ACUTE STIMULATION OF RENIN SECRETION CHANGES THE MULTIPLE FORM PROFILE OF ACTIVE PLASMA-RENIN

Active renin is composed of multiple forms with variable isoelectric points. In this study, the relative proportions of five major active renin forms in human peripheral venous plasma were compared before and 2 h after stimulation of renin secretion with both converting enzyme inhibition (quinapril) and upright posture in five patients with essential hypertension. The five major active renin forms were separated by shallow gradient isoelectric focusing and quantitated by radioimmunoassay of generated angiotensin I. Plasma renin activity increased from 1.2 to 5.1 ng AI/mL/h (P < .05). This was accompanied by a significant increase in the proportions of the two most basic renin forms and a significant decrease in the proportion of the most acidic form in venous plasma. Although the mechanism cannot be determined from this study, the altered renin form profile observed could have resulted from preferential renal secretion and/or altered hepatic extraction of the more basic forms. An altered renin form profile in response to acute stimulation has important physiologic implications. Since the relatively basic renin forms are preferentially degraded they possess shorter half-lives. Additionally, the multiple forms of active renin may be functionally heterogenous. Thus, acute stimulation of renin secretion may result in circulating renin with a shorter duration of action and different functional effects than renin released under steady state conditions.