Ropivacaine attenuates pulmonary vasoconstriction induced by thromboxane A2 analogue in the isolated perfused rat lung

BACKGROUND AND OBJECTIVES: Thromboxane A2 (TXA2) activation is involved in several pathophysiological states in producing pulmonary hypertension. Local anesthetics (LA) inhibit signaling of TXA2 receptors expressed in cell models. Therefore, we hypothesized that LA may inhibit pulmonary vasoconstriction induced by the TXA2 analogue U 46619 in an isolated lung model. METHODS: Isolated rat lungs were perfused with physiological saline solution and autologous blood with or without the LA lidocaine, bupivacaine, ropivacaine, or the permanently charged lidocaine analogue QX 314 (all 1 microg/mL) as a pretreatment. Subsequently, pulmonary vasoconstriction was induced by 3 concentrations of U 46619 (25, 50, and 100 ng/mL) and the change in pulmonary artery pressure (Pa) was compared with each LA. In a second experiment, Pa responses to angiotensin II (0.1 microg), hypoxic pulmonary vasoconstriction (HPV, 3% O2 for 10 minutes), or phenylephrine (0.1 microg) were assessed to determine the specificity of ropivacaine effects on TXA2 receptors. Finally, reversibility of pulmonary vasoconstriction was determined by adding ropivacaine to the perfusate after pulmonary vasoconstriction was established with U 46619. RESULTS: Ropivacaine, but not bupivacaine, lidocaine, or QX 314 significantly attenuated pulmonary vasoconstriction induced by 50 ng/mL U 46619 (35.9%, P<.003) or 100 ng/mL U 46619 (45.2%, P<.001). This effect of ropivacaine was likely to be specific for the thromboxane receptor because pulmonary vasoconstriction induced by angiotensin II, HPV, or phenylephrine was not altered. Ropivacaine did not reverse vasoconstriction when it was administered after U 46619. CONCLUSIONS: Ropivacaine, but not lidocaine, bupivacaine, or QX 314 at 1 microg/mL, attenuates U 46619-induced pulmonary vasoconstriction in an isolated perfused rat lung model. These results support evidence that the clinically used enantiomer S(-)-ropivacaine may inhibit TXA2 signaling.     

Halothane and isoflurane preferentially inhibit prostanoid-induced vasoconstriction of rat aorta

In a previous study, we demonstrated that halothane and isoflurane inhibit binding of thromboxane A₂ to its receptors on human platelets and thus inhibit prostanoid-induced aggregation strongly. The aim of this study was to determine whether volatile anaesthetics inhibit prostanoid-induced vasoconstriction preferentially. Rat isolated aortic rings were mounted in organ baths and their isometric tension was measured. They were contracted with STA2 (a stable thromboxane A₂ analogue), prostaglandin F_2α (PGF_2α), phenylephrine, and 20 mM KCl, and then exposed to halothane (0.5–3%), isoflurane (0.5–3%), and sodium nitroprusside (SNP, 10^?9?3 × 10^?7 M). Halothane (2–3%) and isoflurane (2–3%) induced greater relaxation of aortic rings precontracted with STA2 and PGF_2α than of those precontracted with phenylephrine (P < 0.01). Halothane induced greater relaxation of rings precontracted with KCl than phenylephrine only at 3%, whereas isoflurance relaxed rings precontracted with KCl more than those with phenylephrine at 0.5, 2 and 3% (P < 0.05). In contrast, SNP relaxed rings precontracted with PGF_2α, KCl and phenylephrine equally, but induced smaller relaxations of those precontracted with STA2 (P < 0.05). We conclude that halothane and isoflurane inhibit prostanoid-induced vasoconstriction preferentially, possibly by interacting with prostanoid receptors.     

Characterization of thromboxane A2 receptors in rat kidney

The renal TXA2 receptors were investigated in preparations derived from rat kidney. Perfused rat kidneys were removed and separated into cortex and medulla. Each subcellular fraction was prepared by a sucrose density gradient method for analyzing the subcellular distribution of TXA2 receptors. The membranes were obtained by 40,000 x g centrifugation for analyzing the renal distribution of TXA2 receptors. Bindings of [3H]SQ 29548, a TXA2 receptor antagonist, to these preparations were carried out using a filtration method. Furthermore, the binding of [3H]SQ 29548 to membranes from rat kidney cortex was compared with its binding to rat washed platelets. The membrane fraction had the highest density of TXA2 receptors among subcellular fractions determined. TXA2 receptors appeared in corticomedullary junction with high density. Scatchard analysis using [3H]SQ 29548 as a ligand revealed a single binding site of TXA2 receptors in membranes from rat kidney cortex, and the dissociation constant (Kd) was remarkably higher than the Kd in rat washed platelets. These findings suggest that TXA2 receptors in membranes from rat kidney cortex are different from those in rat platelets, and TXA2 receptor activation in kidney might play a role in renal function.     

Remifentanil produces vasorelaxation in isolated rat thoracic aorta strips

BACKGROUND: Remifentanil can cause transient instability in hemodynamic variables. However this change may not be solely the result of autonomic or central nervous system inhibition or of centrally mediated vagal stimulation. In this study, the aim was to examine the direct effects of remifentanil on isolated thoracic aorta strips in vitro. METHODS: Forty-five Wistar rat thoracic aorta rings were isolated, and contraction-relaxation responses were recorded. RESULTS: In aortic rings precontracted with phenylephrine or potassium chloride, remifentanil produced concentration-dependent relaxation in both endothelium-intact and denuded rings (P<0.001). Remifentanil induced significantly greater relaxation in intact rings than in those denuded of endothelium, regardless of whether they were precontracted with phenylephrine hydrochloride or KCl (P<0.001). When the endothelium was present, remifentanil produced greater relaxation in KCl-contracted rings than in PE-contracted rings at lower concentrations (10-9 and 10-8), and similar relaxation at higher concentrations (10-7 and 10-6). However, when the endothelium was removed, relaxation was similar in both solutions, at all concentrations (10-9 to 10-6). In intact rings, pretreatment with L-NO-ARG or indomethacin reduced the degree of remifentanil-induced relaxation. In Ca+ +/- free media, calcium-dependent KCl contractions were inhibited in a dose-dependent manner by remifentanil (P<0.001). CONCLUSION: Remifentanil vasodilates by an endothelium-dependent mechanism, involving prostacyclin and nitric oxide released from the endothelium. Its endothelium-independent vasodilation probably occurs via the suppression of voltage-sensitive Ca++ channels.     

Bupivacaine inhibits acylcarnitine exchange in cardiac mitochondria

BACKGROUND: The authors previously reported that secondary carnitine deficiency may sensitize the heart to bupivacaine-induced arrhythmias. In this study, the authors tested whether bupivacaine inhibits carnitine metabolism in cardiac mitochondria. METHODS: Rat cardiac interfibrillar mitochondria were prepared using a differential centrifugation technique. Rates of adenosine diphosphate-stimulated (state III) and adenosine diphosphate-limited (state IV) oxygen consumption were measured using a Clark electrode, using lipid or nonlipid substrates with varying concentrations of a local anesthetic. RESULTS: State III respiration supported by the nonlipid substrate pyruvate (plus malate) is minimally affected by bupivacaine concentrations up to 2 mM. Lower concentrations of bupivacaine inhibited respiration when the available substrates were palmitoylcarnitine or acetylcarnitine; bupivacaine concentration causing 50% reduction in respiration (IC50 +/- SD) was 0.78+/-0.17 mM and 0.37+/-0.03 mM for palmitoylcarnitine and acetylcarnitine, respectively. Respiration was equally inhibited by bupivacaine when the substrates were palmitoylcarnitine alone, or palmitoyl-CoA plus carnitine. Bupivacaine (IC50 = 0.26+/-0.06 mM) and etidocaine (IC50 = 0.30+/-0.12 mM) inhibit carnitine-stimulated pyruvate oxidation similarly, whereas the lidocaine IC50 is greater by a factor of roughly 5, (IC50 = 1.4+/-0.26 mM), and ropivacaine is intermediate, IC50 = 0.5+/-0.28 mM. CONCLUSIONS: Bupivacaine inhibits mitochondrial state III respiration when acylcarnitines are the available substrate. The substrate specificity of this effect rules out bupivacaine inhibition of carnitine palmitoyl transferases I and II, carnitine acetyltransferase, and fatty acid beta-oxidation. The authors hypothesize that differential inhibition of carnitine-stimulated pyruvate oxidation by various local anesthetics supports the clinical relevance of inhibition of carnitine-acylcarnitine translocase by local anesthetics with a cardiotoxic profile.     

The inhibition of thromboxane synthesis has no influence on HgCl2-induced acute renal failure in the rat

Renal function parameters and urinary thromboxane B2-excretion were studied in the rat in HgCl2-induced acute renal failure. Studies were performed before and 3 h after the inhibition of thromboxane synthesis alone, after HgCl2 alone, or after the combination of HgCl2 and thromboxane-synthesis inhibition. Thromboxane-synthesis inhibition alone by indomethacin (5 mg/kg i.v.), imidazole (25 and 50 mumol/kg per min i.v.) and dazoxiben (5 mg/kg i.v.) had no effect on glomerular filtration rate (GFR) or para-aminohippuric acid clearance (CPAH), whereas urinary thromboxane excretion was suppressed. Only the administration of the selective blockers imidazole and dazoxiben resulted in a marked increase in urinary volume (V) and fractional sodium excretion (FENa). HgCl2 alone (2 mg/kg i.v.) caused a decrease in GFR and CPAH with -38% (P less than 0.01), and urinary thromboxane B2 excretion increased from 20.3 +/- 1.5 to 30.6 +/- 2.6 pg/min. (P less than 0.01). The administration of indomethacin, imidazole (50 mumol/kg per min) and dazoxiben prevented the increase in thromboxane B2 excretion 3 h after HgCl2 to values of 3.3 +/- 1.2, 6.9 +/- 0.6 and 13.0 +/- 1.6 pg/min respectively (P less than 0.01 versus control for all values). Despite this, the decrease in GFR and CPAH after HgCl2 could not be prevented. A decrease of GFR with -44, -54, -57 and -32% and of CPAH with -37, -49, -57 and -27% were observed for indomethacin, imidazole 25 and 50 mumol/kg per min and dazoxiben respectively. This evolution was not significantly different from what was observed with mercury alone. Selective thromboxane synthesis inhibition resulted in a decrease of serum free ionised calcium.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro effects of antihypertensive drugs on thromboxane agonist (U46619)-induced vasoconstriction in human internal mammary artery

Background. Hypertension is a major problem in the perioperativeperiod of cardiac and non-cardiac surgery. The vascular endotheliumplays a crucial role in modulating vascular tone by producingvasodilators as well as vasoconstrictors. Thromboxane A₂ (TxA₂),a prototypical vasoconstrictor produced by endothelium and platelets,may play an important role in the pathogenesis of hypertensionand subsequent ischaemic events. Although multiple drugs arecurrently available to treat perioperative hypertension, thereis a paucity of data comparing these agents. Therefore, we examinedthe in vitro vascular effects of commonly used antihypertensivedrugs on human internal mammary artery (IMA) segments. Methods. Relaxation responses to adenosine (a nucleoside), enalaprilat(a competitive inhibitor of angiotensin-converting enzyme),fenoldopam (a D₁-dopamine receptor agonist), hydralazine, labetalol(an     

丙泊酚抑制H_2O_2诱导的内皮细胞通透性增加

目的探讨丙泊酚对H2O2诱导的内皮通透性增加的影响。方法实验一:分别用0、0.2、0.4、0.6和0.8mmol/L H2O2刺激人脐静脉内皮细胞(human umbilical vein endothelial cells,HUVECs)后通过测量跨细胞电阻(TER)以观察H2O2对HUVECs通透性的影响。实验二:随机分为对照组(C组,无处理)、PBS组(等体积PBS)、丙泊酚1组(P1组,丙泊酚20μmol/L)、丙泊酚2组(P2组,丙泊酚50μmol/L)、丙泊酚3组(P3组,丙泊酚100μmol/L)及脂肪乳剂组(Ⅰ组,等体积脂肪乳剂)。按实验设计预处理30min后,选用0.6mmol/L H2O2刺激HUVECs 60min(C组无处理),然后分别以TER、免疫荧光染色、western blot检测内皮细胞通透性、细胞肌动蛋白(F-actin)形态学、ERK1/ERK2及p38磷酸化水平。结果与0mmol/L H2O2比较,0.4、0.6、0.8mmol/LH2O2刺激后30~180min HUVECs TER明显减少(P0.05),刺激60min HUVECs TER明显减少并达到峰值,而后均呈恢复趋势,而且0.6、0.8 mmol/L H2O2刺激后HUVECs TER明显低于0.4mmol/L H2O2(P0.05)。与C组比较,0.6mmol/L H2O2刺激后15~60min PBS组、P1组、I组和刺激后45、60min P2组、P3组HUVECs TER明显减少(P0.05)。与PBS组比较,刺激后30~60min P2组、P3组HUVECs TER明显增加(P0.05)。与P2组比较,刺激后30~60min P1组、I组HUVECs TER明显减少(P0.05)。C组F-actin集中分布在内皮细胞周边,无应力纤维形成;PBS组F-actin在细胞内非极性排列成束,应力纤维形成;P2组H2O2诱导的F-actin细胞内束集及应力纤维形成明显得到改善;I组应力纤维形成。与C组比较,PBS组、P2组和I组内皮细胞ERK1/ERK2及p-38磷酸化水平明显升高(P0.05)。与PBS组比较,P2组内皮细胞ERK1/ERK2及p-38磷酸化水明显降低(P0.05)。结论丙泊酚可以抑制H2O2诱导HUVEC通透性增高,其分子机制可能与抑制p38及ERK1/2信号通路激活有关。     

Bupivacaine inhibits whole blood coagulation in vitro.

BACKGROUND AND OBJECTIVES: Epidural anesthesia decreases the risk of postoperative deep venous thrombosis in selected patients. Intravascular local anesthetic levels resulting from epidural anesthesia may contribute to this effect by impacting coagulation. We studied the effects of bupivacaine (1-10 micromol/L) on whole blood coagulation measured by thrombelastography (TEG) and activated clotting time (ACT). METHODS: We incubated whole blood with bupivacaine (1, 2, and 10 micromol/L) or Tyrode's solution (control) for 60 minutes and measured TEG and ACT clotting parameters. RESULTS: Bupivacaine (1 or 10 micromol/L) prolonged ACT when compared with control. The thromboxane A2 (TX) receptor antagonist SQ29548 also prolonged ACT significantly. The combination of SQ29548 and bupivacaine was equally effective as bupivacaine alone, compatible with the hypothesis that bupivacaine at these concentrations blocks TX signaling. Because SQ29548 + bupivacaine prolonged ACT more than did SQ29548 alone, bupivacaine likely inhibits processes in addition to TX signaling. This was evaluated further using TEG. After incubation with 2 microm bupivacaine, TEG reaction time and clot growth time increased significantly, and maximal amplitude decreased. CONCLUSIONS: Bupivacaine in clinically relevant concentrations influences whole blood clotting characteristics as measured by TEG and ACT. Thromboxane receptor antagonism increases ACT, confirming a role for TX in coagulation. Bupivacaine may also inhibit TX signaling, but seems to block additional factors as well. These findings might partly explain the beneficial effects of epidural anesthesia on postoperative thrombotic events.     

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

BACKGROUND: Interactions among angiotensin II (Ang II), endothelin-1 (ET-1) and thromboxane A2 (TXA2) may play an important role in the regulation of renal function. The present study investigated the participation of TXA2 and ET-1 in the increase in renal vascular resistances (RVR) induced by Ang II, as well as the consequences of diabetes, hypertension, and the combination of both on this response. METHODS: Isolated kidneys from male normoglycemic or streptozotocin-induced diabetic Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were used. The increase in perfusion pressure (PP) produced by Ang II was studied in the absence or presence of the TXA2 receptor antagonist, ifetroban, or the ETA/ETB receptor antagonist, PD145065. RESULTS: Systolic arterial pressure (SAP) was higher in SHR than in WKY, but diabetic rats (D) from each strain showed lower SAP values than their respective non-diabetic rats. Basal renal PP was higher in WKY and SHR than in WKY-D and SHR-D. Increases in renal PP produced by Ang II were comparable in the kidneys from all groups. Either ifetroban or PD145065 reduced the maximal Ang II response in all animals. The maximal inhibitory effect of ifetroban was higher (P<0.05) in WKY than in the other groups. However, the maximal inhibitory effect of PD145065 was lower in SHR than in the other groups. CONCLUSION: This study supports a role for ET-1 and TXA2 as mediators of the increase in renal vascular resistance produced by Ang II. These results indicate that the participation of ET-1 in the renal vasoconstriction produced by Ang II was reduced under hypertensive conditions, and that of TXA2 was reduced by both diabetes and hypertension.     

Role of endothelium in the modulation of isoflurane-induced vasodilatation in rat thoracic aorta

The mechanisms by which endothelium attenuates vasodilation caused by isoflurane are not well understood. We examined the role of endothelium- derived substances, nitric oxide (NO), endothelium-derived hyperpolarizing factors (EDHF), prostanoids and endothelins in the response to isoflurane in rat thoracic aorta. Increasing cumulative concentrations of isoflurane were administered to aortic rings suspended in Hepes solution and preconstricted with either phenylephrine 10(-6) mol litre-1 or KCl 40 mmol litre-1 (which inhibit EDHF). Rings were intact, denuded or incubated with an inhibitor of nitric oxide synthesis (N omega-nitro-L-arginine (LNNA 5 x 10(-5) mol litre-1), an inhibitor of prostanoid synthesis (indomethacin 10(-5) mol litre-1) or a blocker of the vascular receptors to endothelins (cyclo (- D-trp-D-Asp-Pro-D-Val-Leu (BQ 123 10(-5) mol litre-1)- Endothelium attenuated isoflurane-induced vasodilation in KCl-constricted rings at concentrations of 4% (mean 95 (SEM 4)% vs 72 (4)%; P = 0.0005) and 5% (100 (4)% vs 80 (4)%; P = 0.0008) and in phenylephrine constricted rings at concentrations of 4% (54 (8)% vs 35 (3)%; P = 0.04) and 5% (78 (10)% vs 49 (5)%; P = 0.03). Relaxation was significantly greater in rings treated with LNNA than in intact rings at concentrations of 4% (85 (4)% vs 72 (4)%; P = 0.0005) and 5% (90 (4)% vs 80 (4)%; P = 0.0008). Indomethacin and BQ 123 did not alter isoflurane-induced vasodilation. We conclude that endothelium attenuated the vasodilator effect of isoflurane by a mechanism which was abolished by inhibition of nitric oxide. We hypothesize that isoflurane inhibits the release of nitric oxide, leading to a relative vasoconstriction counter-balancing its vasodilator effect. In contrast, EDHF, prostanoids and endothelins were not involved in the attenuation of isoflurane-induced vasodilatation.      

Halothane attenuates nitroglycerin-induced vasodilation and a decrease in intracellular Ca2+ in the rat thoracic aorta.

Although halothane inhibits endothelium-mediated vasorelaxation, the sites of inhibition remain controversial. Because the cytosolic concentration of Ca2+ ([Ca2+]i) has crucial roles for tension development, we examined the effects of halothane on nitroglycerin-induced vasorelaxation from the standpoint of [Ca2+]i. Isolated spiral strips of rat thoracic aorta without endothelium were suspended for isometric tension recordings in a physiologic salt solution. Muscle contraction was evoked with 10(-8) M norepinephrine, followed by endothelium-independent vasorelaxation with nitroglycerin 10(-7) and 10(-6) M. The effects of halothane 1.5% and 3% on nitroglycerin-induced vasorelaxation were evaluated along with the concomitant measurement of [Ca2+]i using fura-2-Ca2+ fluorescence. In other muscle strips, incremental doses of norepinephrine were administered during halothane exposure to induce contractions comparable to those without halothane. Nitroglycerin dose-dependently reduced norepinephrine-induced muscle contractions, but the decrease in [Ca2+]i reached a plateau at 10(-7) M, which indicates that nitroglycerin induced [Ca2+]i-dependent and [Ca2+]i-independent vasorelaxation. Both concentrations of halothane inhibited nitroglycerin-induced decreases in muscle tension and [Ca2+]i, not only when the same dose of norepinephrine was used for contraction during halothane exposure, but also at incremental doses of norepinephrine. In conclusion, halothane inhibits nitroglycerin-induced vasorelaxation partly by suppressing Ca2+ changes in the smooth muscle. IMPLICATIONS: We examined nitroglycerin-induced vasorelaxation in the rat thoracic aorta, along with the concomitant measurement of the cytosolic concentrations of Ca2+, and found that halothane attenuated endothelium-independent vasorelaxation by suppressing Ca2+ dynamics in the smooth muscle.     

A unified approach to the torn thoracic aorta

In a 3-year experience treating 12 patients with blunt torn thoracic aorta, the repair technique was "clamp and sew" with an intraluminal graft in the initial six patients and partial left heart bypass using a centrifugal pump in the more recently treated six. Patients in the two groups were similar in regard to age, sex, and injury severity score. In the intraluminal graft group, graft insertion was abandoned for sutured anastomosis in two patients. Two patients sustained spinal cord ischemia, and two developed hypertension due to "pseudo-coarctation" syndrome. Because of these side effects related to the performance of intraluminal graft, partial left heart bypass was adopted as our routine procedure and was successful in all subsequent patients. Based on our experience and on reports in the current literature, we recommend left atrial-femoral bypass with the centrifugal pump for repair of the torn thoracic aorta.     

Bupivacaine inhibits baroreflex control of heart rate in conscious rats

BACKGROUND: Because exposure to intravenously administered bupivacaine may alter cardiovascular reflexes, the authors examined bupivacaine actions on baroreflex control of heart rate in conscious rats. METHODS: Baroreflex sensitivity (pulse interval vs. systolic blood pressure in ms/mmHg) was determined before, and 1.5 and 15.0 min after rapid intravenous administration of bupivacaine (0.5, 1.0, and 2.0 mg/kg) using heart rate changes evoked by intravenously administered phenylephrine or nitroprusside. The actions on the sympathetic and parasympathetic autonomic divisions of the baroreflex were tested in the presence of a muscarinic antagonist methyl atropine and a beta-adrenergic antagonist atenolol. RESULTS: Within seconds of injection of bupivacaine, mean arterial pressure increased and heart rate decreased in a dose-dependent manner. Baroreflex sensitivity was unaltered after administration of 0.5 mg/kg bupivacaine. In addition, 1 mg/kg bupivacaine at 1.5 min depressed phenylephrine-evoked reflex bradycardia (0.776 +/- 0.325 vs. 0.543 +/- 0.282 ms/mmHg, P < 0.05) but had no effect on nitroprusside-induced tachycardia. Bupivacaine (2 mg/kg), however, depressed reflex bradycardia and tachycardia (phenylephrine, 0.751 +/- 0.318 vs. 0.451 +/- 0.265; nitroprusside, 0.839 +/- 0.256 vs. 0.564 +/- 0.19 ms/mmHg, P < 0.05). Baroreflex sensitivity returned to prebupivacaine levels by 15 min. Bupivacaine (2 mg/kg), in the presence of atenolol, depressed baroreflex sensitivity (phenylephrine, 0.633 +/- 0.204 vs. 0.277 +/- 0.282; nitroprusside, 0.653 +/- 0.142 vs. 0.320 +/- 0.299 ms/mmHg, P < 0.05). In contrast, bupivacaine did not alter baroreflex sensitivity in the presence of methyl atropine. CONCLUSIONS: Bupivacaine, in clinically relevant concentrations, inhibits baroreflex control of heart rate in conscious rats. This inhibition appears to involve primarily vagal components of the baroreflex-heart rate pathways.     

A case of asymptomatic thoracic aorta mural thrombi.

The natural history, prognostic significance, and optimal therapy of asymptomatic thoracic aorta mural thrombi detected incidentally is not well defined in the literature. We report a case of asymptomatic thoracic aorta mural thrombi in a 42-year-old woman with a history of smoking and steroid use that was conservatively managed with anticoagulation and had a favorable outcome.     

Urine immunoreactive thromboxane B2 in rat cardiac allograft rejection

Increases in urinary excretion of immunoreactive thromboxane B2 (i-TXB2), the stable break-down product of thromboxane A2, have been described in kidney allograft rejection in patients. We investigated these findings by monitoring daily urine i-TXB2 excretion in a heterotopic cardiac allograft rat model using Lewis rats as recipients. In order to obtain differences in allograft survival, a donor was used that was either ACI or LewisxBrown Norway F1 (LxB-NF1). The ACI-to-Lewis model rejected on day 6.2 +/- 0.2 (n = 6). The LxB-NF1-to-Lewis model received, in addition, azathioprine (5 mg/kg/daily) and rejected on day 9.1 +/- 0.8 (n = 9). Urinary i-TXB2 excretion increased significantly in both groups, compared with i-TXB2 values measured following sham surgery or isograft transplantation. Thus increases in urinary i-TXB2 appear to be associated with cardiac allograft rejection.