Vasoconstrictor effects of iso-prostaglandin F2alpha type-III (8-iso-prostaglandin F2alpha) on human saphenous veins

Paracetamol - An old drug with new mechanisms of action

Paracetamol (acetaminophen) is the most commonly used over-the-counter (OTC) drug in the world. Despite its popularity and use for many years, the safety of its application and its mechanism of action are still unclear. Currently, it is believed that paracetamol is a multidirectional drug and at least several metabolic pathways are involved in its analgesic and antipyretic action. The mechanism of paracetamol action consists in inhibition of cyclooxygenases (COX-1, COX-2, and COX-3) and involvement in the endocannabinoid system and serotonergic pathways. Additionally, paracetamol influences transient receptor potential (TRP) channels and voltage-gated Kv7 potassium channels and inhibits T-type Cav3.2 calcium channels. It also exerts an impact on L-arginine in the nitric oxide (NO) synthesis pathway. However, not all of these effects have been clearly confirmed. Therefore, the aim of our paper was to summarize the current state of knowledge of the mechanism of paracetamol action with special attention to its safety concerns.

Mechanism of thromboxane receptor-induced vasoconstriction in human saphenous vein

Saphenous vein (SV) is one of the most widely used graft material in patients undergoing coronary artery bypass graft surgery (CABG). Thromboxane A2 (TXA2) is implicated in graft failure by inducing vasoconstriction and platelet aggregation. The aim of this study is to investigate the mechanism involved in TXA2-induced vasoconstriction in human SV. The role of different inhibitors and blockers on U46619 (TXA2-mimetic)-induced vasoconstriction is investigated by using an isolated organ bath system. Relaxation responses to several mediators are evaluated in SV pre-contracted with U46619 and compared with those pre-contracted with phenylephrine. Our results demonstrate that U46619-induced contraction is completely blocked by myosin light chain kinase inhibitor ML-9 or TP receptor antagonist BAY u3405. Furthermore, U46619-induced contraction is partially inhibited by phospholipase C inhibitor U73122, protein kinase C inhibitor calphostin C, Rho-kinase inhibitor Y-27632, L-type calcium channel blocker nifedipine, store-operated channel inhibitor SKF96365 or removal of extracellular calcium. Relaxation responses to NO donor (sodium nitroprusside), guanylate cyclase (GC) stimulator (riociguat), phosphodiesterase (PDE) inhibitors (sildenafil, IBMX), adenylate cyclase (AC) activator (forskolin) and acetylcholine (ACh) are markedly reduced when U46619 is used as a pre-contraction agent. Our results demonstrate that influx of extracellular Ca2+ (through L-type calcium channels and store-operated calcium channels) and intracellular Ca2+ release together with Ca2+ sensitization (through Rho-kinase activation) are necessary components for TXA2-induced vasoconstriction in SV. Moreover, more pronounced decrease in vasorelaxation induced by several mediators (SNP, riociguat, sildenafil, IBMX, forskolin, and ACh) in the presence of U46619 when compared with phenylephrine suggests that there is a crosstalk between the TP receptor signaling pathway and PDE, AC, GC enzymes. We believe that the investigation of mechanism of the TXA2-induced vasoconstriction in SV will provide additional information for the prevention of SV graft failure.

Thromboxane receptor signalling in renal ischemia reperfusion injury

F(2)-isoprostanes are formed by oxidative modification of arachidonic acid and are the gold standard for detection of oxidative stress in vivo. F(2)-isoprostanes are biologically active compounds that signal through the thromboxane A(2) (TP) receptor; infusion of F(2)-isoprostanes reduces glomerular filtration in the kidney by constricting afferent arterioles. This study investigated whether endogenous F(2)-isoprostanes contribute to the pathogenesis of ischemic acute kidney injury, which is associated with oxidative stress and reduced glomerular filtration. TP receptor knockout mice-that lack F(2)-isoprostanes and thromboxane A(2) signalling-and wild-type control mice underwent 30 min of renal ischemia and 24 h of reperfusion. Kidney dysfunction, histological injury and the number of infiltrated neutrophils were similar between the two mouse strains, whereas TP receptor knockout mice had significantly more apoptotic cells and tissue lipid peroxidation than their wild-type counterparts. F(2)-isoprostanes and thromboxane B(2) were readily detectable in urine collections after surgery. The findings indicate that F(2)-isoprostanes and thromboxane A(2) signalling do not contribute critically to the pathogenesis of ischemic acute kidney injury and more generally provide evidence against a prominent role for F(2)-isoprostanes signalling in exacerbating acute disease states associated with oxidative stress.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

Mechanisms of agonist-induced constriction in isolated human pulmonary arteries

We determined the calcium signalling pathways involved in the mechanisms of contraction of the vasoconstrictive agonists KCl, U46619 and PDBu in isolated human pulmonary arteries. The influence of gender, vessel diameter and age of the patients was also investigated. Human pulmonary arteries (n = 86) were loaded in a wire myograph and maintained at a tension equivalent to the in vivo pressure of 17.5 mm Hg, bubbled with 95%O2/5%CO2 to maintain pH 7.4 in physiological saline solution (PSS). Cumulative concentration-response curves were obtained to KCl (100 microM-100 mM), U46619 (1 nM-1 microM) or PDBu (1 nM-1 microM), before or after a 30 min incubation with either the voltage-gated calcium channel (VGCC) blocker nifedipine (10 microM), the store-operated calcium channel (SOCC) blocker SK&F96365 (50 microM) or in calcium-free PSS (-Ca2+PSS). The KCl response was partially blocked in -Ca2+PSS and with nifedipine. The U46619 response was partially blocked in -Ca2+PSS and with nifedipine and SK&F96365. Incubation in -Ca2+PSS had no effect on the response to PDBu. Endothelial intact arteries responded significantly higher to U46619 than endothelial denuded arteries. This study demonstrates that KCl induces pulmonary vasoconstriction via activation of extracellular calcium entry through VGCCs, U46619 induces pulmonary vasoconstriction predominantly via activation of VGCCs and PDBu induces pulmonary vasoconstriction via a calcium-independent pathway.

Involvement of endothelial thromboxane A2 in the vasoconstrictor response induced by 15-E2t-isoprostane in isolated human umbilical vein

The present study was undertaken to evaluate the contractile response of several E- and F-ring isoprostanes (IsoP) in human umbilical vein (HUV) and to investigate the role of the endothelium on the effect of 15-E2t-IsoP, the most potent vasoconstrictor isoprostane, in human vessels. HUV rings with or without endothelium were suspended in an organ bath for recording the isometric tension in response to different agonists. The inhibitors to be evaluated were applied 30 min before the addition of the agonist. All of the compounds tested produced concentration-dependent contractions when tested on HUV rings with endothelium. Although these compounds were equieffective, significant differences were observed in their potency, with U46619 being the most potent followed by 15-E2t-IsoP > 15-E1t-IsoP = 15-F2t-IsoP > 15-F1t-IsoP = 9-epi-15-F2t-IsoP in descending rank order of potency. 15-E2t-IsoP was the most potent of the isoprostanes evaluated and, therefore, the one employed in the present study. When intact endothelium HUV rings were used, 15-E2t-IsoP-induced contraction was unaffected by the endothelin-converting enzyme inhibitor, phosphoramidon (10 microM), suggesting that short-term endothelin-1 release is not involved in this response. However, the non-selective cyclooxygenase (COX) inhibitor, indomethacin (10 and 30 microM), and the COX-2 selective inhibitor, NS-398 (3, 10 and 30 microM) produced inhibitory effects on 15-E2t-IsoP-induced contraction of HUV rings with endothelium. These results indicate that COX-derived contractile prostanoids are involved in this effect. Furthermore, the apparent pKb values estimated for indomethacin (5.5) and NS-398 (5.4) suggest that the prostanoids involved are derived from the COX-2 isoenzyme pathway. On HUV rings with endothelium, the phospholipase A2 inhibitor, oleyloxyethyl phosphorylcholine (30 and 100 microM), induced an inhibitory effect on 15-E2t-IsoP-induced contraction, suggesting that the phospholipase A2 pathway is also involved in this effect. In addition, the thromboxane A2 synthase inhibitor furegrelate (10 and 30 microM) also inhibited 15-E2t-IsoP-induced contraction of HUV rings with endothelium, indicating that thromboxane A2 is one of the contractile prostanoids involved in this response. Endothelium denudation clearly diminished the vasoconstrictor potency of 15-E2t-IsoP, demonstrating that the endothelium releases a vasoconstrictor factor in response to 15-E2t-IsoP. The absence of an inhibitory effect at the highest concentration of furegrelate (30 microM) on 15-E2t-IsoP-induced contraction of HUV rings without endothelium suggested that endothelium is the source of thromboxane A2. We conclude that prostanoids derived from the COX-2 isoenzyme pathway participate in 15-E2t-IsoP-induced vasoconstriction of isolated HUV rings. Our results also indicate that endothelial thromboxane A2 is one of the prostanoids involved in this effect.

CONTRIBUTION OF PROSTANOID TP RECEPTORS TO THE PRESSOR AND INTRARENAL HAEMODYNAMIC RESPONSE TO ENDOTHELIN

Previous studies have shown that endothelin (ET)-1 stimulates thromboxane (Tx)A(2) production and so we hypothesized that inhibiting prostanoid TP receptors would prevent the pressor and intrarenal haemodynamic response to an acute infusion of ET-1. 2. Male Sprague-Dawley rats were anaesthetized with Inactin (Sigma Chemical, St Louis, MO, USA; 50 mg/kg) and catheters were inserted into the femoral artery and vein for recording mean arterial pressure (MAP) and infusion of ET-1 and receptor antagonists, respectively. A jugular vein catheter was used for the infusion of bovine serum albumin (6.2% in saline) during surgery (1.25% bodyweight). The pressor response to a 1 h infusion of ET-1 (6 pmol/kg per min) was determined in rats that had been pretreated with vehicle (0.9% NaCl) or the TP receptor antagonist SQ29548 (2 mg/kg per h). Laser Doppler single-optic fibres were implanted in the left kidney for the measurement of medullary blood flow (MBF) and cortical blood flow (CBF). 3. Prostanoid TP receptor blockade completely inhibited the acute pressor response to ET-1; the change in MAP was 14 2% versus -3 4% in vehicle and SQ29548 groups, respectively (P<0.05). Endothelin-1 reduced CBF (-15.2 3.3%), a response that was not significantly changed by SQ29548 (-6.2 7.6%). Similarly, the ET-1-mediated response in MBF was not altered by the TP receptor antagonist (7.7 4.9 vs 6.5 5.2%). 4. To determine the influence of the ET(B) receptor in modulating the response to ET-1 during TP receptor blockade, additional groups were pretreated with A-192621, an ET(B) receptor-selective antagonist (10 mg/kg, i.v.). A-192621 potentiated the increase in MAP produced by ET-1 (32 5%; P<0.05 vs ET-1 alone). SQ29548 significantly inhibited, but did not completely block, the increase in MAP produced by ET-1 during ET(B) antagonist treatment (18 4%; P<0.05). Endothelin-1-induced decreases in CBF were significantly enhanced in rats that were pretreated with A-192621, whereas ET-1 also significantly decreased MBF following A-192621 treatment. During ET(B) receptor blockade, TP receptor inhibition had no effect on the ET-1-mediated response of CBF and MBF. 5. These results suggest that TP receptor activation is not involved in the renal haemodynamic responses to ET-1. However, TP receptor activation contributes to the acute pressor response to ET-1, but does not account for the potentiated increase in MAP during ET(B) receptor blockade.

Vasoconstrictor effects of 8-iso-prostaglandin E2 and 8-iso-prostaglandin F2α on human umbilical vein

The present study was undertaken to determine whether 8-iso-prostaglandin E2 and 8-iso-prostaglandin F(2alpha) posses contractile action on human umbilical vein and to evaluate the possible involvement of prostanoid TP receptors in this effect. Human umbilical vein rings were mounted in organ baths and concentration-response curves to 8-iso-prostaglandin E2 or 8-iso-prostaglandin F(2alpha) were constructed. Both isoprostanes evoked concentration-dependent contraction. 8-iso-prostaglandin E2 (pEC50=6.90+/-0.03) was significantly more potent than 8-iso-prostaglandin F(2alpha) (pEC50=6.10+/-0.04). However, both isoprostanes were equieffective. The prostanoid TP receptor antagonists, ICI-192,605 (4-(Z)-6-(2-o-Chlorophenyl-4-o-hydroxyphenyl-1,3-dioxan-cis-5-yl)hexenoic acid) and SQ-29548 (7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-[1S(1alpha,2alpha(Z),3alpha,4alpha)]-5-Heptenoic acid) produced a competitive rightward shift of 8-iso-prostaglandin E2 concentration-response curves with pKB values of 8.91+/-0.04 and 8.07+/-0.07, respectively. When ICI-192,605 (1 nM) and SQ-29548 (10 nM) were evaluated against 8-iso-prostaglandin F(2alpha) they produced a parallel rightward displacement of 8-iso-prostaglandin F(2alpha) concentration-response curves without affecting the maximum responses giving pA2 values of 9.02+/-0.12 and 8.26+/-0.13, respectively. In conclusion, the present study describes for the first time the vasoconstrictor action of 8-iso-prostaglandin E2 and 8-iso-prostaglandin F(2alpha) in human umbilical vein. Furthermore, the affinity values obtained with ICI-192,605 and SQ-29548 provide strong pharmacological evidence of prostanoid TP receptors involvement in this effect.

Augmentation of bovine airway smooth muscle responsiveness to carbachol, KCl, and histamine by the isoprostane 8-iso-PGE2

Isoprostanes are generated during periods of oxidative stress, which characterize diseases such as asthma and cystic fibrosis. They also elicit functional responses and may therefore contribute to the pathology of these diseases. We set out to examine the effects of isoprostanes on airway responsiveness to cholinergic stimulation. Muscle bath techniques were employed using isolated bovine tracheal smooth muscle. 8-Isoprostaglandin E2 (8-iso-PGE2) increased tone directly on its own, although the magnitude of this response, even at the highest concentration tested, was only a fraction of that evoked by KCl or carbachol. More importantly, though, pretreatment of the tissues with 8-iso-PGE2 (10 microM) markedly augmented responses to submaximal and even subthreshold concentrations of KCl, carbachol, or histamine, whereas maximal responses to these agents were unaffected by the isoprostane. The augmentative effect on cholinergic responsiveness was mimicked by PGE2 (0.1 microM) and by the FP agonists PGF2 (0.1 microM) and fluprostenol (0.1 microM), but not by the EP3 agonist sulprostone (0.1 microM) or the TP agonist U-46619 (0.1 microM). Antagonists of EP1 receptors (AH-6809 and SC-19920, 10 microM) and TP receptors (ICI-192605, 1 microM) had no effect on 8-iso-PGE2-induced augmentation of cholinergic responsiveness. We conclude that 8-iso-PGE2 induces nonspecific airway smooth muscle hyperresponsiveness through a non-TP non-EP prostanoid receptor.

Effects of 8-iso-prostaglandin E2 and 8-iso-prostaglandin F2 alpha on the release of noradrenaline from the isolated rat stomach

In the present experiment, we examined the effect of 8-iso-prostaglandin E(2) and 8-iso-prostaglandin F(2 alpha) on the release of noradrenaline from the isolated rat stomach. The postganglionic sympathetic nerves were electrically stimulated twice at 1 Hz for 1 min and test reagents were added during the second stimulation. 8-Iso-prostaglandin E(2) (10(-8)-10(-6) M) and 8-iso-prostaglandin F(2 alpha) (10(-7)-10(-5) M) dose-dependently reduced the evoked noradrenaline release, and these inhibitory potencies were as follows: 8-iso-prostaglandin E(2)>8-iso-prostaglandin F(2 alpha). The inhibitory effect of 8-iso-prostaglandin F(2 alpha), but not 8-iso-prostaglandin E(2), was abolished by 10(-6) M SQ-29548 ([1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-7-[3-[[2-[(phenylamino)carbonyl]hydrazino] methyl]-7-oxabicyclo[2,2,1]hept-2-yl]-5-heptenoic acid) (a prostanoid TP receptor antagonist). On the other hand, the inhibitory effect of 8-iso-prostaglandin E(2) was abolished by 10(-5) M AH-6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) (a prostanoid EP receptor antagonist), which also attenuated the inhibitory effects of ONO-AE-248 (16S-9-deoxy-9 beta-chloro-15-deoxy-16-hydroxy-17,17-trimethylene 19, 20-didehydro prostaglandin F(2)) (a selective EP(3) receptor agonist) on the evoked release of noradrenaline. The inhibitory effect of 8-iso-prostaglandin F(2 alpha), but not 8-iso-prostaglandin E(2), was abolished by pertussis toxin. These results suggest that 8-iso-prostaglandin F(2 alpha) inhibits noradrenaline release through TP receptors, whereas 8-iso-prostaglandin E(2) seems to inhibit noradrenaline release through EP(3) receptors, located on the gastric sympathetic nerve terminals in rats.

Isoprostane 8-epi-prostaglandin F2 alpha decreases lymph capillary pressure in patients with primary lymphedema

In patients with lymphedema, reduced lymph drainage capacity results in an overloaded superficial microlymphatic network and microlymphatic hypertension. In in vitro experiments, it has been shown that 8-epi-prostaglandin F2 alpha (PGF) induced contractions in human lymphatics. Since lymphatic contractility plays a crucial role in the regulation and generation of lymph transport, we studied the effect of PGF on microlymphatic dynamics by measuring lymph capillary pressure (LCP). Twenty healthy volunteers and 13 patients with primary lymphedema were studied after either PGF or placebo was applied to the skin and occlusively covered for 30 min. Glass micropipettes (7-9 microm) were inserted under microscopic control into initial lymphatics visualized by fluorescence microlymphography and pressure measurements were performed using the servo-nulling technique. The mean LCP in patients with lymphedema was significantly higher (19.8 +/- 12.1 mm Hg) than that in healthy controls (8.4 +/- 4.1 mm Hg) at the placebo-treated site and decreased to normal values after PGF (10.0 +/- 7.7 mm Hg). In healthy volunteers, there was no significant decrease of LCP with PGF compared to placebo. PGF normalizes microlymphatic hypertension in patients with lymphedema by improving lymph transport into deeper channels.

Induction of endothelin-1 expression by oxidative stress in vascular smooth muscle cells

Atherosclerosis is based on endothelial dysfunction leading to impaired vasomotor function. This is partially due to nitric oxide (NO) depletion caused by oxidative stress. Since the vasoconstrictor endothelin-1 (ET-1) might also be involved in endothelial dysfunction, we investigated whether oxidative stress regulates ET-1 expression in vascular smooth muscle cells (VSMC). Human aortic VSMC were treated with H(2)O(2) (200 microM) for up to 8 h. mRNA expression of preproendothelin (prepro-ET) was analyzed by RT-PCR. ET-1 protein and the marker for oxidative stress, 8-isoprostane, were determined by ELISA. Activity of cytosolic phospholipase A2 (cPLA(2)) as an indicator of ET-1 autocrine activity was measured photometrically. Stimulation of VSMC with H(2)O(2) resulted in increased expression of prepro-ET mRNA after 1 h with a maximum after 6 h (fourfold), similar to treatment with angiotensin II. ET-1 protein was significantly increased by H(2)O(2) treatment with a maximum after 8 h (P<.05). This effect was inhibited by the antioxidants resveratrol (100 microM) and quercetin (50 microM). In quiesced VSMC, incubation with H(2)O(2)-conditioned medium resulted in increased cPLA(2) activity compared to the controls (P<.05). This activity was partially inhibited by the ET(A)-receptor antagonist, PD 142893 (10 microM), indicating functional ET-1 in the conditioned medium. The presence of oxidative stress in H(2)O(2)-treated VSMC was associated by significantly increased formation of 8-isoprostane (P<.05). The data indicate for the first time that oxidative stress increases ET-1 generation and autocrine ET-1 activity in VSMC, a mechanism that might contribute to endothelial dysfunction in atherosclerosis.

Characterization of the effects of isoprostanes on platelet aggregation in human whole blood

We tested the effects of 11 commercially-available isoprostanes on platelet aggregation directly or when triggered by the thromboxane receptor agonist U46619 or collagen in healthy human citrated blood using a whole blood aggregometer. None of the isoprostanes tested triggered aggregation alone, nor facilitated aggregation by a sub-threshold dose of U46619 or collagen. Five isoprostanes inhibited aggregation (rank order of potency 8-iso PGE(1)>8-iso PGE(2)>8-iso PGF(2alpha)>8-iso PGF(3alpha)>8-iso-13,14-dihydro-15-keto PGF(2alpha)). Blood incubated with LPS to induce a gross inflammatory response exhibited a time dependent (2 - 12 h) reduction in aggregation to U46619 but maintained a consistent response to collagen. Under these conditions, as in control blood, none of the isoprostanes tested induced aggregation. In fact, the inhibitory actions of isoprostanes on U46619-induced aggregation were enhanced in blood treated with LPS. L-NAME inhibited aggregation induced by U46619 in fresh blood and in blood treated with LPS. In the presence of L-NAME, (with or without LPS) none of the isoprostanes tested induced aggregation but retained their inhibitory action. Thus, in human whole blood the action of 8-iso PGE(1), 8-iso PGE(2), 8-iso PGF(2alpha), 8-iso PGF(3alpha), and 8-iso-13,14-dihydro-15-keto PGF(2alpha) is antiaggregatory. Moreover, this inhibitory capacity is still apparent and may be enhanced in blood subjected to inflammatory stimulation.

Vascular biology of the isoprostanes

Isoprostanes are a family of compounds produced from polyunsaturated fatty acids via a free-radical-catalysed mechanism. F(2)-isoprostanes are prostaglandin F(2alpha) isomers derived from arachidonic acid. These compounds induce potent vasoconstriction, mediated primarily by TP receptor stimulation, and in some vessels by the release of cyclooxygenase products. This vasoconstriction may be modulated by the endothelium through the release of NO. Potent vasoconstriction is also observed with E(2)-isoprostanes. Experimental and clinical data suggest a role for F(2)-isoprostanes in atherogenesis. These compounds can be detected in free forms in biological fluids as well as esterified in low-density lipoproteins or cell membranes. Their quantification represents a reliable marker of lipid peroxidation. Elevated levels of F(2)-isoprostanes in biological fluids in pathological conditions including atherosclerosis, ischaemia-reperfusion injury, and inflammatory vascular diseases, suggest a relationship between lipid peroxidation and such diseases. F(2)-isoprostanes are currently being investigated as non-invasive quantitative markers to monitor the response to anti-oxidant treatment.

Cyclosporine A and cremophor EL induce contractions of human saphenous vein: involvement of thromboxane A2 receptor-dependent pathway

Chronic treatment with Sandimmune (cyclosporine A [CsA] dissolved in Cremophor EL [CrEL]) is often associated with hypertension and nephrotoxicity. The aims of the present study were to assess the effect of Sandimmune and its two main components (CsA and CrEL) on human saphenous veins and to study the underlying mechanism of their contractile responses. In organ bath, concentration-response curves for Sandimmune (36 ng/ml-120 microg/ml of CsA). CsA (36 ng/ml-120 microg/ml), or CrEL (2.4 microg/ml-8 mg/ml) were elicited in the presence of a thromboxane A2 (TXA2) receptor antagonist (GR32191, 0.3 microM), a cyclooxygenase inhibitor (indomethacin, 1 microM), a 5-lipoxygenase inhibitor (AA861, 10 microM), or their respective vehicles. In addition, the production of TXA2 after CsA challenge was assessed by enzyme immunoassay. Sandimmune, CsA, and CrEL induced concentration-dependent contractions on human saphenous veins. In terms of potency, CsA was a more potent vasoconstrictor agent than CrEL (EC50 values: 11.9+/-3.7 microg/ml (CsA, n = 12) vs. 1.2+/-0.4 mg/ml (CrEL, n = 16), p < 0.05). In contrast, in terms of efficacy, CrEL induced greater contractions than CsA (Emax (% of KCl 90 mM-induced contraction): 98.1+/-16.1% (CrEL, n = 16) vs. 17.0+/-4.3% (CsA, n = 12) p < 0.05). Pretreatment with GR32191 significantly reduced by 85% and 56% the contractions elicited by CsA and CrEL, respectively, whereas indomethacin had no effect. Finally, CsA (12 and 120 microg/ml) failed to stimulate TXA2 production. These in vitro data suggest that Sandimmune-induced contractions on human vascular smooth muscle appear to be mediated by CsA in the therapeutic ranges of doses and by both CsA and CrEL, which, in supratherapeutic doses, acted through a TXA2 receptor-dependent pathway.