Radioimmunoassay of unprocessed sheep blood extracts to follow angiotensin metabolism

E. C. Osborn, J. C. Mackenzie, G. V. Rigby, A. Wilton and P. L. Sugden The acceptability of radioimmunoassay to determine the levels of compounds antigenic to anti-angiotensin antibodies, in unprocessed methanolic blood extracts, was established for sheep blood. This approach was used to follow the clearance of antigenic compounds after administration of angiotensins I and II and fragments of angiotensin II in anesthetized sheep. The organs supplied by the systemic circulation and also the lungs effectively removed angiotensin I, but the removal of octapeptide occurred only in the peripheral tissues. The blood concentrations of compounds reacting with the anti-angiotensin II antibody always increased with passage of angiotensin I through the pulmonary circulation but not with passage of angiotensin II. The results indicate that factors other than efficiency of removal by the tissue is important in establishing blood levels. The sites of administration and of sampling were shown to be important in relation to ratios of the concentrations of antigenic material. There was a similar uptake of both hormones in the kidney; the relative inability of angiotensin I to reduce renal blood flow, therefore, does not result from a failure of uptake.