1. Release of pancreatic polypeptide (PP) is largely under vagal control and measurement of change in PP after insulin hypoglycaemia offers a non-invasive method of assessing vagal activity.
2. Changes in blood sugar and PP after intravenous insulin (0·2 unit/kg) were examined in six patients with idiopathic chronic autonomic failure (AF) and 12 control subjects. Six of the controls were studied before and after atropine treatment.
3. The PP levels in controls rose from 32 ± 9 (mean ± sem) to 236 ± 54 pmol/l after 45 min. Patients had similar baseline values (23 ± 5 pmol/l) but a markedly reduced and delayed PP response to hypoglycaemia (49 ± 19 pmol/l at 90 min). This impaired PP response was similar to that seen in controls after atropine.
4. The impaired PP response to insulin hypoglycaemia in patients with AF strongly suggests a dysfunction of vagal activity which is often clinically inapparent.