Novel Series of Methyl 3-(Substituted Benzoyl)-7-Substituted-2-Phenylindolizine-1-Carboxylates as Promising Anti-Inflammatory Agents: Molecular Modeling Studies.

The cyclooxygenase-2 (COX-2) enzyme is considered to be an important target for developing novel anti-inflammatory agents. Selective COX-2 inhibitors offer the advantage of lower adverse effects that are commonly associated with non-selective COX inhibitors. In this work, a novel series of methyl 3-(substituted benzoyl)-7-substituted-2-phenylindolizine-1-carboxylates was synthesized and evaluated for COX-2 inhibitory activity. Compound 4e was identified as the most active compound of the series with an IC50 of 6.71 M, which is comparable to the IC50 of indomethacin, a marketed non-steroidal anti-inflammatory drug (NSAID). Molecular modeling and crystallographic studies were conducted to further characterize the compounds and gain better understanding of the binding interactions between the compounds and the residues at the active site of the COX-2 enzyme. The pharmacokinetic properties and potential toxic effects were predicted for all the synthesized compounds, which indicated good drug-like properties. Thus, these synthesized compounds can be considered as potential lead compounds for developing effective anti-inflammatory therapeutic agents.

Adenosine A2A Receptor as a Potential Drug Target - Current Status and Future Perspectives.

Adenosine receptors (ARs) are a class of G-protein coupled receptors (GPCRs) that are activated by the endogenous substance adenosine. ARs are classified into 4 subtype receptors, namely, the A1, A2A, A2B and A3 receptors. The wide distribution and expression of the ARs in various body tissues as well as the roles they have in controlling different functions in the body make them potential drug targets for the treatment of various pathological conditions, such as cardiac diseases, cancer, Parkinson's disease, inflammation and glaucoma. Therefore, in the past decades, there have been extensive investigations of ARs with a high number of agonists and antagonists identified that can interact with these receptors. This review shall discuss the A2A receptor (A2AAR) subtype of the ARs. The structure, properties and the recent advances in the therapeutic potential of the receptor are discussed with an overview of the recent advances in the methods of studying the receptor. Also, molecular modeling approaches utilized in the design of A2AAR ligands are highlighted with various recent examples.

Current Status in the Design and Development of Agonists and Antagonists of Adenosine A3 Receptor as Potential Therapeutic Agents.

Adenosine receptors (ARs) belongs to the family of G-protein coupled receptors (GPCR) that are responsible for the modulation of a wide variety of physiological functions. The ARs are also implicated in many diseases such as cancer, arthritis, cardiovascular and renal diseases. The adenosine A3 receptor (A3AR) has emerged as a potential drug target for the progress of new and effective therapeutic agents for the treatment of various pathological conditions. This receptor's involvement in many diseases and its validity as a target has been established by many studies. Both agonists and antagonists of A3AR have been extensively investigated in the last decade with the goal of developing novel drugs for treating diseases related to immune disorders, inflammation, cancer, and others. In this review, we shall focus on the medicinal chemistry of A3AR ligands, exploring the diverse chemical classes that have been projected as future leading drug candidates. Also, the recent advances in the therapeuetic applications of A3AR ligands are highlighted.

In vitro assessment of ribose modified two-step etch-and-rinse dentine adhesive.

OBJECTIVE: Collagen fibrils aid in anchoring resin composite restorations to the dentine substrate. The aim of the study was to investigate effect of non-enzymatic glycation on bond strength and durability of demineralized dentine specimens in a modified two-step etch-and-rinse dentine adhesive. METHODS: Dentine surfaces were etched with 37% phosphoric acid, bonded with respective in vitro ethanol and acetone adhesives modified with (m/m, 0, 1%, 2% and 3% ribose), restored with restorative composite-resin, and sectioned into resin-dentine slabs and beams to be stored for 24h or 12 months in artificial saliva. Bond-strength testing was performed with bond failure analysis. Pentosidine assay was performed on demineralized ribose modified dentine specimens with HPLC sensitive fluorescent detection. The structural variations of ribose-modified dentine were analysed using TEM and human dental pulpal cells were used for cell viability. Three-point bending test of ribose-modified dentine beams were performed and depth of penetration of adhesives evaluated with micro-Raman spectroscopy. The MMP-2 and cathepsin K activities in ribose-treated dentine powder were also quantified using ELISA. Bond strength data was expressed using two-way ANOVA followed by Tukey's test. Paired T tests were used to analyse the specimens for pentosidine crosslinks. The modulus of elasticity and dentinal MMP-2 and cathepsin K concentrations was separately analyzed using one-way ANOVA. RESULTS: The incorporation of RB in the experimental two-step etch-and-rinse adhesive at 1% improved the adhesive bond strength without adversely affecting the degree of polymerisation. The newly developed adhesive increases the resistance of dentine collagen to degradation by inhibiting endogenous matrix metalloproteinases and cysteine cathepsins. The application of RB to acid-etched dentine helps maintain the mechanical properties. SIGNIFICANCE: The incorporation of 1%RB can be considered as a potential candidate stabilizing resin dentine bond.

The robustness of subcarrier-index modulation in 16-QAM CO-OFDM system with 1024-point FFT.

We present in numerical simulations the robustness of subcarrier index modulation (SIM) OFDM to combat laser phase noise. The ability of using DFB lasers with SIM-OFDM in 16-QAM CO-OFDM system with 1024-point FFT has been verified. Although SIM-OFDM has lower spectral efficiency compared to the conventional CO-OFDM system, it is a good candidate for 16-QAM CO-OFDM system with 1024-point FFT which uses a DFB laser of 1 MHz linewidth. In addition, we show the tolerance of SIM-OFDM for mitigation of fiber nonlinearities in long-haul CO-OFDM system. The simulation results show a significant penalty reduction, essentially that due to SPM.

Significant reduction of repeat teen pregnancy in a comprehensive young parent program.

OBJECTIVE: To describe a comprehensive, multidisciplinary approach to teen mothers and their children that significantly reduces repeat pregnancies. DESIGN: Retrospective review of repeat teen pregnancy data. SETTING: Young Parent Program (YPP) at a university-based health center. PARTICIPANTS: 1386 teen mothers between the ages of 11 and 19 who participated in the YPP for at least three years. INTERVENTION: Comprehensive Care: for both teen mother and her baby, including prenatal and postnatal care, preventive care, reproductive services, mental health, and acute care visits. Family counseling and similar services were also provided to siblings of the teen. CONTINUITY OF CARE: Patients are seen by the same staff and attending physicians on each visit. The treatment team includes physicians, nurses, social worker, nutritionist, and psychologist, all of whom are available to provide care at each visit. Flexible hours: Including evening clinic to allow teens to attend school or work during the day. Financial incentive: Patients with no insurance are given free contraceptives and a "no charge" clinic visit. Extensive contraceptive counseling is provided prior to start of contraceptive use and at every clinic visit. Routine telephone and/or mail reminders of appointments MAIN OUTCOME MEASURE: Rate of repeat teen pregnancy. RESULTS: Only 11(.79%) had repeat pregnancies. Older youth appeared more likely to repeat a pregnancy. CONCLUSION: Comprehensive intervention for teen mothers can be very successful in reducing repeat teen pregnancy in those teens who participate consistently in the program over a period of years.

Use of activated carbon in removal of some radioisotopes from their waste solutions.

Removal of some radioisotopes namely (152+154)Eu and (65)Zn from radioactive solutions by activated carbon using both batch and column techniques has been performed. Experimental studies were conducted to evaluate and optimize the various process variables, i.e., equilibrium time, carbon dose, solution pH. Sorption data have been interpreted in terms of both Freündlich and Langmuir isotherms. The fixed-bed results indicate the high capacity of the activated carbon for the removal of europium and zinc ions. The data suggest the possible use of activated carbon for the removal of these cations from radioactive waste solutions.

Estrogen-induced relaxation in bovine coronary arteries in vitro: evidence for a new mechanism.

Numerous studies have shown estrogen to be vasoactive in various circulations. Our objective was to determine the effect of estrogen on isolated bovine coronary arteries and the possible mechanism. Bovine coronary arteries, precontracted with thromboxane mimetic U46619 were given doses (0.01-30 microM) of 17B-estradiol in the presence and absence of endothelium and these inhibitors: 10 microM indomethacin (cyclooxygenase inhibitor), 10 microM methylene blue (inhibits soluble guanylate cyclase), 100 microM nitro-L-arginine (inhibits nitric oxide synthesis), 100 microM isobutylmethylxanthine (phosphodiesterase inhibitor) and 30 microM mifepristone (Ru38486 steroid receptor antagonist). Our results indicated that, estrogen, in the highest concentration used (30 microM), elicited an acute dose-dependent relaxation of bovine coronary arteries from 4%-68% (n = 15). No major difference in relaxation was observed between coronary arteries with or without endothelium, indicating that the mechanism was endothelium-independent. Indomethacin, nitro-L-arginine and methylene blue did not alter this relaxation, suggesting that relaxant prostaglandins, l-arginine products and cGMP are not involved (n = 11-16), isobutylmethylxanthine enhanced relaxation from 20%-40% (n = 15 p < 0.01), suggests a role for cAMP. Furthermore, mifepristone reduced the relaxation by more than 50% (n = 15 p < 0.05) consistent with the role for estrogen receptors. Based on our study, estrogen causes a dose-dependent relaxation of bovine coronary arteries that does not appear to utilize endothelium, prostaglandins, cGMP or arginine products, but may involve cAMP and estrogen receptors. This study may help justify treating myocardial ischemia with estrogen.

Hypoplastic external genitalia in association with X;autosome chromosome translocation.

STUDY OBJECTIVE: To learn the relationship between X;autosome chromosome translocation and hypoplastic external genitalia. BACKGROUND: An X;autosome translocation usually presents with phenotypic features similar to Turner syndrome. PARTICIPANTS: We present three female siblings and their mother with X;autosome translocation and hypoplastic external genitalia. METHODS: Case presentation. RESULTS: Three female siblings, ages 14, 16, and 18 years, presented for routine checkup. All had been seen in the past for short stature, learning disability, and other features similar to those seen in Turner syndrome. At time of presentation, all three had primary amenorrhea. On genital exam, each was found to have hypoplastic external genitalia with absent clitoris and labia minora. Pelvic ultrasound in all subjects showed normal but prepubertal uterus and ovaries. Two subjects have unbalanced translocations with karyotype 46,X,der(9)t(9;X)(q11.2;q22.3). This abnormal chromosome complement results in the loss of the short arm of the X chromosome and the gain of an extra copy of the long arm of chromosome 9. The third subject and her mother have balanced translocations with the karyotype 46,X,t(9;X)(q11.2;q22.3). X-inactivation studies showed skewed inactivation of the normal X chromosome in the balanced translocation carriers, while the two girls with the unbalanced karyotype had skewed inactivation of the translocation product. All subjects have growth hormone deficiency. The oldest sibling was able to menstruate regularly after estrogen/progesterone therapy. The other two patients are currently receiving growth hormone and are gaining height. CONCLUSION: X;autosome translocations may be associated with hypoplastic external genitalia but normal internal genitalia. Balanced carriers can be fertile. To our knowledge, the presence of hypoplastic external genitalia in association with X;autosome translocation has not been previously reported. This should be added to the possible causes of hypoplastic external genitalia.

Nebulized nitroglycerin in children with pulmonary hypertension secondary to congenital heart disease.

Pulmonary hypertension continues to be a major cause of morbidity and mortality, despite new treatments. Since inhaled nitric oxide has been reported to be effective in some cases, we investigated using nebulized nitroglycerine to treat pulmonary hypertension in children with congenital heart disease. Four children (ages 6-72 months) with severe pulmonary hypertension secondary to congenital heart disease (all with membranous ventricular septal defect, undergoing cardiac catheterization) were given 3 cc of nebulized normal saline over 10 min as placebo control, followed by nebulized nitroglycerine (20 micrograms/Kg in 3 cc normal saline). Normal saline administration did not elicit any change, but nitroglycerine administration resulted in the following changes (mean +/- SE, paired statistics): systolic pulmonary artery pressure from 68 +/- 8 to 53 +/- 6 at 10 min into treatment (P 0.006), mean pulmonary artery pressure 47 +/- 4 to 38 +/- 4 (P 0.005), heart rate 131 +/- 8 to 127 +/- 7 (P 0.13), systolic blood pressure 85 +/- 8 to 88 +/- 3 (P 0.7), mean blood pressure 59 +/- 6 to 63 +/- 4 (P 0.5). These results indicate that nebulized nitroglycerine may be an effective, easy to administer, inexpensive, and safe alternative for treatment of severe pulmonary hypertension in children with congenital heart disease, especially in areas where other treatments such as extracorporeal membrane oxygenation or inhaled nitric oxide are inaccessible.

Tampon use in young women.

OBJECTIVE: To study the prevalence of tampon use among young females, the factors and persons influencing this choice, the role of primary care physicians, and the potential association of tampon use with sexually transmitted diseases and urinary tract infections. METHODS: An anonymous questionnaire regarding the use of feminine hygiene products was completed by 250 female college students between 17 and 21 years of age and 90 primary care physicians. Percentages were calculated for most outcome measurements and Fisher's Probability Exact Test was used to compare groups. RESULTS: Of the participants, 19% use pads, 29% use tampons, and 52% use both, with a total of 81% using tampons alone or in combination. The choice was influenced mostly by the woman herself or her mother. Only 22% reported that their physician discussed tampon usage with them. Incidence of sexually transmitted diseases was not significantly different between those using pads and tampons. In the pad group, 12% reported urinary tract infections versus 32% in the other group (P = 0.007). Among physicians, only 30% said they discussed hygiene products, although 52% of them thought it was medically important. Of the female physicians, 71% use tampons alone or in combination; 29% exclusively use pads, with 92% citing fear of toxic shock syndrome as a reason for their choice. CONCLUSIONS: The majority of young women use tampons based on own decision or maternal influence for comfort, convenience, and appearance. Physician input in this regard is not routinely provided, probably because of lack of agreement about the importance of the subject among physicians. Based on participants' report in this survey, the incidence of urinary tract infections seems to be significantly higher among tampon users than among pad users. Physicians should assume a more active role in explaining the appropriate use, benefits, and potential risks of feminine hygiene products.

Alteration of human placental vascular tone by antiarrhythmic medications in vitro.

INTRODUCTION: Antiarrhythmic medications are commonly used during pregnancy for treatment of maternal or fetal arrhythmias, but little is known about their effect on human placental vascular tone and, consequently, placental blood flow. The objective of this study was to evaluate the tone responses caused by antiarrhythmic medications in human placental vessels from normal term pregnancies in vitro. METHODS AND RESULTS: Isolated human placental arteries and veins from uncomplicated term pregnancies incubated in Krebs'-bicarbonate under 5% oxygen/5% carbon dioxide/balance nitrogen (PO2 35 to 38 torr) were exposed to cumulative doses of quinidine, procainamide, lidocaine, flecainide, propranolol, amiodarone, verapamil, digoxin, and adenosine after submaximal contraction with 5-hydroxytryptamine. The study was conducted both in the presence and absence of endothelium. The addition of the tested medications caused a significant, dose-dependent relaxation of human placental arteries and veins except for adenosine, which induced a sustained, dose-dependent contraction of human placental vessels regardless of the presence or absence of tone. Removal of the endothelium did not alter these responses. CONCLUSIONS: Based on these results, the medications tested should have no decremental effect on placental blood flow, with the possible exception of adenosine, which causes significant, dose-dependent contraction of human placental vessels in vitro. Should similar contraction be present in vivo, it may have an adverse effect on the fetus when administering adenosine to pregnant women at term or during labor.

Modulation by atrial natriuretic factor of receptor-mediated cyclic AMP-dependent responses in canine pulmonary artery during heart failure.

1. Pacing-induced congestive heart failure (CHF) in dogs is associated with increased plasma levels of atrial natriuretic factor (ANF) and inhibition of receptor-mediated cyclic AMP-dependent relaxation in isolated pulmonary arteries (PA). Since ANF is known to be negatively coupled to adenylate cyclase, we studied cyclic AMP-mediated relaxation to isoprenaline (Iso) and arachidonic acid (AA) in PA from control dogs (C), dogs with pacing-induced CHF (CHF) and dogs with bilateral atrial appendectomy and CHF (ATR APP+CHF). 2. In CHF, plasma ANF levels increased from a baseline of 80 +/- 8 pg ml-1 to 283 +/- 64 pg ml-1 (P < 0.05), but the ATR APP+CHF group failed to show this increase (67 +/- 7 pg ml-1 vs 94 +/- 15 pg ml-1, P = NS). Plasma ANF levels, however, did not influence myocardial dysfunction in CHF. 3. The relaxation of 49 +/- 5% to 1 microM Iso in C was reduced to 23 +/- 4% in CHF (P < 0.05), but relaxation of 49 +/- 12% was observed in the ATR APP+CHF group (P = NS vs C). Relaxation responses to 10 microM AA were as follows: 77 +/- 5% (C, n = 8), 27 +/- 8% (CHF, n = 10, P < 0.05 vs C), and 93 +/- 5% (ATR APP+CHF, n = 5). The presence of CHF, or the plasma ANF levels, did not affect responses to cyclic GMP-mediated relaxing agents in PA. 4. These data indicate that the myocardial performance in CHF is not influenced by plasma ANF levels. However, altered cyclic AMP-mediated relaxation in PA during CHF is, in part, modulated by circulating ANF levels.

Absence of relaxation to lactate in human placental vessels of pregnancies with severe preeclampsia.

OBJECTIVE: Our objective was to determine whether the observed relaxation to lactate and other agents in placental vessels of normal pregnancies is altered in severe preeclampsia. STUDY DESIGN: Isolated placental arteries and veins from women with severe preeclampsia and uncomplicated term pregnancies were precontracted with prostaglandin F2 alpha under 5% oxygen and 5% carbon dioxide with the balance nitrogen (Po2 35 to 38 torr) and then exposed to lactate (1 to 10 mmol/L, pH 7.4, n = 8 to 15), arachidonic acid (0.01 to 10 mumol/L, n = 6 to 13), nitroglycerin (1 nmol to 1 mumol/L, n = 4 to 12), or forskolin (0.01 to 10 mumol/L, n = 6 to 9). The response to lactate was also examined in placental vessels from appropriate-for-gestational-age preterm deliveries (n = 8) for comparison with a similar group with severe preeclampsia (n = 8). The t test and analysis of variance statistics were used. RESULTS: Relaxation to lactate was markedly inhibited in both placental arteries and veins of women with severe preeclampsia compared with vessels from uncomplicated term or preterm pregnancies. Responses to the other relaxing agents were not altered in the severely preeclamptic vessels. CONCLUSIONS: In severe preeclampsia absence of lactate-induced dilatation of placental vessels may contribute to the fetal complications associated with impaired blood flow and vasospasm.

Properties of a progesterone-induced relaxation in human placental arteries and veins.

To study the effects of progesterone on placental vascular tone, we used isolated (1-2 mm in diameter) placental arteries and veins from term uncomplicated pregnancies. These vessels, incubated in Krebs buffer (pH 7.4) under 5% O2-5% CO2 (balance N2, PO2 approximately 35 torr) and precontracted with serotonin were exposed to incremental doses of progesterone (0.01-30 mumol/L) in the presence or absence of endothelium, 10 mumol/L indomethacin (inhibits prostaglandin synthesis), 10 mumol/L methylene blue (a soluble guanylate cyclase inhibitor), 100 mumol/L nitro-L-arginine (inhibits L-arginine metabolism), 1 mmol/L isobutylmethylxanthine (a cAMP phosphodiesterase inhibitor), or 30 mumol/L mifepristone (RU 38486, an antiprogestin). Progesterone elicited an acute dose-dependent relaxation in both arteries and veins that was not altered by removal of the endothelium or pretreatment with indomethacin, nitro-L-arginine, or methylene blue, excluding a role for prostaglandins, L-arginine products, or cGMP in mediating this relaxation. However, isobutylmethylxanthine significantly enhanced the relaxation in response to progesterone, suggesting a role for cAMP. RU 38486 inhibited the relaxation by 50-100%, depending on the progesterone dose, consistent with a role for progesterone receptors. These results suggest that progesterone causes a dose-dependent endothelium-independent relaxation of human placental arteries and veins. This relaxation seems to be mediated by a receptor-activated cAMP mechanism and could be physiologically important in maintaining low resistance and adequate blood flow in the placental circulation.

Properties of a lactate-induced relaxation in human placental arteries and veins.

OBJECTIVE: Our purpose was to determine the vasoactive effects and mechanism of action of lactate in human placental vessels by means of isometric muscle bath studies. STUDY DESIGN: Isolated 1 to 2 mm human placental arteries and veins from normal term pregnancies, precontracted with prostaglandin F2 alpha and incubated under a PO2 of approximately 35 torr were exposed to lactate, 1 to 10 mmol/L, (pH 7.4), pyruvate, hydrogen peroxide, nitroglycerin, or forskolin. The effects of endothelium removal or inhibitors of cyclooxygenase (indomethacin 10 mumol/L) and L-arginine metabolism (nitro-L-arginine 30 mumol/L) on the response to lactate and the effects of an antagonist of guanylate cyclase activation (methylene blue 10 mumol/L), cyanide (1 mmol/L), and hypoxia (PO2 8-10 torr) on responses to all agents were determined by analysis of variance and t test statistics. RESULTS: Lactate-elicited dose-dependent relaxation was not inhibited by endothelium removal, indomethacin, or nitro-L-arginine but was attenuated by methylene blue, cyanide, and hypoxia. Relaxation to hydrogen peroxide was inhibited by methylene blue and cyanide but not hypoxia. Relaxation to nitroglycerin was inhibited only by methylene blue, and relaxation to forskolin was not inhibited by these probes. Pyruvate did not produce a significant relaxation. CONCLUSIONS: These findings suggest that lactate causes relaxation in the human placental vessels by an oxygen and cyclic guanosine-3':5'-monophosphate-dependent mechanism, which may involve the generation of hydrogen peroxide but not the metabolism of arginine. Lactate-induced dilatation may be of importance during labor and in situations of acute and chronic fetal hypoxia.

Gestational diabetes alters human placental vascular responses to changes in oxygen tension.

OBJECTIVE: Our objective was to study tone responses caused by hypoxia, reoxygenation, and hydrogen peroxide in human placental vessels from gestational diabetic and normal term pregnancies. STUDY DESIGN: Isolated placental arteries and veins from women with well-controlled gestational diabetic and uncomplicated term pregnancies were precontracted with U46619 under 5% oxygen/5% carbon dioxide/balance nitrogen (PO2 35 to 38 torr) and then exposed to hypoxia (95% nitrogen/5% carbon dioxide) atmosphere (PO2 8 to 10 torr) for 5 to 7 minutes followed by rapid reoxygenation. Cumulative doses of hydrogen peroxide (1 to 100 mumol/L) were added at 2-minute intervals. The studies were conducted in both the presence and the absence of endothelium. Prostaglandin involvement was examined by treatment with indomethacin. Analysis of variance and t test statistics were used. RESULTS: After incubation under 5% oxygen, hypoxia caused a larger prostaglandin-independent relaxation in arteries and veins of women with gestational diabetes than in normal vessels. Placental vessels of women with gestational diabetes were found to undergo a significantly larger contraction than normal vessels when exposed to posthypoxic reoxygenation or micromolar concentrations of hydrogen peroxide. Both responses were eliminated and reversed to a relaxation by pretreatment with 10 mumol/L indomethacin in both gestational diabetic and normal vessels, consistent with mediation through the formation of prostaglandins. Removal of the endothelium did not appear to alter any of the observed responses. CONCLUSIONS: Gestational diabetes produces an enhancement of the observed relaxation caused by hypoxia and the contraction produced by reoxygenation or hydrogen peroxide.

O2-dependent modulation of calf pulmonary artery tone by lactate: potential role of H2O2 and cGMP.

Lactate was found to produce a relaxation of isolated endothelium-removed calf pulmonary arteries precontracted with 20-30 mM K+. Examination of the mechanism of this response indicates that it appears to be O2 dependent and mediated via guanosine 3',5'-cyclic monophosphate (cGMP), since it is reduced by hypoxia (N2 atmosphere, PO2 = 8-10 Torr) and because the relaxation was both eliminated by inhibition of soluble guanylate cyclase activation with methylene blue and enhanced by an antagonist of cGMP-selective phosphodiesterases (M & B 22948). Relaxation to lactate is not mediated via prostaglandin formation or arginine-derived nitric oxide, since indomethacin or nitro-L-arginine, respectively, did not alter the response. Lucigenin-elicited chemiluminescence, a potential detector of superoxide anion, was significantly increased by lactate only after inhibition of Cu-Zn-superoxide dismutase (via pretreatment with diethyldithiocarbamate). Pyruvate (5 mM) produced only minimal relaxation and did not significantly increase chemiluminescence. In the homogenate fraction of the arterial smooth muscle, NAD plus lactate or NADH was required to observe increased chemiluminescence. The calf pulmonary arterial smooth muscle contraction to hypoxia and relaxation to posthypoxic reoxygenation was observed to be increased by lactate, associated with a reduced level tone generation under O2 but not N2 atmosphere. Thus lactate, but not pyruvate, appears to cause a cGMP-mediated relaxation in the calf pulmonary artery through an increased intracellular H2O2 generation via the NADH-dependent production of superoxide anion, and activation of this relaxing mechanism modulates O2-elicited tone responses.