Supersensitivity to both tyramine and noradrenaline in diabetic autonomic neuropathy.

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Abstract
Cardiovascular responses to intravenously infused tyramine and noradrenaline were measured in five normal subjects, five insulin-independent diabetics and five insulin-independent diabetics with autonomic neuropathy. Tyramine infusion produced a statistically significant increase in systolic blood pressure (BP) in the autonomic neuropaths only (p < 0.001). No change occurred in diastolic BP. Noradrenaline infusion produced a statistically significant increase in systolic BP in the normal subjects (p < 0.01) and in the autonomic neuropaths (p < 0.001). The increase in systolic BP in the neuropaths was significantly greater (p < 0.001) than in normal subjects. Diastolic BP rose significantly only in the normal subjects (p < 0.05). There was no change in heart rate in response to either agent. Thus super-sensitivity to noradrenaline occurred in patients with diabetic autonomic neuropathy indicating post-denervation hypersensitivity. Tyramine hypersensitivity also occurred indicating that denervation is not complete and suggesting dysfunction at a pre-synaptic level.