INS and Hyperinsulinemia: However, the discovery that insulin infusion did not increase sympathetic nerve activity in the skin in humans (Berne et al., 1992) and also that graded increases in plasma insulin failed to significantly increase renal or adrenal sympathetic activity in rats though leading to increased lumbar SNS activity, lead to the hypothesis that hyperinsulinemia produces regionally non-uniform increases in sympathetic nerve activity (Morgan et al., 1993).