Pathophysiology of Erectile Dysfunction - an Organisation/Activation Concept

Erection supposes a process regulated by hormonal and neuro-vascular mechanisms on both cerebral and peripheral levels. The current understanding of erectile function and dysfunction (ED) does not provide, however, a coherent model that accounts for the integration of sex hormones action and neuro-vascular mechanisms. Herein we suggest a model that involves organising and activating roles of sex steroids and neurovascular mechanisms in the regulation of erectile response. The organising role of hormones initiates during fetal life when androgens evoke both organogenesis of a penis and morphogenesis of a male type structure of sexually dimorphic brain regions (SDBR) responsible for male sexual behavior. Due to androgen-stimulation, penile growth proceeds in early childhood, is accelerated at puberty and ceases thereafter despite high androgen levels. Similarly, masculinisation of SDBR may extend to the adulthood but these structures may not be susceptible to hormonal manipulations thereafter. The activating component of erection appears also on both cerebral and peripheral levels. Since puberty male type of androgen/estrogen balance may simultaneously activate cerebral sympathetic tone responsible for sexual drive (libido) and parasympathetic tone responsible for erectile response on spinal cord level. On periphery the neuro-vascular activation of erection is present since fetal life and not dependent on libido. ED, the inability to achieve and maintain the erection to penetrate the vagina, may be of developmental origin as a primary failure or may derivate from organic or psychogenic diseases as secondary failure. As primary, ED may result from the lack or insufficient organising role of sex hormones on penile and behavioral levels, androgen-treatment will be necessary. In turn, secondary ED is more frequent, may result predominantly from the disturbances in the neuro-vascular erection activating mechanisms, and is less responsive to androgen-treatment.