Decreased insulin binding to erythrocytes and mononuclear leucocytes in normal dogs administered with S-nitroso- glutathione

ABSTRACT

Nitric oxide is a pathogenic factor of inflammatory islet cell death in type 1 diabetes. An early event in the pathogenesis of insulin-dependent diabetes mellitus (IDDM) is intraislet accumulation of activated macrophages. Their secretory products such as nitric oxide (NO) are found to play a crucial role in islet destruction. Macrophage activity and progressive islet cell destruction persist during a long period of chronic inflammatory events preceding diabetes, suggesting the presence of nitric oxide contributing to continued immunostimulation. It has been shown previously that the nitric oxide donor, S-nitrosoglutathione (GSNO) caused persistent postprandial hyperglycaemia in normal healthy dogs at 35 and 50mg/kg. parallel with an increase in plasma nitrate concentration and decrease in insulin secretion. This study was designed to investigate differences in cellular binding of insulin in dogs administered with the GSNO. A time course assay of insulin binding, to isolate erythrocytes and mononuclear leucocytes from dog administered with GSNO, was done during the oral glucose tolerance test (OFTT). The erthrocyte receptor assay performed was the methodology used by Ghambir et al (1977). A modification was also done for mononuclear leucocytes insulin binding assay. The plasma glucose levels were measured by the glucose oxidase method, while the insulin levels were determined by radio-immunoassay. The results of these studies show that erythrocytes and mononuclear leucocytes from dogs administered with GSNO have decreased ability to bind insulin when compared to erythrocytes and mononuclear leucocytes from the controls. In dogs administered with GSNO, there was less binding of erythrocytes and mononuclear leucocytes, 44 percent and 29 percent respectively, when compared to the bound free ratio value of the controls. The data also shows that erythrocytes and mononuclear leucocytes from dogs administered with GSNO have 256 and 10.7x10 insulin receptor sites per cell, respectively, compared with 296 and 18.4x10 per cell for the control (P<0.05). Competitive inhibition studies using unlabelled insulin indicate that the affinity of insulin for its receptor on erythrocytes from dogs administered with GSNO was also significantly different from the controls, while that of mononuclear leucocytes from both group was comparable.(AU)