Influence of adrenoceptor agonists and antagonists on fluid secretion in small bowel obstruction

Objectives: To investigate the importance of adrenoceptors on fluid losses in small bowel obstruction. Design: Evaluation of the effects of adrenergic agonists and antagonists on in-vivo net fluid secretion in chronic small bowel obstruction in rats. Methods: Net fluid transport in a jejunal segment was continuously registered in vivo after 18 h of mechanical obstruction of the small bower in anaesthetized rats. The effect on net fluid transport of adrenoceptor agonists and antagonists and of isotonic saline was quantified. Results: Clonidine, an alpha(2)-agonist, had a significant (P<0.05) anti-secretory effect, while yohimbine, an alpha(2)-antagonist, significantly (P<0.05) increased net fluid secretion. Phenylephrine, an alpha(1)-agonist and prazosin, an alpha(1)-antagonist, lacked significant effects on net fluid transport. Similarly, prenalterol, a beta(1)-agonist, and metoprolol, a beta(1)-antagonist, had no significant effect on the net fluid transport. The beta(2)-agonist salbutamol significantly (P< 0.001) increased net fluid secretion, while the beta-antagonist propranolol significantly (P< 0.001) decreased net fluid secretion. Conclusion: Activation of alpha(2)-adrenoceptors and blockade of beta(2)-adrenoceptors significantly reduce net fluid secretion in small bowel obstruction. Results also demonstrate a continuous stimulatory effect on fluid secretion mediated by beta(2)-receptors and a continuous inhibitory effect mediated by alpha(2)-receptors.