Blood pressure normalization in carotid barodenervated rats: role of cardiac output

Abstract

This study evaluated the role of sympathetic nervous system (SNS) activity, peripheral hemodynamic changes, and pressure diuresis in blood pressure (BP) normalization in carotid barodenervated rats. The acute and short-term effects of carotid barodenervation or sham operation on blood pressure, heart rate, cardiac output, stroke volume, total peripheral resistance, and plasma catecholamine levels were determined. Changes in plasma volume, urine output, and water and food intakes were also measured. Surgical denervation of the carotid baroreceptors resulted in rapid rises in blood pressure and heart rate in anesthetized rats. These changes were associated with significant increases in plasma catecholamine levels and total peripheral resistance whereas the cardiac index and stroke volume remained unchanged. After recovery from the anesthesia, the blood pressure of carotid barodenervated rats was still significantly higher than that of sham-operated rats at 3 and 24 h after denervation and returned to sham-operated levels by 48 h. Plasma catecholamine levels and total peripheral resistance were higher in carotid barodenervated than in sham-operated rats on the 2 days following surgery. On the other hand, cardiac index (32 ± 1 vs. 40 ± 2 mL∙min−1∙100 g−1 body mass) and stroke volume (205 ± 13 vs. 283 ± 4 μL/beat) were significantly lower on day 2 in carotid barodenervated than in sham-operated rats, which suggests a compensatory role for carotid output in blood pressure normalization after carotid barodenervaton. Both carotid barodenervation and sham operation caused a reduction in water and food intakes but the responses were greater in carotid barodenervated rats. Urine output was drastically reduced for at least 3 days after denervation and so were body masses and water and food intakes. A pressure diuresis that occurred only on the first day after carotid barodenervation when the blood pressure was still elevated may have contributed to blood pressure normalization. Plasma volumes measured 1 and 5 days after carotid barodenervation or sham operation were similar. These findings suggest that blood pressure normalization in carotid-barodenervated rats cannot be accounted for by restoration of the sympathetic nervous system activity to normal levels but rather to a transient pressure diuresis and a reduction in cardiac output which act to offset increases in sympathetic nervous system activity and total peripheral resistance.Key words: carotid barodenervation, blood pressure, sympathetic nervous system, cardiac output, total peripheral resistance, pressure diuresis.