Ventricular function in norepinephrine-induced cardiomyopathic rabbits.

Catecholamine cardiomyopathy (CM) was produced in rabbits by a 90-min infusion of norepinephrine (NE, 2 micrograms . kg-1 . min-1). Left ventricular (LV) contractility and pump function (VF) were examined 2 days later and compared with control animals. The effects of hypercapnia [CO2 tension (PCO2) greater than 70 mmHg] and inotropic responsiveness to NE were also determined. VF was assessed by means of left ventricular function curves obtained with constant aortic pressure and heart rate and quantified by determining stroke volume at left ventricular end-diastolic pressure of 10 cmH2O (SV10). Mean SV10 was 1.16 +/- 0.06 ml in controls but averaged only 0.93 +/- 0.05 in CM (P less than 0.02). Hypercapnia caused significantly greater depression of VF in CM than in controls. NE dose-response curves demonstrated increases in both LV dP/dtmax and SV10 in each group. The percent increase in LV dP/dtmax was markedly attenuated n CM, but the increments in SV10 did not differ. The mean histological score in the CM animals was 1.6 +/- 0.1, indicating extensive myofiber injury. No histological abnormalities were observed in the controls. Thus functional defects correlated with the presence of histopathological changes. In addition, a dissociation of velocity (dP/dtmax) and force (SV10) responsiveness to inotropic stimulation was identified in the CM group.