Udpglucose: α-1,4-glucan α-4-glucosyltransferase in heart regulation of the activity of the transferase in vivo and in vitro in rat. A dissociation in the action of isulin on transport and on transferase conversion

In the isolated perfused rat heart the nonhormonal control of transferase by glycogen was readily demonstrated. The transferase phosphate converting the D to I form was shown to be inhibited by glycogen in vitro. No hormonal effect of epinephrine, insulin or caffeine on transferase was demonstrated in this preparation although the usual effect of insulin to increase glucoge uptake was presen. In vivo the effect of insulin to increase transferase I activity in heart was readily demonstrated. These findings suggest a 'dissociation' in the action of insulin on the prefused rat heart in terms of the control of transport and the control of transferase conversion. This dissociation is discussed in terms of other dissociations of these two parameters noted in the literature, and it is concluded that there is no required temporal sequencing in the action of insulin on glucose transport and glycogen synthesis.