Time dependent partial loss of the effects of isoproterenol on function and energy metabolism of isolated rat hearts.

In isolated perfused rat hearts (medium: Krebs-Ringer solution containing about 15% bovine red cells) the following parameters were estimated: heart rate (F), left intraventricular peak pressure (P), dP/dt, oxygen consumption (VO2); myocardial tissue content of glycogen, ATP, ADP, AMP, cAMP, phosphocreatin (PC) and inorganic phosphate (Pi). Isoproterenol (ISO) was administered to the non circulating system in the concentration range of 5 x 10(-10) to 5 x 10(-5) M for 4 min and 1 hour respectively by infusion into the perfusate close to the aortic canula. After administration period of 4 min dependent on the concentration of ISO, P, dP/dt, VO2 and the content of cAMP are increased. The ratios of PC/Pi and ATP/ADP as well as glycogen content are reduced. For an administration period of 1 hour at a level of 5 x 10(-9) M the effects of isoproterenol are maintained. At ISO concentration higher than 5 x 10(-9) M the effects on mechanical parameters and VO2 fall to the level of those values which are produced at 5 x 10(-9) M ISO. In contrast, high energy phosphates and glycogen content remain reduced while that of cAMP is elevated.