Noradrenaline as a possible mediator of the actions of angiotensin on fluid transport by rat jejunum in vivo.

1. Net fluid absorption and transmural potential difference were measured in the rat jejunum in vivo.2. Increased rates of net fluid transport were observed following infusions of angiotensin or noradrenaline. There was a small, but significant, fall in transmural p.d. associated with noradrenaline but not with angiotensin infusions.3. The alpha-adrenergic antagonists phentolamine and dihydroergotamine abolished both the angiotensin and the noradrenaline stimulations of transport and the noradrenaline-induced fall in p.d., whereas the beta-adrenergic antagonist propranolol did not significantly affect these responses.4. Phentolamine did not alter the rise in p.d. following administration of the cholinergic agonist pilocarpine.5. The protein synthesis inhibitor cycloheximide abolished both the angiotensin and the noradrenaline-induced stimulation of fluid transport.6. Neither angiotensin nor noradrenaline significantly altered jejunal cyclic AMP levels.7. Bilateral nephrectomy had no apparent effect upon the increase in fluid transport following noradrenaline infusions.8. The noradrenaline-induced stimulation of transport was unaffected, and the fall in p.d. potentiated in rats pre-treated with reserpine, but a marked inhibition of transport was observed following angiotensin infusions.9. The results are consistent with the view that noradrenaline may mediate the actions of angiotensin upon intestinal fluid absorption in the rat.