THE ACTION OF INSULIN ON THE STORAGE AND UTILIZATION OF SUGAR BY THE ISOLATED NORMAL AND DIABETIC HEART

Abstract

The isolated normal heart responds to insulin by storing glycogen provided that the blood sugar does not fall to an extremely low level. In the diabetic heart while insulin administered in physiological dosage maintains glycogen synthesis, it does not do so after the repeated addition of 10 units of insulin half hourly to the blood perfusing the isolated heart-lung preparation: with the reduction in diabetic blood sugar there is a disappearance of glycogen and muscle sugar from the heart. The average figure for the utilisation of sugar by the normal isolated heart without the addition of sugar approximates 2 mgm. per gm. of heart muscle per hr. The addition of sugar to the perfusing blood causes increased utilisation of sugar and glycogen synthesis. The addition of insulin to normal blood perfusing a normal heart gives an utilisation of about 6 mgm. The addition of both sugar and insulin occasions an utilisation approximately 12 mgm. per gm. of muscle per hr. The perfusion of a diabetic heart with normal blood results in a sugar utilisation of about 4 mgm. per gm. of muscle per hr. On the other hand the perfusion of a diabetic heart with diabetic blood, the animals being 7 to 9 days diabetic, results in no utilisation whatsoever. This points to rather complete elimination of insulin from blood and heart muscle in 7 to 9 days after pancreatectomy. Insulin added to the diabetic blood perfusing the diabetic heart increases the power of the heart to utilise sugar up to 7 mgm. per gram per hr., but it appears to produce no synthesis of glycogen.