[Association among urinary polycyclic aromatic hydrocarbons metabolites, SAHH activity and H19 expression in coke oven workers]

Objective: To investigate the relationship of polycyclic aromatic hydrocarbons (PAHs) exposure, S-adenosylhomocysteine hydrolase (SAHH) activity and long noncoding RNA H19 gene expression in the urine of coke oven workers. Methods: In September 2019, in a coking plant in Taiyuan City, 146 male workers who had worked in coke oven operations for one year were selected through a completely random sampling method, and their basic personal information was collected by questionnaire survey, and blood and urine samples were collected. The levels of 4 PAHs metabolites 2-hydroxfluorene (2-FLU), 2- hydroxynaphthalene (2-NAP), 9-hydroxyphenanthren (9-PHE), and 1-hydroxypyrene (1-OHP) in urine were detected by high performance liquid chromatography (HPLC) -fluorescence detection method. HPLC-UV detection method was used to detect the content of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) in plasma, and the SAHH activity value was obtained by calculating the ratio. Reverse transcription PCR method was used to determine the H19 gene expression level. Urine levels of 2-FLU, 2-NAP, 9-PHE, and 1-OHP were divided into Q(1), Q(2), Q(3), and Q(4) groups according to quartiles (P(25), P(50), P(75)). Regression, trend test and restricted cubic splines were used to analyze the relationship among PAHs metabolites, SAHH activity, H19 gene expression and their dose-response. Results: The median age of coke oven workers was 39.60 years old, the median length of service was 20.38 years, and the urinary levels of 2-FLU, 2-NAP, 9- PHE, and 1-OHP were 0.29, 0.74, 0.09, and 0.06 μg/mmol Cr, respectively. The levels of 2-FLU, 2-NAP and 9-PHE in the urine of workers were significantly different between groups with different 1-OHP levels (P<0.05). After adjusting for age, length of service, smoking, drinking, and levels of 2-FLU, 2-NAP and 9-PHE, SAHH activity decreased with the increase of urinary 1-OHP level (OR=0.63, 95%CI: 0.41-0.98, P=0.038), showing a nonlinear relationship (P(nonlinear)= 0.030). H19 gene expression increased with the increase of urinary 1- OHP level (OR=1.51, 95%CI: 1.03-2.19, P=0.033), there was a linear relationship (P(trend)= 0.058). The relationship between the other three metabolites in urine and SAHH activity and H19 gene expression was not statistically significant (P>0.05) . Conclusion: Urinary 1-OHP level may be a risk factor for decreased SAHH activity and increased H19 gene expression in coke oven workers.

Phlorizin alleviates cholinergic memory impairment and regulates gut microbiota in d-galactose induced mice

We explored the effect of phlorizin against cholinergic memory impairment and dysbacteriosis in D-galactose induced ICR mice. The control (CON) group, D-galactose model (DGM) group, and three groups (DG-PL, DG-PM, DG-PH) treated with phlorizin at 0.01%, 0.02%, and 0.04% (w/w) in diets were raised for 12 weeks. Supplementing with phlorizin reversed the loss of organ coefficient and body weight caused by D-galactose. The functional abilities of phlorizin on hippocampal-dependent spatial learning and memory, anti-oxidation, anti-inflammation were also observed. Meanwhile, phlorizin intervention upregulated the gene expression of Nrf2, GSH-PX, SOD1, decreased the gene expression of NF-κB, TLR-4, TNF-α, and IL-1β in the hippocampus, while enhanced the gene expression of JAM-A, Mucin2, Occludin in the caecum. Furthermore, a neurotransmitter of acetylcholine (ACh) was enhanced, while acetylcholinesterase (AChE) activity was inhibited by phlorizin administration. Moreover, phlorizin administration increased short-chain fatty acids (SCFAs) content, and reduced lipopolysaccharides (LPS) levels, which may relate to the rebuilding of gut microbiota homeostasis. Treatment with phlorizin may be an effective intervention for alleviating cognitive decline and gut microbiota dysbiosis.

Transcriptome analysis of sheep follicular development during prerecruitment, dominant, and mature stages after FSH superstimulation

Sheep is usually a monovular animal; superovulation technology is used to increase the number of offspring per individual and shorten generation intervals. To date, mature FSH superstimulatory treatments have been successfully used in sheep breeding, but much remains unknown about genes, pathways, and biological functions involved in follicular development. Therefore, in this study, we performed transcriptome profiling of small follicles (SFs; 2-2.5 mm), medium follicles (MFs; 3.5-4.5 mm), and large follicles (LFs; > 6 mm) in Mongolian ewes after FSH superstimulation. Furthermore, we identified differentially expressed genes and performed Kyoto Encyclopedia of Genes and Genomes pathway and Gene Ontology enrichment analyses in 3 separate pairwise comparisons. We found that ovarian steroidogenesis was significantly enriched in the SFs versus MFs analysis; the associated genes, cytochrome P450 family 19 (CYP19) and Hydroxy-delta-5-steroid dehydrogenase 3 beta- and steroid delta-isomerase 1 (HSD3B1), were significantly upregulated. Moreover, proline metabolism, glutathione metabolism, and PPAR signaling pathways were significantly enriched in the LFs versus SFs analysis; the associated genes, glutamate-cysteine ligase modifier subunit (GCLM) and cystathionine gamma-lyase (CTH), were significantly upregulated, whereas peroxisome proliferator-activated receptor gamma (PPARγ) was significantly downregulated. In summary, our study provides basic data and possible biological direction to further explore the molecular mechanism of sheep follicular development after FSH superstimulation.

Development of a novel quantitative function between spectral value and metmyoglobin content in Tan mutton

This study was aimed to establish a quantitative function between spectral reflectance values and metmyoglobin (MetMb) content in Tan mutton during refrigeration. Near-infrared hyperspectral data combined with generalized two-dimensional correlation spectroscopy (G2D-COS) method to identify characteristic bands and investigate the sequence of chemical waveband changes. Characteristic wavebands identified by G2D-COS analysis had the best performance in predicting the content of MetMb, with a high R²p of 0.849, a low RMSEP of 2.695 and a high RPD of 2.786. The results showed that the G2D-COS may be a powerful tool for describing intensity changes of MetMb band. The partial least square regression method was used to develop the relationships between the spectral values and MetMb content in Tan mutton meat for predicting MetMb content. This study has provided a convenient and rapid non-destructive quantitative method for assessing the color of Tan mutton meat.

[A bibliometric analysis of literature on hand-transmitted vibration in China, 1990-2016]

Objective: To investigate the features of literature on hand-transmitted vibration in China, 1990-2016. Methods: In September 2017, the studies on hand-transmitted vibration in China, which were published in Chinese or English during 1990-2016, with "China" and "Taiwan" as the places where author affiliations were located, were retrieved. A bibliometric analysis was performed to investigate the type of articles, publication time, the journals in which articles were published, author affiliations, author regions, and funding. Results: A total of 205 articles on hand-transmitted vibration were retrieved. There were 7.59 articles on average published annually from 1990 to 2016. In the 205 articles, 114 (55.61%) were published in the journals indexed in one or two core journal databases. In the 64 journals, 22 (34.38%) were indexed in one or two core journal databases. The first authors were from 22 provincial regions (provinces, autonomous regions, or centrally administered municipalities) in China, with 152 articles (74.15%) by the authors in the top five regions. There were a total of 876 authors, and the co-authorship degree was 4.27 (876/205). Most of the first authors (136 articles, 66.34%) were affiliated with universities or institutes for prevention and control of occupational diseases. Among the 205 articles, 103 (50.24%) were original articles or investigations, and 72 (35.12%) were funded. Conclusion: The studies on hand-transmitted vibration fluctuated and increased from 1990 to 2016, with a relatively concentrated distribution in terms of sources, regions, and institutions. Interregional and international academic exchange should be strengthened.

[Correlative factors on prevalence rate of dislipidemia among 1 337 coal miners in Shanxi province]

Objective: To understand the prevalence rate and correlative factors of dislipidemia among Shanxi coal miners and to provide evidence for the development of programs on dislipidemia prevention. Methods: We investigated 1 337 mine workers from a Coal Group in April 2016 and collected data related to their blood biochemistry. We then classified the types in accordance with the diagnostic criteria of " Guidelines for prevention and treatment of dyslipidemia in Chinese adults (2007)" , using χ(2) test and unconditional logistic regression model for analysis. Results: The overall prevalence rate of Dislipidemia was 59.1% (790/1 337), with males as 60.4% (708/1 173) and females as 50.0%(82/164) while males appeared higher (χ(2)=6.386, P<0.05). Among the 20-34, 35-49, 50 and above year-old groups, the rates were 68.8%, 58.7%, 49.5%, respectively. Results from the χ(2) test showed that gender, age and body mass index were the influencing factors on dislipidemia (χ(2)=7.117, P<0.01; χ(2)=37.135, P<0.01; χ(2)=7.009, P<0.05), while logistic regression analysis showed that sex, age, body mass index level, systolic blood pressure were significantly associated with dislipidemia (P<0.05). Male miners appeared 1.501 times (OR=1.501, 95%CI: 1.895-2.516) higher than female miners in suffering from the risk of dyslipidemia. In different age groups, risks of dyslipidemia in the 35-49, 20-34 year-old groups were 1.672 (OR=1.672, 95%CI: 1.501-2.392) and 2.369 times (OR= 2.369, 95% CI: 1.275-3.469) higher than the 50 year-old. Group that with high BMI, the risk of dyslipidemia was 1.443 times (OR=1.443, 95%CI: 1.139-1.828) higher than the normal BMI group. Group with abnormal systolic pressure was 1.829 times (OR=1.829, 95%CI: 1.152-2.906) higher than normal systolic pressure group. However, diastolic blood pressure, blood sugar, uric acid, and electrocardiogram findings did not seem to show statistically significant meanings on dislipidemia. Conclusion: Among the coal mine workers, those who were males, aged from 20 to 34, having high blood pressure (systolic blood pressure abnormalities) or with high BMI (≥24.0 kg/m(2)) need to be taken special attention on care and prevention of dislipidemia.

Effect of melatonin supplementation on cryopreserved sperm quality in mouse

BACKGROUND

Antioxidants protect spermatozoa against cell damage during cryopreservation.

OBJECTIVE

To investigate whether melatonin supplement in the extender may improve the quality of cryopreserved mouse sperm.

METHODS

Kunming mice sperm frozen in extender R18S3 (18% (w/v) raffinose and 3% (w/v) skim milk) supplemented with melatonin were thawed and evaluated.

RESULTS

Mouse spermatozoa were cryopreserved in the freezing extender R18S3 that contained melatonin at 0, 0.125, 0.25 and 0.5 mg/mL melatonin. The extender without melatonin supplement was associated with increased formation of reactive oxygen species (ROS) and decreased sperm motility. Melatonin supplement at 0.125 mg/mL significantly increased the progressive motility of sperm in comparison to other melatonin concentration or control. The percentage of thawed viable sperm with ROS was lower in the melatonin-treated groups than in untreated group. Melatonin supplement also increased antiapoptotic gene Bcl-xl expression in the thawed sperm.

CONCLUSION

Supplement of 0.125 mg/mL melatonin could reduce oxidative damage and apoptosis.

Cloning and expression analysis of terpenoid metabolism-related gene NsyCMS in Nicotiana sylvestris

Terpenoids constitute the main class of secondary metabolites produced in plants with industrial, pharmacological, and agricultural interests. Nicotiana sylvestris has been widely adopted as a diploid model system in plant biology for studies of terpenoid biosynthesis. In this paper, we report the isolation and analysis of the 2-C-methyl-d-erythritol 2,4-cyclodiphosphate synthase (CMS) gene of the MEP (methylerythritol 4-phosphate) pathway from N. sylvestris. We used homologous-based cloning with a RACE method to obtain the full-length coding sequence of the NsCMS. Then, the physical and chemical properties, function, and three-dimensional structure of the NsyCMS protein were predicted. Fluorogenic quantitative PCR was used to conduct an expression analysis at different developmental stages of various tissues of the NsyCMS. The sequence of the NsyCMS consists of a 954-bp open reading frame and encodes a predicted protein of 317 amino acids, with a molecular weight of approximately 49.6 kDa and pi of 6.92. The in vivo localization of the encoded protein was cytoplasmic with no signal peptide, whereas 2 transmembrane regions were found in NsyCMS. The conserved domains of typical 2-C-methyl-d-erythritol 2,4-cyclodiphosphate synthase, aminotransferase, and pyridoxal phosphate-dependent transferase were found in NsyCMS. Differential expression patterns of the NsyCMS were observed throughout the different developmental stages and tissues. NsyCMS messenger RNA was expressed in all tissues, with the highest level of expression in the seedling leaves. NsyMK was expressed at a higher level in the resettling roots. The results from our study set the foundation for exploring the terpenoid biosynthetic pathways in N. sylvestris.

Identification of apple cultivars on the basis of simple sequence repeat markers

DNA markers are useful tools that play an important role in plant cultivar identification. They are usually based on polymerase chain reaction (PCR) and include simple sequence repeats (SSRs), inter-simple sequence repeats, and random amplified polymorphic DNA. However, DNA markers were not used effectively in the complete identification of plant cultivars because of the lack of known DNA fingerprints. Recently, a novel approach called the cultivar identification diagram (CID) strategy was developed to facilitate the use of DNA markers for separate plant individuals. The CID was designed whereby a polymorphic maker was generated from each PCR that directly allowed for cultivar sample separation at each step. Therefore, it could be used to identify cultivars and varieties easily with fewer primers. In this study, 60 apple cultivars, including a few main cultivars in fields and varieties from descendants (Fuji x Telamon) were examined. Of the 20 pairs of SSR primers screened, 8 pairs gave reproducible, polymorphic DNA amplification patterns. The banding patterns obtained from these 8 primers were used to construct a CID map. Each cultivar or variety in this study was distinguished from the others completely, indicating that this method can be used for efficient cultivar identification. The result contributed to studies on germplasm resources and the seedling industry in fruit trees.

Breed-specific transcriptome response of spleen from six to eight week old piglet after infection with Streptococcus suis type 2

Different pig breeds have shown differential susceptibility to the pathogen infection; however, molecular mechanisms of the infection susceptibility are not fully understood. Streptococcus suis type 2 (SS2) is an important zoonotic pathogen. To identify the genes responsible for infection susceptibility, pigs from two different breeds (Enshi black and Landrace) were inoculated with SS2 and their spleen transcriptome profiles were investigated in the present study. The differentially expressed genes (DEGs) were analyzed from infected versus control pigs in each breed, and then compared between both pig breeds. Enshi black pig showed more DEGs than Landrace (830 vs. 611) and most of these were due to down-regulated genes (543 vs. 387). However some DEGs were uniquely expressed in one breed, some were expressed in opposite direction in both breeds. A number of candidate genes and pathways are identified which might be involved in susceptibility to SS2, for example, MMP9 and Resistin were only significantly expressed in Landrace. NPG3 and PMAP23 were up-regulated in Landrace whereas down-regulated in Enshi black. LENG8 in control Landrace have inherently higher expression than control Enshi black. IGKV6 is down-regulated in Landrace but up-regulated in Enshi black. Overall, the transcriptome profiles are consistent with the clinical signs, i.e. the Enshi black is more susceptible to SS2 infection than Landrace. This is the first study to identify differential gene expression between indigenous and modern commercial pigs after in vivo SS2 infection using RNA-seq. The significant DEGs in splenic profiles between two pig breeds suggested considerable involvement of genetic background in susceptibility to the SS2 infection in pigs.

Characterization of EST-derived and non-EST simple sequence repeats in an F₁ hybrid population of Vitis vinifera L

Among different classes of molecular markers, expressed sequence tags (ESTs) are a new resource for developing simple sequence repeat (SSR) functional markers for genotyping and genetic mapping in F1 hybrid populations of Vitis vinifera L. Recently, because of the availability of an enormous amount of data for ESTs in the public domain, the emphasis has shifted from genomic SSRs to EST-SSRs, which belong to transcribed regions of the genome and may have a role in gene expression or function. The objective of this study was to assess the polymorphisms among 94 F1 hybrids from "Early Rose" and "Red Globe" using 25 EST-derived and 25 non-EST SSR markers. A total collection of 362,375 grape ESTs that were retrieved from the National Center for Biotechnology Information (NCBI) and 2522 EST-SSR sequences were identified. From them, 205 primer pairs were randomly selected, including 176 pairs that were EST-derived and 29 non-EST SSR primer pairs, for polymerase chain reaction amplification. A total of 131 alleles were amplified using 50 pairs of primers; 78 alleles were amplified using EST-derived SSR primers and 53 were from non-EST SSR primers. At most, 6 and 5 alleles were amplified by EST-derived and non-EST SSR primers, respectively. The EST-derived SSR markers showed a maximum polymorphic information content (PIC) value of 1 and a minimum of 0.33 while non-EST SSR markers had maximum and minimum PIC values of 1 and 0.25, respectively. The average PIC value was 0.56 for EST-derived SSR markers and 0.45 for non-EST SSR markers.

Homology-based cloning and expression analysis of Rf genes encoding PPR-containing proteins in tobacco

As a model plant, mechanisms of the cytoplasmic male sterility/restoration of fertility (CMS/Rf) system in tobacco are seldom studied. Using Rf gene sequences from other Solanaceae plants and the draft genome of Nicotiana benthamiana, degenerate primers were designed to amplify the cDNA pool of N. tomentosiformis. In total, six possible Rf sequences were identified, two of which contained base-deletion mutations. The other four were intact open reading frames, of which NtomPPR5 harbored a 3-pentatricopeptide repeat (PPR) motif deletion. Structure analysis revealed that they all encoded a PPR-containing protein with putative mitochondrial targeting signals at their N-terminus, and they all belong to the P subfamily. Phylogenetic analysis showed that all of the Rf-coding PPRs clustered together, and recent duplication events might have occurred in tobacco after the divergence of the species. Quantitative reverse transcription polymerase chain reaction analysis demonstrated that the NtomRfs were expressed in all tissues of N. tomentosiformis and (CMS) K326, although the expression levels varied with gene, organ, and developmental stage. Furthermore, the expression levels of Rf sequences in K326 were lower than those in CMS K326. The molecular basis of the CMS/Rf system in tobacco requires further investigation.

Development of highly polymorphic EST-SSR markers and segregation in F₁ hybrid population of Vitis vinifera L

The objectives of this investigation were to develop and validate the expressed sequence tag (EST)-simple sequence repeat (SSR) markers from large EST sequences, and to study the segregation and distribution of SSRs within two grapevine parental lines. In total, 94 F₁ lines crossed between "Early Rose" and "Red Globe" were studied. Approximately 2100 EST-SSR sequences of Vitis vinifera L. were searched for SSRs and analyzed for the design of polymerase chain reaction (PCR) primers amplifying the SSR-rich regions. Trinucleotide repeats were found to be the most abundant, followed by other nucleotide repeats. A total of 182 SSR primer pairs were first developed for the study on the parental polymorphism. Among the 182 SSR primers, 142 primer pairs (78%) could amplify the anticipated PCR products, among which only 52 primer pairs (36.62%) showed polymorphism between the two parents. These polymorphic bands were further surveyed among the 94 F₁ lines, and the results showed that a total of 162 bands were amplified, and 98 of them were polymorphic in both parents (60.86% polymorphism), with an average of 1.88 polymorphic DNA bands for each primer pair. After testing with the chi-square test, 33 of the clearly amplified polymorphic bands followed a 3:1 ratio, and 37 followed a 1:1 ratio. The rest showed distorted segregation ratios.

Studying genetic diversity in the core germplasm of confectionary sunflower (Helianthus annuus L.) in China based on AFLP and morphological analysis

Characterization of germplasm resources of confectionary sunflower is critical to assess collection diversity and enhance utilization which is few referred. 70 germplasm representing 12 provinces of China was characterized using 8 amplified fragment length polymorphic (AFLP) primers and 17 morphological descriptors. Euclidean distance were used for AFLP and morphological data ranged from 0.32 to 1.56 and from 0.30 to 1.48 respectively. No two germplasm had a distance of zero, showing there were no duplicate entries. Cluster analysis of AFLP data were determined by SAS which 70.0% of the total germplasm (49 entries) were including in the two main clusters I and II. A wild germplasm was single in the end cluster which is at 1.56 distance level to other clusters. For morphological data, 75.7% of the germplasm (53 entries) were in two main clusters II and III. This clustering pattern for AFLP and morphological data suggested unique germplasm were generally under represented in the collection. The morphological-based clusters showed some locality separation by germplasm origin, but in general, origin did not correspond closely with the clustering pattern. Principal component analysis (PCA) showed the first seven principal components accounted for 81.33% of the total variation, of which 43.05% was contributed by the first two principal components.

Characterization of an anther- and tapetum-specific gene and its highly specific promoter isolated from tomato

A full-length genomic clone of 2,233 bp long containing an anther- and tapetum-specific gene TomA108 was isolated and characterized from tomato. The gene was present in one copy per haploid genome. The isolated clone contained 5' and 3' untranslated regions of 810 and 170 nucleotides, respectively and a single intron with highly repetitive sequences. The cDNA encoded the protein with an apparent mass of 10.6 kDa and a pI (isoelectric point) of 5.3. It was cysteine-rich and had an N-terminal hydrophobic domain with characteristics of a secretory signal. Amino acid sequence comparisons demonstrated that the protein was closely related to a family of cereal seed storage proteins and protease inhibitors. The fusion of beta-glucuronidase to the TomA108 promoter demonstrated that the promoter was highly active from early-meiosis to free microspores production in tapetum of tobacco. This strong and highly specific promoter can be potentially used to generate male sterility for efficient production of plant hybrids.

Genetic transformation of Leymus chinensis with the PAT gene through microprojectile bombardment to improve resistance to the herbicide Basta

Chinese leymus [Leymus chinensis (Trin.) Tzvel.] is a perennial grass (tribe Gramineae) that is widely distributed throughout northern China and Mongolia where it is produced as a forage product. Severe production losses due to weed growth have serious economic consequences, and as non-selective herbicides not only kill the weeds but are also harmful to this forage grass, the introduction of a foreign gene for resistance to the herbicide Basta is necessary since this species lacks herbicide resistance. We have investigated the transformation of a gene for phosphinothricin acetyltransferase (PAT) through microprojectile bombardment in Chinese leymus. Calli from immature inflorescences cultured on N6 medium supplemented with 2.0 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 5.0 mg/l of glutamine were bombarded. The bombarded calli survived on selection medium with 1.0 mg/l of phosphinothricin (PPT). Twenty-three plantlets regenerated from resistant calli on differentiation medium supplemented with 1.0 mg/l 6-benzylaminopurine, 1.0 mg/l kinetin, and 1.0 mg/l PPT, and five of these regenerated plantlets survived on rooting medium with 1.0 mg/l of PPT. PCR and Southern blotting analyses indicated that the PAT gene had been integrated into the genomes of two Chinese leymus plantlets and that the gene was stably transferred to its clonal offsprings. There were no other phenotypic effects associated with transgene expression during vegetative growth except tolerance to the herbicide Basta.

An effective method for axillary bud culture and RAPD analysis of cloned plants in tetraploid black locust

An efficient micropropagation technique by axillary bud multiplication was established for cloning tetraploid black locust tree (Robinia pseudoacacia L.). The result showed that the optimal medium for shoot multiplication and elongation was Murashige and Skoog (MS) medium supplemented with 0.5 mg/l 6-benzylaminopurine in combination with 0.5 mg/l kinetin and 0.1 mg/l 1-naphthaleneacetic acid. The best medium for rooting was half-strength MS medium with 0.25 mg/l indole-3-butyric acid. In the present report, we examined the genetic fidelity of the micropropagated plants by the randomly amplified polymorphic DNA (RAPD) method with 25 primers. The cloned plants of tetraploid black locust showed complete stability.

Acetylcholine, bradykinin, opioids, and phenylephrine, but not adenosine, trigger preconditioning by generating free radicals and opening mitochondrial K(ATP) channels

It has been assumed that all G(i)-coupled receptors trigger the protective action of preconditioning by means of an identical intracellular signaling pathway. To test this assumption, rabbit hearts were isolated and perfused with Krebs buffer. All hearts were subjected to a 30-minute coronary artery occlusion followed by 120 minutes of reperfusion. Risk area was measured with fluorescent particles and infarct size with triphenyltetrazolium chloride staining. Control hearts showed 29.1+/-2.8% infarction of the risk zone. A 5-minute infusion of acetylcholine (0.55 mmol/L) beginning 15 minutes before the 30-minute occlusion resulted in significant protection (9.2+/-2.7% infarction). This protection could be blocked by administration of 300 micromol/L N-2-mercaptopropionyl glycine (MPG), a free radical scavenger, or by 200 micromol/L 5-hydroxydecanoate (5-HD), a mitochondrial K(ATP) antagonist, for 15 minutes beginning 5 minutes before the acetylcholine infusion (35.2+/-3.9% and 27.8+/-2.4% infarction, respectively). Similar protection was observed with other known triggers, ie, bradykinin (0.4 micromol/L), morphine (0.3 micromol/L), and phenylephrine (0.1 micromol/L), and in each case protection was completely abrogated by either MPG or 5-HD. In contrast, protection by adenosine or its analog N(6)-(2-phenylisopropyl) adenosine could not be blocked by either MPG or 5-HD. Therefore, whereas most of the tested agonists trigger protection by a pathway that requires opening of mitochondrial K(ATP) channels and production of free radicals, the protective action of adenosine is not dependent on either of these steps. Hence, it cannot be assumed that all G(i)-coupled receptors use the same signal transduction pathways to trigger preconditioning.

No confirmation for a causal role of volume-regulated chloride channels in ischemic preconditioning in rabbits

Volume-regulated chloride channels have recently been proposed to be end-effectors in ischemic preconditioning. The present study attempted to confirm this hypothesis by looking both at cardioprotection and channel activity. In isolated rabbit cardiomyocytes, hypo-osmotic stress (167 mosm/l) induced a current with a magnitude of 2-5 pA/pF at 60 mV. That current could be blocked by the selective chloride channel blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) or indanyloxyacetic acid 94 (IAA-94), but only at 100 microM and 1 m M respectively. Lower concentrations were not effective. Because the channel-blocking concentrations were toxic in isolated perfused rabbit hearts, as evidenced by cessation of cardiac contraction and massive infarction, neither agent could be tested against preconditioning's anti-infarct effect. NPPB and IAA-94 at 1 microM and 10 microM, respectively (the doses used in a previous report), did not affect coronary flow, heart rate and developed pressure, and also did not prevent the infarct size reduction of ischemic preconditioning with 5 min global ischemia/10 min reperfusion preceding 30 min of regional ischemia and 120 min of reperfusion [11. 4(+/-3.6) and (11.1(+/-3.7)% infarction of risk area, respectively]. The volume-regulated chloride and organic osmolyte channel blocker 4, 4;-diisothiocyanostilbene-2,2;-disulfonic acid (DIDS) at 100 microM blocked the hypo-osmotically induced current in myocytes, but again could not be used, since it induced total cessation of cardiac contraction and reduced infarct size in non-preconditioned hearts. Our data do not confirm a prior study on a causal role for volume-regulated chloride channels in the protection of ischemic preconditioning. This hypothesis remains to be adequately tested.

Opening of mitochondrial K(ATP) channels triggers the preconditioned state by generating free radicals

The critical time for opening mitochondrial (mito) K(ATP) channels, putative end effectors of ischemic preconditioning (PC), was examined. In isolated rabbit hearts 29+/-3% of risk zone infarcted after 30 minutes of regional ischemia. Ischemic PC or 5-minute exposure to 10 micromol/L diazoxide, a mito K(ATP) channel opener, reduced infarction to 3+/-1% and 8+/-1%, respectively. The mito K(ATP) channel closer 5-hydroxydecanoate (200 micromol/L), bracketing either 5-minute PC ischemia or diazoxide infusion, blocked protection (24+/-3 and 28+/-6% infarction, respectively). However, 5-hydroxydecanoate starting 5 minutes before long ischemia did not affect protection. Glibenclamide (5 micromol/L), another K(ATP) channel closer, blocked the protection by PC only when administered early. These data suggest that K(ATP) channel opening triggers protection but is not the final step. Five minutes of diazoxide followed by a 30-minute washout still reduced infarct size (8+/-3%), implying memory as seen with other PC triggers. The protection by diazoxide was not blocked by 5 micromol/L chelerythrine, a protein kinase C antagonist, given either to bracket diazoxide infusion or just before the index ischemia. Bracketing preischemic exposure to diazoxide with 50 micromol/L genistein, a tyrosine kinase antagonist, did not affect infarction, but genistein blocked the protection by diazoxide when administered shortly before the index ischemia. Thus, although it is not protein kinase C-dependent, the protection by diazoxide involves tyrosine kinase. Bracketing diazoxide perfusion with N:-(2-mercaptopropionyl) glycine (300 micromol/L) or Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (7 micromol/L), each of which is a free radical scavenger, blocked protection, indicating that diazoxide triggers protection through free radicals. Therefore, mito K(ATP) channels are not the end effectors of protection, but rather their opening before ischemia generates free radicals that trigger entrance into a preconditioned state and activation of kinases.

Exogenous nitric oxide can trigger a preconditioned state through a free radical mechanism, but endogenous nitric oxide is not a trigger of classical ischemic preconditioning

Nitric oxide (NO) has been reported to play an important role in the late phase of ischemic preconditioning (PC) in the rabbit heart. However, the role of NO in the early phase of ischemic PC ("classical PC") is controversial. Accordingly, the present study was designed to determine whether NO contributes to the cardioprotective effect of classical PC in rabbits. Isolated hearts experienced 30 min of regional ischemia followed by 120 min of reperfusion. Infarct size was measured with triphenyltetrazolium chloride. In control hearts infarction was 30.2+/-3.3% of the risk zone. PC with 5 min of global ischemia and 10 min of reperfusion reduced infarct size to 10.2+/-2.4% (P<0.05). Perfusion with 2 microm S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, in lieu of ischemia mimicked PC (4.4+/-1.9% infarction, P<0.01 v control). To determine whether this protection was dependent on either protein kinase C (PKC) as has previously been demonstrated for classical PC or free radicals known to be produced during exogenous NO administration, chelerythrine (5 microm), a PKC inhibitor, or N-(2-mercaptopropionyl)-glycine (300 microm), a free radical scavenger, was administered with or shortly after SNAP. Neither drug had any independent effect on infarct size, and each blocked SNAP's cardioprotection (31.0+/-5.1 and 25.7+/-5.2% infarction, resp.). N(omega)-nitro- L -arginine methyl ester (L -NAME, 100 microm), a NO synthase inhibitor, failed to block the cardioprotection from the above ischemic PC protocol (9.5+/-2.8% infarction, P<0.05 v control). L -NAME alone had no effect on infarct size (30.6+/-2.7%). These results suggest that the beneficial effect of exogenous NO production during SNAP pretreatment is mediated by a protein kinase C-dependent pathway via MPG-sensitive oxidants. However, we were unable to show any contribution of endogenous NO to classical PC's protection in isolated rabbit hearts.

Structural changes of atrial myocardium during chronic atrial fibrillation

Of all known arrhythmia's, atrial fibrillation (AF) is the most often met in the clinical setting and it is associated with an increase in mortality risk. Several risk factors for AF have been described and several mechanisms of induction and maintenance have been proposed. Studies in patients with AF have shown that structural changes occur in the atria, but the relationship between the structural remodelling and the chronicity of the arrhythmia are not well understood. The changes mainly concern adaptive (dedifferentiation of cardiomyocytes) and maladaptive (degeneration of cells with replacement fibrosis) features. In order to characterise the time course of the structural remodelling the need for animal models which adequately mimic chronic atrial fibrillation in humans is felt essential. In this review, the structural changes that are observed during prolonged sustained AF in patients and animal models, are described. Furthermore, the time course and potential mechanisms of structural remodelling are discussed and methods for elucidation of the underlying molecular mechanisms are presented.

Protein kinase C-epsilon is responsible for the protection of preconditioning in rabbit cardiomyocytes

The role of protein kinase C (PKC) in the protection of ischemic preconditioning (PC) is still controversial, partly because of the multiple isozymes of PKC and the inability to directly measure PKC activity in vivo. In this study we have used novel peptide inhibitors which correspond to part of the amino acid sequence from the isozyme-specific RACK-binding site on the PKC molecule. The peptides prevent binding of a specific activated PKC isozyme to its RACK, thus halting isozyme translocation and function. The inhibitor peptides are cross-linked to the membrane-translocating antennapedia homeodomain peptide that allows their entry into cells. The effect of inhibitors of PKC-beta, -delta, -epsilon and -eta were evaluated. Rabbit adult ventricular myocytes were obtained by enzymatic dissociation. Ischemia was simulated by centrifuging the myocytes into an oxygen-free pellet for 180 min. PC was induced by 10 min of pelleting followed by resuspension in oxygenated medium for 15 min. During simulated ischemia cells undergo a predictable increase in osmotic fragility as judged by determination of the number of stained cells following their incubation in hypotonic (85 mOsm) trypan blue. The percentage of cells experiencing membrane rupture, and thus cell staining, was considered to be an index of ischemic injury. PC significantly delayed the progression of osmotic fragility during simulated ischemia (P<0.01). The protection of PC was abolished by the peptide inhibitor of PKC-epsilon but not by the peptide inhibitors selective for PKC-beta, PKC-delta, or PKC-eta; each was applied at 100 n N. Protection could also be induced by the PKC activator oleoylacetyl glycerol, and that protection was aborted by the inhibitor selective for PKC-epsilon, but not by the inhibitor for PKC-delta. None of the above peptide treatments affected the osmotic fragility in non-PC cells during simulated ischemia. Our studies further support PKC as a critical part of the signal transduction pathway in PC and indicate that PKC-epsilon alone is responsible for the early phase of PC's protection in rabbit cardiomyocytes.

Ischemic preconditioning depends on interaction between mitochondrial KATP channels and actin cytoskeleton

Both mitochondrial ATP-sensitive K+ (KATP) channels and the actin cytoskeleton have been proposed to be end-effectors in ischemic preconditioning (PC). For evaluation of the participation of these proposed end effectors, rabbits underwent 30 min of regional ischemia and 3 h of reperfusion. PC by 5-min ischemia + 10-min reperfusion reduced infarct size by 60%. Diazoxide, a mitochondrial KATP-channel opener, administered before ischemia was protective. Protection was lost when diazoxide was given after onset of ischemia. Anisomycin, a p38/JNK activator, reduced infarct size, but protection from both diazoxide and anisomycin was abolished by 5-hydroxydecanoate (5-HD), an inhibitor of mitochondrial KATP channels. Isolated adult rabbit cardiomyocytes were subjected to simulated ischemia by centrifuging the cells into an oxygen-free pellet for 3 h. PC was induced by prior pelleting for 10 min followed by resuspension for 15 min. Osmotic fragility was assessed by adding cells to hypotonic (85 mosmol) Trypan blue. PC delayed the progressive increase in fragility seen in non-PC cells. Incubation with diazoxide or pinacidil was as protective as PC. Anisomycin reduced osmotic fragility, and this was reversed by 5-HD. Interestingly, protection by PC, diazoxide, and pinacidil could be abolished by disruption of the cytoskeleton by cytochalasin D. These data support a role for both mitochondrial KATP channels and cytoskeletal actin in protection by PC.

The PKC activator PMA preconditions rabbit heart in the presence of adenosine receptor blockade: is 5'-nucleotidase important?

While there is good evidence that both protein kinase C (PKC) and adenosine are involved in ischemic preconditioning, their sequence in the intracellular signaling cascade is in dispute. One hypothesis proposes that PKC activation causes release of adenosine which then protects the heart, while the other proposes that adenosine stimulates PKC which in turn causes protection. Accordingly, we studied the effects of specified sequences of pharmacologic triggers and blockers on the infarct-sparing effect of a preconditioning protocol. The combination of the adenosine receptor agonist R(-)N6-(2-phenylisopropyl) adenosine (PIA) and the PKC blocker chelerythrine would be protective only if the first hypothesis were correct. On the other hand, the combination of the adenosine receptor blocker 8-(p-sulfophenyl) theophylline (SPT) and a PKC activator would be protective only if the second hypothesis were correct. Isolated, Krebs-perfused rabbit hearts experienced 30 min of regional ischemia and 2 h of reperfusion. Infarct size was quantitated by triphenyltetrazolium chloride staining. In untreated control hearts, 30.0 +/- 2.7% of the risk zone infarcted. Fifty nmol/l PIA for 20 min starting 10 min prior to ischemia resulted in only 8.4 +/- 1.9% infarction (P<0.01), while the combination of PIA and 5 micromol/l chelerythrine resulted in large infarcts of 27.8 +/- 3.2%. This attenuation of the protective effect continued to be observed even when the PIA infusion was continued to the end of the reperfusion period. Conversely, 0.2 nmol of the PKC activator phorbol 12-myristate 13-acetate (PMA) infused during the 10-min interval prior to ischemia protected the hearts (6.5 +/- 1.3% infarction, P<0.01 v control). And protection persisted when PMA-treated hearts were also exposed to 100 microM SPT for 35 min starting 5 min prior to ischemia (9.5 +/- 1.9% infarction, P<0.01 v control). When PKC activation by the PKC-coupled agonist phenylephrine was continued to the end of ischemia and adenosine blockade was extended throughout the reperfusion period by prolonged infusion of SPT, protection was unaffected. The administration of either SPT or chelerythrine alone did not confer any protection (32.5 +/- 3.3 and 34.0 +/- 3.2% infarction, respectively). Thus, because the combination of PKC activation and adenosine receptor blockade was protective while that of adenosine receptor agonist and PKC blockade was not, adenosine receptors must be upstream of PKC in preconditioning.

Mild hypothermia reduces infarct size in the beating rabbit heart: a practical intervention for acute myocardial infarction?

The present study describes a method for rapidly cooling the whole body via its blood pool and tests whether cooling instituted after ischemia has begun can still limit infarction. We also evaluated whether the cardiac protection seen with cooling could be added to that from ischemic preconditioning. Recently it was reported that lowering myocardial temperature by only several degrees greatly slows the extent of myocardial infarction in the beating heart experiencing regional ischemia. To further explore the potential of hypothermia for myocardial protection, rabbits underwent either a 30-, 45- or 60-min coronary artery occlusion and 3-h reperfusion. Blood from a carotid artery was allowed to circulate through a heat exchanger immersed in ice water and return to a jugular vein until the blood temperature in the left atrium reached the target temperature of 35 or 32 degrees C. Furthermore, to elucidate the mechanism of hypothermia's protection, we also examined its effect on isolated cardiomyocytes. Rewarming began upon reperfusion in all protocols. Cooling to 32 degrees C before a 30-min ischemia reduced infarct size from 37.3 +/- 2.5% (n = 6) of the risk zone in normothermic controls to 3.6 +/- 0.3% (n = 6). When cooling was begun 10 or 20 min after the onset of ischemia infarct size was still significantly smaller [8.1 +/- 1.2% and 22.8 +/- 1.8%, respectively (n = 6 in each group)]. Less but significant protection was also seen with cooling to 35 degrees C. Cooling caused only mild bradycardia and hypotension and no apparent arrhythmias. Forty-five min of regional ischemia caused 50.7 +/- 3.3% (n = 6) of risk zone to infarct in untreated hearts. Preconditioning with 5-min ischemia/10-min reperfusion reduced infarct size to 27.5 +/- 2.5% (n = 6). Cooling to 32 degrees C starting 20 min after the onset of ischemia protected the heart (28.7 +/- 2.6% infarction, n = 8), and this protection could be added to the effect from ischemic preconditioning (6.3 +/- 2.3% infarction, n = 6). In the myocyte model, hypothermia and ischemic preconditioning delayed the progressive increase in osmotic fragility that occurs during simulated ischemia in an additive way, but only hypothermia delayed the appearance of contracture suggesting that different mechanisms are involved. Hence blood pool cooling was easily induced and well tolerated and protected the beating heart against infarction even when hypothermia was started after the onset of coronary occlusion. We conclude that hypothermia might be a simple and useful therapy for patients presenting with acute myocardial infarction.

Fostriecin, an inhibitor of protein phosphatase 2A, limits myocardial infarct size even when administered after onset of ischemia

BACKGROUND

The role of protein phosphatases (PPs) during ischemic preconditioning in the rabbit heart was examined.

METHODS AND RESULTS

Fostriecin, a potent inhibitor of PP2A, was administered to isolated rabbit hearts starting either 15 minutes before or 10 minutes after the onset of a 30-minute period of regional ischemia and continuing until the onset of reperfusion. After 2 hours of reperfusion, infarct size was measured with triphenyltetrazolium chloride. In a second study with isolated rabbit cardiomyocytes, the effect of fostriecin pretreatment was assessed by measuring changes in cell osmotic fragility during simulated ischemia. PP1 and PP2A activities of isolated control and ischemically preconditioned cells were also measured. In a third series of experiments, left ventricular biopsies of isolated rabbit hearts were obtained before and at selected times during 60 minutes of global ischemia, and the tissue was assayed for PP1 and PP2A activities. In isolated hearts pretreated with fostriecin, only 8% of the ischemic zone infarcted, significantly less than that in untreated control hearts (33%; P<0.001) but comparable to that in ischemically preconditioned hearts (9%; P<0.001 versus control). Significant protection was also observed in the hearts treated only after the onset of ischemia (18% infarction; P<0.05 versus control). In isolated myocytes, fostriecin also provided protection comparable to that produced by metabolic preconditioning. Preconditioning had no apparent effect on the activity of either PP1 or PP2A in isolated ventricular myocytes or ventricular tissue obtained from heart biopsies.

CONCLUSIONS

Fostriecin, a potent inhibitor of PP2A, can protect the rabbit heart from infarction even when administered after the onset of ischemia. But inhibition of either PP1 or PP2A does not appear to be the mechanism of protection from ischemic preconditioning.

Cyclosporine A limits myocardial infarct size even when administered after onset of ischemia

OBJECTIVE

The role of the immunosuppressant cyclosporine A as a preconditioning-mimetic in the rabbit heart was examined.

METHODS

Cyclosporine A, a potent protein 2B or calcium/calmodulin-dependent phosphatase (PP) inhibitor, was administered isolated rabbit hearts starting either 15 min prior to or 10 or 20 min after the onset of a 30 min period of regional ischemia and continuing until the onset of reperfusion. The effect of pretreatment with a second PP2B antagonist, FK-506, was also examined. In an additional protocol L-NAME was perfused for 50 min starting 5 min before the 45-min infusion of cyclosporine A. After 2 h of reperfusion infarct size was measured with triphenyltetrazolium chloride. In a second study left ventricular biopsies of isolated rabbit hearts were obtained to measure the effect of cyclosporine A on dephosphorylation of [32P] phosphorylase kinase by calcium/calmodulin-dependent phosphatases.

RESULTS

Pretreatment with cyclosporine A resulted in only 10.0%, infarction of the risk zone, significantly less than that in untreated control hearts (28.7%, p < 0.001) but comparable to the extent of infarction in ischemically preconditioned hearts (10.0% p < 0.001 vs. control). Equivalent protection was also observed in hearts with treatment delayed for 10 min following the onset of ischemia (10.4% infarction, p < 0.001 vs. control). However, protection waned when cyclosporine A was administered only during the last 10 min of the 30-min ischemic period (25.5% infarction, p = n.s. vs. control). Pretreatment with FK-506 also resulted in myocardial salvage (10.4% infarction, p < 0.001 vs. control). When hearts were exposed to a co-infusion of L-NAME and cyclosporine A, protection was still evident (18.1% infarction, p < 0.05 vs. L-NAME), although not as robust as that seen with the PP2B blocker alone. In hearts pretreated with cyclosporine A dephosphorylation of [32P] phosphorylase kinase by calcium/calmodulin-dependent phosphatases was inhibited by 67%.

CONCLUSIONS

Cyclosporine A and FK-506, potent PP2B inhibitors, can protect the ischemic rabbit heart, and at least cyclosporine A continues to be effective when infusion is delayed until after the onset of ischemia. The mechanism of this protection may be related to inhibition of phosphatases and prolongation of the phosphorylation state of ischemic cells.

The mechanism of protection from 5 (N-ethyl-N-isopropyl)amiloride differs from that of ischemic preconditioning in rabbit heart

We investigated the effects of 5-(N-ethyl-N-isopropyl)amiloride (EIPA) on infarction in isolated rabbit hearts and cardiomyocytes. Thirty min of regional ischemia caused 29.6 +/- 2.8% of the risk zone to infarct in untreated Krebs buffer-perfused hearts. Treatment with EIPA (1 microM) for 20 min starting either 15 min before ischemia or 15 min after the onset of ischemia significantly reduced infarction to 5.4 +/- 2.0% and 7.0 +/- 1.0%, respectively (p < 0.01 versus untreated hearts). In both cases salvage was very similar to that seen with ischemic preconditioning (PC) (7.1 +/- 1.5% infarction). Unlike the case with ischemic preconditioning, however, protection from EIPA was not blocked by 50 microM polymyxin B, a PKC inhibitor, or 1 microM glibenclamide, a KATP channel blocker. Forty-five min of regional ischemia caused 51.0 +/- 2.9% infarction in untreated hearts. Ischemic preconditioning reduced infarction to 23.4 +/- 3.1% (p < 0.001 versus untreated hearts). In these hearts with longer periods of ischemia pretreatment with EIPA reduced infarction similarly to 28.8 +/- 2.1% (p < 0.01 versus untreated hearts). However, when EIPA was combined with ischemic PC, no further reduction in infarction was seen (23.8 +/- 3.5% infarction). To further elucidate the mechanism of EIPA's cardioprotective effect, this agent was also examined in isolated rabbit cardiomyocytes. Preconditioning caused a delay of about 30 min in the progressive increase in osmotic fragility that occurs during simulated ischemia. In contrast, EIPA had no effect on the time course of ischemia-induced osmotic fragility. Furthermore, EIPA treatment did not alter the salutary effect of ischemic preconditioning when the two were combined in this model. We conclude that Na+/H+ exchange inhibition limits myocardial infarction in the isolated rabbit heart by a mechanism which is quite different from that of ischemic preconditioning. Despite the apparently divergent mechanisms, EIPA's cardioprotective effect could not be added to that of ischemic or metabolic preconditioning in these models.

Phosphorylation of tyrosine 182 of p38 mitogen-activated protein kinase correlates with the protection of preconditioning in the rabbit heart

p38 mitogen-activated protein kinase (MAPK) is known to be activated after exposure to endotoxin, osmotic and environmental stress, and, most recently, during ischemia/reperfusion. We investigated whether ischemic preconditioning also causes phosphorylation of the activation sites on p38 MAPK. Three groups of isolated rabbit hearts were studied. Control hearts experienced 30 min of ischemia only. The second group was preconditioned with 5 min of global ischemia and 10 min of reperfusion. Group 3 was also ischemically preconditioned, but in the presence of 100 microM 8-(p-sulfophenyl)theophylline (SPT). Transmural left ventricular biopsies were taken before and during the long ischemic period. Western blot analysis with either p38 MAPK or phospho-specific p38 MAPK (Tyr-182) antibodies showed a decreased phosphorylation during ischemia in non-preconditioned hearts, but phosphorylation was enhanced several fold after 10 and 20 min of ischemia in preconditioned hearts. Furthermore, when protection from ischemic preconditioning was blocked by SPT, increased phosphorylation of p38 MAPK during ischemia was not present. Therefore the phosphorylation of p38 MAPK at tyrosine 182, which is required for the kinase's activation, occurred during ischemia only when protection from preconditioning was evident. In a second study, changes in osmotic fragility were measured during simulated ischemia in rabbit cardiomyocytes. Reduced fragility in ischemically preconditioned myocytes could be completely abolished by the specific p38 MAPK inhibitor SB-203580. In contrast, anisomycin, an activator of p38 MAPK and JUN kinase pathways, was found to be as protective as ischemic preconditioning. We conclude that p38 MAPK phosphorylation correlates with preconditioning's protection, and that its activation may be an important step in the signal transduction cascade of ischemic preconditioning.

Pinacidil but not nicorandil opens ATP-sensitive K+ channels and protects against simulated ischemia in rabbit myocytes

It has been proposed that ischemic preconditioning involves the regulation of ATP-sensitive potassium (K(ATP)) channels. The evidence is based largely on the ability of certain K(ATP) channel modulators to modify the protection in the various models of preconditioning. This study has investigated how two K(ATP) channel openers, pinacidil and nicorandil, affect both membrane currents and viability in isolated and ischemic rabbit cardiomyocytes. We used the whole-cell recording technique and in separate experiments viability was assessed by exposure to these drugs during ischemia. Pinacidil (50 micromol/l) increased K(ATP) current approximately four-fold in isolated cardiomyocytes. This increase reversed rapidly after treatment with the K(ATP) channel blocker glibenclamide (200 nmol/l). After simulated ischemia, pinacidil protected cardiomyocytes (the area under cell-death curve was 29.5 +/- 1.1% x h) which was significantly less than that in control (46.9 +/- 2.0% x h). The protection from pinacidil could be completely eliminated by pretreatment with 10 microM glibenclamide (46.9 +/- 2.0% x h). In contrast, nicorandil (1 mmol/l), which opens K(ATP) channels in some tissues, caused no detectable effect on the K(ATP) current. Similarly, nicorandil did not produce cardioprotection. These results indicate that pinacidil and nicorandil have very different effects on rabbit cardiomyocyte K(ATP) channels. Furthermore, because protection correlated with the ability of the agent to open the channel, they support a role for K(ATP) channels in preconditioning.

Phospholipase D plays a role in ischemic preconditioning in rabbit heart

BACKGROUND

Activation of protein kinase C (PKC) is thought to be a critical step in ischemic preconditioning. Many receptor agonists activate PKC via stimulation of phospholipase C (PLC), which degrades membrane phospholipids to diacylglycerol (DAG), an important PKC cofactor. However, adenosine receptors, critical components of the prototypical preconditioning pathway, are not thought to couple to PLC in the cardiomyocyte. We therefore tested whether ischemic preconditioning or adenosine might instead activate phospholipase D (PLD) to produce DAG.

METHODS AND RESULTS

PLD activity was measured in isolated rabbit hearts. Ischemic injury was evaluated in either isolated rabbit hearts or dispersed myocytes. PLD activity doubled from a control level of 74.8 +/- 10.0 to 140.0 +/- 11.5 mumol.min-1.g-1 (P < .025) after two 5-minute periods of global ischemia separated by 5 minutes of reperfusion. A similar increase was noted after the heart had been exposed to (R)-N6-(2-phenylisopropyl)-adenosine [(R)-PIA] for 20 minutes. When sodium oleate, which activates PLD, was administered to isolated hearts before a 30-minute coronary occlusion, infarct size (15.6 +/- 2.0% of the risk zone) was significantly smaller than in untreated hearts (30.4 +/- 2.2%; P < .01). Exposure to sodium oleate significantly prolonged the rate of isolated myocyte survival during simulated ischemia. Propranolol 100 mumol/L, which blocks DAG production from metabolites produced by PLD catalysis, completely abolished the protective effects of both metabolic preconditioning and (R)-PIA exposure in myocytes.

CONCLUSIONS

We conclude that PLD stimulation is involved in the protection of ischemic preconditioning in the rabbit heart.

An irreversible A1-selective adenosine agonist preconditions rabbit heart

This study tested whether an irreversible agonist of the A1 adenosine receptor, m-DITC ADAC, can mimic the protective effect of ischemic preconditioning in the rabbit heart. Isolated Krebs buffer-perfused rabbit hearts experienced 30 mins of regional ischemia and 120 mins of reperfusion. Infarct size was measured with tetrazolium staining. In untreated hearts 32 +/- 2% of the risk zone infarcted while only 9 +/- 2% infarction was seen in hearts that were preconditioned with 5 mins of global ischemia followed by 10 mins of reperfusion (P < 0.05 versus control). Exposure to 200 nM of the A1-selective agonist 2-chloro-N6-cyclopentyladenosine (CCPA) for 5 mins followed by 10 mins of washout protected the hearts as well as preconditioning with 13 +/- 7% infarction (P < 0.05 versus control). Protection from CCPA was completely blocked by 200 nM DPCPX (8-cyclopentyl-1,3-dipropylxanthine) with 34 +/- 7% infarction (P < 0.05 versus CCPA) confirming that protection was via the A1 adenosine receptor. m-DITC ADAC, which irreversibly stimulates the A1 adenosine receptor, also protected the hearts with only 15 +/- 4% infarction (P < 0.05 versus control). It was concluded that m-DITC ADAC does mimic ischemic preconditioning and that an irreversible agonist might be a novel way to provide an extended window of protection to the heart from a single intracoronary injection.

Potassium channels and preconditioning of isolated rabbit cardiomyocytes: effects of glyburide and pinacidil

Calcium tolerant rabbit cardiomyocytes, isolated by collagenase perfusion, were preincubated for varying periods of time followed by resuspension in fresh media and centrifugation into an ischaemic pellet with restricted extracellular fluid. Pellets were incubated for 240 min under oil at 37 degrees C to mimic severe ischaemia. Time to onset of ischaemic contracture (rod to square transformation) and trypan blue permeability following resuspension in 85 mOSM media were monitored at sequential times. The protocol of Series 1 was a 5-10 min pre-incubation, immediately followed by ischaemic pelleting. Preincubation with pinacidil (50 microM) protected cells from ischaemic insult, but pinacidil added only into the ischaemic pellet did not protect. Protection was abolished by the protein kinase (PKC) inhibitors chelerythrine (10 microM) added with pinacidil and calphostin C (200nM) added only into the ischaemic pellet. Neither PKC inhibitor had an effect on injury of untreated ischaemic myocytes (data not shown). Series 2-5 were preconditioning protocols with a 10 min intervention period, followed by a 30 min oxygenated drug-free period, prior to ischaemic pelleting. In series 2 pinacidil protected cells from ischaemic insult and this protection was abolished when glyburide (10 microM) was present during preincubation, or during post-incubation and ischaemia. Glyburide only partially inhibited the protection when glyburide was added only into the ischaemic pellet. In Series 3, 8-sulfophenyltheophyline (SPT)(100 microM) or adenosine deaminase during preincubation, or SPT only added into the ischaemic pellet abolished pinacidil's protection. In Series 4, cardiomyocytes were ischaemically preconditioned by pelleting for 10 min followed by 30 min reoxygenation. Glyburide during initial ischaemic blocked protection, but when added during post incubation and into the final pellet protection was not reduced. In Series 5 8-cyclopentyl-1,3,dipropylxanthine (DPCPX) (10 microM) added into the final pellet abolished protection by pinacidil, but not protection following ischaemic preconditioning. In contrast to pinacidil, ischaemically preconditioned cells maintain protection in the presence of glyburide, indicating that: (1) pinacidil does not exactly mimic preconditioning and (2) ischaemically preconditioned cells do not require opened K+ATP channels for protection, although they appear to be important during initiation of the preconditioned state. It is hypothesized that pinacidil opening of K+ channels may facilitate induction of preconditioning.

Depot drug delivery system for 5-fluorouracil after filtration surgery in the rabbit

We investigated the potential value of 50:50 poly (DL glycolic acid-lactic acid) (PGLA) copolymer as a degradable depot delivery system for 5-fluorouracil (5-FU) after filtration surgery. Analysis of retrieved discs after implantation in 22 eyes of 22 pigmented rabbits showed a dual drug release profile and polymer mass loss characteristics. In a second group of pigmented rabbits implantation of PGLA discs impregnated with 5-FU (22 eyes) significantly lengthened the survival time of filtration fistulae compared with discs without 5-FU (18 eyes) or no disc (10 eyes) (p < 0.0001). Use of PGLA copolymer impregnated with 5-FU could prove valuable for patients undergoing glaucoma filtering surgery.

Rat and rabbit heart infarction: effects of anesthesia, perfusate, risk zone, and method of infarct sizing

Rabbits and rats are becoming popular models for in vitro as well as in situ studies of myocardial infarction. In the present analysis we evaluated the results of several of our completed investigations and tested whether blood-free perfusate, anesthesia, or risk zone size affects infarction in these species. In addition, the influence of the method used for determining infarct size (histology or histochemistry) was examined in rabbits. All hearts experienced 30 min of regional ischemia followed by either 2-3 h of reperfusion in animals in which infarct size was assessed by staining with triphenyltetrazolium chloride or 72 h in those in which histological methods were used to measure infarct size. Eighteen rabbit and seven rat hearts perfused with Krebs buffer, seventeen open-chest rabbits, eight rats anesthetized with pentobarbital, and ten conscious rabbits were studied. Risk zone size measured with fluorescent particles was plotted against infarct size. Infarct size was linearly correlated with risk zone size and did not differ among models for each species. In rat hearts the regression line passed through the origin so that zero infarction occurred with zero risk zone size. However, in the rabbit heart there was no apparent infarction for risk zone sizes < 0.3 cm3. Although the relationship between risk zone and infarction was found to be remarkably independent of the model chosen, the nonzero intercept for the rabbit heart can be an important, previously unrecognized source of experimental variability when infarct size is expressed as a percentage of the risk zone.

Ocular timolol levels after drug withdrawal: an experimental model

Carbon 14-labelled timolol maleate was instilled into both eyes of 12 pigmented rabbits daily for 42 days. Drug levels in the aqueous humour and ocular tissues were measured up to 42 days after drug withdrawal. The results indicate that timolol concentrates mainly in melanotic tissues, with slow release. Even 42 days after withdrawal the drug was still present in pigmented ocular tissues. Timolol was detected in the aqueous up to 5 days after withdrawal. These findings explain the long-term depressant effect of topically administered timolol on aqueous production. We conclude that lower or less frequent doses of timolol should be considered in patients with glaucoma.

alpha 1-adrenergic agonists precondition rabbit ischemic myocardium independent of adenosine by direct activation of protein kinase C

Ischemic preconditioning in the rabbit is initiated by adenosine A1-receptor stimulation, which activates protein kinase C (PKC). Additionally, alpha 1-adrenergic agonists can similarly protect ischemic myocardium, but there has been confusion about the role adenosine receptors play in this protection. To characterize the interaction between adrenergic and adenosine receptors and to study the possible role of PKC in this protection, we used isolated rabbit hearts perfused with oxygenated Krebs' buffer. All hearts were subjected to 30 minutes of regional myocardial ischemia and 2 hours of reperfusion. Infarct size was determined by triphenyltetrazolium staining. Pharmacologic preconditioning in hearts with a 5-minute phenylephrine (PE) infusion 10 minutes before the prolonged regional ischemia resulted in significantly smaller infarcts (9.7 +/- 1.3% of risk area) than in control hearts (31.0 +/- 2.6%, P < .05). This protection could be effectively blocked by administration of the alpha-adrenergic blocker phenoxybenzamine. Methoxamine, an alpha 1a-selective agonist, failed to protect, whereas the alpha 1b-selective antagonist chloroethylclonidine aborted the protective effect of PE. Polymyxin B, an inhibitor of PKC, also blocked the protective effect of PE, implying that PKC has an important role in preconditioning. The adenosine receptor blocker 8-(p-sulfophenyl)theophylline (SPT) given at the same time as the PE infusion did not affect the protection, implying that an alpha 1-agonist could initiate protection independent of adenosine, presumably by direct coupling to PKC. However, the protective effect of PE could be blocked if SPT were administered during the 30-minute regional ischemia. This observation suggested that adenosine receptor occupancy is necessary during long ischemia to reactivate PKC and mediate the protection. However, the addition of a second PE infusion beginning 5 minutes before and continuing throughout the long ischemic period restored the protective effect of PE despite the presence of SPT. Thus, as long as at least one of the receptors (alpha 1-adrenegic or adenosine A1) is activated during long ischemia, protection will be realized. These data indicate that alpha 1 receptors do not precondition through an adenosine intermediate but that alpha 1-adrenergic and adenosine receptors activate parallel pathways within the myocyte that can trigger and mediate protection.

Fifty:fifty poly (DL glycolic acid-lactic acid) copolymer as a drug delivery system for 5-fluorouracil: a histopathological evaluation

Fifty:fifty poly (DL glycolic acid-lactic acid) copolymer (PGLA) is a potentially useful depot drug delivery system for 5-fluorouracil (5-FU). The purpose of this study was to evaluate the fibroinflammatory reaction induced by this polymer. Polymer discs without 5-FU were inserted subconjunctivally in one eye of each of two guinea pigs and four pigmented rabbits (control group), and discs containing 20% 5-FU were inserted subconjunctivally in both eyes of nine pigmented rabbits (study group). The tissue reaction to the copolymer did not differ between rabbits and guinea pigs, with a mild mixed inflammatory reaction 1 week after implantation. At 2 weeks a thin fibrous capsule surrounded the discs, with no change in the amount of inflammation. At 4 weeks the disc had disintegrated, but residual polymer was seen within multinucleated giant cells in the episcleral tissue. Granulation tissue and inflammatory responses were mild. Less inflammation and fibrosis occurred in the study eyes, although the pattern of response was similar in the two groups. The inflammatory response to PGLA was markedly less than that to implanted collagen shields, and our findings suggest that PGLA implant is a promising ocular drug delivery system for 5-FU after filtration surgery.

Evidence that the adenosine A3 receptor may mediate the protection afforded by preconditioning in the isolated rabbit heart

OBJECTIVE

Agonists selective for the A1 adenosine receptor mimic the protective effect of ischaemic preconditioning against infarction in the rabbit heart. Unselective adenosine antagonists block this protection but, paradoxically, the A1 adenosine receptor selective antagonist 8-cyclopentyl- 1,3-dipropylxanthine (DPCPX) does not. The aim of this study was to test the hypothesis that the newly described A3 adenosine receptor, which has an agonist profile similar to the A1 receptor but is insensitive to DPCPX, might mediate preconditioning.

METHODS

Isolated rabbit hearts perfused with Krebs buffer experienced 30 min of regional ischaemia followed by 120 min of reperfusion. Infarct size was measured by tetrazolium staining.

RESULTS

In control hearts infarction was 32.2(SEM 1.5)% of the risk zone. Preconditioning by 5 min ischaemia and 10 min reperfusion reduced infarct size to 8.8(2.3)%. Replacing the regional ischaemia with 5 min perfusion with 10 microM adenosine or 65 nM N6-[2-(4-aminophenyl)ethyl]adenosine (APNEA), an adenosine A3 receptor agonist, was equally protective. The unselective antagonist 8-p-sulphophenyl theophylline at 100 microM abolished protection by preconditioning, adenosine, and APNEA, but 200 nM DPCPX did not block protection by any of the interventions. Likewise the potent but unselective A3 receptor antagonist 8-(4-carboxyethenylphenyl)-1,3-dipropylxanthine (BW A1433) completely blocked protection from ischaemic preconditioning.

CONCLUSIONS

Because protection against infarction afforded by ischaemic preconditioning, adenosine, or the A3 receptor agonist APNEA could not be blocked by DPCPX and because the potent A3 receptor antagonist BW A1433 blocked protection from ischaemic preconditioning, these data indicate that the protection of preconditioning is not exclusively mediated by the adenosine A1 receptor in rabbit heart and could involve the A3 receptor.

[Observations of changes in ultrastructure and calcium ion distribution in rabbit heart after various periods of ischemia]

The ultrastructural degenerative changes and calcium ion distribution observed in the rabbit myocardium after various periods of ischemia and 30 minutes after postischemia reperfusion after 30 minutes reperfusion following 15 minutes of ischemia, near complete recovery of substructures is seen, anyhow the number of calcium ion deposits along the sarcolemma are still lower than normal. After 30 and 45 minutes of ischemia, severe degenerative changes in various cellular substructures took place. The sarcolemma of most myocytes became devoid of precipitate. After reperfusion, large calcium ion deposits accumulated in the form of clusters in the mitochondria. It was recognized that the herein described cytochemical calcium ion shifts may be indicative of structural damage bordering irreversibility. After 60 to 75 minutes of ischemia and then postischemia reperfusion, cell damage is observed as disrupted sarcolemma completely devoid of calcium ion deposit, large swollen mitochondria without signs of calcium ions and presence of flocculent precipitates, all signs of terminal impairment of metabolism.

[Free radical scavenging and antifatigue activities of Saussurea involucrata polysaccharides]

The polysaccharides of Saussurea involucrata Kar et Kir was first isolated and identified by us. The polysaccharides scavenged superoxide anions by nitroblue tetraazolium colorimetric method with a median scavenging concentration of 22 micrograms.ml-1 and 95% confidence limit was 19.9-24.1 micrograms.ml-1. The polysaccharides inhibited the formation of thiobarbituric acid reaction substance in mouse liver homogenate and its IC50 was 2.3 mg/g fresh liver and 95% confidence limit was 2.05-2.55 mg/g fresh liver. By ip 25 mg.kg-1.d-1 x d in mice, the polysaccharides decreased oxygen consumption by 34.4% and ip same dosage x 6 d, the polysaccharide prolonged swimming time by 1.69-fold.

Pretreatment with the adenosine A1 selective agonist, 2-chloro-N6-cyclopentyladenosine (CCPA), causes a sustained limitation of infarct size in rabbits

OBJECTIVE

The highly selective adenosine A1 receptor agonist, 2-chloro-N6-cyclopentyl-adenosine (CCPA), has been shown to be as cardioprotective as ischaemic preconditioning when evaluated with an early staining method using tetrazolium. However, tetrazolium-positive tissue measured 3 h after reperfusion may still overestimate the long term salvage. To test for this possible artefact, a 72 h reperfusion rabbit model of myocardial infarction was used, and infarct size was assessed by histology.

METHODS

Myocardial infarction was induced by a 30 min coronary occlusion. Rabbits were assigned to a control group receiving no treatment, pretreatment with 0.125 mg.kg-1 CCPA, or 0.25 mg.kg-1 pretreatment with CCPA (0.25 mg.kg-1) followed by an A1 selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) 30 min after reperfusion to reverse the haemodynamic side effects.

RESULTS

In the 0.125 mg.kg-1 CCPA group, 30.8(SEM 4.2)% of the ischaemic zone was infarcted, which was significantly less than that seen in the control group [46.5(3.0)%; p < 0.01]. Reversing the side effects of CCPA by giving DPCPX soon after reperfusion did not block the protective effects [26.2(1.9)% infarction; p < 0.01 v control].

CONCLUSIONS

This finding confirms a genuine anti-infarct effect of adenosine A1 receptor stimulation when given prior to the onset of ischaemia. Furthermore blocking the A1 receptors soon after reperfusion reverses the side effects but does not block protection.

Pretreatment with pertussis toxin blocks the protective effects of preconditioning: evidence for a G-protein mechanism

We tested whether a pertussis toxin-sensitive G-protein mediates the protective effects of preconditioning. Thirty-one small (1 kg) rabbits were used. All rabbits experienced 30 min regional myocardial ischaemia followed by 3 h reperfusion. Infarct size was determined by tetrazolium. The percentage of the risk zone which infarcted in controls was 37.4 +/- 4.6%. Preconditioning with a 5 min occlusion followed by 10 min reperfusion prior to the 30 min ischaemic insult protected against infarction (5.2 +/- 2.1% infarction). 25 micrograms/kg pertussis toxin, administered 48 h prior to surgery, blocked G-protein signal transduction as tested by challenge with iv acetylcholine which normally slows the heart. Pertussis toxin treatment had no effect on infarct size in non-preconditioned rabbits (37.6 +/- 4.7% infarction) but blocked protection in preconditioned rabbits (27.3 +/- 4.3% infarction). To test the involvement of G-proteins further in preconditioning, we tested the ability of the M2 agonist carbachol to substitute for ischaemic preconditioning and protect the heart from infarction. Rabbits hearts were excised and perfused with Kreb's buffer. Control animals subjected to 30 min of regional ischaemia and 2 h reperfusion yielded 29.4 +/- 2.9% infarction. Preconditioning with 5 min global ischaemia and 10 min reperfusion prior to the 30 min regional ischaemia significantly protected the isolated heart from infarction (8.41 +/- 3.26% infarction). Carbachol, infused for 5 min at 1 microM concentration, protected the hearts as well as preconditioning, yielding 8.90 +/- 2.08% infarction. We conclude that preconditioning involves a pertussis toxin-sensitive G-protein and that the same G-protein couples to muscarinic M2 receptors.

Acadesine lowers temporal threshold for the myocardial infarct size limiting effect of preconditioning

OBJECTIVE

The aim was to test the hypothesis that adenosine A1 receptor activation triggers the cardioprotective effects of ischaemic preconditioning, by determining whether pretreatment with acadesine (5-amino-4-imidazolecarboxamide riboside), an agent which increases cardiac adenosine level during ischaemia, could alter the threshold for preconditioning.

METHODS

A branch of the left coronary artery of rabbit hearts was occluded for 30 min and reperfused for 3 h. Infarct size and risk zone size were determined with tetrazolium and fluorescent particles, respectively. Four groups were studied: untreated controls, a group which was pretreated with acadesine (2.5 mg.kg-1.min-1 for 5 min followed by 0.5 mg.kg-1.min-1 for 30 min ending 10 min prior to ischaemia), a group which was preconditioned with 2 min coronary branch occlusion + 10 min reperfusion, and a group which received pretreatment with acadesine prior to 2 min ischaemic preconditioning.

RESULTS

Percent infarction, normalised as a percentage of the ischaemic zone, in the 2 min preconditioning group was 43.2(SEM 5.1)% which was not different from control [40.2(3.5)%]. Two minutes of preconditioning was not long enough to confer the cardioprotective effect of preconditioning. Acadesine alone had no protective effect on infarct size [38.5(4.5)%], but acadesine + 2 min preconditioning significantly limited infarction [18.1(2.7)%; p < 0.01].

CONCLUSIONS

Acadesine lowered the threshold for preconditioning in the rabbit to below 2 min of ischaemia. This observation supports the theory that endogenous adenosine which accumulates during the preconditioning ischaemia mediates the protective effects, and that this response can be augmented by acadesine.

Ischaemic preconditioning is not dependent on neutrophils or glycolytic substrate at reperfusion in rabbit heart

OBJECTIVE

The aim was to determine whether reperfusion with either neutrophil free reperfusate or perfusate containing only pyruvate as the metabolic substrate would alter the protection against infarction afforded by preconditioning.

METHODS

Rabbit hearts (n = 4-14 per group) underwent 30 minutes of regional ischaemia followed by 120 minutes of reperfusion. Blood reperfused groups experienced both ischaemia and reperfusion in situ while Krebs reperfused groups experienced regional ischaemia in situ but were reperfused with Krebs buffer in vitro. In another group, glucose in Krebs buffer was replaced by pyruvate.

RESULTS

Preconditioning with 5 minutes regional ischaemia caused smaller infarct size in the blood reperfused hearts: 43.0(SEM 5.4)% v 8.8(4.2)%. In Krebs reperfused hearts, preconditioning caused a similar reduction of infarct size [49.9(2.5)% v 22.9(4.3)%] which was not different from that seen in the blood reperfused hearts. Replacing the glucose in the Krebs buffer by pyruvate also had no effect on infarct size in either the control or the preconditioned hearts [40.9(6.1)% v 11.8(5.2)%]. Histology of the ischaemic zones revealed 59.6(15.0) neutrophils per 10 high power fields in hearts reperfused in situ but only 2.6(0.6) in Krebs reperfused hearts, equal to the numbers in nonischemic blood perfused myocardium [2.8(0.9)].

CONCLUSIONS

The mechanism of preconditioning is not due to attenuation of neutrophil function during reperfusion. Furthermore, substituting pyruvate for glucose in the reperfusate did not prevent the protection against infarction afforded by ischaemic preconditioning.