Background: Angiotensin II (ATII) has been suggested to contribute to shock-induced dysfunction of the gastric circulation.
Aim: To substantiate this conjecture, the effects on gastric mucosal haemodynamics and the hyperaemic response to acid back-diffusion of ATII and the angiotensin AT1 receptor antagonist, telmisartan, were examined in normal rats and in animals subjected to haemorrhage.
Methods: Gastric mucosal blood flow in phenobarbital-anaesthetized rats was recorded with the hydrogen clearance technique, and acid back-diffusion was induced by perfusing the stomach with ethanol (25%) in HCl (0.05 M).
Results: Intravenous infusion of ATII (0.3-10 nmol/min/kg) led to dose-dependent hypertension and a reduction of blood flow and vascular conductance in the gastric mucosa. The gastric hyperaemia caused by acid back-diffusion was attenuated by ATII (1 nmol/min/kg). These effects of ATII were antagonized by intravenous injection of telmisartan (1-10 mg/kg) which per se caused hypotension and dilated the gastric mucosal vasculature, but did not modify the gastric mucosal hyperaemia evoked by acid back-diffusion. Hypotension induced by haemorrhage (1.3 mL blood per 100 g body weight) failed to alter the hyperaemia due to acid back-diffusion, but caused gastric mucosal vasoconstriction, an effect that was left unaffected by telmisartan.
Conclusions: ATII constricts the rat gastric microvasculature via an action involving AT1 receptors. The effects of telmisartan indicate that endogenous ATII contributes to the homeostatic regulation of gastric vascular tone but does not compromise the ability of the gastric microvasculature to react to influxing acid. These results negate the concept that ATII contributes to the gastric vascular perturbances in haemorrhagic shock.