Diabetes Mellitus Impairs Neurogenic and Endothelium-Dependent Relaxation of Rabbit Corpus Cavernosum Smooth Muscle

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Abstract
The effect of alloxan-induced diabetes on the reactivity of corporeal nerves, endothelium and smooth muscle was studied in the New Zealand white rabbit. Fifteen rabbits were randomly divided into treated (n = 6) and control (n = 9) groups. The treated group was maintained for 6 weeks. Two control groups were studied. One control group (n = 3) was maintained for 6 weeks as littermate controls for diabetic group. The second control group (n = 6) was not maintained but was weight matched with the 6 week diabetic group. The reactivity of corpus cavernosum tissue from the diabetic animals and the control animals was studied in organ chambers. When tissue contraction was produced with phenylephrine for the study of relaxation to various stimuli, the tension induced was similar in the diabetic and the control groups. Relaxation of corpus cavernosum tissue to electrical stimulation of autonomic nerves as well as relaxation to the endothelium-dependent vasodilator acetylcholine were comparably unaffected in the weight matched and littermate control groups while significantly inhibited in the diabetic group. Treatment of the corporeal tissue with the cyclooxgenase inhibitor indomethacin enhanced the relaxation to electrical stimulation and to acetylcholine in the control and in the diabetic groups but did not improve the significant difference in relaxation between the two groups. Relaxation of corporeal tissue to endothelium-independent vasodilators, papaverine and nitroprusside was similar in the control groups and the diabetic groups. It is concluded that diabetes impairs neurogenic and endothelium-mediated relaxation of rabbit corpus cavernosum smooth muscle. These findings are comparable to those described in corpus cavernosum tissue from diabetic men, showing the validity of this experimental animal model. The mechanism for the nerve or endothelial dysfunction does not appear to involve alteration in cyclooxygenase products of arachidonate or the ability of the corporeal smooth muscle to relax via a cGMP-dependent mechanism. Since nitric oxide has been shown to act as the nonadrenergic noncholinergic neurotransmitter as well as endothelium-derived relaxing factor (EDRF) of the trabecular smooth muscle, it is possible that impairment of neurogenic and endothelium-dependent relaxation due to diabetes is mediated by alteration in the synthesis or availability of nitric oxide in corporeal tissue.