Failure of the nitric oxide synthase inhibitor to stimulate duodenal bicarbonate secretion in streptozotocin-diabetic rats.

We examined the HCO(3)- stimulatory effects of L-NAME (N(G)-nitro-L-arginine methyl ester) in the proximal duodenum of streptozotocin (STZ)-induced diabetic rats and compared with those of 16,16-dimethyl prostaglandin E2 (dmPGE2) and vagal electrical stimulation. Male SD rats were given STZ (70 mg/kg) i.p., and the experiments were done using 1 approximately 6 week STZ-diabetic rats with blood glucose levels of >300 mg/dl. Under urethane anesthesia the HCO(3)- secretion was measured in the proximal duodenal loop using a pH-stat method and by adding 10 mM HCl. Hyperglycemic conditions appeared 1 week after STZ treatment and remained during 6 week-test period. The duodenal HCO(3)- secretory response to L-NAME was significantly decreased in STZ-diabetic rats; the degree of reduction was dependent on the duration of diabetes, and the stimulatory effect disappeared completely in rats after 5 approximately 6 weeks of diabetes. Intravenous administration of L-NAME markedly increased arterial blood pressure with significant decrease in heart rate in normal rats, whereas in STZ-diabetic rats this agent caused only pressor response without any effect on heart rate. STZ-diabetic rats also secreted significantly less amount of HCO(3)- from the duodenum in response to dmPGE2 and vagal electrical stimulation after 5 approximately 6 weeks of diabetes. These all changes observed in STZ-diabetic rats were significantly reversed by daily injection of insulin. These results suggest that 1) L-NAME failed to stimulate duodenal HCO(3)- secretion in STZ-diabetic rats, and 2) impairment of the duodenal HCO(3)- secretory ability in STZ-diabetic conditions is due to both vagal-dependent neuronal dysfunction and decreased sensitivity of the secreting cell.