Role of cyclooxygenase-2-derived metabolites and nitric oxide in regulating renal function

Renal Effects of Cyclooxygenase Inhibition When Nitric Oxide Synthesis Is Reduced and Angiotensin II Levels Are Enhanced

The involvement of both cyclooxygenase (COX) isoforms in regulating renal function is well known but their interactions with other regulatory mechanisms, such as angiotensin II (Ang II) and nitric oxide (NO), are not well defined. This study has evaluated the relative contribution of both COX isoforms in regulating renal function when NO synthesis is reduced with and without a simultaneous increment in Ang II levels. The renal responses to a nonselective (meclofenamate) or a selective COX2 (nimesulide) inhibitor were examined in dogs pretreated with L-NAME with or without an intrarenal Ang II infusion. Meclofenamate induced a greater (P < 0.05) renal vasoconstriction than nimesulide in dogs pretreated with L-NAME. This vasoconstriction seems to be Ang II-dependent because it was reduced (P < 0.05) by captopril administration. Meclofenamate also induced a greater (P < 0.05) renal vasoconstriction than that elicited by nimesulide in dogs with reduced NO synthesis and elevated Ang II levels. The renal vasoconstriction induced by nimesulide but not that elicited by meclofenamate in dogs pretreated with L-NAME and Ang II, decreased (P < 0.05) during an extracellular volume expansion. These results demonstrate that the nonselective COX inhibition induces a greater renal vasoconstriction than that elicited by the selective COX2 inhibition when NO synthesis is reduced, and when NO synthesis is reduced and Ang II levels are elevated.

Influence of genetic background and gender on hypertension and renal failure in COX-2-deficient mice

The present study was undertaken to determine whether the severity of renal failure or hypertension in homozygous cyclooxygenase (COX)-2-deficient (COX-2-/-) mice affected by genetic background or gender. COX-2 deletion was introduced into three congenic genetic backgrounds, 129/Sv (129/COX-2-/-), C57/BL6 (C57/COX-2-/-), and BALB/c (BALB/COX-2-/-), by backcrossing the original mixed-background knockout mice with the respective inbred strains for 9 or 10 generations. Evaluation of the severity of hypertension and renal failure was performed in knockout and wild-type mice at the age of 2.5-3.5 mo. Blood pressure measured by tail-cuff plethysmography was significantly elevated in the male 129/COX-2-/- mice (165.8 +/- 9.2 vs. 116 +/- 5.1 mmHg, P < 0.05), and to a much lesser extent in the female 129/COX-2-/- mice (127.4 +/- 3.3 vs. 102.4 +/- 3.3), whereas it was unchanged in the C57- or BALB/COX-2-/- mice regardless of gender. Urinary excretion of albumin, determined by EIA, was remarkably increased in the 129/COX-2-/- (16.4 +/- 4.1 vs. 0.16 +/- 0.043 mg albumin/mg creatinine, P < 0.001), and to a lesser extent in the male C57/COX-2-/- mice (0.595 +/- 0.416 vs. 0.068 +/- 0.019). Albumin excretion was not elevated in the male BALB/COX-2-/- or in female COX-2-/- mice on any of the three genetic backgrounds. Histological analysis showed abundant protein casts, dilated tubules, and infiltration of inflammatory cells in the male 129/COX-2-/- mice, but not in COX-2-/- mice in other strains or gender. However, the presence of small glomeruli in the nephrogenic zone was observed in all strains of COX-2 knockout mice, regardless of genetic background and gender. Therefore, we conclude that the severity of hypertension and renal failure in COX-2-deficient mice is influenced by genetic background and gender, whereas the incomplete maturation of outer cortical nephrons appears to be independent of genetic background effects.

Nitric oxide synthase-inhibition hypertension is associated with altered endothelial cyclooxygenase function

We reported previously that endothelium-intact superior mesenteric arteries (SMA) from Nω-nitro-l-arginine (l-NNA)-treated hypertensive rats (LHR) contract more to norepinephrine (NE) than SMA from control rats. Others have shown that nitric oxide (NO) synthase (NOS) inhibition increases cyclooxygenase (COX) function and expression. We hypothesized that augmented vascular sensitivity to NE in LHR arteries is caused by decreased NOS-induced dilation and increased COX product-induced constriction. We observed that the EC50 for NE is lower in LHR SMA compared with control SMA (control −6.37 ± 0.04, LHR −7.89 ± 0.09 log mol/l; P < 0.05). Endothelium removal lowered the EC50 (control −7.95 ± 0.11, LHR −8.44 ± 0.13 log mol/l; P < 0.05) and increased maximum tension in control (control 1,036 ± 38 vs. 893 ± 21 mg; P < 0.05) but not LHR (928 ± 30 vs. 1,066 ± 31 mg) SMA. Thus augmented NE sensitivity in LHR SMA depends largely on decreased endothelial dilation. NOS inhibition (l-NNA, 10−4 mol/l) increased maximum tension and EC50 in control arteries but not in LHR arteries. In contrast, COX inhibition decreased maximum tension in control arteries, suggesting that COX products augment contraction. Indomethacin did not affect NE-induced contraction in l-NNA-treated or denuded arteries. In control SMA loaded with the fluorescent NO indicator 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate, indomethacin increased and l-NNA decreased NO release. Therefore, COX products appear to inhibit NO production to augment NE-induced contraction. With chronic NOS inhibition, this modulating influence is greatly diminished. Thus, in NOS-inhibition hypertension, decreased activity of both COX and NOS pathways profoundly disrupts endothelial modulation of contraction.

Role of cyclooxygenase-2 in the control of renal haemodynamics and excretory function

AIM

The available evidence supporting the importance of cyclooxygenase-2 (COX-2) in the regulation of renal haemodynamics and excretory function is summarized. Cyclooxygenase-2-derived metabolites play a very important role in regulating renal haemodynamics when sodium intake is low whereas it plays a minor role in the control of cortical blood flow when sodium intake is normal or elevated. The importance of COX-2 in the regulation of renal haemodynamics seems to be dependent on the endogenous production of other vasoactive products such as nitric oxide (NO) or noradrenaline. The activation of COX-2 in response to a decrease in NO may represent a mechanism aimed at defending the renal vasculature in the face of a decrease in NO levels.

CONCLUSION

Contrary to the important role of COX-2 in the long-term regulation of renal haemodynamics, the metabolites derived from COX-2 seem to be only involved in the acute regulation of renal excretory function.

Role of nitric oxide and cyclooxygenase-2 in regulating the renal hemodynamic response to norepinephrine

We have reported that the renal hemodynamic effects of norepinephrine (NE) are modulated by cyclooxygenase-2 (COX-2)-derived metabolites. Our main objective was to examine whether there is an interaction between nitric oxide (NO) and COX-2 in modulating the renal hemodynamic effects of NE. NE was infused at three doses to anesthetized dogs pretreated with vehicle (n = 8), a selective COX-2 inhibitor (nimesulide) (n = 6), an NO synthesis inhibitor [NG-nitro-l-arginine methyl ester; l-NAME] (n = 8), or with nimesulide and l-NAME (n = 5). During NE infusion, PGE2 excretion increased (125%) in the control group and did not change in the l-NAME-treated dogs. The simultaneous inhibition of NO and COX-2 potentiated to a greater extent the NE-induced renal vasoconstriction than inhibition of either NO or COX-2. The NE-induced renal vasoconstriction during NO and COX-2 inhibition was reduced (P < 0.05) by infusing an AT1 receptor antagonist (n = 6). These results suggest that there is an interaction between NO and COX-2 in protecting the renal vasculature from the NE effects and that angiotensin II partly mediates the NE-induced renal vasoconstriction when NO synthesis and COX-2 activity are reduced.

Cyclo-oxygenase-2 inhibition increases blood pressure in rats

1 It is known that nonselective cyclo-oxygenase (COX) inhibitors have small but significant effects on blood pressure (BP), most notably in hypertensive patients on antihypertensive medication. Whether selective COX-2 inhibitors also interfere with BP regulation is not well understood. Therefore, we aimed to examine the effect of chronic treatment with a selective COX-2 inhibitor (rofecoxib) on systolic blood pressure (sBP) in normotensive Wistar-Kyoto rats (WKY) and on the developmental changes of sBP in young spontaneously hypertensive rats (SHR). In addition, we investigated a possible influence of salt intake on the effects of COX-2 inhibition on BP in these two rat strains. 2 Rofecoxib dose dependently increased sBP and decreased plasma levels of 6-keto prostaglandin (PG)F(1alpha) in WKY rats fed a normal salt diet (0.6% NaCl, wt wt(-1)), without affecting serum thromboxane (TX)B(2) levels. 3 Rofecoxib significantly elevated sBP in both rat strains fed normal salt or high salt diet (8% NaCl, wt wt(-1)), but not in rats on low salt intake (0.02% NaCl, wt wt(-1)). 4 Rofecoxib significantly decreased plasma levels of 6-keto PGF(1alpha) in both rat strains fed normal or high salt diet, but not in rats during low salt intake. 5 Rofecoxib exerted no influence on the changes of body weight nor on water intake. Plasma renin activity (PRA) and renocortical renin mRNA abundance were not changed by rofecoxib, but plasma aldosterone concentration (PAC) was significantly reduced. 6 These results suggest that chronic inhibition of COX-2 causes an increase of blood pressure that depends on prostacyclin synthesis. Furthermore, this increase is independent on genetic predisposition and can be prevented by salt deprivation. Since water intake and body weight gain were not changed by rofecoxib, fluid retention appears not to be a major reason for the development of hypertension. Similarly, an activation of the renin-angiotensin-aldosterone axis appears to be an unlikely candidate mechanism.

Role of renal nerves in stimulation of renin, COX-2, and nNOS in rat renal cortex during salt deficiency

We investigated a possible involvement of the sympathetic nervous system in the parallel increase of renin, cyclooxygenase-2 (COX-2), and neuronal nitric oxide synthase (nNOS) gene expression in the juxtaglomerular apparatus of rat kidneys induced by salt deficiency. Therefore, we determined the effects of renal denervation and the beta-adrenoreceptor antagonist metoprolol (50 mg/kg body wt po, twice a day) on renocortical expression of renin, COX-2, and nNOS in rats fed a low-salt (0.02% wt/wt) diet or treated for 1 wk with ramipril (10 mg/kg body wt) in combination with a low-salt diet. We found that a low-salt diet in combination with ramipril strongly increased renocortical mRNA levels of renin, COX-2, and nNOS 9-, 7-, and 2.5-fold, respectively. Treatment with metoprolol did not change basal expression of the three genes or induction of renin and COX-2 gene expression, while induction of nNOS expression was clearly attenuated. Similarly, unilateral renal denervation attenuated induction of nNOS expression but had no effect on all other parameters. These findings suggest that beta-adrenergic stimulation is not required for stimulation of renin and COX-2 gene expression in the juxtaglomerular apparatus during salt deficiency. However, beta-adrenoreceptor activity or renal nerve activity appears to be required for the full stimulation of nNOS expression by low salt intake or combined with angiotensin-converting enzyme inhibition.

Role of COX-2-derived metabolites in regulation of the renal hemodynamic response to norepinephrine

The objective of this study was to examine the role of cylcooxygenase (COX)-2-derived prostaglandins (PG) in modulating the renal hemodynamic effects of norepinephrine (NE) during low or normal sodium intake. The relative contribution of each COX isoform in producing the PG that attenuate the renal NE effects during normal sodium intake was also evaluated. The renal response to three doses of NE (50, 100, and 250 ng. kg(-1). min(-1)) was evaluated in anesthetized dogs pretreated with vehicle, a selective COX-2 inhibitor (nimesulide), or a nonselective COX inhibitor (meclofenamate). Intrarenal infusion of the two lower doses of NE in vehicle-pretreated dogs with normal sodium intake (n = 8) elicited an increase in renal vascular resistance (RVR; 21 and 34%) without inducing changes in glomerular filtration rate (GFR). The highest dose of NE in this group induced a further increment in RVR (113%) and a decrease in GFR (33%). Pretreatment with nimesulide in dogs with normal sodium intake (n = 7) did not modify the NE-induced increments in RVR but enhanced the decreases in GFR induced by the three NE doses (12, 26, and 64%). The renal hemodynamic response to NE in meclofenamate-pretreated dogs with normal sodium intake (n = 7) was similar to that found in dogs pretreated with nimesulide. Infusion of the lowest dose of NE to vehicle-pretreated dogs with low sodium intake (n = 6) did not modify GFR and elicited an increase in RVR (42%). Infusion of the second and third doses of NE led to a decrease in GFR (35 and 91%) and a rise in RVR (82 and 587%). Infusion of the first two doses of NE in nimesulide-pretreated dogs with low sodium intake (n = 5) induced a fall in GFR (64 and 92%) and an increase in RVR (174 and 2,293%) that were greater (P < 0.05) than those induced by NE in vehicle-pretreated dogs. The elevation in the urinary excretion rates of PGE(2) and 6-keto-PGF(1alpha) elicited by NE was prevented in the nimesulide-pretreated dogs. Our results show that COX-2 inhibition potentiates the renal hemodynamic effects of NE and propose that the PG involved in modulating them are mainly derived from COX-2 activity.