Apparent improvement in diabetic autonomic neuropathy induced by captopril

Eight diabetic subjects with moderately elevated blood pressure (BP) (systolic (SBP) greater than 140 and/or diastolic (DBP) greater than 90 mmHg) were studied. Each had evidence of mild asymptomatic autonomic neuropathy (impairment of forced sinus arrhythmia). The effect of a single oral 25 mg dose of captopril on BP and some aspects of autonomic function was compared with matched placebo in a double-blind, cross-over study. Resting supine SBP and DBP fell significantly (P less than 0.01) over 90 minutes following captopril, indicating that the hypotensive effect of the drug was not dependent on intact autonomic function. There was no significant change in resting heart rate. The bradycardic response to apnoeic face immersion was significantly (P less than 0.01) enhanced following captopril. Sinus arrhythmia did not change. The BP responses to standing and to the cold pressor test were unaffected. There was no exacerbation of postural hypotension. The ingestion of a single dose of captopril appears to increase vagal function, without affecting sympathetic nervous function, in diabetics with evidence of mild vagal impairment.