Gastro-oesophageal variceal haemorrhage is one of the most dreadful complications of
portal hypertension and can be controlled with
vasoconstrictors. Nevertheless, sympathetic tone abnormality and vascular hyporesponsiveness in
portal hypertension may impede the haemostatic effects of
vasoconstrictors.
Propranolol, a β-blocker binding the
G-protein-coupled
adrenoceptor, is a portal hypotensive agent. However, whether
propranolol influences the collateral vasoresponse is unknown.
Portal hypertension was induced by PVL (portal vein
ligation) in Sprague-Dawley rats. In an acute study with an in situ perfusion model, the collateral responsiveness to AVP (
arginine vasopressin) was evaluated with vehicle,
propranolol (10 μmol/l),
propranolol plus
suramin (100 μmol/l, a G(α) inhibitor) or
suramin pre-incubation. G(α)
mRNA expression in the
splenorenal shunt, the most prominent intra-abdominal collateral vessel, was measured. In the chronic study, rats received DW (distilled water) or
propranolol (10 mg x kg(-1) of
body weight x day(-1)) for 9 days. Then the concentration-response relationship of AVP and G(α)
mRNA expression were assessed.
Propranolol pre-incubation elevated the perfusion pressure changes of collaterals in response to AVP, which was inhibited by
suramin. The
splenorenal shunt G(αq) and G(α11)
mRNA expression were enhanced by
propranolol. The group treated with
propranolol plus
suramin had a down-regulation of G(α11) as compared with the
propranolol group. Chronic
propranolol treatment reduced mean arterial pressure, PP (portal pressure) and the perfusion pressure changes of collaterals to AVP. G(αs) expression was up-regulated. In conclusion,
propranolol pre-incubation enhanced the portal-systemic collateral AVP responsiveness in portal hypertensive rats, which was related to G(αq) and G(α11) up-regulation. In contrast, the attenuated AVP responsiveness by chronic
propranolol treatment was related to G(αs) up-regulation. The G(α) signalling pathway may be a therapeutic target to control variceal
bleeding and PP in
portal hypertension.