[Responses of soil microbial biomass and carbon source utilization to simulated nitrogen deposition and drought in a Cunninghamia lanceolata plantation]. / 杉木人工林土壤微生物生物量和碳源利用能力对模拟氮沉降和干旱的响应.

Chinese fir (Cunninghamia lanceolata) plantation is a dominant forest type and carbon sink in the subtropical region in China. An experiment with simulated nitrogen deposition (addition of 40 kg N·hm-2·a-1) and drought (50% of precipitation exclusion, PE) was established in Chinese fir plantation in 2018. Soil samples (0-15 cm) were collected in summer (July 2020) and winter (January 2021). Soil microbial biomass, colony forming units (CFUs) and carbon source utilization were determined through phospholipid fatty acids (PLFAs), plate count, and Biolog methods, respectively. The results showed significant seasonal variations of PLFAs-related microbial biomass and composition. Soil bacterial and fungal CFUs tended to be decreased by nitrogen addition or precipitation exclusion treatment, and bacterial CFUs were more sensitive to the two treatments than fungal CFUs. Soil microbial function (i.e. carbon source utilization) was not affected by nitrogen addition, but significantly decreased by precipitation exclusion. There was a significant positive correlation between bacterial CFUs and microbial function, indicating the crucial roles of culturable bacteria in microbial carbon transformation. Our results highlight the critical effects of nitrogen deposition and 50% reduced precipitation on microbes in topsoil of fir plantation, with implications for unraveling soil microbial ecological function of subtropical forest ecosystem under global changes in future.

[Effects of soil moisture on priming effect of soil organic carbon in meadow in Wuyi Mountain, China.] / 水分对武夷山草甸土壤有机碳激发效应的影响.

Moisture is an important factor affecting the priming effect of soil organic carbon (SOC). However, empirical evidence for its effect in mountain meadows soil is lacking. We conducted a 126-day laboratory incubation experiment with the high altitude (2130 m) mountain meadow soil in Wuyi Mountain, by adding 13C-labelled glucose combined with controlling soil moisture (30% and 60% of field water capacity, FWC). The CO2 concentration and 13C-CO2 abundance were measured regularly to examine the differences of SOC mineralization and priming effects under different water conditions and the driving factors. Our results showed that SOC mineralization rate increased with increasing soil water content. The priming effect of meadow soil with different soil moisture showed a decreasing trend with the increases of incubation time. The priming effect in soils with low FWC soil was significantly greater than that with high FWC. At the end of incubation, the cumulative priming effect of low FWC soil was 61.4% higher than that of high FWC soil. Compared with low FWC soil, high FWC soil released more CO2 from glucose, and the ratio of cumulative primed carbon to glucose mineralization under low FWC was significantly higher than that under high FWC soil, indicating that soil microorganisms under the high FWC condition might preferentially mineralize more glucose than SOC and consequently lower priming effect. Therefore, the priming effect under high FWC was smaller than that under low FWC. There was a significant positive relationship between priming effect and microbial biomass carbon, microbial biomass carbon/microbial biomass nitrogen, and NH4+-N, indicating that soil microbial biomass and composition could be changed under low FWC condition. The improved microbial "nitrogen-mining" would increase priming effect. Consequently, the decline of soil moisture of mountain meadow induced by global climate change may increase the priming effect of carbon, with consequences on carbon loss.

[Characteristics of soil organic carbon mineralization in low altitude and high altitude forests in Wuyi Mountains, southeastern China]. / 武夷山低海拔和高海拔森林土壤有机碳的矿化特征.

Examining the variations of soil organic carbon mineralization at different altitudes is crucial for better understanding of soil organic carbon (SOC) dynamics. We selected the low altitude and high altitude broad-leaved forest soils in Wuyi Mountains as the research object, and incubated them under particular annual average temperature (17 and 9 ℃, respectively) in laboratory to investigate the difference of SOC mineralization characteristics. The results showed that the cumulative SOC mineralization had no significant difference between forest soils at low and high altitude in a 126-day incubation period under ambient temperature. Soil organic carbon content of high altitude soil was significantly higher than that from low altitude. The dynamics of SOC mineralization could fitted by the first-order kinetics. Both mineralization potential (CP) and mineralization rate constant (K) values of two soils had no significant difference, but CP/SOC value and mineralization ratio were significantly higher at low altitude, indicating that the carbon sequestration capacity of low altitude soil was relatively lower than that of high altitude under ambient temperature. Soil microbial biomass carbon and microbial quotients were significantly higher than that of low altitude with the increase of incubation time, indicating that the ability of microbial carbon assimilation was greater at high altitude. On the other hand, the activities of ß-1,4-glucosidase and cellobiohydrolase in high altitude soil were higher, suggesting that more labile carbon would be decomposed by soil microbes. The carbon sequestration capacity and microbial carbon utilization efficiency in high altitude soil would be reduced and thus result in a decline of soil organic carbon storage under the scenarios of climate warming.

Preparation of bioactive neoagaroligosaccharides through hydrolysis of Gracilaria lemaneiformis agar: A comparative study.

Hydrolysis of Gracilaria lemaneiformis agar by ß-agarase was compared with HCl hydrolysis. The results showed that optimum catalysis conditions for the ß-agarase were pH 7.0 at 45°C. Mass spectroscopy, thin-layer chromatography and GPC results showed that the polymerization degrees of the hydrolysis products by the ß-agarase were mainly four, six and eight (more specific than the hydrolysate by HCl). The enzymatic degradation products of agar were distinctly different from those of HCl hydrolysis in the ratios among galactose and 3,6-anhydro-galactose and sulfate group contents. The NMR spectrometry proved that the products of ß-agarase were neoagaroligosaccharides, which was not found in the agarolytic products by HCl. The neoagarotetraose inhibited tyrosinase activity competitively with the KI value of 16.0mg/ml. Hydroxyl radical-scavenging ability of neoagaroligosaccharides was much greater than that of agar HCl hydrolysate. This work suggests that neoagaroligosaccharide products produced by our ß-agarase could be more effective in function than products from acid hydrolysis.

[Comparison on concentrations and quality of dissolved organic matter in throughfall and stemflow in a secondary forest of Castanopsis carlesii and Cunninghamia lanceolata plantation].

In this paper, monthly variation of dissolved organic matter (DOM) concentrations as well as humification and aromaticity indices in throughfall and stemflow from secondary broadleaved Castanopsis carlesii (BF) forest and Cunninghamia lanceolata plantation (CP) were measured. The DOC concentrations in throughfall were significantly higher with greater variation in BF than in CP. The concentrations of DOC in throughfall were averagely 7.2 and 3.2 times of those in rainfall in BF and CP forests, respectively. The DOC concentrations of stemflow in CP were averagely 2.5 times as much as those in BF, and the DOC concentrations in stemflow tended to be greater in dry season than in rain season for the two forests. A significantly negative relationship was' found between the DOC concentrations in stemflow and the amounts of stemflow for both BF and CP. Moreover, the humification and aromaticity indices of DOM in throughfall in BF was significantly greater than in CP. In contrast, the humification and aromaticity indices of DOM from stemflow of CP were significantly greater than those of BF. This result indicated that the structure of DOM from throughfall was more complex in BF than in CP, and the structure of DOM from stemflow was vice versa. These results indicated that DOM in stemflow and throughfall showed significant variations in quantity and quality between BF and CP and may greatly impact the accumulation of soil organic carbon.

[Dynamics of unprotected soil organic carbon with the restoration process of Pinus massoniana plantation in red soil erosion area].

By the method of spatiotemporal substitution and taking the bare land and secondary forest as the control, we measured light fraction and particulate organic carbon in the topsoil under the Pinus massoniana woodlands of different ages with similar management histories in a red soil erosion area, to determine their dynamics and evaluate the conversion processes from unprotected to protected organic carbon. The results showed that the content and storage of soil organic carbon increased significantly along with ages in the process of vegetation restoration (P < 0.01). The unprotected soil organic carbon content and distribution proportion to the total soil organic carbon increased significantly (P < 0.05) after 7-11 years' restoration but stabilized after 27 and 30 years of restoration. It suggested that soil organic carbon mostly accumulated in the form of unprotected soil organic carbon during the initial restoration period, and reached a stable level after long-term vegetation restoration. Positive correlations were found between restoration years and the rate constant for C transferring from the unprotected to the protected soil pool (k) in 0-10 cm and 10-20 cm soil layers, which demonstrated that the unprotected soil organic carbon gradually transferred to the protected soil organic carbon in the process of vegetation restoration.

[Mutation analysis and prenatal diagnosis of FBN1 gene mutations for four patients with Marfan syndrome].

OBJECTIVE: To screen for mutations of fibrillin-1 (FBN1) gene in 4 patients with Marfan syndrome in order to provide prenatal diagnosis and genetic counseling. METHODS: Potential mutations of the FBN1 gene in the probands were detected with PCR and DNA sequencing. Subsequently, genomic DNA was extracted from amniotic fluid sampled between 18 to 20 weeks gestation. The mutations were confirmed with denaturing high-performance liquid chromatography - robust microsatellite instability (DHPLC-MSI) analysis with maternal DNA as reference. The products were further analyzed by direct sequencing and BLAST search of NCBI database. RESULTS: An IVS46+1G>A substitution was identified in patient A at +1 position of intron 46 of the FBN1 gene. Two novel missense mutations were respectively discovered at positions +4453 of intron 35 in patient B (Cys1485Gly) and position +2585 of intron 21 in patient C (Cys862Tyr). In patient D, a novel deletion (c.3536 delA) was found at position +3536 of intron 28. In all of the 4 cases, the same mutations have been identified in the fetuses. CONCLUSION: FBN1 gene analysis can provide accurate diagnosis of Marfan syndrome, which can facilitate both prenatal diagnosis and genetic counseling.

[Effects of temperature on CH4 emission from subtropical common tree species leaves].

Laboratory incubation test was conducted to study the effects of temperature on the CH4 emission from the leaves of subtropical common tree species Castanopsis carlesii, Schima superb, Cinnamomum chekiangense, Castsanopsis fabri, Cunninghamia lanceolata, and Citrus reticulata. Among the six tree species, only S. superb, C. reticulate, and C. fabri emitted CH4 at 10 degrees C. At above 20 degrees C, all the six species emitted CH4, and the average CH4 emission rate at above 30 degrees C (1.010 ng CH4 x g(-1) DM x h(-1)) was 2.96 times higher than that at 10-30 degrees C (0.255 ng CH4 x g(-1) DM x h(-1)). Moreover, increasing temperature had much more effects on the CH4 emission rate of C. reticulata and C. lanceolata than on that of the other four tree species. Incubation time affected the CH4 emission rate of all test tree species significantly, suggesting that the effects of temperature stress on the CH4 emission could be controlled by plant activity. Dry leaves could not emit CH4 no matter the temperature was very high or low. It was suggested that high temperature stress had important effects on the CH4 emission from subtropical tree leaves, and global warming could increase the CH4 emission from plants.

Exon 47 skipping of fibrillin-1 leads preferentially to cardiovascular defects in patients with thoracic aortic aneurysms and dissections.

Excessive activation of the transforming growth factor beta signaling pathway and disorganized cellular skeleton caused by genetic mutations are known to be responsible for the inherited thoracic aortic aneurysms and dissections (TAAD), a life-threatening vascular disease. To investigate the genotype-phenotype correlation, we screened genetic mutations of fibrillin-1 (FBN1), transforming growth factor-ß receptor-1 (TGFBR1) and transforming growth factor-ß receptor-2 (TGFBR2) for TAAD in 7 affected families and 22 sporadic patients. Of 19 potential mutations identified in FBN1, 11 appeared novel while the others were recurrent. Two mutations were detected in TGFBR2. Eight patients carried no mutation in either of these genes. Characterization of FBN1 c.5917+6T>C in transfected HEK293 cells demonstrated that it caused skipping of exon 47, leading to the loss of the 33th calcium binding epidermal growth factor-like domain associated with Marfan syndrome. Compared with exon 46, skipping of 47 did not cause patients ectopia lentis in all carriers. To correlate genotypes with phenotypes in different human ancestries, we reviewed the published mutational studies on FBN1 and found that the probability of cardiovascular defects were significantly increased in Chinese patients with premature termination codon or splicing mutations than those with missense mutations (91.7 % vs 54.2 %, P = 0.0307) or with noncysteine-involved point mutations than those with cysteine-involved mutations (88.9 % vs 33.3 %, P = 0.0131). Thus, we conclude that exon 47 skipping of FBN1 leads preferentially to cardiovascular defects and human ancestries influence genotype-phenotype correlation in TAAD.

[Seasonal variations of soil CH4 uptake rate in Castanopsis carlesii forest in mid-subtropical China].

A monthly measurement of soil CH4 uptake rate (V(CH4)) in a natural Castanopsis carlesii forest in Wanmulin Natural Reserve of Fujian Province, East China was conducted from March 2010 to February 2011. The VCH4 showed a pronounced seasonal fluctuation, being higher in summer-autumn than in winter-spring, with the maximum value (95.13 microg x m(-2) x h(-1)) in September and the minimum value (9.13 microg x m(-2) x h(-1)) in March. With the increase of soil temperature and moisture, the V(CH4) showed an increasing and a decreasing trend, respectively, but the correlations of the V(CH4) with soil temperature and moisture were not significant. The annual soil CH4 flux of the forest (3.93 kg x hm(-2) x a(-1)) was higher than the average value of global natural forests (2.4 kg x hm(-2) x a(-1)) and of Asian tropical natural forests (2.07 kg x hm(-2) x a(-1)), but lower than that of Asian temperate natural forests (8.12 kg x hm(-2) x a(-1)).

[Efficacy of minimally invasive left ventricular epicardial lead placement for cardiac resynchronization therapy].

OBJECTIVE: Ventricular resynchronization might be achieved via minimally invasive left ventricular epicardial lead placement. METHOD: Six patients with congestive heart failure underwent minimally invasive left ventricular epicardial lead placement after failed coronary sinus cannulation were followed up for 1 year, cardiac function and LV lead threshold were evaluated. RESULTS: There were no in-hospital deaths, intraoperative complications and diaphragm stimulation. Correct lead positioning was achieved in all 6 patients. LV lead thresholds remained unchanged [(1.2 ± 0.5) V vs (1.1 ± 0.4) V, P = 0.68] at 12 months follow-up. Improvements on 6 min walking test [(327 ± 77) m vs (267 ± 68) m, P = 0.001], LVEF [(26.1 ± 6.0)% vs (38.2 ± 4.7)%, P = 0.004], and NYHA functional class were evidenced at 12 months follow-up. CONCLUSION: Minimally invasive left ventricular epicardial lead placement is a safe and reliable technique and should be considered as an alternative option in case of difficult coronary venous anatomy and inability to position the lead for resynchronization therapy.

[Litter fall production and carbon return in Cunninghamia lanceolata, Schima superba, and their mixed plantations].

From March 2005 to April 2007, an investigation was made on the litter fall production and carbon return of Cunninghamia lanceolata, Schima superba, and their mixed plantations in the Jian' ou Science and Education Park of Soil and Water Conservation, Fujian. In these three plantations, the mean annual litter fall production was from 2470.85 kg x hm(-2) x a(-1) to 4285.99 kg x hm(-2) x a(-1), and dominated by leaf litter, accounting for 68.62%-87.26% of the total production. In C. lanceolata plantation, the litter fall production peaked in April-May, July, and December; while in S. superba and mixed plantations, this production only peaked in March. Comparing with pure plantations, mixed plantation had a higher litter fall production per tree of broadleaved S. superba while a lower litter fall production per tree of coniferous C. lanceolata. Leaf litter in the three plantations was the main body of the litter falls carbon return, and the total amount of the carbon return was the largest (2.12 t C x hm(-2) x a(-1)) in mixed plantation and the smallest (1.19 t C x hm(-2) x a(-1)) in C. lanceolata plantation, which was in accordance with the annual litter fall production of the plantations. This study demonstrated that comparing with pure coniferous or broadleaved plantation, coniferous-broadleaved mixed plantation had higher annual litter fall production and carbon return, and thus, higher potential of C sequestration.

[Clinical outcome of mitral valve repair in primary infective endocarditis with mitral insufficiency].

OBJECTIVE: To study the clinical results of mitral valve repair in patients of primary infective endocarditis with mitral insufficiency. METHODS: From January 2004 to July 2007, 40 patients who had undergone valve repair procedure for infective endocarditis with mitral insufficiency were analyzed retrospectively. There were 26 male and 14 female patients, with an average age of (34.0 +/- 3.5) years old, including 6 patients of underlying heart disease, 34 patients of no previously underlying heart disease. There were 12 patients in NYHA functional class II, 19 patients in class III, 9 patients in class IV preoperatively. Preoperative echocardiography showed moderate to severe MR in all patients. The surgery was performed under extracorporeal circulation and moderate hypothermia. The distribution of anatomical lesion according to surgical findings were vegetation in 32 patients, leaflet prolapsed in 34 patients, leaflet perforation in 16 patients, chordal rupture in 32 patients, and annular abscess in 2 patients. The vegetations and infected tissues were debrided. The surgery consisted of complex methods to repair mitral valve, including direction leaflet closure in 5 patients, pericardial patch closure of leaflet perforation in 18 patients, chords reimplantation in 4 patients and chords transference in 6 patients, quadrangular resection in 12 patients, double orifice method in 17, closure of the commissure in 8, rings annuloplasty in 28 cases, and so on. There were 28 selective surgeries and 12 emergent ones. Patients were evaluated for early and long-term clinic and echocardiographic outcome before and after operation. RESULTS: There were no early postoperative death. Mitral valve repair was feasible in 39 patients, one patient was transformed to mitral valve replacement during the operation. Postoperative echocardiography demonstrated no (n = 24) or mild (n = 15) mitral regurgitation at the discharge examination and observed significant reductions in left ventricular end diastolic [from (62 +/- 7) mm to (51 +/- 6) mm, P < 0.05] and end systolic dimensions [from (45 +/- 3) mm to (40 +/- 4) mm, P < 0.05] and left atrial dimensions [from (49 +/- 4) mm to (42 +/- 6) mm, P < 0.05]. Mean follow-up (25.6 +/- 3.2) months, freedom from recurrent moderate to severe MR, freedom from repeat operation or infective endocarditis, revealed patients were 36 cases in NYHY class I, 3 cases in class II. CONCLUSION: Mitral valve repair for mitral valve endocarditis is feasible with a satisfied clinical outcome, maintains valve competency with significant reductions in left atrial and left ventricular dimensions after surgery.

[Seasonal variation of light fraction organic matter in degraded red soil after vegetation restoration].

This paper studied the seasonal variation of light fraction organic matter (LFOM) in the red soils of severely eroded bare land, and of the bare lands restored to Pinus massoniana forest land, Castanea mollissima plantation, and Paspalum notatum grassland in the Hetian Town of Changting County, Fujian Province, with secondary forest soil as the control. The results showed that in the surface soil of the bare land, LFOM content was between 0.05-0.14 g x kg(-1) and with no significant seasonal variation, while in that of P. massoniana forest land, C. mollissima plantation and P. notatum grassland, LFOM content had a distinct seasonal variation, and was 58%-122% higher in spring, autumn, and winter than in summer. The C content and C/N ratio of the LFOM in the three restored lands were lower in summer than in other seasons, while the nitrogen content of the LFOM was in adverse, indicating that the high temperature and humidity in summer induced a rapid decomposition of soil LFOM. The LFOM in secondary forest soil had the similar variation trend to that in the three restored lands, but the variation range was significantly narrower. The seasonal dynamics of surface soil LFOM was affected not only by micro-climate but also by vegetation types, and the variation range was greater in P. notatum grassland than in forest lands. It was suggested that to enhance the observation precision of soil LFOM, repeated sampling or integrating the factors such as climate, vegetation type, and management measures should be taken to determine the appropriate sampling time.

[Application and results of Robicsek procedure for dilated ascending aorta associated with aortic valve disease].

OBJECTIVE: To introduce the Robicsek procedure and summarize its short to mid-term results for patients with dilatation of the ascending aorta associated with aortic valve disease. METHODS: From December 2002 to June 2006, 30 patients with a moderately dilated ascending aorta [mean diameter, (46.7+/-3.1) mm] underwent concomitant aortic valve replacement (AVR) or repairing and reinforced aortoplasty with a well-tailored Dacron vascular graft. Follow-up was obtained on all patients with ultrasonic cardiography (UCG) or computed tomography (CT) scan and was (18.0+/-10.5) months. RESULTS: The total average cardio-pulmonary bypass (CPB) time was (103.4+/-21.7) min (80-151 min), and aortic arrest time was (73.0+/-21.6) min (48-120 min), whereas the average CPB time and aortic arrest time of 19 patients who underwent the isolated Robicsek procedure were only (91.3+/-8.9) min (80-118 min) and (61.6+/-11.3) min (48-82 min). No mortality occurred in the hospital. During follow-up of 18 months, no recurrent ascending aortic dilatation and dissection were observed, and the average aortic diameter was reduced to (33.7+/-2.5) mm. Sixteen of the 30 patients were diagnosed as bicuspid aortic valve (BAV). The ascending aortic media were histologically abnormal in 23 patients. CONCLUSION: Considering the underlying wall deficiency and the homodynamic stress, the Robicsek operation should be an optimal choice to those patients with a mild to moderate dilated ascending aorta caused by aortic valve lesion. Compared with the Bentall and David procedures, the Robicsek procedure could achieve the same or even better clinical results with less operative time and risks.

[Clinical analysis of pregnancy and postpartum cardiovascular complications in Marfan syndrome].

OBJECTIVE: To investigate the management of pregnancy and cardiovascular complications in women with Marfan syndrome (MFS). METHODS: From October 1994 to September 2006, 30 patients with MFS undergoing cardiovascular surgery were studied retrospectively. RESULTS: In the labor of 46 offsprings given birth by 30 women, 5 cases (11%) were performed elective cesarean section because of the existence of aortic complication, and 12 (26%) were diagnosed as MFS. The gestation in two patients was terminated due to deterioration of aortic abnormalities during their third trimester, and they received surgical treatment with Bentall procedure. Two developed acute aortic dissection during labor and post delivery respectively. With the manipulation of anticoagulation peripartum, one who had the implantation with mechanical prosthesis went through pregnancy and delivery uneventfully. The average duration between delivery and cardiovascular surgery was (15 +/- 9) years. CONCLUSIONS: Vaginal delivery can be done safely in patients with the MFS who do not have or have mild cardiovascular system abnormalities, aortic dissection, or other important cardiac abnormalities, cesarean section should be the preferred method of delivery. Women with MFS are at increased risk for dissection and congestive heart failure during pregnancy and should be counseled before pregnancy about these risks, as well as the inheritance of the condition.

Cardiac repair with intramyocardial injection of allogeneic mesenchymal stem cells after myocardial infarction.

Although clinical trials of autologous whole bone marrow for cardiac repair demonstrate promising results, many practical and mechanistic issues regarding this therapy remain highly controversial. Here, we report the results of a randomized study of bone-marrow-derived mesenchymal stem cells, administered to pigs, which offer several new insights regarding cellular cardiomyoplasty. First, cells were safely injected by using a percutaneous-injection catheter 3 d after myocardial infarction. Second, cellular transplantation resulted in long-term engraftment, profound reduction in scar formation, and near-normalization of cardiac function. Third, transplanted cells were pre-prepared from an allogeneic donor and were not rejected, a major practical advance for widespread application of this therapy. Together, these findings demonstrate that the direct injection of cellular grafts into damaged myocardium is safe and effective in the perii-nfarct period. The direct delivery of cells to necrotic myocardium offers a valuable alternative to intracoronary cell injections, and the use of allogeneic mesenchymal stem cells provides a valuable strategy for cardiac regenerative therapy that avoids the need for preparing autologous cells from the recipient.

Imbalance between xanthine oxidase and nitric oxide synthase signaling pathways underlies mechanoenergetic uncoupling in the failing heart.

Inhibition of xanthine oxidase (XO) in failing hearts improves cardiac efficiency by an unknown mechanism. We hypothesized that this energetic effect is due to reduced oxidative stress and critically depends on nitric oxide synthase (NOS) activity, reflecting a balance between generation of nitric oxide (NO) and reactive oxygen species. In dogs with pacing-induced heart failure (HF), ascorbate (1000 mg) mimicked the beneficial energetic effects of allopurinol, increasing both contractility and efficiency, suggesting an antioxidant mechanism. Allopurinol had no additive effect beyond that of ascorbate. Crosstalk between XO and NOS signaling was assessed. NOS inhibition with N(G)-monomethyl-L-arginine (L-NMMA; 20 mg/kg) had no effect on basal contractility or efficiency in HF, but prevented the +26.2+/-3.5% and +66.5+/-17% enhancements of contractility and efficiency, respectively, observed with allopurinol alone. Similarly, improvements in contractility and energetics due to ascorbate were also inhibited by L-NMMA. Because of the observed NOS-XO crosstalk, we predicted that in normal hearts NOS inhibition would uncover a depression of energetics caused by XO activity. In normal conscious dogs, L-NMMA increased myocardial oxygen consumption (MVO2) while lowering left ventricular external work, reducing efficiency by 31.1+/-3.8% (P<0.005). Lowered efficiency was reversed by XO inhibition (allopurinol, 200 mg) or by ascorbate without affecting cardiac load or systemic hemodynamics. Single-cell immunofluorescence detected XO protein in cardiac myocytes that was enhanced in HF, consistent with autocrine signaling. These data show that both NOS and XO signaling systems participate in the regulation of myocardial mechanical efficiency and that upregulation of XO relative to NOS contributes to mechanoenergetic uncoupling in heart failure.