BLOCKADE OF REFLEX VENOUS CAPACITANCE RESPONSES IN LIVER AND SPLEEN BY HEXAMETHONIUM, ATROPINE, AND SURGICAL SECTION

Since hexamethonium and surgical section have been used to prevent reflex splanchnic capacitance responses, we examined the effectiveness of these procedures in blocking responses to direct stimulation of preganglionic fibres in the splanchnic nerves. Liver blood volume was measured by plethysmography and splenic blood volume by weighing in cats anesthetized by pentobarbital. The cats were adrenalectomized to prevent adrenal catecholamine secretion in response to splanchnic nerve stimulation. Hexamethonium (10 and 20 mg/kg) alone or atropine (1 mg/kg) alone caused only a small variable block of the responses to preganglionic nerve stimulation. A combination of the two drugs essentially produced a complete block of the liver capacitance response, but a significant response still persisted in the spleen. Surgical section of the postganglionic nerve bundles around the hepatic and splenic arteries completely abolished the responses to preganglionic stimulation. It is concluded that a relatively complete block of reflex splanchnic capacitance responses requires either a combination of hexamethonium and atropine or surgical section of the postganglionic nerves.