Endoscopic demonstration that vasopressin but not propranolol produces gastric mucosal ischemia in dogs with portal hypertension.

Endoscopic reflectance spectrophotometry was used to compare the effect of vasopressin and propranolol on gastric mucosal hemodynamics in dogs with surgically induced esophageal varices and prehepatic portal hypertension. Reflectance spectrophotometry provides indices of mucosal hemoglobin concentration (IHB) and oxygen saturation (ISO2). Hyperemia (increased IHB, normal ISO2), ischemia without congestion (decreased IHB, decreased ISO2), and ischemia with congestion (increased IHB, decreased ISO2) are accompanied by characteristic patterns of IHB and ISO2. Under anesthesia, measurements were obtained on separate days from the gastric corpus mucosa of eight dogs before and 2 to 10 min after either 1 to 5 units of intravenous vasopressin or 1 mg of propranolol. Results revealed that vasopressin (in doses that significantly reduced variceal and portal venous pressure in this animal model) produced a reduction in both IHB and ISO2, indicating gastric mucosal ischemia secondary to splanchnic vasoconstriction. On the other hand, propranolol in a dose that significantly reduced pulse rate by 27 +/- 2% had no effect on IHB or ISO2, suggesting that this dose of propranolol has no direct vasoactive effect on the gastric (splanchnic) circulation.