Effect of carotid or aortic baroreceptor denervation on arterial pressure during hemorrhage in conscious dogs

We studied the effect of chronically denervating aortic baroreceptors (ABR; n = 6) or carotid baroreceptors (CBR; n = 7) on mean arterial pressure (MA P) and heart rate (HR) responses to hemorrhage in the dog. Neither denervat ion had a significant effect on basal MAP, the variability (standard deviat ion) of MAP, or resting HR. However, the breakpoint of MAP (defined as the volume of blood removed when MAP fell more than 10% below control and decli ned monotonically thereafter) was significantly reduced in dogs with only A BR functional (12.4 +/- 1.4 ml/kg) compared with the volume in the intact c ondition (18.9 +/- 1.8 ml/kg). In contrast, there was no difference in the breakpoint or the MAP at any time during hemorrhage in dogs with both CBR f unctional compared with their intact responses. In a different group of dog s (n = 6), responses were determined with both CBR operating and again afte r unilateral denervation, leaving only one CBR (1CBR) functional. Basal MAP and the variability of MAP were not altered in dogs with only 1CBR functio nal, but the breakpoint (11.7 +/- 1.4 ml/kg) during hemorrhage was signific antly different compared with responses with two CBR (21.2 +/- 2.3 ml/kg), and MAP fell to much lower levels. These results indicate that the CBR can compensate fully for loss of ABR during hemorrhage but not vice versa; and bilateral CBR inputs are required for normal responses to hemorrhage.