Showing papers by "Suzanne Oparil published in 1970"

Role of Renin in Acute Postural Homeostasis

Abstract: Plasma renin activity has been measured by radioimmunoassay at frequent intervals after passive upright tilting and correlated with pulse and blood pressure in normotensive man. In the normal response to upright posture, renin activity in both peripheral and renal veins increases consistently within a few minutes. The renin rise lags behind the increase in pulse rate and diastolic blood pressure. Renin activity falls to base-line level soon after return to the horizontal position. In the 25% of normal subjects who develop vasovagal syncope after upright tilting, the increase in renin activity is smaller in magnitude and duration than in the normal response. Renin levels fall just before syncope appears and rise sharply after return to the horizontal position. Anephric patients are able to effect adequate postural adjustments even in the absence of renin activity. This study indicates that the renin angiotensin system participates in the acute response to postural change in normal man and that it functions abnormally in vasovagal syncope.

In-Vivo and In-Vitro Conversion of Angiotensin I to Angiotensin II in Dog Blood

Abstract: The conversion of angiotensin I to angiotensin II was studied in vivo in the intact anesthetized dog and in vitro in whole blood and plasma treated with various anticoagulants by fractionation of radioactively labeled peptides and by radioimmunoassay. After injection of angiotensin I into the pulmonary artery at 10,000 times the physiologic level, approximately 50% of the injected material was recovered in the aorta. Fifty three percent of the material recovered had been converted to angiotensin II, as measured both by peptide release and by radioimmunoassay. Following injection of 1000 to 10,000 times physiologic levels of angiotensin I into the renal artery, 7 to 10% of the immunoreactive material in the venous effluent after a single circulation time was angiotensin II. There was no evidence of conversion in the liver or hindlimb. Conversion in vitro was far slower than in vivo, the half-life in fresh blood being 3 minutes, with longer times observed in anticoagulated plasmas. The major metabolite of in-vivo conversion was leucine, of in-vitro conversion, histidyl leucine. These observations indicate that the major site of conversion of angiotensin I to angiotensin II is in the pulmonary capillary bed. The kidnev may participate as a secondary site. Conversion in plasma probably plays no important physiologic role. The mechanism of organ and plasma conversion may differ, as indicated by the different metabolites.