Cardiovascular, metabolic, and hormonal responses to noradrenaline in diabetic patients with autonomic neuropathy

Denervation hypersensitivity is a well-known phenomenon in patients with autonomic failure. In diabetic autonomic neuropathy hypersensitivity to beta-adrenergic stimulation has been demonstrated. We infused noradrenaline, mainly an alpha-adrenoceptor agonist, in three escalating doses (0.5, 2.5, and 5 micrograms min-1) in three age and sex matched groups of eight subjects: healthy volunteers, diabetic patients with and without autonomic neuropathy. During steady state in each infusion period we measured heart rate, blood pressure, cardiac output, hepato-splanchnic blood flow, vascular resistance, glucose kinetics, metabolites (beta-hydroxybuturate, glycerol, and lactate), and glucoregulatory hormones (noradrenaline, adrenaline, growth hormone, pancreatic polypeptide, cortisol, and insulin). Systolic and mean blood pressure increased in all groups but diabetic patients with autonomic neuropathy showed a significantly higher increase (p < 0.01) than the other two groups, with a lower threshold for increase in blood pressure. Cardiac output, hepato-splanchnic blood flow, vascular resistance, and heart rate did not change in any of the groups. The incremental increase in glucose and beta-hydroxybuturate was higher in patients with autonomic neuropathy. Otherwise, only minor changes were seen in hormonal and metabolic parameters. The cardiovascular hypersensitivity seen in diabetic autonomic neuropathy was mainly explained by increased peripheral vascular resistance, which increased significantly (p < 0.05) more in these patients. In conclusion, diabetic patients with autonomic neuropathy show denervation hypersensitivity to alpha-adrenergic stimulation by noradrenaline, especially as regards cardiovascular effects.