the untreated old rats, the old animals receiving either T or DHT showed a similar and significant (p < 0.01) increase (56%) in the maximal intracavernosal pressure (MIP) to a level slightly above that of the untreated adult rats, The respon se was sensitive to the nitric oxide synthase (NOS) inhibitor Nw-nitro -L-arginine methyl ester (L-NAME), The MIP:MAP ratio in the treated an imals was nearly double that found in the old untreated controls. Peni le NOS activity was measured by the [H-3]L-arginine-citrulline convers ion, and neuronal NOS (nNOS) levels were estimated by a semiquantitati ve Western blot assay with antibodies against human nNOS, No significa nt variations were observed in either NOS levels or NOS activity betwe en the treated and untreated old rats. These results suggest that agin g-related erectile dysfunction in the intact rat may be responsive to androgen therapy and that this correction is not associated with an in crease in the basal levels of penile NOS, in contrast to what occurs i n castrated rats.