Pressor Response to Infusion of Angiotensin into the Portal Vein of the Rat

Abstract

THE physiological importance of enzymes that degrade angiotensin in plasma and in tissue extracts has been questioned by Johnson and Ryan¹. They have shown that aqueous extracts of rabbit liver hydrolyse all the peptide bonds of Asp¹-Ile⁵-angiotensin II amide and Asp¹-Val⁵-angiotensin amide when incubated at pH 7.4 and 37° C. There is also evidence that the liver plays an active part in the destruction of angiotensin in vivo^2–5. Bumpus et al.² have shown that the liver of nephrectomized rats infused with tritiated angiotensin accumulates more labelled peptide fragments than do other organs. Chamberlain et al.³ found a smaller rise in the blood pressure of four dogs and two humans when Asp¹-Val⁵-angiotensin amide was infused into the portal venous system than when it was infused into the femoral vein. It is difficult to interpret their results because full details of the techniques used are lacking, and it is not clear how the doses were matched against each other. Hodge et al.⁴ have measured concentrations of angiotensin in circulating blood both before and after passage through various tissues in anaesthetized dogs. They find a marked decrease in the concentration of angiotensin after passage through the liver, as shown by the change in response of the isolated gut preparations used to assay angiotensin in their experiments.