Sponsored by an educational grant from Ipsen
Testosterone is important for libido, energy, sense of well being, as well as for integrity of muscle and bone. The Adam questionnaire, however, recognizes erectile dysfunction as a major symptom of hypogonadsim. Testosterone is indeed important in erectile physiology itself. This basic model has been shown by Traish and others. It is comprised of stimulating the pelvic nerve of an animal and monitoring the erection produced. A castrated animal will not respond, but replacing the testosterone will restore the function. This group further showed that giving a PDE-5 inhibitor to a castrated animal will not achieve a significant erection. It is known in humans that these drugs lose their potency in the presence of hypogonadism.
Rajfer reported that testosterone affects the endothelial cell by showing that nitric oxide activity decreases in castrated animals, only to be restored with testosterone replacement. This group also showed that dihydrotestosterone is the active hormone in penile physiology. Lewis reported that by blocking endothelial function biochemically, erections are inhibited after pelvic stimulation in castrated animals. Under these conditions, testosterone administration produces a moderate erectile response, indicating an endothelial independent pathway. There is also evidence by Wingard and others that testosterone may affect adrenergic penile tone.
Clinically, we have shown that men with erectile dysfunction and low testosterone levels have a decreased responsiveness to sildenafil. Aversa reported that men who had hypogonadsim, and who failed sildenafil, responded again when testosterone was replaced, a study that was confirmed by Shabsigh. Jain, in a meta-analysis, found five crossover studies that studied the effect of testosterone therapy on erectile dysfunction. The response rate for erectile improvement was 65.4%, over 16.7% for placebo. We found a 75% improvement in erectile function when testosterone levels were raised in men with secondary hypogonadsim.
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