Impaired potency for feedback regulation of glomerular filtration rate in DOCA escaped rats

The present experiments were performed to study the effect of chronic extracellular volume expansion on the magnitude of tubulo-glomerular feedback responses in the rat kidney. Extracellular volume expansion was achieved by giving isotonic saline as drinking water and by injecting DOCA in a dose of 2.5 mg/kg - day. When Ringer perfusion rate through the loop of Henle was elevated in control rats (receiving only saline as drinking water) stop flow pressure (SFP) fell by an average of 0.47 +/- 0.81 mm Hg (mean +/- S.D.) and 7.93 +/- 2.85 mm Hg at the flow rate steps of 0--15 nl/min and 15--40 nl/min respectively. SN-GFR was reduced by a mean of 1.3 +/- 0.97 nl/min (0--15 nl/min) and 10.3 +/- 2.45 nl/min (15--40 nl/min). In DOCA treated rats the mean reductions of SFP were 0.98 +/- 0.9 mmHg and 2.1 +/- 1.4 mmHg and of SN-GFR 0.06 +/- 1.8 nl/min and 1.94 +/- 2.3 nl/min. Thus, significantly smaller changes of both SFP and SN-GFR were found in DOCA treated animals when flow rate was elevated from 15--40 nl/min. Net loop NaCl absorption rates did not significantly differ between control and DOCA rats. Renin activity of 5 pooled microdissected glomeruli was 15.6 +/- 17.1 ng/hr-0.1 ml in control and 2.94 +/- 2.6 ng/hr-0.1 ml in DOCA treated rats (P less than 0.01). It is possible therefore that the reduced feedback reactivity in DOCA treated rats is related to the diminished juxtaglomerular renin activity.