Acute effects of adrenergic-mediated ischemia on nerve conduction in subjects with type 2 diabetes

Abstract

Several lines of evidence support peripheral nerve ischemia as a contributing factor in the etiology of human diabetic neuropathy. We questioned whether diabetic subjects with relatively normal nerve function in the baseline state would be more likely than healthy control subjects to show either improvement of ulnar nerve function with acute intraarterial infusion of nitroprusside (vasodilation) or be more sensitive than control subjects to worsening of nerve function with acute intraarterial infusion of norepinephrine (vasoconstriction). We measured forearm blood flow (FABF) using venous occlusion plethysmography and assessed ulnar nerve function at baseline and during two intrabrachial artery infusions. Six nondiabetic control subjects (mean age, 56 years) and 11 subjects with type 2 diabetes (mean age, 58 years) in good general health participated. Only three type 2 diabetic subjects had peripheral sensory neuropathy, which was mild. Among control subjects, there was no significant change in sensory distal latency, motor distal latency, motor proximal latency, or sensory or motor conduction velocity during norepinephrine infusion. In contrast, among type 2 diabetic subjects, there was a significant increase in sensory (baseline v norepinephrine, 2.73 ± 0.10 v 2.94 ± 0.10 milliseconds [MS], P ≤ .01) and motor distal latencies (baseline v norepinephrine, 2.90 ± 0.06 v 3.18 ± 0.1 ms, P ≤ .001) and motor proximal latency (baseline v norepinephrine, 7.15 ± 0.18 v 7.60 ± 0.23 ms, P < .01) and a decrease in sensory conduction velocity (baseline v norepinephrine, 52.1 ± 2.0 v 47.7 ± 1.6 m/s, P < .01) during norepinephrine infusion. There were no consistent changes in nerve function during nitroprusside infusion in either group. In summary, we found that subjects with type 2 diabetes, but not control subjects, demonstrate a decrement in nerve function with vasoconstriction during intraarterial infusion of norepinephrine, but no consistent change during nitroprusside-induced vasodilation. These findings suggest there may be enhanced sensitivity of nerve function to ischemia in type 2 diabetic subjects with mild or absent clinical neuropathy.