Androgens in Physiology and Pathophysiology of Erectile Dysfunction
Trabecular Smooth Muscle
Androgens regulate growth and differentiation of vascular smooth muscle cells. Several researchers have hypothesized that androgens promote the commitment of pluripotent stem cells into a muscle lineage and inhibit their differentiation into an adipocyte lineage. The total number of circulating vascular progenitor cells may also be dependent on testosterone levels. Viagra Australia shop
Androgen deprivation by surgical castration results in a significant decrease in trabecular smooth muscle content which appear disorganized, with large number of cytoplasmic vacuoles, and decreased amounts of cytoplasmic myofilaments. It is thought that androgen deprivation might initiate tissue degeneration and trabecular smooth muscle apoptosis, thus causing an imbalance in the ratio of smooth muscle to extracellular matrix, leading to venoocclusive dysfunction. Studies suggest that venoocclusion is modulated by the balance between the smooth muscle and connective tissue content of the corpus cavernosum.
The smooth muscle content of the corpora cavernosa relative to the connective tissue.
Connective Tissue
Several studies suggested that androgens modulate the extracellular matrix through expression of growth factors. In animal models, androgen deprivation produced significant reduction in trabecular smooth muscle content and increased deposition of extracellular connective tissue matrix. This change in tissue architecture is associated with reduction in intracavernosal pressure in response to pelvic nerve stimulation. Androgen treatment of castrated animals results in a reversible increase in smooth muscle, concomitant decrease in connective tissue, and restoration of erectile function.
Cavernosal tissues from men with erectile dysfunction have been demonstrated to exhibit reduced lacunar spaces, reduced smooth muscle content, and a concomitant increase in connective tissue deposition. Discount viagra online
Tunica Albuginea
The venoocclusive mechanism depends on the integrity and function of the cavernosal smooth
muscle and on the elastic properties and function of the tunica albuginea. In an aging rat model with reduced plasma testosterone levels, Davila et al. used dynamic infusion caverno-sometry and cavernosography to demonstrate the presence of venoocclusive dysfunction (venous leakage) in aged male rats with low plasma testosterone levels compared to young adult rats. In a rat model, Shen et al. found that 4 weeks after castration the elastic fibers in the tunica albuginea were replaced by collagen fibers resulting in a loss of its elasticity. The authors concluded that androgens are essential for maintaining the normal structure of the tunica albuginea and corpus cavernosum.
These studies provide ample evidence of a direct effect of androgens on penile structures involved in erectile function.
