Studies on the physiological role of brain-derived neurotrophic factor and neurotrophin-3 in knockout mice

Brain-derived neurotrophic factor and neurotrophin-3 deficient mice were generated by gene targeting. The analysis of these mice has led to the characterization of their role in the survival of neurons in the peripheral nervous system. NT-3 deficient mice displayed severe movement defects and most died shortly after birth. The mutation causes loss of substantial portions of cranial and spinal peripheral sensory and sympathetic neurons. Significantly, spinal proprioceptive afferents and their peripheral sense organs (muscle spindles and Golgi tendon organs) were completely absent in homozygous mutant mice. BDNF deficient mice displayed deficiencies in coordination and balance. Excessive loss of neurons was detected in most of the peripheral sensory ganglia examined, but the survival of sympathetic neurons was not affected. The most marked reduction of neurons was observed in the vestibular ganglion, leading to a loss of innervation of the sensory epithelia of the vestibular compartments of the inner ear.

Differential role of the low affinity neurotrophin receptor (p75) in retrograde axonal transport of the neurotrophins

The receptor mechanisms mediating the retrograde axonal transport of the neurotrophins have been investigated in adult rats. We show that transport of the TrkB ligands NT-4 and BDNF to peripheral neurons is dependent on the low affinity neurotrophin receptor (LNR). Pharmacological manipulation of LNR in vivo using either an anti-LNR antibody or a soluble recombinant LNR extracellular domain completely blocked retrograde transport of NT-4 and BDNF to sensory neurons, while having minimal effects on the transport of NGF in either sensory or sympathetic neurons. Furthermore, in mice with a null mutation of LNR, the transport of NT-4 and BDNF, but not NGF, was dramatically reduced. These observations demonstrate a selective role for LNR in retrograde transport of the various neurotrophins from distinct target regions in vivo.

Fatal intra-cranial haemorrhage in 2 cases of beta-thalassaemia major

Spontaneous intracranial haemorrhage is one of the cerebrovascular complications in beta-thalassaemia major patients. This is a report of 2 cases of fatal intracranial haemorrhage. Their ages were 12 and 7 years respectively, and they had been receiving regular blood transfusion for the past 3 and 2 years respectively. They developed acute onset of headache, loss of consciousness and convulsions at 5 and 2 days respectively after their last blood transfusion. C-T scan of the brain showed massive intracranial haemorrhage with extension into the ventricles. The spontaneous intracranial haemorrhages in these two cases was probably multi-factorial in origin. The predisposing factors included recent blood transfusion, prolonged prothrombin time and partial thromboplastin time as well as reduced platelet count.

A bacterial methyltransferase M.EcoHK311 requires two proteins for in vitro methylation

The genes encoding EcoHK311 restriction-modification (R-M) system were isolated from a clinically-isolated Escherichia coli strain HK31. The entire R-M system of EcoHK311 is located in a 2.1 kb fragment. R.EcoHK311 is an isoschizomer of Eael which recognizes and cleaves Y decreases GGCCR. M.EcoHK31l consists of two polypeptides alpha and beta with sizes 309 and 176 aa, respectively. Polypeptide beta is encoded within aa, alternative reading frame of polypeptide alpha. All the conserved motifs in mC5-MTases can be found in polypeptide alpha except motif IX which is present in polypeptide beta. Polypeptides alpha and beta were separately synthesized in a T7 promoter controlled over-expression system and in vitro methylation occurred only when the two extracts were mixed and thus confirms that two polypeptides are required for methylation.

Anatomy and physiology of the pleural space

The pleural cavity is created between the 4th and 7th week of embryologic development and is lined by the splanchnopleurae and somatopleurae. These embryonic components of visceral and parietal pleurae develop different anatomic characteristics with regard to vascular, lymphatic, and nervous supply. Both pleurae have two layers: a superficial mesothelial cell layer facing the pleural space and an underlying connective tissue layer. Various ultrastructures of the pleura show a close relationship to the basic functions of the pleural membranes, such as local inflammatory response and maintenance of the pleural fluid. The latter function is especially important in the mechanical coupling of the lung and chest wall. The fluid in the pleural space transmits transpleural forces involved in normal respiration, and the maintenance of the optimal volume and thickness is regulated closely. Fluid is filtered into the pleural space according to the net hydrostaticoncotic pressure gradient. It flows downward along a vertical pressure gradient, presumably determined by hydrostatic pressure and resistance to viscous flow. There also may be a net movement of fluid from the costal pleura to the mediastinal and interlobar regions. In these areas, pleural fluid is resorbed primarily through lymphatic stomata on the parietal pleural surface.

Lack of neurotrophin-3 leads to deficiencies in the peripheral nervous system and loss of limb proprioceptive afferents

Neurotrophin-3-deficient (NT-3-deficient) mice were generated by gene targeting. Mutant mice displayed severe movement defects of the limbs, and most died shortly after birth. Substantial portions of peripheral sensory and sympathetic neurons were lost while motor neurons were not affected. Significantly, spinal proprioceptive afferents and their peripheral sense organs (muscle spindles and Golgi tendon organs) were completely absent in homozygous mutant mice. This correlated with a loss of parvalbumin and carbonic anhydrase-positive neurons in the dorsal root ganglion. No gross abnormalities were seen in Pacinian corpuscles, cutaneous afferents containing substance P and calcitonin gene-related peptide, and deep nerve fibers in the joint capsule and tendon. Importantly, the number of muscle spindles in heterozygous mutant mice was half of that in control mice, indicating that NT-3 is present at limiting concentrations in the embryo.

p75-deficient embryonic dorsal root sensory and neonatal sympathetic neurons display a decreased sensitivity to NGF

To understand the role of low-affinity neurotrophin receptor p75 in neural development, we previously generated mice carrying a null mutation in the p75 locus (Lee, K. F., Li, E., Huber, L. J., Landis, S. C., Sharpe, A. H., Chao, M. V. and Jaenisch, R. (1992) Cell 69, 737–749). To elucidate the mechanisms leading to deficits in the peripheral nervous system in p75 mutant mice, we have employed dissociated cultures to examine the responses of p75-deficient dorsal root ganglion (DRG) and superior cervical ganglion (SCG) neurons to different neurotrophins. We found that p75-deficient DRG and SCG neurons displayed a 2- to 3-fold decreased sensitivity to NGF at embryonic day 15 (E15) and postnatal day 3 (P3), respectively, ages that coincide with the peak of naturally occurring cell death. Furthermore, while p75-deficient E15 DRG neurons did not change their response specificity to BDNF, NT-3, and NT-4/5, P3 SCG neurons became more responsive to NT-3 at higher concentrations (nanomolar ranges). These results may help explain the deficits in the peripheral nervous system in p75 mutant mice and provide evidence that p75 can modulate neurotrophin sensitivity in some neurons.

Dependence on p75 for innervation of some sympathetic targets

The low-affinity neurotrophin receptor p75 binds all neurotrophins with similar affinity. For elucidation of its function, mice bearing a null mutation in the p75 locus were generated. Examination of sympathetic innervation of target tissues revealed that pineal glands lacked innervation and sweat gland innervation was absent or reduced in particular footpads. The absence of adult innervation reflects the failure of axons to reach these targets during development rather than a target deficit. These results indicate that p75 facilitates development of specific populations of sympathetic neurons, for which it may support axon growth.

Mice lacking brain-derived neurotrophic factor develop with sensory deficits

During vertebrate development, neuronal survival depends on target-derived neurotrophic factors. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, can prevent the death of particular peripheral sensory neurons in vitro, and of central motor neurons as well as dopaminergic and cholinergic neurons of the basal forebrain during development. It also prevents the death of motor neurons and midbrain dopaminergic neurons induced by lesions. Here we show that mutant mice lacking BDNF have severe deficiencies in coordination and balance, associated with excessive degeneration in several sensory ganglia including the vestibular ganglion. The few remaining vestibular axons fail to contact the vestibular sensory epithelia, and terminate in the adjacent connective tissue. Survival of sympathetic, midbrain dopaminergic and motor neurons is not affected. These results indicate that BDNF is required for the survival and target innervation of particular neuronal populations.

Activin/inhibin beta B subunit gene disruption leads to defects in eyelid development and female reproduction

Inhibins and activins are dimeric growth factors of the transforming growth factor-beta superfamily, a class of peptides that can regulate the growth and differentiation of a variety of cell types. Recently, activins have been implicated in early vertebrate development through their ability to evoke, in Xenopus embryo explants, both morphological and molecular changes characteristic of mesoderm induction. To understand these processes further, we have used homologous recombination in embryonic stem cells to create mouse strains carrying mutations in the gene encoding the activin/inhibin beta B subunit. These mice are expected to be deficient in activin B (beta B:beta B), activin AB (beta A:beta B), and inhibin B (alpha:beta B). Viable mutant animals were generated, indicating that the beta B subunit is not essential for mesoderm formation in the mouse. Mutant animals suffered, however, from distinct developmental and reproductive defects. An apparent failure of eyelid fusion during late embryonic development led to eye lesions in mutant animals. Whereas beta B-deficient males bred normally, mutant females manifested a profoundly impaired reproductive ability, characterized by perinatal lethality of their offspring. The phenotype of mutant mice suggests that activin beta B (1) plays a role in late fetal development and (2) is critical for female fecundity. In addition, we have found that expression of the related beta A subunit of activin is highly upregulated in ovaries of mutant females. Altered regulation of beta A activin in beta B-deficient mice may contribute to the mutant phenotype.

p75-deficient trigeminal sensory neurons have an altered response to NGF but not to other neurotrophins

The role of the common low affinity neurotrophin receptor, p75, is controversial. Studies using cell lines suggest that p75 is either essential or dispensable for neurotrophin responsiveness. To resolve this issue, we studied the survival response of developing neurons obtained from normal mouse embryos and embryos with a null mutation in the p75 gene. Embryonic cranial sensory and sympathetic neurons from mutant embryos responded normally to NGF, BDNF, NT-3, and NT-4/5 at saturating concentrations. Dose responses of sympathetic and visceral sensory neurons from mutant embryos were also normal. In contrast, embryonic cutaneous sensory trigeminal neurons isolated from mutant embryos displayed a consistent displacement in the NGF dose response. Compared with wild-type neurons, the concentration of NGF that promoted half-maximal survival was 3- to 4-fold higher for neurons from homozygous embryos and was 2-fold higher for neurons from heterozygous embryos. These findings indicate that p75 enhances the sensitivity of NGF-dependent cutaneous sensory neurons to NGF and may explain, at least in part, the cutaneous sensory abnormalities of mice homozygous for the p75 mutation.

Normal development and growth of mice carrying a targeted disruption of the alpha 1 retinoic acid receptor gene

Three unlinked genes encode receptors for retinoic acid (RAR alpha, -beta, and -gamma). Each gene expresses two major protein isoforms differing in the amino terminal A domain by alternative promoter use, fused to common exons encoding most of the receptor protein. The two RAR alpha transcripts (RAR alpha 1 and -alpha 2) are differentially expressed and evolutionarily conserved, as are the RAR beta and -gamma transcripts, suggesting that each isoform may have specific functions in the development of animals. To address the biological function of the alpha 1 receptor, we have disrupted the portion of the RAR alpha gene encoding this isoform by homologous recombination in mouse embryonic stem cells. Surprisingly, offspring homozygous for this mutation were viable and showed no apparently altered phenotype. RNA analysis confirmed that the RAR alpha 1 transcript was absent in homozygous tissues, and no evidence for a compensatory increase of RAR alpha 2 or of another RAR gene was obtained to account for the vitality of the mutant animals. These results clearly demonstrate that loss of RAR alpha 1 function does not disrupt embryonic development and argue for combinatorial or overlapping functions among the RAR isoforms.

Dynamic cardiomyoplasty

In end-stage heart failure marked by progressive impairment of myocardial function, enlarged chamber size, and excessive workload, dynamic cardiomyoplasty may have a direct role in improving the mechanical conditions of the left ventricle and increasing its contractility on a long-term basis. The chronic use of positive inotropic drugs; e.g., amrinone and milrinone, in end-stage cardiomyopathy has not been beneficial because of the severely limited contractile reserve of the heart and progressive myocardial cell damage related to extreme workloads and disadvantaged myocardial energetics. In contrast, dynamic cardiomyoplasty enhances left ventricular contractility with an extrinsic energy source (the muscle wrap), and in theory, at decreased levels of myocardial oxygen requirement because of associated workload reduction. These conceptual advantages are supported by the functional and mechanical data from the laboratory. Although clinical experience with the procedure is still largely experimental, dynamic cardiomyoplasty may have an important future role in the treatment of end-stage congestive heart failure.

Phospholamban expressed in slow-twitch and chronically stimulated fast-twitch muscles minimally affects calcium affinity of sarcoplasmic reticulum Ca(2+)-ATPase

Chronic excitation, at 2 Hz for 6-7 weeks, of the predominantly fast-twitch canine latissimus dorsi muscle promoted the expression of phospholamban, a protein found in sarcoplasmic reticulum (SR) from slow-twitch and cardiac muscle but not in fast-twitch muscle. At the same time that phospholamban was expressed, there was a switch from the fast-twitch (SERCA1) to the slow-twitch (SERCA2a) Ca(2+)-ATPase isoform. Antibodies against Ca(2+)-ATPase (SERCA2a) and phospholamban were used to assess the relative amounts of the slow-twitch/cardiac isoform of the Ca(2+)-ATPase and phospholamban, which were found to be virtually the same in SR vesicles from the slow-twitch muscle, vastus intermedius; cardiac muscle; and the chronically stimulated fast-twitch muscle, latissimus dorsi. The phospholamban monoclonal antibody 2D12 was added to SR vesicles to evaluate the regulatory effect of phospholamban on calcium uptake. The antibody produced a strong stimulation of calcium uptake into cardiac SR vesicles, by increasing the apparent affinity of the Ca2+ pump for calcium by 2.8-fold. In the SR from the conditioned latissimus dorsi, however, the phospholamban antibody produced only a marginal effect on Ca2+ pump calcium affinity. These different effects of phospholamban on calcium uptake suggest that phospholamban is not tightly coupled to the Ca(2+)-ATPase in SR vesicles from slow-twitch muscles and that phospholamban may have some other function in slow-twitch and chronically stimulated fast-twitch muscle.

Targeted mutation of the gene encoding the low affinity NGF receptor p75 leads to deficits in the peripheral sensory nervous system

We have generated mice carrying a mutation of the gene encoding the low affinity NGF receptor p75NGFR by targeted mutation in embryonic stem cells. Mice homozygous for the mutation were viable and fertile. Immunohistochemical analyses of the footpad skin of mutant mice revealed markedly decreased sensory innervation by calcitonin gene-related peptide- and substance P-immunoreactive fibers. The defective innervation was correlated with loss of heat sensitivity and associated with the development of ulcers in the distal extremities. Complicated by secondary bacterial infection, the ulcers progressed to toenail and hair loss. Crossing a human transgene encoding p75NGFR into the mutant animals rescued the absent heat sensitivity and the occurrence of skin ulcers and increased the density of neuropeptide-immunoreactive sensory innervation of footpad skin. The mutation in the gene encoding p75NGFR did not decrease the size of sympathetic ganglia or the density of sympathetic innervation of the iris or salivary gland. Our results suggest that p75NGFR has an important role in the development and function of sensory neurons.

Restriction endonuclease from thermophilic bacterial species III. Isolation and characterization of BsiHKA I

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Coronary artery endothelial cell and smooth muscle dysfunction after global myocardial ischemia

We hypothesized that coronary artery endothelial cell function and smooth muscle function are modified by global myocardial ischemia and used bradykinin-induced secretion of endothelium-derived relaxing factor as a marker of endothelial cell function. Bradykinin and sodium nitroprusside together determined maximum smooth muscle relaxation. Potassium chloride-induced contraction determined smooth muscle contractility. Endothelium-mediated smooth muscle relaxation expressed as a ratio of total coronary smooth muscle relaxation before and after ischemia quantified endothelial cell function. The effect of global normothermic ischemia on in situ coronary arteries from 7 swine hearts was studied. Coronary arterial rings taken from 0 to 220 minutes of ischemia at 20-minute intervals were studied in vitro. The data revealed unexpected tolerance of endothelium-mediated relaxation to ischemia. Endothelium-derived relaxing factor function was maintained to 160 minutes and smooth muscle function, to 120 minutes of ischemia. Coronary artery dysfunction seen in other studies after less ischemia may be the result of injury introduced during reperfusion, may be the consequence of myocardial injury, or may be due to events operative at the level of small arterioles.

Reactivity of gastroepiploic and internal mammary arteries. Relevance to coronary artery bypass grafting

The gastroepiploic artery is an alternate conduit for coronary artery bypass grafting. To test the hypothesis that its vasoreactive properties are different from those of the internal mammary artery, we obtained gastroepiploic artery segments from human gastrectomy specimens. Trimmed internal mammary artery segments were obtained during coronary artery bypass. Ring segments were mounted on a strain gauge and stretched to optimum resting length (90% of the internal circumference at 100 mm Hg). Potassium chloride, serotonin, and norepinephrine were chosen to simulate physiologic vasospasm induced by depolarization, platelet aggregation, or adrenergic stimulation, respectively. Contractions to potassium and a concentration-response curve to serotonin or norepinephrine were obtained. Sodium nitroprusside was used to assess relaxation. Gastroepiploic artery segments had stronger contractions to the depolarizing agent (potassium chloride), adrenergic stimulation (norepinephrine), and product of platelet aggregation (serotonin). The gastroepiploic and internal mammary arteries showed equal sensitivity, measured by concentration causing half-maximal contraction to norepinephrine and serotonin. There was no difference in relaxation to sodium nitroprusside. These data suggest that prevention of platelet-, adrenergic-, or potassium-induced contraction may be more important when the gastroepiploic artery is used as an alternate conduit for coronary artery bypass, reinforcing consideration of nitrovasodilators and platelet inhibitors in the perioperative interval.

Analysis of excitation-contraction-coupling components in chronically stimulated canine skeletal muscle

The chronic stimulation of predominantly fast-twitch mammalian skeletal muscle causes a transformation to physiological characteristics of slow-twitch skeletal muscle. Here, we report the effects of chronic stimulation on the protein components of the sarcoplasmic reticulum and transverse tubular membranes which are directly involved in excitation-contraction coupling. Comparison of protein composition of microsomal fractions from control and chronically stimulated muscle was performed by immunoblot analysis and also by staining with Coomassie blue or the cationic carbocyanine dye Stains-all. Consistent with previous experiments, a greatly reduced density was observed for the fast-twitch isozyme of Ca(2+)-ATPase, while the expression of the slow-twitch Ca(2+)-ATPase was found to be greatly enhanced. Components of the sarcolemma (Na+/K(+)-ATPase, dystrophin-glycoprotein complex) and the free sarcoplasmic reticulum (Ca(2+)-binding protein sarcalumenin and a 53-kDa glycoprotein) were not affected by chronic stimulation. The relative abundance of calsequestrin was slightly reduced in transformed skeletal muscle. However, the expression of the ryanodine receptor/Ca(Ca2+)-release channel from junctional sarcoplasmic reticulum and the transverse tubular dihydropyridine-sensitive Ca2+ channel, as well as two junctional sarcoplasmic reticulum proteins of 90 kDa and 94 kDa, was greatly suppressed in transformed muscle. Thus, the expression of the major protein components of the triad junction involved in excitation-contraction coupling is suppressed, while the expression of other muscle membrane proteins is not affected in chronically stimulated muscle.

Skeletal muscle extraaortic counterpulsation. A true arterial counterpulsation

Reduction of left ventricular work load during systole, a critical component of arterial counterpulsation, has not previously been documented for skeletal muscle-powered extraaortic counterpulsation. To assess its capacity for afterload reduction, a skeletal muscle extraaortic counterpulsator was connected to the thoracic aorta and counterpulsated. Canine hearts (n = 7) were instrumented with left ventricular Millar catheters (Millar Instruments, Inc., Houston, Tex.) for pressure measurements and with piezoelectric ultrasonic crystals for measurement of the left ventricular minor axis dimension and wall thickness. During systole, skeletal muscle extraaortic counterpulsation resulted in a significant change in all three determinants of left ventricular circumferential wall stress compared with control conditions (no counterpulsation). Pressure decreased (peak systole, 100 +/- 5 versus 75 +/- 6 mm Hg; p less than 0.05 by paired t test), minor axis dimension decreased (end systole, 46.4 +/- 1.1 versus 45.8 +/- 1.1 mm; p less than 0.05 by paired t test), and wall thickness increased (end systole, 10.4 +/- 0.7 versus 10.6 +/- 0.7 mm; p less than 0.05 by paired t test). Left ventricular wall stress/dimension work loops showed a shift downward and to the left, a shift consistent with afterload reduction. The mean systolic left ventricular wall stress was significantly reduced, from 67.3 +/- 10.6 to 47.7 +/- 8.1 10(3) dyne/cm2 (p less than 0.05 by paired t test). Skeletal muscle extraaortic counterpulsation increased the diastolic aortic pressure from 72 +/- 6 to 105 +/- 8 mm Hg (p less than 0.05 by paired t test). Our data, which documented the counterpulsator's direct effects on left ventricular functional mechanics, showed that skeletal muscle extraaortic counterpulsation is capable of both diastolic augmentation of arterial pressure and systolic unloading of the left ventricle. Skeletal muscle extraaortic counterpulsation has potential application for ventricular unloading in the treatment of chronic end-stage heart failure.

Inotropic stimulation and oxygen consumption in a canine model of dilated cardiomyopathy

Inotropic support for the dilated, failing ventricle results in complex hemodynamic changes affecting preload, afterload, contractility, and heart rate, each of which affects myocardial oxygen consumption. Appreciation of a hierarchy of hemodynamic determinants of myocardial oxygen consumption may be helpful to the clinician trying to balance oxygen demands and hemodynamic performance. We tested the hypothesis that epinephrine alters the hierarchy of hemodynamic determinants of myocardial oxygen consumption in a canine model of dilated cardiomyopathy created by rapid ventricular pacing. Dogs (n = 10) were instrumented to record left ventricular pressure and dimension, and a modified right heart bypass preparation was used to control left ventricular workload. Coronary sinus effluent was quantitatively collected and analyzed for oxygen content and used to calculate myocardial oxygen consumption. Epinephrine administration significantly increased myocardial oxygen consumption in the empty, beating heart; however, when the relationships of multiple determinants of left ventricular work and load were compared before and after epinephrine administration, no oxygen wasting effect was observed. Using multivariate linear regression analysis, a hierarchy of hemodynamic determinants of myocardial oxygen consumption was created. In the untreated heart, stroke work and cardiac output were the primary hemodynamic determinants of oxygen consumption; epinephrine significantly altered the determinants such that wall stress became the dominant hemodynamic determinant of myocardial oxygen consumption. Focused manipulation of wall stress in the treated, failing heart may limit the potentially deleterious effects of inotropic stimulation in this setting.

Cardiac transplantation with corticosteroid-free immunosuppression: long-term results

To assess the long-term safety of an immunosuppressive regimen without corticosteroids, we retrospectively evaluated 42 long-term (greater than 1 year) survivors of orthotopic cardiac transplantation. We determined the incidence of (1) conversion of the immunosuppressive regimen from cyclosporine and azathioprine alone (group I) to cyclosporine, azathioprine, and prednisone (group II), (2) late acute graft rejection (defined as occurring at greater than 1 postoperative year), and (3) major postoperative complications related to corticosteroids. Of the 42 patients who were started on cyclosporine and azathioprine, 48% remained in group I, and 52% converted to group II. Forty-five percent of group II patients were able to taper and discontinue prednisone in 15.6 +/- 2.2 months. Among the patients on long-term corticosteroid-free immunosuppression, the incidence of late rejection was 2.1% per endomyocardial biopsy. The incidence of late infectious episodes was not significantly different between the two groups of patients, although diabetes mellitus and hypercholesterolemia were more prevalent in group II than in group I. These data suggest that cardiac transplant recipients who chronically remain on corticosteroid-free immunosuppression represent a select group of patients with an acceptably low risk of late graft rejection and associated reduction of potential risk factors of accelerated coronary artery disease.

Effects of dynamic cardiomyoplasty on left ventricular performance and myocardial mechanics in dilated cardiomyopathy

We tested the hypothesis that dynamic cardiomyoplasty produces beneficial changes in the functional mechanics of the dilated, failing left ventricle. Chronic dilated cardiomyopathy was induced in seven mongrel dogs by rapid ventricular pacing (260 beats/min) for 3 to 4 weeks. After completion of the induction period, dynamic cardiomyoplasty was performed with the left latissimus dorsi muscle, paced synchronously with the R waves of the electrocardiogram (Medtronic SP1005). Instruments included an aortic flow probe, a left ventricular Millar pressure catheter, and piezoelectric sonomicrometric crystals on the left ventricle for measurements of wall thickness and minor and major axis dimensions. Data were obtained with the stimulator off and on. Statistical comparisons were made with Student's t test for paired data. Dynamic cardiomyoplasty increased the cardiac output of the failing heart (966 +/- 124 versus 1166 +/- 112 ml/min; p less than 0.01). Systolic shortening of both minor and major axis dimensions increased (3.1 +/- 0.3 versus 4.7 +/- 0.3 mm, p less than 0.01, and 4.6 +/- 0.3 versus 7.3 +/- 0.9 mm, p less than 0.05, respectively). Left ventricular end-diastolic pressure decreased by 16% (18 +/- 1 versus 15 +/- 1 mm Hg, p less than 0.01). Although skeletal muscle contraction increased the pressure development in the left ventricular chamber, mean systolic wall stress was diminished by concomitant changes in left ventricular dimensions (116,144 +/- 11,530 versus 101,268 +/- 7464 dynes/cm2, p less than 0.05). At end-systole, wall thickness increased (11.8 +/- 1.1 versus 12.7 +/- 1.1 mm, p less than 0.01), minor axis dimension decreased (51.3 +/- 1.4 versus 49.2 +/- 1.8 mm, p less than 0.01), and major axis dimension also decreased (85.6 +/- 3.3 versus 79.0 +/- 2.3 mm, p less than 0.05). Our detailed evaluation of left ventricular chamber mechanics suggests that dynamic cardiomyoplasty may have a role in ameliorating the functional and mechanical derangements associated with progression of dilated cardiomyopathy both by augmenting cardiac performance and by diminishing determinants of myocardial oxygen consumption. (All values are expressed as mean +/- standard error of the mean.)