Effects of heart work and insulin on glycogen metabolism in the perfused rat heart.

DAS, INDRAJIT. Effects of heart work and insulin on gbcogen metabolism in the perfused rat heart. Am. J. Physiol. 224(l): 7-12. 1973.-A study was made in the isolated perfused rat heart of key enzymes for the synthesis and breakdown of glycogen and the major intermediates on the glycogen pathway. Hearts from normal animals, animals rendered insulin deficient by injection of antiinsulin serum, and animals made diabetic with streptozotocin were perfused both retrogradely via the aorta (Langendorff) and atrially, while they were pumping liquid against a hydrostatic pressure head (working), with and without insulin in the perfusate. Hexokinase isoenzyme type II was reduced by 35% in streptozotocin diabetic hearts. Heart work also significantly reduced the normal hexokinase isoenzyme type II. Insulin prevented the loss of hexokinase isoenzyme II in the *working heart, but it did not have any effect on the diabetic perfused hearts. Total glycogen synthetase activity was affected neither by heart work nor by insulin deficiency. Heart work increased the glycogen synthetase I/D (active/inactive) ratio in both normal and diabetic hearts. Insulin in the perfusate was unable to increase the I/D ratio in working hearts, but insulin in vivo increased the I/D ratio significantly within 30 min in diabetic hearts. Phosphorylase activity was not affected by heart work or insulin. Significant increases of the tissue contents of glucose 6-phosphate, glucose 1 -phosphate, and UDPglucose and glycogen were observed in both Langendorff and working hearts of normal rats with insulin in the perfusate.