POTASSIUM HOMEOSTASIS DURING HYPERINSULINEMIA - EFFECT OF INSULIN LEVEL, BETA-BLOCKADE, AND AGE

The euglycemic glucose clamp technique was used to evaluate the influence of level and duration of hyperinsulinemia, presence of .beta.-adrenergic blockade, and subject age on insulin-mediated changes in plasma K. In 16 young subjects, 2 h insulin infusions at 20 (6), 80 (13), and 200 (8) mU .cntdot. m-2 per min resulted in dose-dependent declines in plasma K (P < 0.001 at all doses) during the 1st h. During the 2nd h plasma K declined during the 20 mU .cntdot. m-2 per min infusions, was stable during the 80 mU .cntdot. m-2 per min infusions, and rose slightly during the 200 mU .cntdot. m-2 per min infusions. There was a significant reciprocal relationship between the changes in plasma K during the 1st and 2nd h of study (r = 0.99, P < 0.01). During 4 h infusions (80 mU .cntdot. m-2 per min, 6) plasma k declined during the first 90 min (P < 0.001) and rose thereafter until the end of the infusion (P < 0.05). Studies with and without propranolol infusion at 2 insulin dose levels (20 and 80 mU .cntdot. m-2 per min) in 6 young subjects showed no effect of .beta.-blockade, and studies at 3 insulin dose levels [20 (5), 80 (6), and 200 (6) mU .cntdot. m-2 min in 10 older males (63-77 yr)] showed no effect of age on the changes in plasma K during hyperinsulinemia. These results suggest the presence of a regulatory mechanism influencing insulin-mediated alterations in plasma K. This mechanism appears uninfluenced by age or .beta.-adrenergic blockade.