Impaired pancreatic polypeptide response to a meal in type 1 diabetic patients: vagal neuropathy or islet cell dysfunction?

The pancreatic polypeptide (PP) response to a mixed meal was investigated in seven insulin-dependent diabetics without measurable signs of diabetic autonomic neuropathy, and in seven healthy subjects. Since acute changes in metabolic regulation might influence the meal-induced PP response, the insulin-dependent diabetic patients were studied during normo- and hyperglycemic experimental conditions at blood glucose levels of 5 and 15 mmol/l, respectively. The PP response was identical on the two occasions, the response being significantly smaller than in the healthy subjects. Thus, PP response is independent of short-term changes in metabolic control. Since the response was attenuated in the insulin-dependent diabetic patients, who had no otherwise measurable signs of neuropathy, the PP response to a meal could be a sensitive indicator of dysfunction of the reflex arc controlling PP secretion in insulin-dependent diabetic patients. Alternatively, the reduction in PP secretion in these patients reflects dysfunction of the PP secreting cells of the pancreas. Iv injection of cholecystokinin-8 elicited a small but significant increase in PP concentrations, while iv secretin did not increase PP concentrations at all in healthy subjects. These stimuli are therefore less suitable in the assessment of vagal neuropathy.