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Cardiovascular changes in chronically adrenalectomized conscious rats
R D Stith1, M Bhaskar, Y S Reddy
1Department of Physiology and Biophysics, University of Oklahoma Health Sciences Center, Oklahoma City 73190.
Insights
Chronic adrenalectomy (ADX) in rats leads to hypotension and reduced cardiac output, with full cardiovascular effects developing over weeks. This study highlights the importance of conscious models for understanding ADX impacts.
Area of Science:
- Cardiovascular Physiology
- Endocrinology
Background:
- Adrenalectomy (ADX) significantly impacts cardiovascular function.
- Understanding the long-term cardiovascular consequences of ADX requires careful experimental design.
Purpose of the Study:
- To investigate the chronic cardiovascular effects of adrenalectomy in conscious rats.
- To assess the impact of adrenalectomy on cardiovascular responses to epinephrine.
- To evaluate the influence of anesthesia on cardiovascular measurements in adrenalectomized rats.
Main Methods:
- Measurements of 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) in sham-operated (SO) and adrenalectomized (ADX) rats.
- Cardiovascular responses to epinephrine infusion were assessed in conscious rats.
- Comparisons were made between conscious and anesthetized states.
Main Results:
- Adrenalectomized rats exhibited hypotension, tachycardia, and diminished SVI and CI by 3 weeks post-surgery.
- Heart rate decreased and SVRI increased between 3 and 6 weeks after ADX.
- Anesthesia masked the cardiovascular changes observed in conscious ADX rats.
- Epinephrine responsiveness was unaltered, but peak MABP response was reduced in ADX rats, indicating impaired blood pressure regulation.
- No significant electrolyte or hematocrit differences explained these effects.
Conclusions:
- Chronic adrenalectomy impairs cardiovascular function, leading to hypotension and reduced cardiac output over several weeks.
- Conscious rat models are crucial for accurately studying the cardiovascular effects of adrenalectomy.
- Enflurane anesthesia has a significant cardio-depressant effect that can obscure findings.
Abstract:
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.