Abstract 3512: Disruption of Whole Nitric Oxide Synthase System Causes Impaired Glucose Tolerance and Insulin Resistance in Mice in Vivo
Background: Nitric oxide (NO) synthase (NOS) system consists of 3 different isoforms, including neuronal (nNOS), inducible (iNOS), and endothelial NOSs (eNOS). We have recently succeeded in developing mice lacking all NOS genes (triply n/i/eNOS-KO mice) (PNAS 2005). Our preliminary study has revealed that the triply-KO mice develop acute myocardial infarction (AMI). The present study was designed to investigate abnormalities of glucose metabolism, an important risk factor of MI, in those mice.
Methods and Results: Experiments were performed in 3-month-old male wild-type (WT) and triply-KO mice (n=5–7). At 15 minutes after intravenous glucose administration (1 g/kg), plasma glucose levels (mg/dl) were significantly higher in the triply-KO (475 ± 44) than in the WT mice (241 ± 20) (P<0.05), and plasma insulin levels (ng/dl) were significantly lower in the triply-KO (0.50 ± 0.03) than in the WT mice (0.78 ± 0.03) (P<0.05). In the triply-KO mice, the size of pancreatic islets (islet/pancreatic area, 0.64 ± 0.16 vs. 2.81 ± 0.64%) was significantly smaller (P<0.05), and significant apoptosis of pancreatic islets (apoptotic/total islets, 19 ± 2 vs. 3 ± 1%) (TUNEL staining) was noted as compared with the WT mice (P<0.05). Furthermore, insulin sensitivity (as assessed by insulin-induced [3H]-glucose uptake in isolated soleus muscle) (fold increase) was markedly reduced in the triply-KO mice (1.1 ± 0.03) as compared with the WT mice (2.1 ± 0.3) (P<0.05), associated with an impairment of insulin-induced translocation of glucose transporter-4 (GLUT-4) to the cellular membrane (immunofluorescent staining) (P<0.05). Importantly, supplementation of NO by long-term treatment with isosorbide dinitrate (0.4 mg/day, 6 weeks, dermal application) significantly reversed all these abnormalities of glucose metabolism in the triply-KO mice; plasma glucose (280 ± 28) and insulin levels (0.89 ± 0.10) after glucose tolerance test, insulin sensitivity (1.5 ± 0.08), and GLUT-4 translocation were all improved (all P<0.05).
Conclusions: These results indicate that disruption of whole NOSs system causes impaired glucose tolerance and insulin resistance in mice in vivo, suggesting a critical role of endogenous NO/NOSs system in maintaining glucose metabolism.