Effect of histamine and histamine antagonists on portal blood pressure in patients with hepatosplenic schistosomiasis.

1 Histamine injection via the cannulated portal vein significantly raised the portal pressure in normal volunteers. This elevation was reversed by an H1-receptor blocker but not an H2-receptor blocker. When an H1-receptor blocker was injected first followed by histamine, no significant change in portal pressure was obtained. On the other hand, an H2-receptor blocker failed to antagonize the effect of histamine. 2 Histamine injection induced a non-significant increase in the portal pressure in patients with schistosomal portal hypertension, but when an H1-receptor blocker was injected a significant drop in the portal pressure was obtained. No similar effect was found after an H2-receptor blocker injection. 3 Angiographic study showed that histamine induced intrahepatic portal vasoconstriction in the normal controls. A similar change was obtained in the schistosomal group, particularly on the periportal neovascular formation. 4 In the light of the present study, it is suggested that histamine may contribute in part to the physiopathologic changes that lead to portal hypertension in hepatosplenic schistosomiasis. H1-receptor antagonists may have a role in the treatment of portal hypertension, particularly in bleeding varices.