The effect of the calcium antagonist nifedipine on peripheral nerve function in streptozotocin-diabetic rats

Recent data suggests that reduced nerve blood flow is implicated in the aetiology of experimental diabetic neuropathy, which may be prevented by manipulations that reduce receptor-mediated vasoconstrictor activity. This investigation examines the effects of nifedipine, a voltage-sensitive calcium channel antagonist which has a direct vasodilatory effect on vessels, on nerve conduction, hypoxic resistance and capillary density in streptozotocin-induced diabetic rats. Treated and non-treated non-diabetic and diabetic groups were employed. Diabetes duration was 2 months. Treatment was preventive, groups received a nifedipine dietary supplement (40 mg.kg-1.day-1) for 2 months from the start of the study. Conduction was measured in sciatic motor branches supplying tibialis anterior and gastrocnemius muscles, and sensory saphenous nerve. Diabetes resulted in a 23-28% reduction in motor conduction velocity (p < 0.001), and a 15% deficit for sensory saphenous nerve (p < 0.001). In the nifedipine-treated diabetic group, motor and sensory conduction deficits were minimal compared with non-treated diabetes (p < 0.001). Nifedipine treatment had no significant effect on conduction velocity in non-diabetic rats. In vitro measurement of sciatic nerve hypoxic resistance revealed a 60% increase in the time taken for compound action potential amplitude to reach half its initial value with diabetes (p < 0.001). This was not significantly affected by nifedipine treatment. Experimental diabetes or nifedipine treatment did not significantly alter sciatic nerve endoneurial capillary density. We conclude that nifedipine, a vasodilator which acts directly on vascular smooth muscle, prevents nerve conduction deficits in experimental diabetes.