Relationship between contraction and relaxation in human and rabbit corpus cavernosum.

Although alterations in corporeal smooth muscle tone undoubtedly play an important role in the etiology of erectile dysfunction, the relationship between the degree of corporeal smooth muscle contraction and the magnitude of the observed relaxation response has never been quantitated. Thus, in vitro studies were conducted to examine the relationship between alpha 1-adrenergic contractility, and relaxations elicited by the clinically and physiologically relevant vasorelaxants, nitroglycerin, nitroprusside, and prostaglandin E1. Corporeal tissues strips were isolated from impotent and potent men, as well as sexually mature rabbits, and precontracted over a wide range of phenylephrine doses, prior to exposure of each tissue to the same dose of vasorelaxant. Plots of percent contraction versus percent relaxation revealed that the relationship between contraction and relaxation was accurately described by a first order linear equation, and characterized by an inverse relationship in all tissues studied, for all vasorelaxants examined. Statistical analysis indicated that the slope of the regression line was significantly greater than unity in all corporeal tissues obtained from patients with organic impotence; however, corporeal tissues obtained from patients with documented erections and from sexually mature rabbits had significantly lower slopes that were indistinguishable from unity. The existence of an inverse relationship between contraction and relaxation, even in the absence of organic disease, emphasizes the importance of the level of basal corporeal smooth muscle tone per se. These studies provide further evidence implicating heightened adrenergic tone as a significant etiologic factor in erectile dysfunction.