Changes in activity of the renin-angiotensin system of the rat by induction of acute inflammation.

Angiotensinogen is the precursor of biologically active peptide angiotensin II and its hepatic synthesis is increased by the induction of acute inflammation. Studies were carried out to know whether the rise in plasma angiotensinogen is actually involved in the activity of the renin-angiotensin system during acute inflammation. The plasma level of angiotensinogen in rats was increased to 2.5 times the normal level 16 h after the induction of acute inflammation by administration of lipopolysaccharide (LPS). The plasma renin concentration (PRC) was decreased to about 40% of the normal level concomitantly with a reduction of plasma renin activity (PRA) at 4 h after LPS administration. In contrast, 16 h after LPS injection, when plasma angiotensinogen showed a high level and PRC had recovered to the normal range, PRA was increased to 1.7 times the normal level. These results indicate that acute inflammation induced by LPS causes a biphasic change in the generation of angiotensin I, i.e., an early decrease depending upon the reduction of PRC and later increase depending upon elevation of the angiotensinogen concentration.