1. Plasma pancreatic polypeptide (PP), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT) and noradrenaline (NA) were measured in eight healthy subjects and 12 long-term insulin-dependent diabetic patients with and without autonomic neuropathy, before and after intravenous infusion of the ganglionic blocking agent trimethaphan camsylate, in order to determine the influence of the autonomic nervous system on the baseline values of the substances.
2. The basal levels of the measured substances were not significantly different in healthy subjects and patients with or without diabetic autonomic neuropathy.
3. In healthy subjects, the ganglionic blockade induced a significant decrease in PP (80%) (P < 0.02), NA (58%) (P <0.05), NT (27%) (P < 0.05) and a significant increase in SP (30%) (P < 0.05), while the VIP concentration remained unchanged.
4. The diabetic patients had nearly the same significant decrease in PP (68%) (P < 0.01), NA (50%) (P < 0.01), NT (22%) (P < 0.02), VIP (21%) (P < 0.05) and increase in SP (73%) (P < 0.01). No relationship was found between the autonomic neuropathy and changes of the substances during ganglionic blockade.
5. The results indicate that the postganglionic part of the autonomic nervous system participates in the maintenance of a normal baseline level of PP, NT and NA, but not of VIP. The regulation of VIP may be disturbed in long-term diabetic subjects.