Measurement of cardiac output by the thermodilution method in rats. II. Simultaneous measurement of cardiac output and blood pressure in conscious rats.

A method is described for the simultaneous measurement of cardiac output (CO), using the thermodilution method, and arterial blood pressure in conscious unrestrained rats. For the injection of the indicator solution (ice-cold, 0.9% saline) and for the measurement of systolic and diastolic blood pressure, chronically-implanted polyethylene cathethers were used, while CO was measured transpulmonarily with a commercially available CO computer and an acutely-implanted (via caudal artery) arterial thermistor catheter. The following were observed in 10 rats at rest: a CO of 40.2 +/- 1.9 ml/min/100 g, a mean arterial blood pressure of 106 +/- 5 mmHg, a heart rate of 417 +/- 20 beats/min and a peripheral vascular resistance of 2.68 +/- 0.13 mmHG/(ml/min/100 g). After injection of the beta-adrenergic agonist isoprenaline, there was a rise in CO and heart rate, while peripheral resistance and blood pressure were lowered. Injection of the beta-receptor-blocked propranolol caused decreases in CO and heart rate, while peripheral resistance and blood pressure rose. It is concluded, that the method described here for the simultaneous measurement of CO and arterial blood pressure is suitable for the investigation of drug-induced cardiovascular effects in conscious rats.