Concentration of renin in the renal interstitium, as reflected in lymph.

The relationship between renin activity in renal venous plasma and in renal interstitial fluid, as reflected in the hilar lymph, was observed. Control measurements in 28 dogs demonstrated that renin levels in the hilar lymph were 3.5 +/-- (SEM) 0.4 times higher than in renal venous plasma and 6.1 +/- 1.0 times higher than in arterial plasma. Renin activity was increased to varying levels by raising ureteric pressure and by the administration of different doses of furosemide. Under all conditions, the changes in renin activity in renal venous plasma and in the interstitium, as reflected in the hilar lymph, were in parallel although often marked in the hilar lymph. Thus, the study shows that under conditions of increased renin release, the interstitial renin activity rises in consort with increases in arteriovenous plasma differences. This increase in interstitial renin activity occurred even under circumstances when renal blood flow is known to increase, thereby suggesting that angiotensin generated in the interstitium may have little effect on the cortical arteriolar caliber.