The Metabolism of Angiotensin I I

• Several investigators have found that many patients with primary hypertension have more angiotensin II in their blood than normoten-sive subjects.1"8 Furthermore, many workers have implicated angiotensin II in the etiology of primary hypertension.2"17 Our own efforts were aimed at a critical examination of the metabolism of angiotensin II.4"0 We developed methods, therefore, to label this peptide with I131 in order to determine its distribution and degradation both in vivo and in vitro. Methods We employed tho Newerly modification of the Pressman and Eisen method to accomplish the iodination of nngiotensin II (val-5-angiotensin II and ileu-5-angiotensin II).18 '1B With this proce-dure, approximately 30 to 35 per cent of the I181 was bound to the peptide. Resin columns were employed to effect complete removal of the iodide and iodate remaining after iodination. The prep-arations employed in our studies contained less than 1.5 atoms of iodine per molecule of angio-tensin II. The angiotensin II-I181 preparations used in these studies had a specific activity of 50 to 250 me. per nig. at the time of use. Angiotensin II-I181 preparations containing an average of 0.1 to 1.5 iodine atom per molecule of angiotensin II produced the same hypertensive response in the dog as equivalent amounts of unlabeled angiotensin II when they were intravenously administered. Before the intravenous administration of angioten-sin II-I131 preparations to human subjects, the material was passed through a Seitz filter and cultured in order to assure sterility. The blood, urine and angiotensin II-I181 prep-arations were assayed for radioactivity in a 5 ml.-capacity well-type scintillation counter with a sen