Tonic inhibition of renin secretion by the 12 lipoxygenase pathway: Augmentation by high salt intake

Abstract

Recent evidence suggests that lipoxygenase (LO) metabolites inhibit renin production in vitro. However, the physiological significance of this effect has not been determined. This study examined the role of the LO pathway in the regulation of plasma renin concentration (PRC) in vivo. The acute administration of two structurally unrelated LO inhibitors, phenidone (30 and 60 mg/kg) and esculetin (60 mg/kg), resulted in suppression of platelet 12 hydroxyeicosatetraenoic acid (12HETE) production, reduction in systemic arterial pressure and n 2 to 3-fold increase in PRC. To determine whether the esculetin-induced increase in PRC was secondary to hypotension, esculetin was also administered to rats preinfused with a pressor dose of norepinephrine. In these acutely hypertensive rats, esculetin still induced a 2.9-fold increase in PRC, whereas blood pressure remained over 40 mm Hg above basal levels. Further, esculetin (10-6 M) increased renin release in renal slices from 150 ± 10 to 310 ± 20 ng/ml · h (P < 0.05) and this rise was entirely blocked in the presence of 12HETE (10-7 M; 130 ± 40 ng/ml · h). In rats placed on high salt intake, 12HETE concentration in renal slices from the outer cortex was considerably higher than in renal slices from salt- restricted rats (116.5 ± 15.7 vs. 65 ± 12 pg/mg protein; P < 0.05). Chronic administration of the LO inhibitor phenidone also resulted in an increase of PRC, which was independent of changes in blood pressure. On either high salt (3.15%) or low salt (0.05%) diet phenidone-treated rats had higher PRC levels than the respective control groups [high salt 9.7 ± 3.5 vs. 1.9 ± 1.4 ng/ml · h; P < 0.05; low salt 33.2 ± 5.3 vs. 19.4 ± 3.10 ng/ml · h; P < 0.05]. The finding that LO blockers are potent stimulators of PRC in vivo suggests the existence of a physiological tonic inhibition of renin secretion by LO products that is operative under a wide range of salt intake. High salt intake enhances this inhibitory tone by increasing renal cortical 12 LO activity and, in fact, normal suppression of PRC during high salt diet does not occur in LO-blocked animals. Thus, the LO pathway exerts a tonic inhibitory effect on renin release, which appears particularly important for renin suppression during high salt intake.