MODIFICATION OF RENIN REACTIVITY BY LIPIDS EXTRACTED FROM NORMAL, HYPERTENSIVE, AND UREMIC PLASMA

Plasma renin reactivity (PRR), the in vitro rate of angiotensin generation after addition of renin, is greater in plasma of hypertensive patients and uremic patients than in plasma of normotensive control subjects. To determine if this difference is due to different substrate reactivities, substrate was denatured and replaced with homologous substrate. After a 180 min incubation, PRR in normal plasma (73 ng/ml .+-. 5 SE) was less (P < 0.01) than that in hypertensive (112 ng/ml .+-. 15 SE) or uremic (123 ng/ml .+-. 39 SE) plasma. To determine if uremic plasma lacks a renin inhibitor, buffer or plasma was added to renin-renin substrate. Less angiotensin was generated (P < 0.05) with normal (72 ng/ml .+-. 4 SE) and uremic (88 ng/ml .+-. 4 SE) plasma during 30 min than with buffer (107 ng/ml .+-. 4 SE). After 180 min, less angiotensin was generated with normal (P < 0.05) but not uremic plasma (P > 0.6), than with buffer. In vitro angiotensin generation was inhibited by lipids extracted from normal plasma. Lipids were separated into acetone soluble (neutral lipids) and acetone insoluble (phospholipid) fractions. Acetone soluble lipids, extracted from normal plasma, competitively inhibit renin; renin was not inhibited by acetone insoluble lipids. Acetone soluble lipids extracted from uremic plasma inhibited PRR to a lesser extent than lipids from either normal plasma or hypertensive plasma (P < 0.01). Increased PRR in uremic plasma may be related to the deficiency of a circulating acetone soluble renin inhibiting factor.