Abstract-The platelet-type 12-lipoxygenase (12-LO) catalyzes the transformation of arachidonic acid into 12-hydroperoxyeicosatetraenoic acid [12-(S)HPETE], which is reduced to 12-hydroxyeicosatetraenoic acid [12-(S)HETE]. These metabolites exhibit a variety of biological activities such as mediation of angiotensin II-induced intracellular calcium transients in cultured rat vascular smooth muscle cells. It has recently been reported that platelet 12(S)-HETE production is enhanced in the spontaneously hypertensive rat. The pronounced hypotensive effect of LO inhibition in SHR suggests that LO activity may play a role in this form of hypertension. The aim of this study was to determine the basal and thrombin-induced platelet 12(S)-HETE production and the urinary 12(S)-HETE excretion in essential hypertension. We studied 19 patients with this disease (57Ϯ2 years of age) and 9 normotensive control subjects (48Ϯ5 years of age) (Pϭ0.074). 12(S)-HETE was measured in Sep-Pack-extracted samples with specific ELISA and high-performance liquid chromatography. The platelet basal level of 12(S)-HETE was significantly higher in patients than in control subjects (3.56Ϯ1.22 versus 0.64Ϯ0.13 ng/10 6 platelets, PϽ0.025). In contrast, there were no differences in thrombin-stimulated (1 U/mL) 12(S)-HETE generation: 7.66Ϯ2.14 in patients versus 4.87Ϯ1.46 in control subjects (Pϭ0.61). Platelet 12-LO protein levels, measured by Western blotting with a polyclonal antibody, were higher in the patients than in the control subjects. The urinary excretion of 12(S)-HETE was higher in patients than in control subjects: 36.8Ϯ7.24 versus 17.1Ϯ3.14 ng/mg creatinine (PϽ0.01). These results indicate that 12(S)-HETE levels and 12-LO protein are increased in patients with essential hypertension, suggesting a role for this metabolite in human hypertension. (Hypertension. 2001;37:334-338.)

Aldosterone classically modulates Na transport in tight epithelia such as the renal collecting duct (CD) through the transcellular route, but it is not known whether the hormone could also affect paracellular permeability. Such permeability is controlled by tight junctions (TJ) that form a size- and charge-selective barrier. Among TJ proteins, claudin-4 has been highlighted as a key element to control paracellular charge selectivity. In RCCD2 CD cells grown on filters, we have identified novel early aldosterone effects on TJ. Endogenous claudin-4 abundance and cellular localization were unaltered by aldosterone. However, the hormone promoted rapid (within 15-20 min) and transient phosphorylation of endogenous claudin-4 on threonine residues, without affecting tyrosine or serine; this event was fully developed at 10 nM aldosterone and appeared specific for aldosterone (because it is not observed after dexamethasone treatment and it depends on mineralocorticoid receptor occupancy). Within the same delay, aldosterone also promoted an increased apical-to-basal passage of 125I (a substitute for 36Cl), whereas 22Na passage was unaffected; paracellular permeability to [3H]mannitol was also reduced. Later on (45 min), a fall in transepithelial resistance was observed. These data indicate that aldosterone modulates TJ properties in renal epithelial cells.

The mineralocorticoid receptor (MR) is a major regulator of renal sodium reabsorption and body fluid homeostasis. However, little is known about glucocorticoid receptor (GR)-dependent renal effects. Glucocorticoids may activate both receptors, so it is difficult to distinguish between MR- and GR-mediated effects in vivo. To overcome this complexity, we used a transgenic mouse model allowing conditional GR overexpression (doxycycline inducible TetON system, Hoxb7 promoter) in the renal collecting duct (CD) to identify GR-regulated genes involved in sodium transport in the CD. In microdissected cortical CD, induction of GR expression led (after 2 d of doxycycline) to increased alpha-epithelial sodium channel and glucocorticoid-induced leucine zipper and decreased abundance of with-no-lysine kinase 4 transcripts, without modification of Na,K-ATPase, serum- and glucocorticoid-kinase-1, or MR expression. No changes occurred in the upstream distal and connecting tubules [distal convoluted tubule (DCT), connecting tubule (CNT)]. Sodium excretion was unaltered, but the urinary aldosterone concentration was reduced, suggesting compensation of transitory extracellular volume expansion that subsequently disappeared. At steady state, i.e. after 15 d of doxycycline administration, transcript abundance remained altered in the CD, whereas mirror changes appeared in the DCT and CNT. Plasma aldosterone or glucocorticoids and blood pressure were all unaffected. These experiments show that: 1) GR, in addition to MR, controls epithelial sodium channel- and glucocorticoid-induced leucine zipper expression in vivo in the CD; 2) with-no-lysine kinase 4 is negatively controlled by GR; and 3) the DCT and CNT compensate for these alterations to maintain normal sodium reabsorption and blood pressure. These results suggest that enhanced GR expression may contribute to enhanced sodium retention in some pathological situations.