Role of respiratory changes in the modulation of arterial pressure in rats submitted to sino-aortic denervation.

NEW FINDINGS: What is the central question of this study? The arterial baroreflex regulates arterial pressure within a narrow range of variation. After sino-aortic denervation (SAD), rats show a large increase in arterial pressure variability, but mean arterial pressure levels remain similar to those of control rats. Considering that breathing influences the control of arterial pressure, the question is: to what extent does SAD cause changes in breathing? What is the main finding and its importance? Removal of arterial baroreceptors produced changes in breathing in rats, marked by a reduction in respiratory frequency, but not hypertension. These findings are indicative of a possible interaction of respiratory and autonomic neural mechanisms in the regulation of arterial pressure after SAD. Sino-aortic denervated (SAD) rats exhibit a mean arterial pressure (MAP) similar to that of control rats. Given that respiration modulates MAP, we hypothesized that conscious SAD rats show respiratory changes associated with the normal MAP. In this study, we evaluated the cardiovascular and respiratory activities and arterial blood gases in control and SAD rats. Male juvenile Wistar rats (postnatal day 19-21) were submitted to SAD, sham surgery or selective removal of the carotid bodies (CBX), and the three groups were evaluated 10 days after the surgery (SAD, n = 21; Sham, n = 18; and CBX, n = 13). The MAP in Sham, SAD and CBX groups was similar (P > 0.05), but the variability of MAP was significantly higher in SAD than in Sham and CBX rats (P < 0.0001). The duration of expiration and inspiration increased in SAD rats compared with Sham and CBX rats, which resulted in a reduced respiratory frequency and minute ventilation (P < 0.05). The arterial partial pressure of O2 and the haemoglobin saturation were reduced in SAD and CBX compared with Sham rats, whereas the arterial partial pressure of CO2 was increased in SAD compared with Sham rats. The short- and long-term respiratory variability were significantly higher in SAD than in Sham and CBX rats (P < 0.05). In addition, the reductions in MAP during deep breaths were greater in SAD than in Sham and CBX rats (P < 0.0001). The data show that SAD rats exhibit respiratory changes, which may be one of the compensatory mechanisms associated with the maintenance of normal levels of MAP in the absence of arterial baroreceptors.