Roles of right versus left vagal sensory nerves in cardiopulmonary reflexes of conscious dogs

This study examined the relative roles of the right vs. left vagi in mediating the inhibitory influence of vagal sensory input on sympathetic outflow to the cardiovascular system. This objective was pursued through examination of responses to 1) interruption of tonic vagal input and 2) intracoronary administration of veratridine (Bezold-Jarisch effect). Bilateral vagal cold block (BVB) (n = 16) increased arterial pressure 25 ± 3 mmHg and heart rate 66 ± 7 beat/min, whereas right vagal cold block (RVB) and left vagal cold block (LVB) increased arterial pressure 13 ± 2 and 4 ± 2 mmHg, respectively. The relative differences in the change in mean arterial pressure were independent of heart rate since similar changes in arterial pressure were observed with preelevation of heart rate with atropine. Sinoaortic baroreceptor denervation augmented the pressure responses approximately fourfold, with the relative pressure changes produced by BVB, RVB, or LVB remaining proportionally the same. Intracoronary administration of veratridine (0.1 g/kg) produced a hypotension action (-44 ± 6 mmHg), bradycardia (-48 ± 8 beat/min), and a negative intropic effect (-482 ± 68 mmHg/s, left ventricular (LV) (dP/dt)(max). During RVB the depressor effect of veratridine was reduced to -18 ± 5 mmHg, and changes in heart rate or LV (dP/dt)(max) were abolished. Veratridine administration during LVB decreased arterial pressure (-39 ± 6 mmHg), heart rate (-22 ± 6 beat/min), and LV (dP/dt)(max) (-250 ± 60 mmHg). We conclude that in the conscious dog the tonic inhibitory influence of vagal afferent nerves on vasomotor outflow is predominantly associated with the right vagus as is the Bezold-Jarisch effect.