Pseudoaffective cardioautonomic responses to gastric distension in rats.

We examined the heart rate response to gastric distension, the involvement of vagal and sympathetic sensory afferents, adrenergic and cholinergic neural pathways, and the effects of capsaicin on this response in anesthetized rats. Gastric distension volume dependently decreased heart rate by 24.5% (resting rate = 219.87 +/- 14.06 beats/min, mean rate during gastric distension with 15 ml = 165.97 +/- 17.36 beats/min, P < 0.05). The bradycardic response was significantly decreased after removal of the celiac plexus (9.71 +/- 1.77 vs. 38.03 +/- 7.06% in controls, P < 0.05) or after bilateral subdiaphragmatic vagotomy (6.38 +/- 2.65%, P = 0.05). The response to gastric distension was largely prevented by systemic capsaicin (29.92 +/- 4.93% in controls, 2.58 +/- 4.19% after systemic capsaicin, P < 0.05) and decreased by perivagal capsaicin (18.72 +/- 4.75%, P < 0.05). Atropine almost completely prevented the cardiac response to distension, while propranolol and bretylium partially blocked it, implying the response is primarily mediated by cholinergic efferents but also involves adrenergic pathways. We conclude that unmyelinated, capsaicin-sensitive vagal afferents are essential to the pseudoaffective cardioautonomic response to a noxious gastric stimulus.