Reflex cardiovascular depression induced by capsaicin injection into canine liver

J. H. Ashton, G. A. Iwamoto, J. C. Longhurst and J. H. Mitchell Capsaicin was injected into the portal circulation of 29 dogs after a blood delay pathway was constructed between the liver and right heart, through which capsaicin-contaminated blood could be replaced while systemic hemodynamics were maintained constant. Capsaicin (500 micrograms) rapidly decreased left ventricular systolic pressure (-10%), mean arterial pressure (-12%), heart rate (-4%), renal vascular resistance (-7%), maximal rate of left ventricular pressure rise (dP/dtmax) (-12%), and dP/dt at 25 mmHg developed left ventricular pressure (-15%) in animals with paced hearts. Left ventricular end-diastolic pressure did not change. Vagus nerve interruption at the level of the diaphragm did not alter hemodynamic changes occurring during capsaicin injections, but anterior hepatic nerve interruption eliminated the changes, suggesting that the cardiovascular responses were reflex in origin and that the principal afferent pathway traverses the hepatic nerve. This study demonstrates that activation of afferent fiber receptors within the liver tissue can contribute to neural regulation of the cardiovascular system, but the natural stimulus for these receptors is not known.