Combined galanin with insulin improves insulin sensitivity of diabetic rat muscles

Although administration of galanin or insulin alone may enhance insulin sensitivity and glucose transporter 4 (GLUT4) trafficking, their cooperative effect on insulin sensitivity is still unclear. In the present study, we evaluated the cooperative effect of both reagents compared with solitary treatment with galanin or insulin in type 2 diabetic rats. Galanin and/or insulin were injected singly or together into type 2 diabetic rats once a day for 15 days. The results indicated that coadministration of both reagents compared with treatment with galanin or insulin alone significantly increased glucose infusion rates in euglycemic-hyperinsulinemic clamp tests, 2-deoxy-[(3)H]d-glucose contents, GLUT4 densities, and pAS160 and protein kinase C activity levels, but reduced blood glucose and insulin levels, as well as retinol-binding protein 4 contents, and did not affect Glut4 (Slc2a4) mRNA expression levels in myocytes. The changes in the ratios of GLUT4 immunoreaction in plasma membranes to total cell membranes of myocytes were higher in the coadministrative group compared with either the insulin or the galanin group. These results indicate that cooperation of the two hormones plays a synergic role to improve GLUT4 translocation and insulin sensitivity. This finding indicates the possibility of combining galanin with insulin with the aim of obtaining better antidiabetic efficacy than that of the canonical treatment with insulin alone.