Endothelial nitric oxide synthase protein expression, localization, and activity in the penis of the alloxan-induced diabetic rat.
OBJECTIVE
To explore the possible relevance of endothelial nitric oxide synthase (eNOS) in the pathophysiology of erectile dysfunction (ED) associated with diabetes mellitus, we compared the catalytic activity, protein expression, and cellular localization of eNOS with those of neuronal nitric oxide synthase (nNOS) in the penis of rats with alloxan-induced diabetes.


METHODS
Adult male Sprague-Dawley rats were given alloxan or vehicle only and monitored weekly by Dextrostix for confirmation of glucosuria. Tail-flick immersion and penile reflex testing were used to evaluate sensory neuropathy and ED, respectively. At 4 to 5 weeks (early) and 10 to 11 weeks (late), animals were sacrificed, and their penes were subjected to nNOS and eNOS catalytic activity assay, Western immunoblotting, and immunohistochemistry examination. Masson's trichrome staining of penile tissue and serum testosterone measurements were performed for light microscopy and sex steroidogenic analysis, respectively.


RESULTS
Confirmed diabetic rats showed significant reductions in penile nNOS expression and eNOS activity and expression early, prior to observed ED, and nNOS and eNOS activities and expressions late, synchronous with ED. Decreased intensities of both nNOS staining, localized to the dorsal and cavernosal nerves distributing to the penis, and eNOS staining, localized to penile vascular and sinusoidal endothelium, were assessed in diabetic animals. Penile vascular and cavernosal tissue appeared intact in diabetic rats. Testosterone levels were equivalent in nondiabetic and diabetic rats.


CONCLUSIONS
In the penis of the alloxan-induced diabetic rat, eNOS protein expression and synthetic activity were reduced compared with the normal rat penis, independent of testosterone influence and in the absence of significant erectile tissue degenerative changes. These eNOS effects apparently preceded nNOS effects. Full elucidation of the possible mechanisms affecting eNOS function in the diabetic rat penis requires further investigation.
Akingba
A G
AG
Department of Urology, The James Buchanan Brady Urological Institute, The Johns Hopkins Hospital and The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-2411, USA.
Burnett
A L
AL
D000496:Alloxan; D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000150:complications; D003928:Diabetic Nephropathies / Q000201:enzymology; D007172:Erectile Dysfunction / Q000201:enzymology* / Q000209:etiology / Q000473:pathology; D007150:Immunohistochemistry; D008297:Male; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III; D010147:Pain Measurement; D010413:Penis / Q000201:enzymology* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex; D013739:Testosterone / Q000097:blood
D013739:Testosterone; D000496:Alloxan; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III; C496322:Nos1 protein, rat; C496316:Nos3 protein, rat