Chronic dietary salt loading: resetting of tubuloglomerular feedback control of renal hemodynamics by an adrenal hormone.

Experiments were performed in chronically salt loaded rats (4 g% NaCl diet for 2 weeks) to determine whether the resetting of tubuloglomerular feedback (TGF) by a humoral inhibitor in tubular fluid is caused by a humoral factor from the adrenal glands. TGF response was assessed by measuring NGFR in the absence of loop of Henle perfusion and during perfusion at 40 nl/min with tubular fluid from normal or salt loaded rats and expressed as NGFR40/NGFR0. (1) Loop of Henle perfusion with tubular fluid from normal rats elicited a TGF response of 50.3% +/- 7.9% (mean +/- SEM) in normal rats and 57.2% +/- 7.9% in salt loaded rats. With tubular fluid from high salt rats, TGF response in normal rats was 97.4% +/- 6.3% and in salt loaded rats 98.0% +/- 1.6%. Participation of adrenal steroids in the inhibition is suggested by the following results: (2) Acute adrenalectomy (ADX) in high salt rats abolished the TGF inhibitory potency of high salt tubular fluid. TGF response in salt loaded rats with high salt tubular fluid from high salt ADX rats was 62.3% +/- 3.0%. Substitution of high salt ADX rats with matching adrenal venous blood from high salt rats restored TGF inhibition. (3) With cross over experiments the effect of heterologous adrenal venous blood substitution on TGF inhibitory activity was studied. The TGF response in high salt rats with high salt tubular fluid and tubular fluid from normal ADX rats substituted with adrenal venous blood collected from high salt rats was 88.9% +/- 5.5% and 91.7% +/- 6.0%.(ABSTRACT TRUNCATED AT 250 WORDS)