Neonatal capsaicin treatment does not prevent splanchnic vasodilatation in portal-hypertensive rats

It has been suggested that the peripheral sensory neurons are involved in the splanchnic hemodynamic changes of portal hypertension. Therefore the influence of permanent ablation of sensory neurons by neonatal capsaicin pretreatment (50 mg/kg, subcutaneously) on the development of the hyperdynamic splanchnic circulation in portal-hypertensive rats was studied. In adulthood, portal hypertension was induced with partial portal vein ligation. In study 1, systemic and splanchnic hemodynamics were measured by means of a radiolabeled-microsphere technique in portal-hypertensive rats, under ketamine anesthesia, pretreated with capsaicin or vehicle. Mean arterial pressure, heart rate, cardiac index, systemic and splanchnic vascular resistance, portal pressure, portal venous inflow, portal-collateral resistance and portal-systemic shunting were not significantly different between capsaicin-pretreated and vehicle-pretreated rats. In study 2, gastric mucosal blood flow, measured by means of hydrogen gas clearance, and the hemoglobin and oxygen content of the gastric mucosa, as assessed with reflectance spectrophotometry, were not significantly different in the two groups of anesthetized portal-hypertensive rats pretreated with capsaicin or vehicle. In study 3, we confirmed the effectiveness of neonatal capsaicin pretreatment by measuring calcitonin gene-related peptide content of the gastric corpus wall. Capsaicin pretreatment caused a depletion of calcitonin gene-related peptide by at least 98% compared with that in vehicle-pretreated rats. These results do not support a role of capsaicin-sensitive sensory neurons that innervate the gastrointestinal tract in the development of the splanchnic vasodilatation characteristically observed in chronic portal hypertension.