Glucoregulation During Moderate Exercise in Insulin Treated Diabetics

Abstract

To characterize glucoregulation during exercise in insulin treated non-obese diabetics, the response to controlled exercise after an overnight fast was compared to that of normal controls. The diabetics were divided into two groups: ten received insulin by continuous iv infusion while nine received one-third their usual intermediate acting insulin by so injection in the thigh 1 h prior to exercise. Exercise was on a bicycle ergometer for 45 min at 50% maximum O₂ consumption. In the sc insulin group glucose was 227 ± 16 mg/dl at rest and exercise induced a progressive fall to 156 ± 18 mg/dl at the end of the exercise period. In both insulin-infused diabetic subjects and normal controls exercise did not affect plasma glucose. Glucose turnover was measured by a method employing 3-³H-glucose by primed infusion. Glucose production in the normal controls increased approximately two-fold with exercise and glucose disappearance paralleled production. Similarly, in the normoglycemic insulin-infused diabetics, glucose production and disappearance increased synchronously. By contrast, in the sc insulin diabetics, there was decreased glucose production despite increased disappearance, accounting for the fall in plasma glucose. Plasma immunoreactive insulin (IRI) increased during exercise when insulin was administered by subcutaneous injection. These studies demonstrate: a) moderate exercise in diabetics receiving sc insulin is associated with a rapid fall in plasma glucose; b) plasma glucose in diabetics receiving insulin by constant iv infusion is unaffected by exercise; c) the fall in plasma glucose during exercise in sc treated diabetics is the result of decreased glucose production, perhaps related to insulin mobilization from the sc depot injection site.