Pseudoaffective cardioautonomic responses to gastric distension in rats

We examined the heart rate response to gastric distension, the involvement of vagal and sympathetic eas sensory afferents, adrenergic and cholinergic neural pathways, and the effects of capsaicin on this response in anestheti zed rats. Gastric distension volume dependently decreased heart rate by 24. 5% (resting rate = 219.87 +/-: 14.06 beats/min, mean rate during gastric di stension with 15 mi = 165.97 +/- 17.36 beats/min, P < 0.05). The bradycardi c 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 gast ric distension was largely prevented by systemic capsaicin (29.92 +/- 4.93% in controls, 2.58 +/- 4.19% after systemic capsaicin, P < 0.05) and decrea sed by perivagal capsaicin (18.72 +/- 4.75%, P < 0.05). Atropine almost com pletely prevented the cardiac response to distension, while propranolol and bretylium partially blocked it, implying the response is primarily mediate d by cholinergic efferents but also involves adrenergic pathways. We conclu de that unmyelinated, capsaicin-sensitive vagal afferents are essential to the pseudoaffective cardioautonomic response to a noxious gastric stimulus.