Role of endothelin-1 and thromboxane A2 in renal vasoconstriction induced by angiotensin II in diabetes and hypertension

Macrophages in Skin Wounds: Functions and Therapeutic Potential

Macrophages regulate cutaneous wound healing by immune surveillance, tissue repair and remodelling. The depletion of dermal macrophages during the early and middle stages of wound healing has a detrimental impact on wound closure, characterised by reduced vessel density, fibroblast and myofibroblast proliferation, delayed re-epithelization and abated post-healing fibrosis and scar formation. However, in some animal species, oral mucosa and foetal life, cutaneous wounds can heal normally and remain scarless without any involvement of macrophages. These paradoxical observations have created much controversy on macrophages' indispensable role in skin wound healing. Advanced knowledge gained by characterising macrophage subsets, their plasticity in switching phenotypes and molecular drivers provides new insights into their functional importance during cutaneous wound healing. In this review, we highlight the recent findings on skin macrophage subsets, their functional role in adult cutaneous wound healing and the potential benefits of targeting them for therapeutic use.

Metformin in cardiovascular diabetology: a focused review of its impact on endothelial function

As a first-line treatment for diabetes, the insulin-sensitizing biguanide, metformin, regulates glucose levels and positively affects cardiovascular function in patients with diabetes and cardiovascular complications. Endothelial dysfunction (ED) represents the primary pathological change of multiple vascular diseases, because it causes decreased arterial plasticity, increased vascular resistance, reduced tissue perfusion and atherosclerosis. Caused by “biochemical injury”, ED is also an independent predictor of cardiovascular events. Accumulating evidence shows that metformin improves ED through liver kinase B1 (LKB1)/5'-adenosine monophosphat-activated protein kinase (AMPK) and AMPK-independent targets, including nuclear factor-kappa B (NF-κB), phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt), endothelial nitric oxide synthase (eNOS), sirtuin 1 (SIRT1), forkhead box O1 (FOXO1), krüppel-like factor 4 (KLF4) and krüppel-like factor 2 (KLF2). Evaluating the effects of metformin on endothelial cell functions would facilitate our understanding of the therapeutic potential of metformin in cardiovascular diabetology (including diabetes and its cardiovascular complications). This article reviews the physiological and pathological functions of endothelial cells and the intact endothelium, reviews the latest research of metformin in the treatment of diabetes and related cardiovascular complications, and focuses on the mechanism of action of metformin in regulating endothelial cell functions.

Eicosanoid blood vessel regulation in physiological and pathological states

Arachidonic acid can be metabolized in blood vessels by three primary enzymatic pathways; cyclooxygenase (COX), lipoxygenase (LO), and cytochrome P450 (CYP). These eicosanoid metabolites can influence endothelial and vascular smooth muscle cell function. COX metabolites can cause endothelium-dependent dilation or constriction. Prostaglandin I2 (PGI2) and thromboxane (TXA2) act on their respective receptors exerting opposing actions with regard to vascular tone and platelet aggregation. LO metabolites also influence vascular tone. The 12-LO metabolite 12S-hydroxyeicosatrienoic acid (12S-HETE) is a vasoconstrictor whereas the 15-LO metabolite 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) is an endothelial-dependent hyperpolarizing factor (EDHF). CYP enzymes produce two types of eicosanoid products: EDHF vasodilator epoxyeicosatrienoic acids (EETs) and the vasoconstrictor 20-HETE. The less-studied cross-metabolites generated from arachidonic acid metabolism by multiple pathways can also impact vascular function. Likewise, COX, LO, and CYP vascular eicosanoids interact with paracrine and hormonal factors such as the renin-angiotensin system and endothelin-1 (ET-1) to maintain vascular homeostasis. Imbalances in endothelial and vascular smooth muscle cell COX, LO, and CYP metabolites in metabolic and cardiovascular diseases result in vascular dysfunction. Restoring the vascular balance of eicosanoids by genetic or pharmacological means can improve vascular function in metabolic and cardiovascular diseases. Nevertheless, future research is necessary to achieve a more complete understanding of how COX, LO, CYP, and cross-metabolites regulate vascular function in physiological and pathological states.

Mechanisms of U46619-induced contraction in mouse intrarenal artery

Thromboxane A₂ (TXA₂ ) has been implicated in the pathogenesis of vascular complications, but the underlying mechanism remains unclear. The contraction of renal arterial rings in mice was measured by a Multi Myograph System. The intracellular calcium concentration ([Ca²⁺ ]_i ) in vascular smooth muscle cells (VSMCs) was obtained by using a fluo-4/AM dye and a confocal laser scanning microscopy. The results show that the U46619-induced vasoconstriction of renal artery was completely blocked by a TXA₂ receptor antagonist GR32191, significantly inhibited by a selective phospholipase C (PI-PLC) inhibitor U73122 at 10 μmol/L and partially inhibited by a Phosphatidylcholine - specific phospholipase C (PC-PLC) inhibitor D609 at 50 μmol/L. Moreover, the U46619-induced vasoconstriction was inhibited by a general protein kinase C (PKC) inhibitor chelerythrine at 10 μmol/L, and a selective PKCδ inhibitor rottlerin at 10 μmol/L. In addition, the PKC-induced vasoconstriction was partially inhibited by a Rho-kinase inhibitor Y-27632 at 10 μmol/L and was further completely inhibited together with a putative IP₃ receptor antagonist and store-operated Ca²⁺ (SOC) entry inhibitor 2-APB at 100 μmol/L. On the other hand, U46619-induced vasoconstriction was partially inhibited by L-type calcium channel (Cav1.2) inhibitor nifedipine at 1 μmol/L and 2-APB at 50 and 100 μmol/L. Last, U46619-induced vasoconstriction was partially inhibited by a cell membrane Ca²⁺ activated C1^- channel blocker 5-Nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) at 50 and 100 μmol/L. Our results suggest that the U46619-induced contraction of mouse intrarenal arteries is mediated by Cav1.2 and SOC channel, through the activation of thromboxane-prostanoid receptors and its downstream signaling pathway.

Incidence and Progression of Chronic Kidney Disease After Hepatitis C Seroconversion: Results from ERCHIVES

BACKGROUND AND AIMS

We aimed to assess the incidence and progression of chronic kidney disease (CKD) following hepatitis C virus (HCV) seroconversion.

METHODS

This retrospective cohort study included Veterans with a confirmed HCV seroconversion between 2001 and 2014 and Veterans with negative HCV testing over the same time period. The outcomes included development of advanced CKD (eGFR < 60 mL/min/1.73 m(2) on two separate occasions at least 90 days apart, plus a ≥ 10 mL/min/1.73 m(2) decline from baseline) and progressive CKD (decline in eGFR of ≥ 30 mL/min/1.73 m(2) from baseline). Multivariable Cox proportional hazards models were used to evaluate the association between HCV and incident advanced and progressive CKD.

RESULTS

The final cohort consisted of 71,528 Veterans, including 2589 with recently seroconverted HCV. Over a mean follow-up of 6 years, 36% of patients with and 31% without HCV developed advanced CKD (p < 0.001), and 35% of patients with vs. 26% without HCV developed progressive CKD (p < 0.001). After controlling for traditional risk factors, recently seroconverted HCV+ patients were significantly less likely to develop advanced CKD (HR 0.86; 95% CI 0.79, 0.92), and HCV status was not significantly associated with progressive CKD (HR 0.93; 95% CI 0.86, 1.00). Factors associated with developing advanced and progressive CKD included older age, female sex, diabetes, hypertension, development of cirrhosis, and substance abuse.

CONCLUSIONS

In this cohort of newly infected US Veterans, HCV infection was associated with decreased incidence of advanced and unchanged risk of progressive CKD, suggesting a larger role for traditional risk factors in the development of CKD after HCV seroconversion.

Chronic Kidney Disease in Aged Cats: Clinical Features, Morphology, and Proposed Pathogeneses

Chronic kidney disease (CKD) is the most common metabolic disease of domesticated cats, with most affected cats being geriatric (>12 years of age). The prevalence of CKD in cats exceeds that observed in dogs, and the frequency of the diagnosis of CKD in cats has increased in recent decades. Typical histologic features include interstitial inflammation, tubular atrophy, and fibrosis with secondary glomerulosclerosis. In contrast to people and dogs, primary glomerulopathies with marked proteinuria are remarkably rare findings in cats. Although a variety of primary renal diseases have been implicated, the disease is idiopathic in most cats. Tubulointerstitial changes, including fibrosis, are present in the early stages of feline CKD and become more severe in advanced disease. A variety of factors-including aging, ischemia, comorbid conditions, phosphorus overload, and routine vaccinations-have been implicated as factors that could contribute to the initiation of this disease in affected cats. Factors that are related to progression of established CKD, which occurs in some but not all cats, include dietary phosphorus intake, magnitude of proteinuria, and anemia. Renal fibrosis, a common histologic feature of aged feline kidneys, interferes with the normal relationship between peritubular capillaries and renal tubules. Experimentally, renal ischemia results in morphologic changes similar to those observed in spontaneous CKD. Renal hypoxia, perhaps episodic, may play a role in the initiation and progression of this disease.

Oxidative Stress-Dependent Coronary Endothelial Dysfunction in Obese Mice

Obesity is involved in several cardiovascular diseases including coronary artery disease and endothelial dysfunction. Endothelial Endothelium vasodilator and vasoconstrictor agonists play a key role in regulation of vascular tone. In this study, we evaluated coronary vascular response in an 8 weeks diet-induced obese C57BL/6 mice model. Coronary perfusion pressure in response to acetylcholine in isolated hearts from obese mice showed increased vasoconstriction and reduced vasodilation responses compared with control mice. Vascular nitric oxide assessed in situ with DAF-2 DA showed diminished levels in coronary arteries from obese mice in both basal and acetylcholine-stimulated conditions. Also, released prostacyclin was decreased in heart perfusates from obese mice, along with plasma tetrahydrobiopterin level and endothelium nitric oxide synthase dimer/monomer ratio. Obesity increased thromboxane A2 synthesis and oxidative stress evaluated by superoxide and peroxynitrite levels, compared with control mice. Obese mice treated with apocynin, a NADPH oxidase inhibitor, reversed all parameters to normal levels. These results suggest that after 8 weeks on a high-fat diet, the increase in oxidative stress lead to imbalance in vasoactive substances and consequently to endothelial dysfunction in coronary arteries.

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

Obesity in kidney transplantation affects renal function but not graft and patient survival

INTRODUCTION

The number of overweight and obese patients undergoing renal transplantation has increased dramatically over the past two decades. Studies on graft survival and posttransplantation complications have often yielded conflicting results. Some authors have reported similar results for graft and patient survivals between obese and normal weight patients, but with a marginally increased rate of postoperative complications. In contrast, other reports note higher percentage of graft losses as well as increased mortality. In our study, we analyzed early- and long-term outcomes among obese versus nonobese kidney transplant recipients.

PATIENTS AND METHODS

Between January 2000 and December 2008, we performed 563 cadaveric kidney transplantations. Recipients were classified in 1 of 5 groups based on their body mass index (BMI) at the time of transplantation: group A (n = 68; BMI < 18.5); group B (n = 310; 18.6 < BMI < 24.9); group C (n = 143; 25 < BMI < 29.9); group D (n = 32; 30 < BMI < 34.9); and group E (n = 10; BMI ≥ 35). The comparative analysis included patient and graft survivals, postoperative complications, onset of delayed graft function (DGF), acute rejection episodes, hospital stay, and serum creatinine values in the first 3 years posttransplantation.

RESULTS

At a mean follow-up of 53 months (range, 3-112 months), DGF was observed in 20 patients in group A (29.4%), 82 in group B (26.4%), 43 in group C (30%), 16 in group D (50%), and 4 in group E (40%). Nevertheless, obese patients (groups D and E) showed higher mean serum creatinine values and worse renal function at 6 months (P = .001), 1 year (P < .001), and 3 years (P = .001). Moreover, they were at increased risk of an acute rejection episode (P = .01) and more susceptible to cardiovascular and metabolic complications (P = .01). Morbidly obese patients displayed a higher incidence of postsurgical complications (P = .002). There were no differences in the incidences of chronic allograft nephropathy (CAN) or infectious complications. Despite the differences in morbidity among the 5 groups, we failed to observe significant differences in patient or graft survivals at 6, 12, 36, or 60 months.

CONCLUSION

Our findings suggested that obese patients should not be discriminated against simply based on the BMI. At our center, obese (BMI >35) transplantation candidates undergo a thorough cardiac evaluation, as well as pulmonary, endocrine, and nutritional counseling seeking to minimize medical and surgical complications and improve survival and quality of life.

Low-dose nesiritide improves renal function in heart failure patients following acute myocardial infarction

This study was designed to investigate the effect of low-dose nesiritide on renal function and major cardiac events in patients with acute decompensated heart failure following acute myocardial infarction. Sixty patients were randomized into nesiritide (loading dose 0.5 microg/kg, maintenance dose 0.0075 microg/kg/min) and nitroprusside groups. Compared with the nitroprusside group, the nesiritide group had a greater heart rate reduction (P < 0.05), higher 24 h urine volume (P < 0.001), and more significant alleviation in dyspnea (P < 0.001). The prevalence of hypotension in the nesiritide group was lower than in the nitroprusside group (7.4% vs 28.5%, P < 0.05). The nesiritide group had a greater reduction in serum noradrenaline, angiotensin II, aldosterone, endothelin, and N-terminal prohormone brain natriuretic peptide (all P < 0.01). The mean serum creatinine in the nesiritide group was reduced (109.4 +/- 26.6 vs 102.8 +/- 21.6 micromol/l, P < 0.01), whereas it remained unchanged in the nitroprusside group (106.8 +/- 20 vs 106.0 +/- 19.2 micromol/l, P > 0.05). The rehospitalization or mortality rate was similar between the two groups 3 months after the therapy (P > 0.05). We conclude that low-dose nesiritide is more effective in suppressing the activation of the sympathetic and renin-angiotensin systems. It also improves the clinical symptoms and enhances renal function, but its effect on hospital readmission or mortality rate needs further investigation.

Short-term ANG II produces renal vasoconstriction independent of TP receptor activation and TxA2/isoprostane production

The relative contributions of vasoconstrictor and of dilator systems are balanced in health. The balance is reset in disease, often favoring a predominant role of vasoconstrictors, perhaps due to positive interactions between constrictor systems. For example, in hypertension, chronic high levels of angiotensin II (ANG II) stimulate the production of thromboxane (TxA2/PGH2) and/or isoprostane that activate constrictor thromboxane prostanoid (TP) receptors in the vasculature. The present study evaluated a modest concentration of ANG II administered acutely into the renal artery on urinary excretion of TxB2 and isoprostane and possible renal TP receptor activation that might amplify ANG II-induced renal vasoconstriction. TP receptors were blocked with SQ29548 coinfused with ANG II. Results were compared with a time control group of continuous ANG II infusion (40 ng.min(-1).kg body wt(-1)) over 90 min. TP receptor antagonism during 30-60 min had no effect on the reduction in renal blood flow (RBF) produced by ANG II (15.8 +/- 2.8 vs. 13.2 +/- 4.9%) (P > 0.6). Likewise, there was no difference between groups during ANG II-induced renal vasoconstriction between 60-90 min in presence or absence of TP receptor antagonist (RBF -8.6 +/- 4.0 vs. -9.6 +/- 4.5%) (P > 0.8). Systemic arterial pressure was stable throughout, so RBF changes reflected localized changes in renal vascular resistance. Urinary excretion of TxB2 and isoprostane were nearly doubled by ANG II. The present data indicate that short-term intrarenal infusion of ANG II rapidly increases renal production of TxA2 but that the ANG II-induced renal vasoconstriction is independent of TP receptor activation during the initial 90 min of local challenge with ANG II.

Stimulation of serum- and glucocorticoid-regulated kinase-1 gene expression by endothelin-1

The serum- and glucocorticoid-regulated kinase-1 (SGK1) participates in the regulation of sodium homeostasis and blood pressure by mineralocorticoids. Aldosterone rapidly induces SGK1 transcription, which contributes to the activation of renal epithelial sodium channels. Another important regulator of blood pressure is the vasoactive hormone endothelin-1 (ET-1) that is systemically upregulated in chronic renal failure. In the present study, we investigated whether ET-1 modulates SGK1 expression, and thereby might explain some of its hypertensive effects. As assessed by real-time PCR analysis, ET-1 triggered the rapid increase of SGK1 mRNA levels in A-10 smooth muscle cells and also in intact aortas of adult rats. In A-10 cells transcriptional activation was associated with a more than 6-fold upregulation of SGK1 protein expression and in similar range as found after treatment with aldosterone. A stimulatory effect of ET-1 was not only observed in isolated cells, but also in an animal model. Upon subtotal nephrectomy (SNX) of rats, myocardial ET-1 levels strongly increased, which was followed by a more than 2-fold induction of SGK1 expression in the left ventricle. The myocardial upregulation of SGK1 was completely abrogated by a specific ET(A) receptor antagonist, thereby substantiating the in vivo role of ET-1 in SGK1 expression. Thus, these data demonstrate that ET-1 increases expression of SGK1 in vivo and in vitro, and therefore indicate that SGK1 upregulation might be involved in ET-1-dependent regulation of blood pressure and cardiac modelling during mild renal failure.

Obesity and outcome following renal transplantation

Single institution series have demonstrated that obese patients have higher rates of wound infection and delayed graft function (DGF), but similar rates of graft survival. We used UNOS data to determine whether obesity affects outcome following renal transplantation. From the UNOS database, we identified patients who underwent primary kidney-only transplantation between 1997 and 1999. Recipient and donor body mass index (BMI) was categorized as underweight (BMI < 18.5), normal (BMI 18.5-24.9), overweight (BMI 25-29.9), obese (BMI 30-34.9) or morbidly obese (BMI > or = 35). We correlated BMI with intermediate measures of graft outcome and overall graft survival, and created multivariate models to evaluate the independent effect of BMI on graft outcome, adjusting for factors known to affect graft success. The study sample comprised 27,377 recipients. Older age, female sex, African American race and increased comorbidity were associated with obesity (p < 0.001). Compared with normal weight patients, morbid obesity was independently associated with an increased risk of DGF (p < 0.001), prolonged hospitalization (p < 0.001), acute rejection (p = 0.006) and decreased overall graft survival (p = 0.001). Donor BMI did not affect overall graft survival (p > or = 0.07). Recipient obesity is associated with an increased risk of DGF and decreased graft survival following renal transplantation.

AT-1 receptor antagonism modifies the mediation of endothelin-1, thromboxane A2, and catecholamines in the renal constrictor response to angiotensin II

OBJECTIVE

The present study investigated the consequences of partial AT(1) receptor blockade on the participation of catecholamines, thromboxane A(2) (TXA(2)), and endothelin-1 (ET-1) in the renal vasoconstriction induced by angiotensin II (Ang II).

METHODS

For this purpose, the increase in renal perfusion pressure (RPP) produced by Ang II was studied in isolated kidneys from untreated or irbesartan-treated Wistar Kyoto and spontaneously hypertensive rats (SHR), in absence or presence of the alfa-1 receptor antagonist, prazosin, the TXA(2) receptor antagonist, ifetroban, or the ET(A)/ET(B) receptor antagonist, PD145065.

RESULTS

Systolic arterial pressure (SAP) was higher (P < 0.05) in SHR than in WKY. Increases in RPP produced by Ang II were comparable in kidneys from both untreated groups. Treatment with irbesartan reduced SAP and RPP in both strains in a comparable extent. Presence of prazosin, ifetroban, or PD145065 in perfusion media reduced (P < 0.05) Ang II maximal response in all groups. Maximal inhibition of Ang II-induced vasoconstriction produced by the 3 antagonists was comparable in untreated WKY, but that of ifetroban and PD145065 was lower (P < 0.05) than that of prazosin in untreated SHR. Maximal inhibition of Ang II-induced vasoconstriction produced by the 3 antagonists was comparable in WKY treated with irbesartan, and not different to that observed in untreated WKY. Maximal inhibitory effect of the 3 antagonists was higher (P < 0.05) in treated than in untreated SHR.

CONCLUSION

The study further supports the importance of catecholamines, TXA(2), and ET-1 as mediators of the renal vasoconstriction induced by Ang II in both normotensive and hypertensive rats. Hypertensive conditions appeared to reduce the participation of TXA(2) and ET-1 in Ang II-induced vasoconstriction when compared with normotensive conditions. Chronic partial blockade of AT(1) receptors did not affect the participation of catecholamines, TXA(2), and ET-1 in normotensive rats, but increased the participation of the 3 mediators in SHR. This suggests that when AT(1) receptors are partially blocked, other vasoconstrictor factors could exert part of the renal vasoconstrictor effects of Ang II.

The relationship between glycemic control and plasma vascular endothelial growth factor and endothelin-1 concentration in diabetic patients

Understanding the causes of diabetic vascular complications has become an increasingly important issue because of the rapidly rising prevalence of diabetes. Recently discovered vasoconstrictors and angiogenesis regulators, such as endothelin (ET) and vascular endothelial growth factor (VEGF), have been intensely studied for possible pathogenic roles in diabetic vascular complications. The present study was undertaken to clarify the effect of glycemic control on serum VEGF and plasma ET-1 concentrations in diabetic patients, and to identify other factors that may cause fluctuations of these substances. Plasma VEGF and ET-1 concentrations of 45 hospitalized diabetic patients and 54 control subjects were measured by enzyme immunoassay (EIA) and radioimmunoassay (RIA), respectively. Plasma VEGF was elevated in poorly controlled diabetic patients compared with healthy subjects and plasma VEGF concentrations declined after hospitalized treatment with either insulin or oral hypoglycemic agents in combination with diet. There was a significant correlation between plasma VEGF concentration and both fasting plasma glucose (FPG) and hemoglobin A(1c) (HbA(1c)). Plasma ET-1 in poorly controlled diabetic patients was higher than in healthy controls, but improved glycemic control did not affect plasma ET-1 concentrations. Thus, poor glycemic control causes increased levels of plasma VEGF, which may result in hypertension and vascular complications in diabetes. Short-term treatment resulting in good glycemic control can improve levels of VEGF and may provide beneficial effects on diabetic vascular complications.

Cyclooxygenase involvement in thromboxane-dependent contraction in rat mesenteric resistance arteries

The influence of cyclooxygenase pathway activation following thromboxane-endoperoxide (TP) receptor stimulation was studied in rat mesenteric resistance arteries (n=6 to 10 per group). We studied isolated, perfused, and pressurized mesenteric resistance arteries (mean internal diameter 214 microm) using an arteriograph, enabling us to study arteries in physiological conditions of flow and pressure. Changes in diameter were continuously recorded, and contractions measured as internal diameter reduction. Release of cyclooxygenase pathway metabolites was also assessed by enzyme immunoassay (EIA) analysis of mesenteric bed perfusions. The thromboxane A2 (TxA2) analog U-46619 (1 micromol/L) induced a significant contraction (108 microm maximal diameter reduction). Inhibition by 3 chemically different cyclooxygenase inhibitors (ie, flurbiprofen, indomethacin, and aspirin) potently reduced the contraction to 27%, 25%, and 6% of control, respectively. The selective cyclooxygenase-1 inhibitor SC-58560 inhibited U-46619 contraction, whereas selective cyclooxygenase-2 inhibition (SC-58236) had no effect. Thromboxane synthase inhibition (furegrelate) did not affect U-46619-induced contraction, but it was reduced by cytosolic phospholipase A2 inhibition. Measurement of cyclooxygenase derivatives produced by the isolated mesenteric bed showed that PGE2 was produced after TxA2-receptor stimulation with U-46619. Exogenous prostaglandin E2 (in the presence of the TxA2 receptor antagonist SQ 29 548) and U-46619 contracted mesenteric arteries with a similar potency (EC50: 0.30 and 0.48 micromol/L, respectively). This study provides the first evidence that TxA2-receptor-dependent contraction in a resistant artery involved cyclooxygenase stimulation and, at least in part, a PGE2 formation. This mechanism of TxA2-dependent contraction in resistant arteries might be of importance in the understanding of diseases affecting resistant arteries and involving TxA2, such as hypertension.