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In mammalian kidney, dopamine produced in the proximal tubule (PT) acts as an autocrine/paracrine natriuretic hormone that inhibits salt and fluid reabsorption in the PT. In high-salt-treated animals, PT dopamine activity increases and inhibits reabsorption, leading to increased salt and fluid.delivery to the macula densa (MD) and subsequent natriuresis and diuresis. Regulated cyclooxygenase-2 (COX-2) in the MD represents another intrinsic system mediating renal salt and water homeostasis. Renal cortical COX-2 is inversely related to salt intake, and decreased extracellular NaC1 stimulates COX-2 expression in cultured MD/cortical thick ascending limb cells. The current study investigated interactions between renal dopamine and cortical COX-2 systems. In rats fed a control diet, the dopamine precursor L-dihydroxyphenylalanine (L-DOPA) or the DAI receptor agonist SKF-81297 suppressed cortical COX-2 expression. High salt suppressed cortical COX-2 expression, which was attenuated by inhibition of dopamine production with benserazide or the DA1 receptor antagonist, SCH-23390. In contrast, L-DOPA or the dopamine-metabolizing enzyme inhibitor entacapone suppressed low-salt-induced cortical COX-2 expression. Inhibition of PT reabsorption with the carbonic anhydrase inhibitor acetazolamide suppressed cortical COX-2 expression. In contrast, treatment with distally acting diuretics led to elevation of cortical COX-2. These results indicate that dopamine modulates renal cortical COX-2 expression by modifying PT reabsorption. prostaglandin synthase [G.sub.2]/[H.sub.2]; cortex; proximal tubule reabsorption

Zhang, Ming-Zhi, Su-wan Wang, Huifang Cheng, Yahua Zhang, James A. McKanna, and Raymond C. Harris. Regulation of renal cortical cyclooxygenase-2 in young rats. Am J Physiol Renal Physiol 285: F881-F888, 2003. First published July 8, 2003; 10.1152/ajprenal.00154. 2003.--Cyclooxygenase-2 (COX-2) is involved in kidney morphogenesis and is transiently elevated in the immature kidney. In adult rats, renal cortical COX-2 expression is tonically suppressed by mineralocorticoids (MC) and glucocorticoids (GC) and induced by chronic salt restriction. Young rats have low levels of GC and are in a state of relative volume depletion. The present study was designed to investigate the mechanisms underlying elevated cortical COX-2 expression in the immature kidney. Supplementation of GC or MC suppressed cortical COX-2 expression in suckling rats. GC suppression was significantly, but not completely, prevented by either an MC receptor antagonist or a GC receptor antagonist. MC suppression was completely prevented by a mineralocorticoid receptor antagonist. Salt supplementation suppressed cortical COX-2 expression in a dose- and time-dependent pattern in the suckling rats. Cortical COX-2 expression in the weanling rats was upregulated by a low-salt diet and downregulated by a high-salt diet. These results suggest that relative volume depletion and reduced GC levels are involved in elevated cortical COX-2 expression in the immature rodent kidney. prostaglandin synthase [G.sub.2]/[H.sub.2]; mineralocorticoid; glucocorticoid; salt supplementation

The renal inner medulla and its distal one-third, the papilla, are major sites of prostanoid synthesis involved in water and electrolyte homeostasis. These sites contain variable levels of cyclooxygenase (COX)-2, a key prostaglandin synthase enzyme that is sensitive to adrenal steroids. Immunoreactive renal medullary COX-2, restricted to interstitial cells in control adult rats, shows a gradient of intense staining at the tip of the papilla that gradually diminishes to undetectable levels in the proximal inner medulla. We used adrenalectomy (ADX) and steroid replacement to investigate the effects of steroids on papillary COX-2. Immunoblots demonstrate that papillary COX-2 was reduced by one-half after 2 wk ADX; glucocorticoid replacement ameliorated the decline but not to control levels. Mineralocorticoid (deoxycorticosterone acetate; DOCA) replacement stimulated papillary COX-2 more than fivefold over control; both the intensity of immunostaining and the numbers of COX-2-positive cells in the inner medulla increased. Similar stimulation of papillary COX-2 resulted from DOCA treatment of normal control rats, but the response was blunted in rats fed a low-salt diet and absent in Brattleboro rats. DOCA treatment of mouse renal medullary interstitial cells in culture had no effect, but increased tonicity of the culture medium with NaCl caused strong upregulation of COX-2. Urea, a permeant molecule, had no effect. Together, these results suggest that mineralocorticoids lead to upregulation of COX-2 in rat renal medulla by indirect pathways, probably involving induced electrolyte hypertonicity in the interstitial fluid. adrenal steroid; prostaglandin G/H synthase; papilla; deoxycorticosterone acetate

It is well known that nonselective, nonsteroidal anti-inflammatory drugs inhibit renal renin production. Our previous studies indicated that angiotensin-converting enzyme inhibitor (ACEI)-mediated renin increases were absent in rats treated with a cyclooxygenase (COX)-2-selective inhibitor and in COX-2 -/- mice. The current study examined further whether COX-1 is also involved in mediating ACEI-induced renin production. Because renin increases are mediated by cAMP, we also examined whether increased renin is mediated by the prostaglandin [E.sub.2] receptor E[P.sub.2] subtype, which is coupled to [G.sub.s] and increases cAMP. Therefore, we investigated if genetic deletion of COX-1 or E[P.sub.2] prevents increased ACEI-induced renin expression. Age- and gender-matched wild-type (+/+) and homozygous null mice (-/-) were administered captopril for 7 days, and plasma and renal renin levels and renal renin mRNA expression were measured. There were no significant differences in the basal level of renal renin activity from plasma or renal tissue in COX-1 +/+ and -/- mice. Captopril administration increased renin equally [plasma renin activity (PRA): +/+ 9.3 [+ or -] 2.2 vs. 50.1 [+ or -] 10.9; -/- 13.7 [+ or -] 1.5 vs. 43.9 [+ or -] 6.6 ng ANG I * [ml.sup.-1] * [h.sup.-1]; renal renin concentration: +/+ 11.8 [+ or -] 1.7 vs. 35.3 [+ or -] 3.9; -/- 13.0 [+ or -] 3.0 vs. 27.8 [+ or -] 2.7 ng ANG I * mg [protein.sup.-1] * [h.sup.-1]; n = 6; P < 0.05 with or without captopril]. ACEI also increased renin mRNA expression (+/+ 2.4 [+ or -] 0.2; -/- 2.1 [+ or -] 0.2 fold control; n = 6-10; P < 0.05). Captopril led to similar increases in E[P.sub.2] -/- compared with +/+. The COX-2 inhibitor SC-58236 blocked ACEI-induced elevation in renal renin concentration in E[P.sub.2] null mice (+/+ 24.7 [+ or -] 1.7 vs. 9.8 [+ or -] 0.4; -/- 21.1 [+ or -] 3.2 vs. 9.3 [+ or -] 0.4 ng ANG I * mg [protein.sup.-1] * [h.sup.-1]; n = 5) as well as in COX-1 -/- mice (SC-58236-treated PRA: +/+ 7.3 [+ or -] 0.6; -/- 8.0 [+ or -] 0.9 ng ANG I * [ml.sup.-1] * [h.sup.-1]; renal renin: +/+ 9.1 [+ or -] 0.9; -/- 9.6 [+ or -] 0.5 ng ANG I * mg [protein.sup.-1] * [h.sup.-1]; n = 6-7; P < 0.05 compared with no treatment). Immunohistochemical analysis of renin expression confirmed the above results. This study provides definitive evidence that metabolites of COX-2 rather than COX-1 mediate ACEI-induced renin increases. The persistent response in E[P.sub.2] nulls suggests involvement of prostaglandin [E.sub.2] receptor subtype 4 and/or prostacyclin receptor (IP). angiotensin-converting enzyme inhibitor; cyclooxygenase-2 -/-; prostaglandin [E.sub.2] receptor subtype 2

The expression of two isoforms of cyclooxygenase-2 (COX-2) was investigated after subtotal renal ablation in the rat. Results show that selective increases in renal cortical COX-2 mRNA and immunoreactive expression was observed. Aside from the dominant expression of COX-2 in the cortical thick ascending loop of Henle in the region of the macula densa, a detectable COX-2 immunoreactivity was also observed in some glomeruli with high expression in visceral epithelial cells and mesangial cells.

The inducible isoform of cyclooxygenase, COX-2 is the one constitutively expressed in the vas deferens of males. The expression of COX-2 in the vas deferens epithelium is not affected by vasectomy but is significantly inhibited by castration. The reaction catalyzed by cyclooxygenase is the limiting step in the synthesis of prostaglandins. The constitutive expression of one of its isoforms in the vas deferens is suggestive of its role in erectile mechanisms.

Kidney research shows that genetic expression of enzyme cyclooxygenase (COX-2) occurs under normal physiological conditions. Evidence suggests that COX-2 influences cell differentiation within the kidney. Experiments using Sprague-Dawley and Long-Evans rats are described. Northern analysis techniques are used to demonstrate COX-2 messenger ribonucleic acid levels.

Cheng, Hui-Fang, Jun-Ling Wang, Ming-Zhi Zhang, Su-Wan Wang, James. A. McKanna, and Raymond C. Harris. Genetic deletion of COX-2 prevents increased renin expression in response to ACE inhibition. Am J Physiol Renal Physiol 280: F449-F456, 2001.--Cyclooxygenase-2 (COX-2) is expressed in macula densa (MD) and surrounding cortical thick ascending limb of the loop of Henle (cTALH) and is involved in regulation of renin production. We and others have previously found that selective COX-2 inhibitors can inhibit renal renin production (Cheng HF, Wang JL, Zhang MZ, Miyazaki Y, Ichikawa I, McKanna JA, and Harris RC. J Clin Invest 103: 953-961, 1999; Harding P, Sigmon DH, Alfie ME, Huang PL, Fishman MC, Beierwaltes WH, and Carretero OA. Hypertension 29: 297-302, 1997; Traynor TR, Smart A, Briggs JP, and Schnermann J. Am J Physiol Renal Physiol 277: F706-F710, 1999; Wang JL, Cheng HF, and Harris RC. Hypertension 34: 96-101, 1999). In the present studies, we utilized mice with genetic deletions of the COX-2 gene in order to investigate further the potential role of COX-2 in mediation of the renin-angiotensin system (RAS). Age-matched wild-type (+/+), heterozygotes (+/-), and homozygous null mice (-/-) were administered the angiotensin-converting enzyme inhibitor (ACEI), captopril, for 7 days. ACEI failed to significantly increase plasma renin activity, renal renin mRNA expression, and renal renin activity in (-/-) mice. ACEI increased the number of cells expressing immunoreactive renin in the (+/+) mice both by inducing more juxtaglomerular cells to express immunoreactive renin and by recruiting additional renin-expressing cells in the more proximal afferent arteriole. In contrast, there was minimal recruitment of renin-expressing cells in the more proximal afferent arteriole of the -/- mice. In summary, these results indicate that ACEI-mediated increases in renal renin production were defective in COX-2 knockout (K/O) mice and provide further indication that MD COX-2 is an important mediator of the renin-angiotensin system. macula densa; juxtaglomerular; angiotensin-converting enzyme; cyclooxygenase-2

Nitric oxide regulates renal cortical cyclooxygenase-2 expression. Am J Physiol Renal Physiol 278: F122-F129, 2000.--We have previously shown that cyclooxygenase-2 (COX-2) is localized to the cortical thick ascending limb of the loop of Henle (cTALH)/macula densa of the rat kidney, and expression increases in response to low-salt diet and/or angiotensin-converting enzyme (ACE) inhibition. Because of the localization of neuronal nitric oxide synthase (nNOS) to macula densa and surrounding cTALH, the present study investigated the role of nitric oxide (NO) in the regulation of COX-2 expression. For in vivo studies, rats were fed a normal diet, low-salt diet or low-salt diet combined with the ACE inhibitor captopril. In each group, one-half of them were treated with the nNOS inhibitors 7-nitroinidazole (7-NI) or S-methyl-thiocitrulline. Both of these NOS inhibitors inhibited increases in COX-2 mRNA and immunoreactive protein in response to low salt and low salt+captopril. For in vitro studies, COX-2 expression was studied in primary cultures of rabbit cTALH cells immunodisssected with Tamm-Horsfall antibody. Basal COX-2 immunoreactivity expression was stimulated by S-nitroso-N-acetyl-penicillamine (SNAP), an NO donor, and intracellular cGMP concentration. The cultured cells expressed immunoreactive nNOS, and 7-NI inhibited basal COX-2 immunoreactivity expression, which could be partially overcome by cGMP. In summary, these studies indicate that NO is a mediator of increased renal cortical COX-2 expression seen in volume depletion and suggest important interactions between the NO and COX-2 systems in the regulation of arteriolar tone and the renin-angiotensin system by the macula densa. cyclooxygenase; nitric oxide synthase; renin; macula densa