Effects of S-Nitroso-N-acetyl-penicillamine Administration on Glucose Tolerance and Plasma Levels of Insulin and Glucagon in the Dog

It has been suggested that nitric oxide (NO, nitrogen monoxide) is a regulator of carbohydrate metabolism in skeletal muscle. The present study was undertaken to investigate the acute effects of the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) on blood glucose levels and on the gluco-regulatory hormones insulin and glucagon in healthy dogs. The acute effects of SNAP on mean arterial pressure and heart rate were also investigated. The drug was administered intravenously and the pre- and postprandial blood glucose, plasma insulin, and glucagon concentrations were determined at half-hour time intervals postadministration after a glucose challenge. The plasma nitrate and nitrite concentrations were measured and taken as the biochemical markers of in vivo NO formation. The oral glucose tolerance test revealed an impaired glucose tolerance in SNAP-treated dogs as reflected by the area under the glucose curve, 1150.50 ± 63.00 mmol × 150 min and 1355.25 ± 102.01 mmol/L × 150 min in dogs treated with 10 and 20 mg/kg of SNAP, respectively, compared with 860.25 ± 60.68 mmol/L × 150 min in captopril-treated controls (P < 0.05). The 2-h blood glucose concentration in dogs treated with 20 mg/kg body wt of SNAP was 9.17 ± 1.10 mmol/L compared with 5.59 ± 0.26 mmol/L for captopril-treated controls (P = 0.015). The oral glucose tolerance test also confirmed an impaired insulin secretion in the SNAP-treated dogs. While the plasma insulin concentration increased gradually in the captopril-treated controls to a peak value of 39.50 ± 2.55 μIU/ml, 1.5 h after a glucose challenge there was a decrease in the plasma insulin concentration in SNAP-treated dogs to a low value of 20.67 ± 0.88 μIU/ml (P = 0.006). In contrast, there were no significant differences in plasma glucagon concentration in SNAP-treated dogs and captopril-treated dogs at any time points. Using the Griess reaction, we found that there was a 27–95% increase in plasma nitrate/nitrite concentration on administration of SNAP. The sustained hyperglycemic effect observed in SNAP-treated dogs was accompanied by a marginal decrease in the mean arterial blood pressure and a significant increase in heart rate (P < 0.05). We conclude that acute administration of SNAP in the oral glucose tolerance test releases NO that modulates the parameters of carbohydrate metabolism.