Sodium nitroprusside (10^-5 M) diminished tension prolongation during recovery from hypoxia in cat papillary muscles (TTP 208 vs 300 msec), whereas nitroglycerin had no effect.
Does sodium nitroprusside or nitroglycerin prevent tension prolongation in isolated cat papillary muscles recovering from hypoxia?
Sodium nitroprusside, but not nitroglycerin, blocks tension prolongation during recovery from hypoxia in isolated cat papillary muscles, suggesting different mechanisms of action on myocardial relaxation.
Because of recent studies suggesting that vasodilators affect ventricular compliance, we studied the effect of sodium nitroprusside and nitroglycerin on the mechanical performance of 21 isolated cat papillary muscles. The muscles were stimulated isometrically at 36 beats/min. Sixteen of the muscles were made hypoxic (95% N2, 5% CO2) for 50 minutes and then reoxygenated. Sodium nitroprusside (10(-5) M) added to four of these muscles prior to hypoxia substantially diminished the tension prolongation (both the time to peak tension, TTP, and time for tension to fall to 1/2 its peak value, RT 1/2) that characterizes recovery from hypoxia. TTP and RT 1/2 measured 2 minutes after reoxygenation were 300 +/- 20 msec and 528 +/- 26 msec for the control muscles compared to 208 +/- 13 msec and 248 +/- 22 msec for the muscles pretreated with nitroprusside. Nitroprusside had no effect on the fall and recovery of peak developed force or on the rise and fall of resting force. Furthermore, nitroprusside had no effect on the above parameters in nonhypoxic muscles. We also found that nitroprusside in concentrations of 10(-7) M and nitroglycerin in concentrations of 10(-5) M had little or no effect on tension prolongation. The results of the study indicate that nitroprusside is capable of blocking the tension prolongation that occurs during recovery from hypoxia and may prevent the incomplete myocardial relaxation thought to characterize this phenomenon. Since nitroglycerin had no effect on tension prolongation, it is possible that other factors also may be important in the apparent increase in left ventricular compliance associated with administration of vasodilators to patients.
Brodie et al. (1976) studied Hypoxia (n=21). Sodium nitroprusside vs. Control muscles was evaluated on Tension prolongation (time to peak tension and time for tension to fall to 1/2 its peak value). Sodium nitroprusside (10^-5 M) diminished tension prolongation during recovery from hypoxia in cat papillary muscles (TTP 208 vs 300 msec), whereas nitroglycerin had no effect.