REDUCTION OF ENDOTHELIAL AND SMOOTH MUSCLE DENSITY IN THE CORPORA CAVERNOSA OF THE STREPTOZOTOCIN INDUCED DIABETIC RAT

Diabetes induced erectile dysfunction and apoptosis in penile crura are recovered by insulin treatment in rats

PURPOSE

We hypothesized that apoptosis is a downstream event in erectile dysfunction, and pro-apoptotic (Bak and Bax) and anti-apoptotic (Bcl-2 and Bcl-x) factors are involved in the etiology of diabetes induced erectile dysfunction. To test this hypothesis the intracavernous pressure of diabetic and insulin treated rats was measured to assess erectile function. Molecular and immunohistochemical analyses for apoptosis were then performed in rat crura to assess their role in diabetes induced erectile dysfunction and insulin treatment.

MATERIALS AND METHODS

A total of 70, 6-month-old male Sprague-Dawley rats were divided into 2 groups, including a diabetic (50) and a healthy control (20) group. The diabetic group received intraperitoneal injection of streptozotocin (STZ) (Sigma-Aldrich Co., St. Louis, Missouri) to induce diabetes. Subcutaneous injection of insulin was administered daily to 9 diabetic rats 4 and 8 weeks after STZ injections for 4 and 8 weeks, respectively. Functional studies were performed in 9 diabetic rats each 4, 8 and 12 weeks after STZ injections, in 6 age matched control rats and in insulin treated rats at the termination of therapy. After the completion of functional study the penile crura were collected from rats for molecular and immunohistochemical studies.

RESULTS

Mean intracavernous pressure of diabetic rats was significantly lower than in control rats and the decrease in intracavernous pressure was significantly recovered by insulin treatment. Gene expressions of pro-apoptotic and anti-apoptotic factors were present in control, diabetic and insulin treated rat crura. However, anti-apoptotic protein expression was lacking in diabetic rat crura and pro-apoptotic protein expression was lost in insulin treated rat crura. The apoptotic index of diabetic rat crura was significantly higher than that of control rat crura and this index was significantly decreased in insulin treated rat crura.

CONCLUSIONS

There was a significant correlation between the decrease and recovery in intracavernous pressure, and protein expression of apoptotic factors in diabetic and insulin treated rat crura. To our knowledge this is the first report demonstrating that the relief of diabetes associated erectile dysfunction by insulin treatment is due to alterations in the protein expression of apoptotic factors in rat crura.

Penile weight and cell subtype specific changes in a post-radical prostatectomy model of erectile dysfunction

PURPOSE

We evaluated neurogenic erectile dysfunction, focusing on the post-radical prostatectomy model. We investigated changes in DNA, protein and apoptotic cells of the rat penis after denervation. Gross morphometry was measured to elucidate the impact of chemical changes.

MATERIALS AND METHODS

Postpubertal male Sprague-Dawley rats were randomized to bilateral or unilateral cavernous nerve transection, or sham operation. Wet weight, DNA content and protein content were measured. Tissue sections were stained for apoptosis by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling and the apoptotic index was calculated. Dual staining was performed for endothelial and smooth muscle cells to identify apoptotic cells.

RESULTS

Penile wet weight was significantly decreased at all time points after bilateral neurotomy (p <0.0005). Unilateral neurotomy allowed much greater preservation of penile weight. DNA content was significantly decreased in bilaterally denervated penes and unchanged in unilaterally operated penes. Protein content was not significantly altered in the bilateral or unilateral cohorts. Bilateral neurotomy induced significant apoptosis, while unilateral surgery caused significantly less apoptosis. Each population had apoptotic clustering just beneath the tunica albuginea, which was mostly smooth muscle cells.

CONCLUSIONS

These data suggest the importance of neural integrity to maintain penile homeostasis. The loss in penile weight was consistent with the anecdotal experience of many clinicians. Decreased DNA content may have been due to significant levels of apoptosis in smooth muscle cells. Preserved protein content may suggest an increase in extracellular protein, as postulated in corporeal fibrosis. The subtunical population of apoptotic smooth muscle cells revealed a mechanism for veno-occlusive dysfunction observed after radical prostatectomy. These effects were significantly moderated in the unilateral model, reinforcing the critical nature of neural integrity.

Etiology and treatment of erectile failure in diabetes mellitus

Men with diabetes are especially prone to neuronal and endothelial disease and are afflicted with erectile dysfunction (ED) at a much higher incidence and prevalence than normal men, with a consequent reduction in quality of life. ED in diabetes results from combinations of impairments from nearly every step in the production of a penile erection. These include the failed transmission of neural signals to and from the spinal cord due to neuropathy resulting in reduced neural nitric oxide (NO) delivery to cavernosal smooth muscle, impaired sinusoidal endothelial cell NO release because of endothelial dysfunction, reduced arterial and arteriolar inflow due to peripheral vascular disease, and failure of relaxation of the corpora from glycation of the elastic fibers. The evaluation of men with diabetes and ED is similar to that in nondiabetic men. It includes assessment of gonadal, neural, arterial, and on occasion, venous function, along with marital and psychological status. Although treatment options for diabetic men with ED have fortunately expanded, the risk factors for ED are the same as those for cardiovascular disease; a flagging penis should raise a red flag of warning to evaluate and treat the risk factors for coronary, cerebral, and peripheral vascular disease, which are common in persons, of either sex, afflicted by diabetes.