Insulin Receptors of Erythrocytes and Liver Membranes in Dogs.

Abstract

Insulin receptor assays using canine liver membranes and erythrocytes were validated for use in evaluating insulin receptor binding parameters within a healthy population of dogs. Association, dissociation, saturability and specificity were demonstrated for insulin receptors of canine liver membranes and erythrocytes. Assay precision was evaluated by measuring interassay coefficient of variation (liver membrane = 25.0%; erythrocytes = 9.3%). Because the number of high-affinity receptor sites and high-affinity K$\sb{\rm D}$ were determined using physiological concentrations of insulin, they were considered to be more physiologically important than the total number of receptor sites, low-affinity K$\sb{\rm D}$ and Ke, which were derived using supra-physiological concentrations of insulin. The % maximum binding correlated with the number of high-affinity receptor sites and Ke, but negatively correlated with high-affinity K$\sb{\rm D}.$. In addition to correlating binding parameters within and between tissues, the effects of sex, anesthesia and prednisone treatment were evaluated. Erythrocyte insulin receptor binding did not correlate well with liver insulin receptor binding (3 samples of 12 dogs; Pearson's correlation coefficient). This lack of correlation was possibly due to different mechanisms of receptor regulation or poor precision in the liver membrane assays. No significant differences were observed in mean values for binding parameters observed when comparing male versus female dogs for either liver membranes or erythrocytes using an unpaired t test (p $>$ 0.05). However, there was a significantly greater variation in the % maximum binding and the number of high-affinity receptor binding sites for erythrocytes among females (Prob (a greater F) = 0.0405 % MB; 0.0035 Hi-Affinity Sites). A significant decrease in the % maximum binding of erythrocyte insulin receptors was observed as a result of anesthesia (paired t test; p = 0.028). No significant changes in erythrocyte insulin binding were observed in 6 male dogs given daily prednisone, when evaluated at 52 hours and 3 weeks after onset of treatment (paired t test; p $>$ 0.05). Canine erythrocyte insulin receptors are a potentially valuable tool in evaluating clinical syndromes where alterations in insulin receptor binding may occur.