Perturbation of insulin oscillations by nerve blockade in the in vitro canine pancreas.

The in vitro canine pancreas produces an oscillatory pattern of insulin secretion during a constant glucose concentration despite the lack of external nervous modulation or recirculating hormone feedback. The normal period of insulin fluctuations (7.4 +/- 0.34 min) is unaffected by combined adrenergic and cholinergic blockade by 5 microM atropine, 4 microM propranolol, and 4 microM phentolamine (8.0 +/- 0.31 min, P less than 0.20). To test the theory that the coordination of islet secretion may be controlled by an intrapancreatic nervous system (nonadrenergic, noncholinergic), nerve blockade was attempted by the infusion of tetrodotoxin (TTX) on a background of combined autonomic blockade. TTX infusion resulted in a change in the oscillatory pattern of insulin release by increasing net insulin release and shifting the period of oscillation to 4.5 +/- 0.29 min (P less than 0.0005) at both 88 and 200 mg/dl glucose. These results suggest that an intrinsic autonomously functioning pancreatic nervous system is responsible for the coordination of islet secretion and the production of periodic fluctuations of insulin secretion.