Role of nNOS in regulation of renal function in hypertensive Ren-2 transgenic rats

The present study was performed to evaluate the role of neuronal nitric oxide synthase (nNOS)-derived nitric oxide (NO) during the developmental phase of hypertension in transgenic rats harboring the mouse Ren-2 renin gene (TGR). The first aim of the present study was to examine nNOS mRNA expression in the renal cortex and to assess the renal functional responses to intrarenal nNOS inhibition by S-methyl-L-thiocitrulline (L-SMTC) in heterozygous TGR and in age-matched transgene-negative Hannover Sprague-Dawley rats (HanSD). The second aim was to evaluate the role of the renal sympathetic nerves in mediating the renal functional responses to intrarenal nNOS inhibition. Thus, we also evaluated the effects of intrarenal L-SMTC administration in acutely denervated TGR and HanSD. Expression of nNOS mRNA in the renal cortex was significantly increased in TGR compared with HanSD. Intrarenal administration of L-SMTC decreased the glomerular filtration rate (GFR), renal plasma flow (RPF) and sodium excretion and increased renal vascular resistance (RVR) in HanSD. In contrast, intrarenal inhibition of nNOS by L-SMTC did not alter GFR, RPF or RVR and elicited a marked increase in sodium excretion in TGR. This effect of intrarenal L-SMTC was not observed in acutely denervated TGR. These results suggest that during the developmental phase of hypertension TGR exhibit an impaired renal vascular responsiveness to nNOS derived NO or an impaired ability to release NO by nNOS despite enhanced expression of nNOS mRNA in the renal cortex. In addition, the data indicate that nNOS-derived NO increases tubular sodium reabsorption in TGR and that the renal nerves play an important modulatory role in this process.     

Chronic endothelin receptor blockade reduces end-organ damage independently of blood pressure effects in salt-loaded heterozygous Ren-2 transgenic rats

The present study was performed to evaluate the role of an interaction between the endothelin (ET) and the renin-angiotensin systems (RAS) in the development and maintenance of hypertension and in hypertension-associated end-organ damage in heterozygous male and female transgenic rats harboring the mouse Ren-2 renin gene (TGR). Twenty-eight days old heterozygous TGR and age-matched transgene-negative normotensive Hannover Sprague-Dawley rats (HanSD) were randomly assigned to groups with normal-salt (NS) or high-salt (HS) intake. Nonselective ET(A)/ET(B) receptor blockade was achieved with bosentan (100 mg.kg(-1).day(-1)). All male and female HanSD as well as heterozygous TGR on NS exhibited 100 % survival rate until 180 days of age (end of experiment). HS diet in heterozygous TGR induced a transition from benign to malignant phase hypertension. The survival rates in male and in female heterozygous TGR on the HS diet were 46 % and 80 %, respectively, and were significantly improved by administration of bosentan to 76 % and 97 %, respectively. Treatment with bosentan did not influence either the course of hypertension (measured by plethysmography in conscious animals) or the final levels of blood pressure (measured by a direct method in anesthetized rats) in any of the experimental groups of HanSD or TGR. Administration of bosentan in heterozygous TGR fed the HS diet markedly reduced proteinuria, glomerulosclerosis and attenuated the development of cardiac hypertrophy compared with untreated TGR. Our data show that the ET receptor blockade markedly improves the survival rate and ameliorates end-organ damage in heterozygous TGR exposed to HS diet. These findings indicate that the interaction between the RAS and ET systems plays an important role in the development of hypertension-associated end-organ damage in TGR exposed to salt-loading.     

Interactions between 11beta-hydroxysteroid dehydrogenase and COX-2 in kidney

The syndrome of apparent mineralocorticoid excess (SAME) is an autosomal recessive form of salt-sensitive hypertension caused by deficiency of the kidney type 2 11beta-hydroxysteroid dehydrogenase (11betaHSD2). In this disorder, cortisol is not inactivated by 11betaHSD2, occupies mineralocorticoid receptors (MRs), and causes excessive sodium retention and hypertension. In renal medulla, prostaglandins derived from cyclooxygenase-2 (COX-2) stimulate sodium and water excretion, and renal medullary COX-2 expression increases after mineralocorticoid administration. We investigated whether medullary COX-2 also increases in rats with 11betaHSD2 inhibition and examined its possible role in the development of hypertension. 11betaHSD2 inhibition increased medullary and decreased cortical COX-2 expression in adult rats and induced high blood pressure in high-salt-treated rats. COX-2 inhibition had no effect on blood pressure in control animals but further increased blood pressure in high-salt-treated rats with 11betaHSD2 inhibition. COX-1 inhibition had no effect on blood pressure in either control or experimental animals. 11betaHSD2 inhibition also led to medullary COX-2 increase and cortical COX-2 decrease in weaning rats, primarily through activation of MRs. In the suckling rats, medullary COX-2 expression was very low, consistent with a urinary concentrating defect. 11betaHSD2 inhibition had no effect on either cortical or medullary COX-2 expression in the suckling rats, consistent with low levels of circulating corticosterone in these animals. These data indicate that COX-2 plays a modulating role in the development of hypertension due to 11betaHSD2 deficiency and that 11betaHSD2 regulates renal COX-2 expression by preventing glucocorticoid access to MRs during postnatal development.     

Role of NO and COX pathways in mediation of adenosine A1 receptor-induced renal vasoconstriction

The mechanism of adenosine A1 receptor-induced intrarenal vasoconstriction is unclear; it depends on sodium intake and may be mediated by changing the intrarenal activity of the nitric oxide (NO) and/or cyclooxygenase (COX) pathway of arachidonic acid metabolism. The effects of 2-chloro-N(6)-cyclopentyl-adenosine (CCPA), a selective A1 receptor agonist, on renal hemodynamics were examined in anesthetized rats maintained on high sodium (HS) or low sodium (LS) diet. Total renal (i.e., cortical) blood flow (RBF) as well as superficial cortical (CBF), outer medullary (OMBF), and inner medullary (IMBF) flows were determined by laser-Doppler. In HS rats, suprarenal aortic infusions of 8-40 nmol/kg/hr CCPA decreased IMBF (15%) and other perfusion indices (22%-27%); in LS rats, IMBF increased 3% (insignificant) and other indices decreased 13%-24%. In LS rats, pretreatment with N-nitro-L-arginine methyl ester prevented the A1 receptor-mediated decrease in RBF and CBF but not OMBF; the response in IMBF was not altered. Pretreatment with indomethacin prevented the decreases in RBF, CBF, and OMBF and did not change the response of IMBF. Thus, within the cortex the vasoconstriction that follows A1 receptor activation results both from inhibition of NO synthesis and from stimulation of vasoconstrictor products of the COX pathway. In the outer medulla, the latter products seem exclusively responsible for CCPA-induced vasoconstriction. The observation that in LS rats IMBF was not affected by stimulation of adenosine A1 receptors suggests that limiting salt intake may help protect medullary perfusion against vasoconstrictor stimuli which have the potential to disturb long-term control of arterial pressure.     

Effect of high and low sodium intake on urinary aquaporin-2 excretion in healthy humans

The degree of water transport via aquaporin-2 (AQP2) water channels in renal collecting duct principal cells is reflected by the level of the urinary excretion of AQP2 (u-AQP2). In rats, the AQP2 expression varies with sodium intake. In humans, the effect of sodium intake on u-AQP2 and the underlying mechanisms have not previously been studied. We measured the effect of 4 days of high sodium (HS) intake (300 mmol sodium/day; 17.5 g salt/day) and 4 days of low sodium (LS) intake (30 mmol sodium/day; 1.8 g salt/day) on u-AQP2, fractional sodium excretion (FE(Na)), free water clearance (C(H2O)), urinary excretion of PGE(2) (u-PGE(2)) and cAMP (u-cAMP), and plasma concentrations of vasopressin (AVP), renin (PRC), ANG II, aldosterone (Aldo), atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP) in a randomized, crossover study of 21 healthy subjects, during 24-h urine collection and after hypertonic saline infusion. The 24-h urinary sodium excretion was significantly higher during HS intake (213 vs. 41 mmol/24 h). ANP and BNP were significantly lower and PRC, ANG II, and Aldo were significantly higher during LS intake. AVP, u-cAMP, and u-PGE(2) were similar during HS and LS intake, but u-AQP2 was significantly higher during HS intake. The increases in AVP and u-AQP2 in response to hypertonic saline infusion were similar during HS and LS intake. In conclusion, u-AQP2 was increased during HS intake, indicating that water transport via AQP2 was increased. The effect was mediated by an unknown AVP-independent mechanism.     

Urinary prostaglandin E excretion: Effect of chronic alterations in sodium intake and inhibition of prostaglandin synthesis in the rabbit

On the basis of acute experiments in animals, a role for prostaglandin E (PGE) in the regulation of urinary sodium excretion has been suggested. Limited information is available, however, concerning the possible role of PGE in chronic adjustments to sodium intake. These studies were designed to determine whether chronic changes in sodium balance would modify renal PGE excretion and whether partial inhibition of prostaglandin synthesis would after the ability of the kidney to adjust to an alteration in sodium intake. Thus, we measured sodium and PGE excretion in rabbits on chronic high and low salt diets before and after inhibition of prostaglandin synthesis with indomethacin or meclofenamate. Although the alterations in salt intake resulted in large changes in sodium excretion there was no significant change in urinary PGE excretion. After administration of either indomethacin or meclofenamate for several days there was a significant fall in PGE excretion, but no significant change in sodium excretion. These results suggest that in the rabbit 1) chronic changes in sodium excretion can occur without modifying PGE excretion (and presumably renal PGE synthesis) and 2) inhibition of PGE synthesis does not impair the kidney's ability to adjust to a chronic high or low sodium intake.     

Role of sodium balance on maintenance of blood pressure in the chronic phase of two-kidney, one-clip hypertension

Blood pressure and sodium balance have been studied after unclipping, nephrectomy and sham operation of ischemic kidney in the chronic phase (16 weeks) of two-kidney, one clip hypertension. In hypertensive rats the fractional excretion of sodium was 85.5 +/- 2.3% and blood pressure (BP) was significantly increased (187.1 +/- 4.5 mmHg, p less than 0.001). Removal of either the constricting clip or ischemic kidney induced a decrease of BP to normal level whereas sham operation did not produce any change. However, rats submitted to these three experimental manipulations showed, at 1, 2, 3 and 4 days, and at 3 weeks, similar changes in sodium excretion. In the groups with unclipping or nephrectomy of ischemic kidney, water intake was less and urine volume smaller than in the sham operated group. These results suggest that a positive sodium balance is not important to maintain hypertension at this stage and that changes in sodium balance, after both unclipping and nephrectomy of ischemic kidney, have no influence in BP normalization.     

Development of Inverse Circadian Blood Pressure Pattern in Transgenic Hypertensive Tgr(mREN2)27 Rats

TGR(mREN2)27 (TGR) rats are transgenic animals with an additional mouse renin gene, which leads to overactivity of the renin-angiotensin system. Adult TGR rats are characterized by fulminant hypertension, hypertensive end-organ damage, and an inverse circadian blood pressure pattern. To study the ontogenetic development of cardiovascular circadian rhythms, telemetric blood pressure transmitters were implanted in male Sprague-Dawley (SPRD, n = 5) and heterozygous, transgenic TGR rats before 5 weeks of age. The TGR received either drinking water or enalapril 10 mg/L in drinking water (n = 5 per group). Drug intake was measured throughout the study by computerized monitoring of drinking volume. Circadian patterns in blood pressure and heart rate were analyzed from 5 to 11 weeks of age. In the first week after transmitter implantation, blood pressure did not differ among SPRD, untreated, and enalapril-treated TGR rats. In parallel with the rise in blood pressure of untreated TGR rats, a continuous delay of the circadian acrophase (time of fitted blood pressure maximum) was observed, leading to a complete reversal of the rhythm in blood pressure at an age of 8 weeks. Enalapril reduced blood pressure at night, but was less effective during the day, presumably due to the drinking pattern of the animals, which ingested about 90% of their daily water intake during the nocturnal activity period. After discontinuation of treatment, blood pressure returned almost immediately to values found in untreated TGR rats. In conclusion, the inverse circadian blood pressure profile in TGR rats develops in parallel with the increase in blood pressure. Direct effects of the brain renin-angiotensin system may be involved in the disturbed circadian rhythmicity in TGR(mREN2)27 rats.     

Dietary sodium restriction and blood pressure response to sympathetic blockade in young versus adolescent spontaneously hypertensive rats

The effects of dietary sodium restriction on the maintenance of blood pressure (BP) by sympathetic tone were evaluated in young versus more mature spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Sympathetic activity was assessed by BP responses to alpha 1-receptor blockade (prazosin), central inhibition of sympathetic outflow (clonidine), and by ganglionic blockade (hexamethonium). On regular sodium intake, SHR showed elevated BP and increased BP responses to sympathetic blockade at both 10 and 16 weeks of age. Sodium restriction to 9 or 17 mumols Na+/g food prevented or blunted development of hypertension in SHR when started at 4 weeks of age but did not affect BP when started at 10 weeks of age. Sodium restriction initiated in young SHR also prevented development of increased BP responses to sympathetic blockade. However, sodium restriction in more mature SHR did not decrease the increased BP responses to sympathetic blockade. We conclude that prevention of development of sympathetic hyperactivity in young SHR represents a major mechanism in the antihypertensive effect of sodium restriction in young SHR.     

Enhanced food and water intake in renin transgenic rats.

In short term experiments angiotensin II (Ang II) is a potent stimulant of thirst, however it is not known whether prolonged activation of the renin-angiotensin system is associated with chronic alteration of water or food intake. Renin transgenic rats TGRmRen(2)27 (TGR) exhibit significant elevation of AngII in the brain regions involved in regulation of body fluid balance. The purpose of the present study was to find out whether TGR rats manifest also different water (WI) and food (FI) intake and renal excretory functions in comparison to their parent Sprague Dawley (SD) strain. To this end 24 h WI and FI as well as urine excretion (Vu) and urinary outputs of solutes (Cosm), sodium (UNaV) and potassium (UKV) were compared under baseline conditions in 16 TGR and 15 SD rats having free access to water and food. In 15 TGR and 17 SD rats effect of 24 h dehydration on water intake was investigated. Under baseline conditions TGR rats consumed significantly greater amount of food and water than SD rats. Vu, UNaV and UKV were not significantly different in both strains. Cumulative water intakes in SD and TGR rats subjected to 24 h dehydration did not differ. The results reveal that under baseline conditions TGR rats manifest greater food and water intakes than SD rats whereas stimulation of thirst by water deprivation is similar in both strains. The results suggest that the ingestive behavior may be chronically altered by upregulation of the renin-angiotensin system.     

Phorbol ester stimulates cyclooxygenase-2 expression and prostanoid production in cardiac myocytes

Phorbol-12-myristate- 13-acetate (PMA) has been shown to induce hypertrophy of cardiac myocytes. The prostaglandin endoperoxide H synthase isoform 2 (cyclooxygenase-2, COX-2) has been associated with enhanced growth and/or proliferation of several types of cells. Thus we studied whether PMA induces COX-2 and prostanoid products PGE(2) and PGF(2alpha) in neonatal ventricular myocytes and whether endogenous COX-2 products participate in their growth. In addition, we examined whether PMA affects interleukin-1beta (IL-1beta) stimulation of COX-2 and PGE(2) production. PMA (0.1 micromol/l) stimulated growth, as indicated by a 1.6-fold increase in [(3)H]leucine incorporation. PMA increased COX-2 protein levels 2. 8-fold, PGE(2) 3.7-fold, and PGF(2alpha) 2.9-fold. Inhibition of either p38 kinase or protein kinase C (PKC) prevented PMA-stimulated COX-2. Inhibition of COX-2 with either indomethacin or NS-398 had no effect on PMA-stimulated [(3)H]leucine incorporation. Exogenous administration of PGF(2alpha), but not PGE(2), stimulated protein synthesis. Treatment with IL-1beta (5 ng/ml) increased COX-2 protein levels 42-fold, whereas cotreatment with IL-1beta and PMA stimulated COX-2 protein only 32-fold. IL-1beta did not affect control or PMA-stimulated protein synthesis. These findings indicate that: 1) PMA, acting through PKC and p38 kinase, enhances COX-2 expression, but chronic treatment with PMA partially inhibits IL-1beta stimulation of COX-2; and 2) exogenous PGF(2alpha) is involved in neonatal ventricular myocyte growth but endogenous COX-2 products are not.     

Hypertension after bilateral kidney irradiation in young and adult rats

The mechanism of a rise in blood pressure after kidney irradiation is unclear but most likely of renal origin. We have investigated the role of the renin-angiotensin system and dietary salt restriction in the development of systolic hypertension after bilateral kidney irradiation in young and adult rats. Three to 12 months after a single X-ray dose of 7.5 or 12.5 Gy to both kidneys of young and adult rats, the systolic blood pressure (SBP) and plasma renin concentration (PRC) were measured regularly. A single X-ray dose of 12.5 Gy caused a moderate rise in SBP and a slight reduction in PRC in both young and adult rats. A dose of 7.5 Gy did not significantly alter the SBP or PRC during the follow-up period of 1 year. In a second experiment, the kidneys of young rats received an X-ray dose of 20 Gy. Subsequently, rats were kept on a standard diet (110 mmol sodium/kg) or a sodium-poor diet (10 mmol sodium/kg). On both diets, SBP started to rise rapidly 3 months after kidney irradiation. Sodium balance studies carried out at that time revealed an increased sodium retention in the irradiated rats compared to controls on the same diet. In rats on a low sodium intake, there was neither a delay nor an alleviation in the development of hypertension. Compared to controls, the PRC tended to be lower in irradiated rats up to 4 months after irradiation. Subsequently, malignant hypertension developed in all 20 Gy rats, resulting in pressure natriuresis, stimulating the renin-angiotensin system. Our findings indicated that hypertension after bilateral kidney irradiation was not primarily the result of an activation of the renin-angiotensin system. Although there were some indications that sodium retention played a role, dietary sodium restriction did not influence the development of hypertension.     

HO-1 and JAK-2/STAT-1 signals are involved in preferential inhibition of iNOS over COX-2 gene expression by newly synthesized tetrahydroisoquinoline alkaloid, CKD712, in cells activated with lipopolysacchride

We found that CKD712, an S enantiomer of YS49, strongly inhibited inducible nitric oxide synthase (iNOS) and NO induction but showed a weak inhibitory effect on cyclooxygenase-2 (COX-2) and PGE(2) induction in LPS-stimulated RAW 264.7 cells. We, therefore, investigated the molecular mechanism(s) responsible for this by using CKD712 in LPS-activated RAW264.7 cells. Treatment with either SP600125, a specific JNK inhibitor or TPCK, a NF-kappaB inhibitor, but neither ERK inhibitor PD98059 nor p38 inhibitor SB203580, significantly inhibited LPS-mediated iNOS and COX-2 induction. CKD712 inhibited NF-kappaB (p65) activity and translocation but failed to prevent JNK activation. However, AG490, a specific JAK-2/STAT-1 inhibitor, efficiently prevented LPS-mediated iNOS induction but not the induction of COX-2, and CKD712 completely blocked STAT-1 phosphorylation by LPS, suggesting that the NF-kappaB and JAK-2/STAT-1 pathways but not the JNK pathway are important for CKD712 action. Interestingly, CKD712 induced heme oxygenase 1 (HO-1) gene expression in LPS-treated cells. LPS-induced NF-kappaB and STAT-1 activation was partially prevented by HO-1 overexpression. Furthermore, HO-1 siRNA partly reversed not only the LPS-induced NF-kappaB activation and STAT-1 phosphorylation but also inhibition of these actions by CKD 712. Additionally, silencing HO-1 by siRNA prevented CKD712 from inhibiting iNOS expression but not COX-2. When examined plasma NO and PGE(2) levels and iNOS and COX-2 protein levels in lung tissues of mice injected with LPS (10 mg/kg), pretreatment with CKD712 greatly prevented NO and iNOS induction in a dose-dependent manner and slightly affected PGE(2) and COX-2 production as expected. Taken together, we conclude that inhibition of JAK-2/STAT-1 pathways by CKD 712 is critical for the differential inhibition of iNOS and COX-2 by LPS in vitro and in vivo where HO-1 induction also contributes to this by partially modulating JAK-2/STAT-1 pathways.     

COX-2 inhibition attenuates anorexia during systemic inflammation without impairing cytokine production

Anorexia and weight loss are frequent complications of acute and chronic infections and result from induction of cytokines, prostaglandins, and other inflammatory mediators that are critical for pathogen elimination. Selective attenuation of the hypophagic response to infection and maintenance of the production of factors essential for infection control would be a useful addition to antimicrobial therapy in the treatment of human disease. Here, we evaluate the relative contribution of cyclooxygenase (COX)-1- and COX-2-derived prostaglandins to anorexia and weight loss precipitated by systemic immune activation by lipopolysaccharide (LPS). Using COX isoform-selective pharmacological inhibitors and gene knockout mice, we found that COX-2 inhibition during LPS-induced inflammation results in preserved food intake and maintenance of body weight, whereas COX-1 inhibition results in augmented and prolonged weight loss. Regulation of neuropeptide Y, corticotropin-releasing hormone, leptin, and interleukin-6 does not change as a function of COX-2 inhibition after LPS administration. Our data implicate COX-2 inhibition as a therapeutic target to maintain nutritional status while still allowing a normal cytokine response during infection.     

Combination of direct renin inhibition with angiotensin type 1 receptor blockade improves aldosterone but does not improve kidney injury in the transgenic Ren2 rat

Enhanced renin-angiotensin-aldosterone system (RAAS) activation contributes to proteinuria and chronic kidney disease by increasing glomerular and tubulointerstitial oxidative stress, promotion of fibrosis. Renin activation is the rate limiting step in angiotensin (Ang II) and aldosterone generation, and recent work suggests direct renin inhibition improves proteinuria comparable to that seen with Ang type 1 receptor (AT(1)R) blockade. This is important as, even with contemporary use of AT(1)R blockade, the burden of kidney disease remains high. Thereby, we sought to determine if combination of direct renin inhibition with AT(1)R blockade in vivo, via greater attenuation of kidney oxidative stress, would attenuate glomerular and proximal tubule injury to a greater extent than either intervention alone. We utilized the transgenic Ren2 rat with increased tissue RAS activity and higher serum levels of aldosterone, which manifests hypertension and proteinuria. Ren2 rats were treated with renin inhibition (aliskiren), AT(1)R blockade (valsartan), the combination (aliskiren+valsartan), or vehicle for 21days. Compared to Sprague-Dawley controls, Ren2 rats displayed increased systolic pressure (SBP), circulating aldosterone, proteinuria and greater urine levels of the proximal tubule protein excretory marker beta-N-acetylglucosaminidase (β-NAG). These functional and biochemical alterations were accompanied by increases in kidney tissue NADPH oxidase subunit Rac1 and 3-nitrotyrosine (3-NT) content as well as fibronectin and collagen type III. These findings occurred in conjunction with reductions in the podocyte-specific protein podocin as well as the proximal tubule-specific megalin. Further, in transgenic animals there was increased tubulointerstitial fibrosis on light microscopy as well as ultrastructural findings of glomerular podocyte foot-process effacement and reduced tubular apical endosomal/lysosomal activity. Combination therapy led to greater reductions in SBP and serum aldosterone, but did not result in greater improvement in markers of glomerular and tubular injury (i.e. β-NAG) compared to either intervention alone. Further, combination therapy did not improve markers of oxidative stress and podocyte and proximal tubule integrity in this transgenic model of RAAS-mediated kidney damage despite greater reductions in serum aldosterone and BP levels.     

Prostacyclin protects against elevated blood pressure and cardiac fibrosis

Specific inhibitors of COX-2 have been associated with increased risk for cardiovascular complications. These agents reduce prostacyclin (PGI2) without affecting production of thromboxane (Tx) A2. While this abnormal pattern of eicosanoid generation has been implicated in the development of vascular disease associated with COX-2 inhibition, its role in the development of hypertension, the most common cardiovascular complication associated with COX-2 inhibition, is not known. We report here that mice lacking the receptor for PGI2 (IPKOs) develop salt-sensitive hypertension, cardiac hypertrophy, and severe cardiac fibrosis. Coincidental deletion of the TxA2 (TP) receptor does not prevent the development of hypertension, but cardiac hypertrophy is ameliorated and fibrosis is prevented in IPTP double knockouts (DKOs). Thus, deletion of the IP receptor removes a constraint revealing adverse cardiovascular consequences of TxA2. Our data suggest that adjuvant therapy that blocks unrestrained Tx actions might protect against end-organ damage without affecting blood pressure in patients taking COX-2 inhibitors.     

Hypertensinogenic factors and renal alpha-adrenoceptors in young SHR and WKY rats

The effects of high sodium intake (drinking 1% NaCl), DOCA and DOCA + 1%NaCl for 6 weeks on renal alpha 1- and alpha 2-adrenoceptors and on systolic blood pressure (SBP) were examined in young spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). On normal sodium intake, SHR rats had higher renal alpha 1 (p less than .001) and alpha 2-adrenoceptor densities (p less than .001) and SBP (p less than .001) than WKY rats. Although, WKY rats given either 1% NaCl, DOCA, and DOCA + 1% NaCl developed hypertension after 6 weeks of treatment, only 1% NaCl administration for the same period produced an increase in the alpha 1- and alpha 2-adrenoceptor densities when compared to the control (p less than .01 and p less than .001, respectively). In the SHR rats, to the contrary, ingestion of 1% NaCl and DOCA + 1% NaCl increased the already elevated alpha 2-adrenoceptor density (p less than .001) and SBP even more in this strain after 6 weeks of treatment. Equilibrium dissociation constants (KD), however, were similar for both classes of receptors in experimental and control rats. This study indicates that postweaning exposure of the WKY and SHR rats to a high salt treatment and DOCA can influence the renal alpha-adrenoceptor densities. Although the functional significance of the changes is unclear, it is reasonable to speculate that postweaning exposure to a hypertensinogenic stimuli such as a 1% NaCl and/or DOCA may ultimately interfere with the functional development of the kidney differently in rats genetically predisposed to hypertension (SHR) from normotensive (WKY) rats.     

Inhibition of both COX-1 and COX-2 is required for development of gastric damage in response to nonsteroidal antiinflammatory drugs.

We examined the gastric ulcerogenic property of selective COX-1 and/or COX-2 inhibitors in rats, and investigated whether COX-1 inhibition is by itself sufficient for induction of gastric damage. Animals fasted for 18 h were given various COX inhibitors p.o., either alone or in combination, and they were killed 8 h later. The nonselective COX inhibitors such as indomethacin, naproxen and dicrofenac inhibited PG production, increased gastric motility, and provoked severe gastric lesions. In contrast, the selective COX-2 inhibitor rofecoxib did not induce any damage in the stomach, with no effect on the mucosal PGE(2) contents and gastric motility. Likewise, the selective COX-1 inhibitor SC-560 also did not cause gastric damage, despite causing a significant decrease in PGE(2) contents. The combined administration of SC-560 and rofecoxib, however, provoked gross damage in the gastric mucosa, in a dose-dependent manner. SC-560 also caused a marked gastric hypermotility, whereas rofecoxib had no effect on basal gastric motor activity. On the other hand, the COX-2 mRNA was expressed in the stomach after administration of SC-560, while the normal gastric mucosa expressed only COX-1 mRNA but not COX-2 mRNA. These results suggest that the gastric ulcerogenic property of conventional NSAIDs is not accounted for solely by COX-1 inhibition and requires the inhibition of both COX-1 and COX-2. The inhibition of COX-1 up-regulates the COX-2 expression, and this may counteract the deleterious influences, such as gastric hypermotility and the subsequent events, due to a PG deficiency caused by COX-1 inhibition.     

Role of cyclooxygenase isoforms in prostacyclin biosynthesis and murine prehepatic portal hypertension

Portal hypertension (PHT) is a common complication of liver cirrhosis and significantly increases morbidity and mortality. Abrogation of PHT using NSAIDs has demonstrated that prostacyclin (PGI(2)), a direct downstream metabolic product of cyclooxygenase (COX) activity, is an important mediator in the development of experimental and clinical PHT. However, the role of COX isoforms in PGI(2) biosynthesis and PHT is not fully understood. Prehepatic PHT was induced by portal vein ligation (PVL) in wild-type, COX-1(-/-), and COX-2(-/-) mice treated with and without COX-2 (NS398) or COX-1 (SC560) inhibitors. Hemodynamic measurements and PGI(2) biosynthesis were determined 1-7 days after PVL or sham surgery. Gene deletion or pharmacological inhibition of COX-1 or COX-2 attenuated but did not ameliorate PGI(2) biosynthesis after PVL or prevent PHT. In contrast, treatment of COX-1(-/-) mice with NS398 or COX-2(-/-) mice with SC560 restricted PGI(2) biosynthesis and abrogated the development of PHT following PVL. In conclusion, either COX-1 or COX-2 can mediate elevated PGI(2) biosynthesis and the development of experimental prehepatic PHT. Consequently, PGI(2) rather then COX-selective drugs are indicated in the treatment of PHT. Identification of additional target sites downstream of COX may benefit the >27,000 patients whom die annually from cirrhosis in the United States alone.