Pathophysiology of erectile dysfunction: the contributions of trabecular structure to function and the role of functional antagonism.

Erectile dysfunction (ED) is estimated to impact more than 150 million men this year worldwide. An understanding of the pathophysiology of ED both furthers the basic scientific knowledge of disease processes and provides a rational design of pharmacotherapy. At present, there are two major views regarding the pathophysiology of ED. In the first hypothesis, the oxygen tension-dependent changes in the penis during erection are proposed to impact corpus cavernosum structure by inducing various cytokines, vasoactive factors and growth factors at the two different oxygen tensions (flaccidity and erection) which, in turn, alter smooth muscle metabolism and connective tissue synthesis. Decreases in the corpus cavernosum smooth muscle/connective tissue ratio have been correlated with an increased likelihood of diffuse venous leak and a failure of the veno-occlusive mechanism in prospective patient studies. Evidence for such a hypothesis incorporates nocturnal penile tumescence and circadian changes in oxygenation as important in maintaining erectile health. The alternate hypothesis proposes that ED is the result of a metabolic imbalance between relaxatory and contractile processes within the trabecular smooth muscle such that contractile processes predominate. Based on this hypothesis, therapy can be accomplished via drugs which shift this balance towards vasodilatation, or by gene therapy approaches to supplement the deficient components favoring smooth muscle relaxation. Both of these hypotheses predict a management strategy for ED that impacts pharmacotherapeutics. In this review of the pathophysiology of ED, each hypothesis will be examined and a synthesis devised incorporating both views. The future of research in this area as well as pharmacotherapy in ED in terms of pathophysiology is discussed including the merits and drawbacks of prophylaxis and prevention of ED. International Journal of Impotence Research (2000) 12, Suppl 4, S39-S46.