Influence of Selective α- and β-Adrenoceptor Antagonists on the Control of Motor Activity and Transmural Potential Differences in the Rabbit Ileum in Vitro

Although the sympathetic nervous system influences intestinal motility and intestinal fluid and electrolyte transport, the role of sympathetic nerves in the relationship between the two processes has not been characterized. We investigated the effect of sympathetic nerve stimulation of intestinal function by monitoring concurrently predominantly longitudinal smooth muscle activity and transmural potential difference as an on-line marker of intestinal ion transport. In a segment of rabbit small intestine in vitro, perivascular nerve stimulation inhibits spontaneous phasic motor activity and reduces transmural potential difference, which reflects enhanced absorption of fluids and electrolytes. The aim of this study was to investigate the particular adrenoceptors involved in both the smooth muscle and epithelial responses. Using the selective antagonists for the α1-(prazonsin), α2-(idazoxan), β1-(atenolol), and β2-adrenoceptors (butoxamine), we demonstrated that the enhanced fluid absorption, as shown by a fall in transmural potential difference, is α-mediated with both α1-and α2-adrenoceptors being involved. However, there was considerable variation with regard to the type of α-adrenoceptor subtype exerting the dominant effect. The sympathetically induced loss of spontaneous smooth muscle motor activity was found to be predominantly β1-mediated, with the remainder of the response involving β2-adrenoceptors.