Histamine and histamine receptor antagonists in splanchnic compartments in schistosomal portal hypertension

The type and distribution of histamine receptors in the portal circulation were studied in patients with schistosomal hypertension. At laparotomy, the umbilical, left gastric, splenic, and superior mesenteric veins were cannulated. Blood samples were drawn from the systemic circulation and from each vein for histamine assay. Portal pressures were then estimated in each vein. One group of patients received local injections of pheniramine p-aminosalicylate (H1-antagonist) in the four cannulated veins simultaneously. A second group received cimetidine (H2-antagonist), and a third group received a mixture of both drugs. Reestimation of portal pressures indicated that all treatments produced a significant drop in pressure in the four compartments. The highest drop was in the splenic vein after the H1-antagonist and in the gastric vein after the H2-antagonist. The histamine level was somewhat higher in the splenic compartment. These results suggest that both H1- and H2-receptors are present in the four portal compartments, but their distribution may not be uniform.