This study evaluated the role of
PPARalpha in renal function and whether
PPARalpha knockout (KO) mice are hypertensive or
salt-sensitive. We hypothesize that
PPARalpha modulation of ion transport defines the capacity for
sodium excretion (U(Na)V).
PPARalpha KO and wild-type (WT) mice were placed on a normal
salt (NS, 0.5% NaCl) or high
salt (8% NaCl, HS) diet for 28 days and mean arterial blood pressure (MABP) and heart rate (HR) determined. In a group of anesthetized animals on NS diet, pressure natriuresis (P/N) was determined and in another group, acute
sodium load (
0.9% NaCl) was administered and U(Na)V compared in mice pretreated with
amiloride (200 microg/kg) or
hydrochlorothiazide (3 mg/kg), in vivo measurements of
sodium hydrogen exchanger or
Na-Cl-cotransporter activity, respectively. MABP and HR were similar in
PPARalpha KO and WT mice placed on a NS diet (116+/-6 mmHg, 587+/-40 beats/min, KO; 116+/-4 mmHg, 551+/-20 beats/min, WT). HS diet increased MABP to a greater extent in KO mice (Delta = 29+/-3 vs 14+/-3 mmHg, p<0.05) as did
proteinuria (8- vs 2.5-fold, p<0.05). P/N was blunted in untreated KO mice. In response to an acute NaCl-load, U(Na)V was faster in
PPARalpha KO mice (4.31+/-1.11 vs 0.77+/-0.31 micromol, p<0.05). However, U(Na)V was unchanged in
hydrochlorothiazide-treated KO mice but increased 6.9-fold in WT mice. Similarly, U(Na)V was less in
amiloride-treated KO mice (3.4- vs 15.5-fold). These data suggest that
PPARalpha participates in pressure natriuresis and affects Na transport via
amiloride- and
thiazide-sensitive mechanisms. Thus, despite defective
fatty acid oxidation,
PPARalpha null mice are not hypertensive but develop
salt-sensitive
hypertension.