Mean arterial blood pressure (MABP), heart rate (HR), stroke volume index (SVI), cardiac index (CI), systemic vascular resistance index (SVRI), and central venous pressure (CVP) were measured in conscious, freely moving, sham-operated (SO) and chronically adrenalectomized (ADX) rats. After 3 weeks of ADX, the rats exhibited hypotension, tachycardia, and diminished SVI and CI. From 3 to 6 weeks after surgery, the HR decreased and SVRI increased. These changes were obscured when the same measurements were obtained in the same rats under enflurane anesthesia. Cardiovascular responses to an epinephrine (0.4 microgram/kg/min) infusion were measured in conscious SO and ADX rats. The magnitude of change from baseline to peak was similar in all groups, indicating that ADX did not alter the responsiveness of the cardiovascular system to epinephrine. The peak MABP response to epinephrine in ADX rats was significantly below that of SO control rats, suggesting that ADX impaired the ability of the cardiovascular system to maintain normal arterial blood pressure. No differences were found in plasma concentrations of Na+, K+, Cl-, PO4 =, or hematocrit that would help to explain the effect of long-term adrenalectomy. The data underscore the cardio-depressant effect of enflurane anesthesia, demonstrate the importance of a conscious rat model in studying the effects of ADX on the cardiovascular system, and emphasize that the full effects of ADX occur over a period of several weeks.
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