A depressed response of left ventricular contractile force to isoproterenol and norepinephrine in dogs with congestive heart failure.

The inotropic response of the left ventricle to intravenous administration of norepinephrine (NE) and isoproterenol (I) was studied in dogs with congestive heart failure (CHF) resulting from aortocaval fistula. Left ventricular contractile force (CF) was recorded at the peak of the length-tension curve with a modified Walton-Brodie strain gauge arch in five dogs with CHF and five control animals. Arterial blood pressure (ABP) and heart rate (HR) were also monitored. Graded dose-response curves (0.0125 to 1.6 mug per kilogram) were obtained to NE and I. The response of CF was significantly depressed at all dose levels to both NE and I ni dogs with CHF. For example, at the dose of 0.8 mug per kilogram the CF response to I in the control dogs was 201 +/- 32 per cent above control level, whereas in CHF dogs the response was 92 +/- 31.5 per cent. Similarly, NE at this dose level produced a 168.6 +/- 14.7 per cent increase in CF in control dogs and 71 +/- 21.3 per cent in CHF dogs. I was approximately four times as potent as NE and this ratio was not altered in CHF dogs. The response of HR and diastolic ABP to drug administration was not altered by CHF. These data clearly suggest a depressed inotropic response to beta-adrenergic stimulation in this CHF model and a separation of the inotropic and chronotropic response.