Effects of somatostatin and octreotide on portal-systemic collaterals in portal hypertensive rats

BACKGROUND/AIMS: Somatostatin and its long-acting analogue, octreotide, have been used to cease variceal bleeding with uncertain mechanisms. This study investigated whether somatostatin and octreotide have a direct vasoconstrictive effect on the portal-systemic collaterals of portal-hypertensive rats and potentiate the vasoconstriction induced by endothelin-1 in these vascular beds. METHODS: The vascular responses of collateral vessels to graded concentrations of somatostatin (10(-9)-10(-5) mol/l), octreotide (10(-10)-10(-6) mol/l), norepinephrine (10(-9)-10(-5) mol/l) and vehicle (Krebs solution) were evaluated in perfused collateral vascular beds of rats with portal hypertension induced by partial portal vein ligation. In addition, the perfusion pressure changes of collateral vessels to endothelin-1 (10(-8) mol/l) in the presence of vehicle(control), somatostatin (10(-6) mol/l) and octreotide (10(-6) mol/l) were tested. RESULTS: Compared with the vehicle group, norepinephrine significantly increased the perfusion pressure of collateral vessels at concentrations between 10(-7) and 10(-5) mol/l. In contrast, neither somatostatin nor octreotide significantly changed the perfusion pressure. Somatostatin and octreotide significantly enhanced the endothelin-1-induced vasoconstrictive effect on the collaterals. CONCLUSIONS: Somatostatin and octreotide exert no direct vasoconstrictive effect on the collateral vessels of portal hypertensive rats. In the presence of endothelin-1, somatostatin and octreotide exert a local vasoconstrictive effect on these vascular beds.