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Biomedical subjects

K Li

Publications and source records attributed to K Li.

At least 343 records · Page 19Linked to original sources
PubMed1994

Role of endothelial cells in cardiovascular function.

Since the first description of vascular endothelium-dependent relaxation in response to acetylcholine, the role of endothelial cells in the regulation of cardiovascular function has been increasingly studied. The identification of endothelial releasing factors such as nitric oxide and endothelin has enabled us to better understand the mechanisms involved in autoregulation. It has also been shown that both vascular and endocardial endothelium can modify the contractile characteristics of their adjacent myocardium. In the heart, these modulating effects of endothelial cells are more widespread than previously thought and, can be the result of the direct effects of endocardial and vascular endothelial cells and their indirect effects, via modulation of the myocardial response to inotropic agents.

Animals↗
PubMed1994

Subcellular partitioning of MRP RNA assessed by ultrastructural and biochemical analysis.

A small RNA encoded within the nucleus is an essential subunit of a RNA processing endonuclease (RNase MRP) hypothesized to generate primers for mitochondrial DNA replication from the heavy strand origin of replication. Controversy has arisen, however, concerning the authenticity of an intramitochondrial pool of MRP RNA, and has called into question the existence of pathways for nucleo-mitochondrial transport of nucleic acids in animal cells. In an effort to resolve this controversy, we combined ultrastructural in situ hybridization and biochemical techniques to assess the subcellular partitioning of MRP RNA. Cryosections of mouse cardiomyocytes were hybridized with biotin-labeled RNA probes complementary to different regions of MRP RNA and varying in length from 115 to 230 nucleotides, followed by immunogold labeling. In addition, we transfected mouse C2C12 myogenic cells with constructs bearing mutated forms of the mouse MRP RNA gene and compared the relative abundance of the resulting transcripts to that of control RNAs within whole cell and mitochondrial fractions. In the former analysis we observed preferential localization of MRP RNA to nucleoli and mitochondria in comparison to the nucleoplasm and cytoplasm. In the latter series of studies we observed that wild-type MRP RNA partitions to the mitochondrial fraction by comparison to other RNA transcripts that are localized to the extramitochondrial cytoplasmic space (28S rRNA) or to the nucleoplasm (U1 snRNA). Deletions within 5' or 3' regions of the MRP RNA gene produced transcripts that remain competent for mitochondrial targeting. In contrast, deletion of the midportion of the coding region (nt 118 to 175) of the MRP RNA gene resulted in transcripts that fail to partition to the mitochondrial fraction. We conclude that an authentic intramitochondrial pool of MRP RNA is present in these actively respiring cells, and that specific structural determinants within the MRP RNA molecule permit it to be partitioned to mitochondria.

Animals↗
PubMed1994

Molecular biology of the 230-kD bullous pemphigoid antigen. Cloning of the BPAG1 gene and its tissue-specific expression.

The 230-kD bullous pemphigoid antigen is a hemidesmosomal protein of the cutaneous basement membrane zone. We have previously cloned overlapping cDNAs corresponding to the human 230-kD bullous pemphigoid antigen gene (BPAG1), located at the human chromosomal locus 6p11-12. Utilizing the cDNA clones, a genomic DNA lambda FIX II phage library was screened. Seven over-lapping genomic clones, spanning approximately 20 kb, were isolated. These clones were shown to contain the entire approximately 9-kb coding sequence of BPAG1, and it consisted of 22 separate exons which varied from 78 to 2,810 bp in size. Elucidation of 2.6 kb of 5'-flanking DNA was found to contain several putative transcriptional response elements, and development of promoter chloramphenicol acetyltransferase (CAT) reporter gene constructs allowed identification of putative cis-elements which confer keratinocyte-specific expression to the gene. In particular, a putative AP2-binding sequence (KRE2) in the position -(1,786-1778) was shown to be responsible for marked enhancement of the endogenous promoter, as well as of a heterologous thymidine kinase/CAT construct, activity in normal human keratinocytes. Normal human keratinocyte nuclear extracts contained a protein, designated as KTP1, which complexed with the KRE2 oligomer by gel mobility shift assays. UV cross-linking and Southwestern analysis suggested that KTP1 is a DNA-binding protein clearly distinct from AP2, and this protein may be responsible for the basal keratinocyte-specific expression of the BPAG1 gene.

Autoantigens↗
PubMed1994

A rhesus monkey model to characterize the role of gastrin-releasing peptide (GRP) in lung development. Evidence for stimulation of airway growth.

Gastrin-releasing peptide (GRP) is developmentally expressed in human fetal lung and is a growth factor for normal and neoplastic lung but its role in normal lung development has yet to be clearly defined. In this study we have characterized the expression of GRP and its receptor in fetal rhesus monkey lung and determined the effects of bombesin on fetal lung development in vitro. By RNA blot analysis, GRP mRNA was first detectable in fetal monkey lung at 63 days gestation, reached highest levels at 80 days gestation, and then declined to near adult levels by 120 days gestation; a pattern closely paralleling GRP expression in human fetal lung. As in human lung, in situ hybridization localized GRP mRNA to neuroendocrine cells though during the canalicular phase of development (between 63-80 days gestation) GRP mRNA was present not only in classic pulmonary neuroendocrine cells, but also in cells of budding airways. Immunohistochemistry showed that bombesin-like immunoreactivity was present in neuroendocrine cells, but not in budding airways, suggesting that in budding airways either the GRP mRNA is not translated, is rapidly secreted, or a related, but different RNA is present. RNase protection analysis using a probe to the monkey GRP receptor demonstrated that the time course of receptor RNA expression closely paralleled the time course of GRP RNA expression. In situ hybridization showed that GRP receptors were primarily expressed in epithelial cells of the developing airways. Thus GRP would appear to be secreted from neuroendocrine cells to act on target cells in developing airways. This hypothesis was confirmed by organ culture of fetal monkey lung in the presence of bombesin and bombesin antagonists. Bombesin treatment at 1 and 10 nM significantly increased DNA synthesis in airway epithelial cells and significantly increased the number and size of airways in cultured fetal lung. In fact, culturing 60 d fetal lung for 5 d with 10 nM bombesin increased airway size and number nearly to that observed in cultured 80 d fetal lung. The effects of bombesin could be blocked by specific GRP receptor antagonists. Thus this study demonstrates that GRP receptors are expressed on airway epithelial cells in developing fetal lung and that the interaction of GRP with the GRP receptor stimulates airway development.

Amino Acid Sequence↗
PubMed1994

Recombinant human granulocyte colony stimulating factor in cyclic neutropenia: use of a new 3-day-a-week regimen.

BACKGROUND: G-CSF has been shown to be beneficial in cyclic neutropenia when given as a daily subcutaneous injection. We investigated the usefulness of a new three-day-a-week regimen. METHODS: A ten year old boy with cyclic neutropenia was initially treated with G-CSF 7 micrograms/kg given on alternate days for seven months. He was then placed on the same dose, given three days a week. The effectiveness of these regimens were assessed by serial CBCs and by the frequency and duration of the symptoms. RESULTS: The mean absolute neutrophil count (ANC) increased from 1282 before therapy to 11,718/microliters on alternate day regimen and 7716/microliters on three-day-a-week regimen. The nadir ANC improved from 30/microliters before therapy to 546/microliters and 198/microliters on treatment. The duration and frequency of mouth sores were significantly less on therapy, and there was an estimated cost savings of $23,826/year on three-day-a-week regimen compared to a daily regimen. CONCLUSION: The three-day-a-week G-CSF regimen is clinically effective and cost saving in the treatment of cyclic neutropenia and should be studied in a larger cohort of patients.

Child↗
PubMed1994

[Expression of HPV16E6 gene and preparation of monoclonal antibody against the expression product].

The recombinant plasmid PAS1-HPV16E6 containing the HPV16E6 gene was expressed in E. coli AR120 under nalidixic acid induction. A 19KD expression protein was isolated, purified and identified. Mice were immunized with the purified E6 expression protein. A murine hybridoma, RAC6, was obtained by fusing splenic cells from an immunized BABL/c mouse with mouse myeloma cell line SP2/0-Ag14 cells, followed by screening in HAT medium, cloning and recloning in methyl cellulose. The hybridoma RAC6 stably produces specific monoclonal antibody against the E6 expression protein.

Animals↗
PubMed1993

Cloning of type XVII collagen. Complementary and genomic DNA sequences of mouse 180-kilodalton bullous pemphigoid antigen (BPAG2) predict an interrupted collagenous domain, a transmembrane segment, and unusual features in the 5'-end of the gene and the 3'-untranslated region of the mRNA.

Thus far, 16 distinct vertebrate collagens (types I-XVI) have been delineated. In this study, we have cloned a mouse collagenous protein, the 180-kDa bullous pemphigoid antigen (BPAG2). Isolation of over-lapping clones, together with 5' and 3' rapid amplification of cDNA ends, allowed delineation of the entire coding sequence. The 5' and 3' ends of the mRNA transcripts were confirmed by primer extension and anchored reverse transcription polymerase chain reaction analyses. The deduced polypeptide contained 1,433 amino acids, including a collagenous domain that consisted of 13 separate segments. Computer analysis of the deduced amino acid sequence demonstrated the presence of a membrane-associated segment. Examination of the 5' end of the BPAG2 gene revealed that the 295-base pair (bp) exon 1 contained two segments of (T)13AA and TT(A)11, whereas exon 2 was shown to contain the translation initiation codon. The 3' end of the mRNA transcript identified two 6-bp inverted repeat sequences that could form a stem for a 30-bp hairpin loop followed by a series of U residues. Comparison of mouse and human BPAG2 sequences demonstrated 86% homology and the unit of evolutionary period of 4.2 million years. In summary, we have cloned full-length mouse BPAG2 cDNA sequences that encode a collagenous polypeptide. We propose that this polypeptide be designated as the alpha 1-chain of type XVII collagen.

Amino Acid Sequence↗
PubMed1993

Benextramine-neuropeptide Y receptor interactions: contribution of the benzylic moieties to [3H]neuropeptide Y displacement activity.

Analogs of N,N'-bis[6-[(2-methoxybenzyl)amino]hex-1-yl]cystamine (benextramine, BXT, 2) were synthesized using solution-phase peptide synthesis methodology and analyzed for activity in displacing specifically bound 1 nM N-[propionyl-3H]neuropeptide Y([3H]NPY) from benextramine-sensitive neuropeptide Y (NPY) binding sites in rat brain. Our new synthetic approach to these analogs began with the acylation of cystamine with the N-hydroxysuccinimide ester of tert-butyloxycarbonyl (t-Boc) protected 6-aminohexanoic acid, followed by deprotection of the t-Boc groups with 4 N HCl in dioxane. Acylation of this symmetric diamine with N-hydroxysuccinimide esters of appropriately substituted benzoic acids, followed by reduction of the resultant tetraamides with diborane in refluxing THF, afforded the target compounds. The BXT analog lacking the benzylic group (i.e., compound 11) had no [3H]NPY displacement activity at concentrations up to 1.4 x 10(-3) M. The 9-fold range in activities observed for the ortho, meta, and para regioisomers of the methoxy, chloro, and hydroxy benextramine analogs at benextramine-sensitive NPY rat brain binding sites does not differ from the range of potencies observed at alpha-adrenoceptors. However, the order of potencies at [3H]NPY sites differs from the order of potencies at alpha-adrenoceptors, with the m-methoxyphenyl (9a), m-hydroxyphenyl (10b), and 2-naphthyl (9f) analogs being the most active at [3H]NPY binding sites. The present results demonstrate the importance of the benzylic moiety for BXT's NPY antagonist activity, and suggest that the BXT binding site on the NPY receptor is significantly distinct from that on the alpha-adrenoceptor.

Adrenergic alpha-Antagonists↗
PubMed1993

Heat-shock gene expression and cell cycle changes during mammalian embryonic development.

Synchronized regulation of cell division during gastrulation is essential for the regional proliferation of cells and pattern formation of the early CNS. The neural plate and neuroectoderm cells are a rapidly dividing and differentiating population of cells with a unique and rapid heat-shock response. Heat shock and the heat-shock genes were studied during neural plate development in a whole rat embryo culture system at 9.5-11.5 days. A lethal shock can cause cell death and severe developmental defects to the forebrain and eye during organogenesis. Heat shock can also result in acquired thermotolerance whereby cell progression is delayed at the G1/S and S/G2 boundaries of the cell cycle. This delay in cell cycle progression caused an overall lengthening of the cell cycle time of at least 2 hr. The heat shock genes may therefore function as cell cycle regulators in neuroectoderm induction and differentiation. The kinetics and expression of the hsp genes were examined in neuroectodermal cells by flow cytometry and Northern analysis. The levels of hsp mRNA 27, 71, 73, and 88 were identified following exposure at 42 degrees C (nonlethal), 43 degrees C (lethal) and 42 degrees/43 degrees C (thermotolerant) heat shock. Examination of hsp gene expression in the neural plate showed tight regulation in the cell cycle phases. Hsp 88 expression was enhanced at Go and hsp71 induction at G2 + M of the cell cycle. Cells exposed to a thermotolerant heat shock of 42 degrees C induced hsp71 mRNA expression in all phases of the cell cycle with the mRNA levels of hsp27, 73, and 88 increased but relatively constant. Following a lethal heat shock, dramatic changes in hsp expression were seen especially enhanced hsp71 induction in late S phase. The regulated expression of hsps during the cell cycle at various phases could play a unique and important role in the fate and recovery of neuroectoderm cells during early mammalian embryo development.

Animals↗
PubMed1993

Chromosomal localization of mouse bullous pemphigoid antigens. BPAG1 and BPAG2: identification of a new region of homology between mouse and human chromosomes.

Two bullous pemphigoid antigens, BPAG1 and BPAG2, have been recently cloned and mapped to human chromosomes 6p12-p11 and 10q24.3, respectively. In this study, we localized the corresponding mouse genes by interspecific backcross analysis. Bpag-1 mapped to the proximal region of mouse chromosome 1, identifying a new region of homology between human chromosome 6 and mouse chromosome 1. Bpag-2 mapped to the distal end of mouse chromosome 19 in a region of homology to human chromosome 10q. These assignments confirm and extend the relationships between the human and the mouse chromosomes.

Amino Acid Sequence↗
PubMed1993

cDNA cloning and chromosomal mapping of the mouse type VII collagen gene (Col7a1): evidence for rapid evolutionary divergence of the gene.

Type VII collagen is the major component of anchoring fibrils, critical attachment structures at the dermal-epidermal basement membrane zone. Genetic linkage analyses with recently cloned human type VII collagen cDNAs have indicated that the corresponding gene, COL7A1, is the candidate gene in the dystrophic forms of epidermolysis bullosa. To gain insight into the evolutionary conservation of COL7A1, in this study we have isolated mouse type VII collagen cDNAs by screening a mouse epidermal keratinocyte cDNA library with a human COL7A1 cDNA. Two overlapping mouse cDNAs were isolated, and Northern hybridization of mouse epidermal keratinocyte RNA with one of them revealed the presence of a mRNA transcript of approximately 9.5 kb, the approximate size of the human COL7A1 mRNA. Nucleotide sequencing of the mouse cDNAs revealed a 2760-bp open reading frame that encodes the 5' half of the collagenous domain and a segment of the NC-1, the noncollagenous amino-terminal domain of type VII collagen. Comparison of the mouse amino acid sequences with the corresponding human sequences deduced from cDNAs revealed 82.5% identity. The evolutionary divergence of the gene was relatively rapid in comparison to other collagen genes. Despite the high degree of sequence variation, several sequences, including the size and the position of noncollagenous imperfections and interruptions within the Gly-X-Y repeat sequence, were precisely conserved. Finally, the mouse Col7a1 gene was located by interspecific backcross mapping to mouse Chromosome 9, a region that corresponds to human chromosome 3p21, the position of human COL7A1. This assignment confirms and extends the relationship between the mouse and the human chromosomes in this region of the genome.

Amino Acid Sequence↗
PubMed1993

Endocardial function in pacing-induced heart failure in the dog.

Endocardial endothelium has been shown to modulate the contractile characteristics and alpha-1-adrenergic responsiveness of its adjacent myocardium. This study was designed to evaluate whether this was also the case in the pacing-overdrive model of heart failure in the dog, a model in which changes in contractile characteristics and changes in alpha-1-adrenergic responsiveness similar to those caused by endocardial endothelial removal, occur prior to endocardial endothelial removal. Pacing-overdrive heart failure caused a decrease in total tension (TT) (5.1 +/- 0.5 g/mm2 in controls to 2.2 +/- 0.4 g/mm2 in pacing-overdrive, P < 0.01) and twitch configuration (time to 1/2 tension decline [RT1/2] 659 +/- 23 to 517 +/- 41 ms P < 0.01) to occur in isolated papillary muscles. Endocardial endothelial removal in control muscles caused similar but less marked changes (TT to 3.8 +/- 0.3 g/mm2, and RT1/2 to 563 +/- 21 ms). Endocardial endothelium removal also decreased TT (to 1.6 +/- 0.3 g/mm2) and RT1/2 (459 +/- 28 ms) in pacing-overdrive muscles indicating that even in this model of heart failure, endocardial endothelium continued to modulate the contractile characteristics of its adjacent myocardium. The addition of phenylephrine caused proportionately similar changes in contractile characteristics in both control and pacing-overdrive muscles prior to and after endocardial endothelial removal. However, in control muscles, endocardial endothelial removal caused a rightward shift in phenylephrine concentration-response curve (EC50 0.6 +/- 0.2 x 10(-6)M to 3.4 +/- 1.0 x 10(-6)M, P < 0.05). Pacing-overdrive muscles already had a rightward shift (EC50 = 4.1 +/- 1.0 x 10(-6)M) prior to endocardial endothelium removal, such that endocardial endothelial removal caused no further shift in EC50 (2.8 +/- 1.0 x 10(-6)M) indicating that the decrease in alpha-1-adrenergic responsiveness in this model was endocardial endothelium dependent. Taken together, these results suggest that the direct modulating effects of the endocardial endothelium on its adjacent myocardium are not necessarily related to its modulatory role on the myocardial effects of circulating substances in the plasma and, that in heart failure, the decrease in alpha-1-adrenergic responsiveness that occurs is related to endocardial endothelium dysfunction.

Animals↗
PubMed1993

Thrombolytic therapy in an isolated limb.

Intraoperative thrombolytic therapy is a useful adjunct to balloon catheter thromboembolectomy for treatment of acute embolism or thrombosis, but the technique is frequently limited by incomplete thrombolysis and systemic hemorrhage. In an attempt to improve results and reduce complications of conventional thrombolytic therapy, urokinase was infused into a limb that was isolated with a tourniquet. This isolated limb perfusion technique was initially developed in an animal model and subsequently used for limb salvage in patients who failed thromboembolectomy. The animal model demonstrated that a fibrinolytic state could be achieved and isolated to the extremity, even when using extremely high dose (20,000 to 50,000 IU/kg) of thrombolytic agents. The fibrinogen level was unmeasurable and the prothrombin, partial thromboplastin, and thrombin times were significantly prolonged in the isolated limb (p < 0.001), whereas no changes occurred in these parameters in the systemic circulation. In seven patients, streptokinase (27,000 to 200,000 IU) and urokinase (150,000 to 300,000 IU) were infused into isolated extremities after thrombectomy alone had failed to restore blood flow. All extremities showed improved perfusion after thrombolytic therapy and five remained viable 6 months after treatment. There were no systemic bleeding complications despite two patients having undergone major operations within 6 days. Tourniquet isolation of the limb can achieve extremely high concentrations of thrombolytic drugs while reducing the potential for systemic fibrinolysis and allows lysis of previously inaccessible thrombus.

Adult↗
PubMed1993

Caffeine does not increase synthesis of heat shock proteins in rat embryos.

Caffeine exposure in utero in rats is known to result in intrauterine growth retardation and lowered birth weight as well as changes to behaviour and brain biochemistry. We have investigated whether caffeine's embryotoxicity is a result of the events associated with increased hsp synthesis, i.e., disruption to normal protein synthesis. Caffeine (30 mg/kg) was administered orally to pregnant rats as single or repeated doses. Embryos were removed 3 h after dosing on gestation day (GD) 9, 10, 11 and 12 and total embryonic protein and RNA analysed. There was no change in the mRNA or protein levels of hsp 88, 71/73, and 25 after acute or chronic treatment. To separate the direct effect of caffeine from those mediated through the mother, whole rat embryo culture was used. Caffeine (50 micrograms/ml) for 90 min did not increase hsp 88, 73 or 25 mRNA levels in 9.5, 10.5 and 11.5 GD cultured embryos. We conclude that in vivo or in vitro treatment of 9-12 GD rat embryos with moderate to high doses of caffeine does not increase the synthesis of the major mammalian hsps. Hence, hsp induction is unlikely to play a role in the embryotoxic actions of caffeine.

Animals↗
PubMed1993

Age related changes in contractility and alpha 1 adrenergic responsiveness of myocardium from normal hamsters and hamsters with hereditary cardiomyopathy.

OBJECTIVE: The aim was to evaluate age related changes in myocardial contractility and alpha 1 adrenergic responsiveness in myocardium from normal and cardiomyopathic hamsters. METHODS: 50 male cardiomyopathic hamsters (CHF 147) and 45 golden Syrian hamsters were killed at 30, 50, 100, 200, or 300 days of age. Left ventricular papillary muscles were isolated and mounted in an isolated bath and isometric, isotonic, and unloaded contractions were recorded during a phenylephrine dose-response curve. The effects of increasing stimulation rate from 6 to 45 x min-1 and of increasing temperature from 29 degrees C to 35 degrees C before and after the addition of phenylephrine were verified in 100 day old hamsters. RESULTS: At 30 days of age, tension generation and shortening indices were similar in both strains. Thereafter, contractility increased in normal hamsters, to reach a peak at 50 d which was maintained until 300 d, when a slight decrease occurred. In cardiomyopathic hamsters, contractility increased more slowly, such that by 50 d tension was lower than in normals, at 15.8(SEM 1.9) v 26.5(2.2) mN.mm-2 (p < 0.01). This decrease persisted until 200 d, when it normalised and then decreased again by 300 d. The response of normal and cardiomyopathic muscles to phenylephrine was similar at 30 days of age. Thereafter, the response of cardiomyopathic muscles decreased more than in normals. This decrease was accompanied by a rightward shift in the dose-response curve. Increasing stimulation rate had no effect under basal conditions; however, once phenylephrine was added it caused tension to increase in cardiomyopathic muscles instead of decreasing, thereby rendering the relative effects of phenylephrine at 45 stimuli.min-1 similar in both groups. CONCLUSIONS: Force generating and shortening indices in normal and cardiomyopathic hamster myocardium are similarly immature at 30 days of age. Normal myocardium reaches its full potential by 50 d, but cardiomyopathic myocardium does not reach it until 200 d, and it decreases thereafter. A decrease in alpha 1 adrenergic responsiveness in cardiomyopathic myocardium at lower stimulation rates can be reversed by increasing the stimulation rate.

Aging↗
PubMed1993

RNA subunit of mitochondrial RNA-processing enzyme is induced by contractile activity in striated muscle.

A small RNA encoded within the nucleus of yeast and mammalian cells is an essential subunit of a mitochondrial RNA-processing endonuclease (RNase MRP) that generates primers for mitochondrial DNA (mtDNA) replication. We examined expression of MRP-RNA in specialized subtypes of mammalian striated muscles that differ markedly in respiratory activity and in muscles subjected to chronic stimulation via the motor nerve, a potent stimulus to mitochondrial biogenesis. MRP-RNA was more abundant in mitochondria-rich cardiac and slow-twitch skeletal muscles than in glycolytic fast-twitch skeletal muscles. Forced contractile activity resulting from nerve stimulation increased expression of MRP-RNA by 3.5-fold within the first day and by 14-fold within 14 days. Changes in abundance of MRP-RNA preceded but otherwise occurred in parallel to changes in specific activity of citrate synthase, a marker of mitochondrial proliferation shown previously to correlate with mtDNA copy number in this model. Another small RNA (U1) also was induced transiently (1-3 days) by nerve stimulation, but such changes were not sustained and were of less magnitude (< 4-fold) than changes in MRP-RNA. These findings are consistent with the hypothesis that MRP-RNA may have a regulatory function with respect to mtDNA replication and mitochondrial biogenesis.

Animals↗
PubMed1993

Effect of dysfunctional vascular endothelium on myocardial performance in isolated papillary muscles.

Vascular endothelium has been shown to modify the contractile characteristics of vascular smooth muscle, and endocardial endothelium has been shown to modify the contractile characteristics of adjacent myocardium. In this study, whether vascular endothelium also modifies the contractile characteristics of adjacent myocardium and whether these effects are additive to those of endocardial endothelium were investigated. Rabbit hearts (n = 54) were excised and mounted in a Langendorff preparation. Vascular reactivity was verified by acetylcholine infusion. One group of these hearts had Triton X-100 injected as a bolus into the coronaries to render the vascular endothelium dysfunctional. The other portion served as control hearts. Triton X-100 bolus injection resulted in little or no pathological changes on morphological examination; however, the vasodilatory response to acetylcholine in these hearts was abolished, suggesting vascular endothelial dysfunction. Vascular smooth muscle reactivity was verified in Triton X-100-injected hearts by nitroprusside infusion. In the control Langendorff-perfused hearts, there was little evidence of vascular endothelial dysfunction, with the coronary perfusion rate increasing from 8.9 +/- 0.4 to 11.0 +/- 0.3 ml/g per minute (p < 0.01) in response to acetylcholine. All hearts were then removed, and right ventricular papillary muscles were excised for myocardial mechanical studies. Control Langendorff-perfused hearts had myocardial mechanical characteristics similar to those of muscles from 18 other control hearts without Langendorff perfusion, indicating that the Langendorff perfusion itself had little effect on myocardial mechanics. The muscles from the Triton X-100-injected Langendorff hearts had marked changes: a shortening of twitch duration (363 +/- 16 versus 449 +/- 9 msec, p < 0.01) and decreases in total tension (2.2 +/- 0.2 versus 2.9 +/- 0.2 g/mm2, p < 0.01), dT/dt (9 +/- 1 versus 12 +/- 1 g/mm2 per second, p < 0.05), and maximum velocity of unloaded muscle shortening (Vmax) (0.89 +/- 0.06 versus 1.14 +/- 0.07 length at which maximum developed tension occurred [Lmax]/sec, p < 0.05). Endocardial endothelial removal of the papillary muscles in the two control groups (with and without Langendorff perfusion) by Triton X-100 caused the same changes in twitch characteristics as occurred in muscles from the Langendorff-perfused hearts injected with Triton X-100 but with intact endocardial endothelium, suggesting that vascular endothelial dysfunction had similar effects on contractile characteristics as endocardial endothelial removal.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗