SEXUALIDAD EN LA VEJEZ: ¿MITO O REALIDAD?

Nitric oxide has been identified as an endothelium-derived relaxing factor in blood vessels. We tried to determine whether it is involved in the relaxation of the corpus cavernosum that allows penile erection. The relaxation of this smooth muscle is known to occur in response to stimulation by nonadrenergic, noncholinergic neurons. We studied strips of corpus cavernosum tissue obtained from 21 men in whom penile prostheses were inserted because of impotence. The mounted smooth-muscle specimens were pretreated with guanethidine and atropine and submaximally contracted with phenylephrine. We then studied the smooth-muscle relaxant responses to stimulation by an electrical field and to nitric oxide. Electrical-field stimulation caused a marked, transient, frequency-dependent relaxation of the corpus cavernosum that was inhibited in the presence of N-nitro-L-arginine and N-amino-L-arginine, which selectively inhibit the biosynthesis of nitric oxide from L-arginine. The addition of excess L-arginine, but not D-arginine, largely reversed these inhibitory effects. The specific liberation of nitric oxide (by S-nitroso-N-acetylpenicillamine) caused rapid, complete, and concentration-dependent relaxation of the corpus cavernosum. The relaxation caused by either electrical stimulation or nitric oxide was enhanced by a selective inhibitor of cyclic guanosine monophosphate (GMP) phosphodiesterase (M&B 22,948). Relaxation was inhibited by methylene blue, which inhibits cyclic GMP synthesis. Our findings support the hypothesis that nitric oxide is involved in the nonadrenergic, noncholinergic neurotransmission that leads to the smooth-muscle relaxation in the corpus cavernosum that permits penile erection. Defects in this pathway may cause some forms of impotence.

Serum androgen levels decline with aging in normal males, such that a significant number of men over 60 yr of age will have a mean serum total testosterone (T) level near the low end of the normal adult range. It is not known whether lower T levels in older men have an effect on androgen-responsive organ systems, such as muscle, bone, bone marrow, and prostate, nor are there data to evaluate the relative benefits and risks of T supplementation in older men. We assessed the physiological and biochemical effects of T therapy in 13 healthy men, 57-76 yr old, who had low or borderline low serum T levels (< or = 13.9 nmol/L). Intramuscular testosterone enanthate (TE; 100 mg weekly) and placebo injections were given for 3 months each. Before treatment and at the end of both 3-month treatment regimens, lean body mass, body fat, biochemical parameters of bone turnover, hematological parameters, lipoprotein profiles, and prostate parameters [such as prostate-specific antigen (PSA)] were evaluated. Serum T levels rose in all subjects with TE treatment, such that the lowest level of T during a week's period was 19.7 +/- 0.7 nmol/L (mean +/- SE). After 3 months of TE treatment, lean body mass was significantly increased, and urinary hydroxyproline excretion was significantly depressed. With TE treatment, there was a significant increase in hematocrit, a decline in total cholesterol and low density lipoprotein cholesterol, and a sustained increase in serum PSA levels. Placebo treatment led to no significant changes in any of these parameters. We conclude that short term (3 months) TE supplementation to healthy older men who have serum T levels near or below the lower limit of normal for young adult men results in an increase in lean body mass and possibly a decline in bone resorption, as assessed by urinary hydroxyproline excretion, with some effect on serum lipoproteins, hematological parameters, and PSA. The sustained stimulation of PSA and the increase in hematocrit that occur with physiological TE supplementation suggest that older men should be screened carefully and followed periodically throughout T therapy.