Isoform-specific regulation by N(G),N(G)-dimethylarginine dimethylaminohydrolase of rat serum asymmetric dimethylarginine and vascular endothelium-derived relaxing factor/NO.

Asymmetric dimethylarginine (ADMA), which inhibits NO synthase, is inactivated by N(G),N(G)-dimethylarginine dimethylaminohydrolase (DDAH). We tested whether DDAH-1 or -2 regulates serum ADMA (S(ADMA)) and/or endothelium-derived relaxing factor (EDRF)/NO. Small inhibitory (si)RNAs targeting DDAH-1 or -2, or an siRNA control were given intravenously to rats. After 72 hours, EDRF/NO was assessed from acetylcholine-induced, NO synthase-dependent relaxation and 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate for NO activity in isolated mesenteric resistance vessels (MRVs). Expression of mRNA for DDAH-1 versus -2 was 2- and 7-fold higher in the kidney cortex and liver, respectively, whereas expression of DDAH-2 versus -1 was 5-fold higher in MRVs. The proteins and mRNAs for DDAH-1 or -2 were reduced selectively by 35% to 85% in the kidney cortex, liver, and MRVs 72 hours following the corresponding siRNA. S(ADMA) was increased only after siDDAH-1 (266+/-25 versus 342+/-39 [mean+/-SD] nmol x L(-1); P<0.005), whereas EDRF/NO responses and NO activity were not changed consistently by siDDAH-1 but were greatly reduced after siDDAH-2. Mean arterial pressure was not changed significantly by any siRNA. In conclusion, S(ADMA) is regulated by DDAH-1, which is expressed at sites of ADMA metabolism in the kidney cortex and liver, whereas EDRF/NO is regulated primarily by DDAH-2, which is expressed strongly in blood vessels. This implies specific functions of DDAH isoforms.

Roles of vasoconstrictor prostaglandins, COX-1 and -2, and AT1, AT2, and TP receptors in a rat model of early 2K,1C hypertension.

Angiotensin (ANG) II activating type 1 receptors (AT(1)Rs) enhances superoxide anion (O(2)*(-)) and arachidonate (AA) formation. AA is metabolized by cyclooxygenases (COXs) to PGH(2), which is metabolized by thromboxane (Tx)A(2) synthase to TxA(2) or oxidized to 8-isoprostane PGF(2alpha) (8-Iso) by O(2)*(-). PGH(2), TxA(2), and 8-Iso activate thromboxane-prostanoid receptors (TPRs). We investigated whether blood pressure in a rat model of early (3 wk) two-kidney, one-clip (2K,1C) Goldblatt hypertension is maintained by AT(1)Rs or AT(2)Rs, driving COX-1 or -2-dependent products that activate TPRs. Compared with sham-operated rats, 2K,1C Goldblatt rats had increased mean arterial pressure (MAP; 120 +/- 4 vs. 155 +/- 3 mmHg; P < 0.001), plasma renin activity (PRA; 22 +/- 7 vs. 48 +/- 5 ng x ml(-1) x h(-1); P < 0.01), plasma malondialdehyde (1.07 +/- 0.05 vs. 1.58 +/- 0.16 nmol/l; P < 0.01), and TxB(2) excretion (26 +/- 4 vs. 51 +/- 7 ng/24 h; P < 0.01). Acute graded intravenous doses of benazeprilat (angiotensin-converting enzyme inhibitor) reduced MAP at 20 min (-36 +/- 5 mmHg; P < 0.001) and excretion of TxA(2) metabolites. Indomethacin (nonselective COX antagonist) or SC-560 (COX-1 antagonist) reduced MAP at 20 min (-25 +/- 5 and -28 +/- 7 mmHg; P < 0.001), whereas valdecoxib (COX-2 antagonist) was ineffective (-9 +/- 5 mmHg; not significant). Losartan (AT(1)R antagonist) or SQ-29548 (TPR antagonist) reduced MAP at 150 min (-24 +/- 6 and -22 +/- 3 mmHg; P < 0.001), whereas PD-123319 (AT(2)R antagonist) was ineffective. Acute blockade of TPRs, COX-1, or COX-2 did not change PRA, but TxB(2) generation by the clipped kidney was reduced by blockade of COX-1 and increased by blockade of COX-2. 2K,1C hypertension in rats activates renin, O(2)*(-), and vasoconstrictor PGs. Hypertension is maintained by AT(1)Rs and by COX-1, but not COX-2, products that activate TPRs.

Acute antihypertensive action of nitroxides in the spontaneously hypertensive rat.

Tempol is an amphipathic radical nitroxide (N) that acutely reduces blood pressure (BP) and heart rate (HR) in the spontaneously hypertensive rat (SHR). We investigated the hypothesis that the response to nitroxides is determined by SOD mimetic activity or lipophilicity. Groups (n = 6-10) of anesthetized SHRs received graded intravenous doses of Ns: tempol (T), 4-amino-tempo (AT), 4-oxo-tempo (OT), 4-trimethylammonium-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT-1), 3-carbamoyl-proxyl (3-CP), or 3-carboxy-proxyl (3-CTPY). Others received native or liposomal (L) Cu/Zn SOD. T and OT are uncharged, AT is positively charged and cell-permeable, and CAT-1 is positively charged and cell-impermeable. 3-CP and 3-CTPY have five-member pyrrolidine rings, whereas T, AT, OT, and CAT-1 have six-member piperidine rings. T and AT reduced mean arterial pressure (MAP) similarly (-48 +/- 2 mmHg and -55 +/- 8 mmHg) but more (P < 0.05) than OT and CAT-1. 3-CP and 3-CTPY were ineffective. The group mean change in MAP with piperidine Ns correlated with SOD activity (r = -0.94), whereas their ED(50) correlated with lipophilicity (r = 0.89). SOD and L-SOD did not lower BP acutely but reduced it after 90 min (-32 +/- 5 and -31 +/- 6 mmHg; P < 0.05 vs. vehicle). Pyrrolidine nitroxides are ineffective antihypertensive agents. The antihypertensive response to piperidine Ns is predicted by SOD mimetic action, and the sensitivity of response is by hydrophilicity. SOD exerts a delayed hypotensive action that is not enhanced by liposome encapsulation, suggesting it must diffuse to an extravascular site.

Antihypertensive response to prolonged tempol in the spontaneously hypertensive rat.

INTRODUCTION: Tempol is a permeant nitroxide superoxide dismutase (SOD) mimetic that lowers mean arterial pressure (MAP) in spontaneously hypertensive rats (SHRs). We investigated the hypothesis that the antihypertensive response entails a negative salt balance, blunting of plasma renin activity (PRA), endothelin-1 (ET-1), or catecholamines or correction of oxidative stress as indexed by 8-isoprostane prostaglandin F(2alpha) (PGF(2alpha)) (8-Iso). METHODS: Groups (N= 6 to 8) of SHRs were infused for 2 weeks with vehicle or tempol (200 nmol/kg/min) or given tempol (2 mmol/L) in drinking water. RESULTS: Tempol infusion reduced the MAP of anesthetized SHRs (150 +/- 5 vs. 126 +/- 6 mm Hg) (P < 0.005). Oral tempol did not change the heart rate but reduced the MAP of conscious SHRs (-23 +/- 6 mm Hg) (P < 0.01) but not Wistar-Kyoto (WKY) rats. Tempol infusion increased the PRA (2.2 +/- 0.2 vs. 5.0 +/- 0.9 ng/mL/hour) (P < 0.005), did not change excretion of nitric oxide (NO) [NO(2)+ NO(3) (NOx)], ET-1, or catecholamines but reduced excretion of 8-Iso (13.2 +/- 1.4 vs. 9.6 +/- 0.9 ng/24 hours; P < 0.01). Cumulative Na(+) balance and gain in body weight were unaltered by tempol infusion. Tempol prevented a rise in MAP with high salt intake. CONCLUSION: Tempol corrects hypertension without a compensatory sympathoadrenal activation or salt retention. The response is independent of nitric oxide, endothelin, or catecholamines and occurs despite increased PRA. It is accompanied by a reduction in oxidative stress and is maintained during increased salt intake.

Cyclooxygenase-1-deficient mice have high sleep-to-wake blood pressure ratios and renal vasoconstriction.

We used cyclooxygenase-1 (COX-1)-deficient mice to test the hypothesis that COX-1 regulates blood pressure (BP) and renal hemodynamics. The awake time (AT) mean arterial pressures (MAPs) measured by telemetry were not different between COX-1(+/+) and COX-1(-/-) (131+/-2 versus 126+/-3 mm Hg; NS). However, COX-1(-/-) had higher sleep time (ST) MAP (93+/-1 versus 97+/-2 mm Hg; P<0.05) and sleep-to-awake BP ratio (+8.6%; P<0.05). Under anesthesia with moderate sodium loading, COX-1(-/-) had higher MAP (109+/-5 versus 124+/-4 mm Hg; P<0.05), renal vascular resistance (23.5+/-1.6 versus 30.7+/-1.7 mm Hg . mL(-1) . min(-1) . g(-1); P<0.05) and filtration fraction (33.7+/-2.1 versus 40.2+/-2.0%; P<0.05). COX-1(-/-) had a 89% reduction (P<0.0001) in the excretion of TxB2, a 76% reduction (P<0.01) in PGE2, a 40% reduction (P<0.0002) in 6-ketoPGF1alpha (6keto), a 27% reduction (P<0.02) in 11-betaPGF2alpha (11beta), a 35% reduction (P<0.01) in nitrate plus nitrite (NOx), and a 52% increase in metanephrine (P<0.02). The excretion of normetanephrine, a marker for sympathetic nervous activity, was reduced during ST in COX-1(+/+) (6.9+/-0.9 versus 3.2+/-0.6 g . g(-1) creatinine . 10(-3); P<0.01). This was blunted in COX-1(-/-) (5.1+/-0.9 versus 4.9+/-0.7 g . g(-1) creatinine . 10(-3); NS). Urine collection during ST showed lower excretion of 6keto, 11beta, NOx, aldosterone, sodium, and potassium than during AT in both COX-1(+/+) and COX-1(-/-), and there were positive correlations among these parameters (6keto versus NOx; P<0.005; 11beta versus NOx; P<0.005; and NOx versus sodium; P<0.005). In conclusion, COX-1 mediates a suppressed sympathetic nervous activity and enhanced NO, which may contribute to renal vasodilatation and a reduced MAP while asleep or under anesthesia. COX-1 contributes to the normal nocturnal BP dipping phenomenon.

TP receptors regulate renal hemodynamics during angiotensin II slow pressor response.

We investigated the hypothesis that thromboxane A2 (TxA2)-prostaglandin H2 receptors (TP-Rs) mediate the hemodynamic responses and increase in reactive oxygen species (ROS) to ANG II (400 ng x kg(-1) x min(-1) sc for 14 days) using TP-R knockout (TP -/-) and wild-type (+/+) mice. TP -/- had normal basal mean arterial blood pressure (MAP) and glomerular filtration rate but reduced renal blood flow and increased filtration fraction (FF) and renal vascular resistance (RVR) and markers of ROS (thiobarbituric acid-reactive substances and 8-isoprostane PGF2alpha) and nitric oxide (NOx). Infusion of ANG II into TP +/+ increased ROS and thromboxane B2 (TxB2) and increased RVR and FF. ANG II infusion into TP -/- mice reduced ANG I and increased aldosterone but caused a blunted increase in MAP (TP -/- : +6 +/- 2 vs. TP +/+: +15 +/- 3 mmHg) and failed to increase FF, ROS, or TxB2 but increased NOx and paradoxically decreased RVR (-2.1 +/- 1.7 vs. +2.6 +/- 0.8 mmHg x ml(-1) x min(-1) x g(-1)). Blockade of AT1 receptor of TP -/- mice infused with ANG II reduced MAP (-8 mmHg) and aldosterone but did not change the RVR or ROS. In conclusion, during an ANG II slow pressor response, AT1 receptors activate TP-Rs that generate ROS and prostaglandins but inhibit NO. TP-Rs mediate all of the increase in RVR and FF, part of the increase in MAP, but are not implicated in the suppression of ANG I or increase in aldosterone. TP -/- mice have a basal increase in RVR and FF associated with ROS.