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D Sedmera

Publications and source records attributed to D Sedmera.

13 recordsLinked to original sources
PubMed2001

Pacing redistributes glycogen within the developing myocardium.

Electrical pacing at physiological rate induces myocardial remodeling associated with regional changes in workload, blood flow and oxygen consumption. However, to what extent energy-producing pathways are also modified within the paced heart remains to be investigated. Pacing could particularly affect glycogen metabolism since hypertrophy stimulates glycolysis and increased workload favors glucose over fat oxidation. In order to test this hypothesis, we used the embryonic chick heart model in which ventricular pacing rapidly resulted in thinning of the ventricle wall and thickening of the atrial wall. Hearts of stage 22HH chick embryos were submitted in ovo to asynchronous and intermittent ventricular pacing delivered at physiological rate during 24 h. The resulting alterations of glycogen content were determined in atrium, ventricle and conotruncus of paced and sham-operated hearts. Hemodynamic parameters of the paced and spontaneously beating hearts were derived from computerized image analysis of video recordings. With respect to sham, paced hearts showed a significant decrease in glycogen content (nmoles glucose units/microg protein; mean+/-S.D.) only in atrium (1.48+/-0.40 v 0.84+/-0.34, n=8) and conotruncus (0.75+/-0.28 v 0.42+/-0.23, n=8). Pacing decreased the end diastolic and stroke volumes by 34 and 44%, respectively. Thus, the rapid glycogen depletion in regions remote from the stimulation site appears to be associated with regional changes in workload and remodeling. These findings underscore the importance of the coupling mechanisms between metabolic pathways and myocardial remodeling in the ectopically paced heart.

Animals↗
PubMed2000

Structure and function of the developing zebrafish heart.

The combination of optical clarity and large scale of mutants makes the zebrafish vital for developmental biologists. However, there is no comprehensive reference of morphology and function for this animal. Since study of gene expression must be integrated with structure and function, we undertook a longitudinal study to define the cardiac morphology and physiology of the developing zebrafish. Our studies included 48-hr, 5-day, 2-week, 4-week, and 3-month post-fertilization zebrafish. We measured ventricular and body wet weights, and performed morphologic analysis on the heart with H&E and MF-20 antibody sections. Ventricular and dorsal aortic pressures were measured with a servonull system. Ventricular and body weight increased geometrically with development, but at different rates. Ventricle-to-body ratio decreased from 0.11 at 48-hr to 0.02 in adult. The heart is partitioned into sinus venosus, atrium, ventricle, and bulbus arteriosus as identified by the constriction between the segments at 48-hr. Valves were formed at 5-day post-fertilization. Until maturity, the atrium showed extensive pectinate muscles, and the atrial wall increased to two to three cell layers. The ventricular wall and the compact layer increased to three to four cell layers, while the extent and complexity in trabeculation continued. Further thickening of the heart wall was mainly by increase in cell size. The bulbus arteriosus had similar characteristics to the myocardium in early stages, but lost the MF-20 positive staining, and transitioned to smooth muscle layer. All pressures increased geometrically with development, and were linearly related to stage-specific values for body weight (P < 0.05). These data define the parameters of normal cardiac morphology and ventricular function in the developing zebrafish.

Animals↗
PubMed2000

Developmental patterning of the myocardium.

The heart in higher vertebrates develops from a simple tube into a complex organ with four chambers specialized for efficient pumping at pressure. During this period, there is a concomitant change in the level of myocardial organization. One important event is the emergence of trabeculations in the luminal layers of the ventricles, a feature which enables the myocardium to increase its mass in the absence of any discrete coronary circulation. In subsequent development, this trabecular layer becomes solidified in its deeper part, thus increasing the compact component of the ventricular myocardium. The remaining layer adjacent to the ventricular lumen retains its trabeculations, with patterns which are both ventricle- and species-specific. During ontogenesis, the compact layer is initially only a few cells thick, but gradually develops a multilayered spiral architecture. A similar process can be charted in the atrial myocardium, where the luminal trabeculations become the pectinate muscles. Their extent then provides the best guide for distinguishing intrinsically the morphologically right from the left atrium. We review the variations of these processes during the development of the human heart and hearts from commonly used laboratory species (chick, mouse, and rat). Comparison with hearts from lower vertebrates is also provided. Despite some variations, such as the final pattern of papillary or pectinate muscles, the hearts observe the same biomechanical rules, and thus share many common points. The functional importance of myocardial organization is demonstrated by lethality of mouse mutants with perturbed myocardial architecture. We conclude that experimental studies uncovering the rules of myocardial assembly are relevant for the full understanding of development of the human heart.

Animals↗
PubMed1999

Remodeling of chick embryonic ventricular myoarchitecture under experimentally changed loading conditions.

Adult myocardium adapts to changing functional demands by hyper- or hypotrophy while the developing heart reacts by hyper- or hypoplasia. How embryonic myocardial architecture adjusts to experimentally altered loading is not known. We subjected the chick embryonic hearts to mechanically altered loading to study its influence upon ventricular myoarchitecture. Chick embryonic hearts were subjected to conotruncal banding (increased afterload model), or left atrial ligation or clipping, creating a combined model of increased preload in right ventricle and decreased preload in left ventricle. Modifications of myocardial architecture were studied by scanning electron microscopy and histology with morphometry. In the conotruncal banded group, there was a mild to moderate ventricular dilatation, thickening of the compact myocardium and trabeculae, and spiraling of trabecular course in the left ventricle. Right atrioventricular valve morphology was altered from normal muscular flap towards a bicuspid structure. Left atrial ligation or clipping resulted in hypoplasia of the left heart structures with compensatory overdevelopment on the right side. Hypoplastic left ventricle had decreased myocardial volume and showed accelerated trabecular compaction. Increased volume load in the right ventricle was compensated primarily by chamber dilatation with altered trabecular pattern, and by trabecular proliferation and thickening of the compact myocardium at the later stages. A ventricular septal defect was noted in all conotruncal banded, and 25% of left atrial ligated hearts. Increasing pressure load is a main stimulus for embryonic myocardial growth, while increased volume load is compensated primarily by dilatation. Adequate loading is important for normal cardiac morphogenesis and the development of typical myocardial patterns.

Animals↗
PubMed1999

The chick embryo heart as an experimental setup for the assessment of myocardial remodeling induced by pacing.

The mechanisms regulating remodeling of the heart are not well understood and only rarely investigated for pacing. We therefore developed a model based on the well-established chick embryo heart preparation. Hamburger Hamilton 21 stage Leghorn chick embryos were used. Access to the heart was obtained after having dissected the shell membranes. The electrodes (platinum wires) were placed in ovo: the anode on the vitelline membrane and the cathode at different sites of the heart (sinus venosus, base/apex of the ventricle). Sensing and stimulation thresholds were measured. Survival of the paced chick was studied. Among 30 chick embryonic hearts, the stimulation thresholds were 1.4 mV +/- 0.5 SD for the atrium, 2.6 V +/- 1.4 SD at the base, and 3.2 V +/- 1.5 SD at the apex of the ventricle, while the sensing signals were 1.3 mV +/- 0.5 SD at the atrium, 19.6 mV +/- 4.1 SD at the base, and 21.6 mV +/- 3.9 SD at the apex of the ventricle. Continuous pacing (pacing rate = intrinsic rate + 10%) could be maintained for 1.5 hours +/- 0.5 SD at the atrium, 8.9 hours +/- 0.7 SD at the base of the ventricle, and 7.9 hours +/- 1 SD at the apex of the ventricle up to death of the embryos. By using intermittent electrical stimulation, the association of 5 minutes on/5 minutes off pattern during 18 hours and 5 minutes on/15 minutes off, during 30 hours resulted in an effective pacing period of 19 hours in 60% of the experiments, reflecting 15 cell turnover cycles. This experimental setup will allow the study of morphological, metabolic, and molecular bases of ventricular remodeling induced by electrical stimulation.

Animals↗
PubMed1999

Pacing-induced ventricular remodeling in the chick embryonic heart.

Chronic ectopic pacing in the adult heart induces myocardial hypotrophy close to the pacing site. We have recently described a similar localized decrease of compact myocardium thickness in the chick embryonic heart after 48 h of intermittent apical ventricular pacing. Here we analyze the cellular mechanisms underlying the response of the embryonic heart to pacing. Because the developing heart had been found to adjust its morphology according to functional demands by undergoing cellular hyperplasia or hypoplasia, we hypothesized that the stimulation should result in hypoplasia of the apical ventricular compartment. Morphologic analysis of hearts submitted to 18 h of effective pacing during 48 h showed a mild to moderate ventricular dilatation, a 28% decrease in the apical compact layer thickness with no changes in other ventricular locations, and atrial wall thickening. These modifications were caused by changes in the number of cell layers, whereas cell size was similar between paced and control hearts. Analysis of proliferative activity after 24 h of pacing showed a decrease of 32% in the rate of cell proliferation limited to the apical compact layer exposed to stimulation. No ultrastructural injury or increased cell death was found. These changes were accompanied by down-regulation of the myocardial growth factor fibroblast growth factor-2 but no differences were found in the expression of platelet-derived growth factor. Thus, chronic intermittent ventricular pacing induces myocardial remodeling in the chick embryonic heart, on the basis of locally regulated rates of cell proliferation.

Animals↗
PubMed1999

Optimisation of the formation and distribution of protoporphyrin IX in the urothelium: an in vitro approach.

PURPOSE: To optimize conditions for photodynamic detection (PDD) and photodynamic therapy (PDT) of bladder carcinoma, urothelial accumulation of protoporphyrin IX (PpIX) and conditions leading to cell photodestruction were studied. MATERIALS AND METHODS: Porcine and human bladder mucosae were superfused with derivatives of 5-aminolevulinic acid (ALA). PpIX accumulation and distribution across the mucosa was studied by microspectrofluorometry. Cell viability and structural integrity were assessed by using vital dyes and microscopy. RESULTS: ALA esters, especially hexyl-ALA, accelerated and regularized urothelial PpIX accumulation and allowed for necrosis upon illumination. CONCLUSIONS: hexyl-ALA used at micromolar concentrations is the most efficient PpIX precursor for PDD and PDT.

Aminolevulinic Acid↗
PubMed1998

A quantitative study of the ventricular myoarchitecture in the stage 21-29 chick embryo following decreased loading.

During the early developmental period, ventricular myoarchitecture undergoes a transition from a smooth-walled cardiac tube, to left and right ventricular chambers filled with a sponge-like network of trabecular struts. We measured the quantitative changes of ventricular myocardium properties in normal stage 21-29 chick embryos and after chronic verapamil suffusion, which is known to decrease work load and decelerate ventricular growth. The morphologic parameters (compact layer thickness, ventricular wall composition, porosity of different layers and trabecular orientation) were determined from scanning electron micrographs of transversely dissected perfusion-fixed hearts. A vascular bed of stage 21 chick embryos was suffused with 1 ng of verapamil at 1 microliter per hour up to stages 24, 27 and 29 via a miniosmotic pump. From stage 24, the thickness of the compact myocardium in the left ventricle was greater than that of the right. The increase in thickness was minimal between stages 24 and 27, while the predominantly radially arranged trabeculae comprised up to 75% to total myocardial mass. The ratio of intertrabecular spaces to trabeculae (local porosity) decreased form the ventricular center (70%) towards the compact myocardium (0%). In verapamil-treated embryos, the hearts were smaller and showed delayed development. The compact myocardium was thinner than normal, and the proportion of trabeculae was higher than in controls. The local porosity values were similar in control and experimental groups. Decreased load resulted in delayed growth and morphogenesis, expressed as persistence of trabeculae and a thinner compact myocardium. Embryonic heart pumping function is largely based on extensively developed trabeculation with regionally different properties.

Animals↗
PubMed1998

The role of cell death in limb development of rats manifesting Lx allele on different genetic backgrounds.

Control of vertebrate digital pattern is a phylogenetically old mechanism. Animal strains with abnormal digital counts are a useful model system to study tissue, cell and molecular factors involved in limb patterning. The aim of this study was to investigate rat limb morphogenesis on gestation days 13 to 16 in normodactylous, polydactylous and oligodactylous fetuses where the deviation from the normal pentadactylous phenotype is caused by interaction of mutant Lx allele with different genetic backgrounds. General development was assessed by measurements of crown-rump length, and limb morphogenesis by hand and foot plate width. Skeletogenesis was studied histologically and by whole mount staining with Alcian Blue and Acridine Orange. Cell death was demonstrated by supravital staining and fluorescence microscopy and by standard histology on serial sections. No phenotypic differences among the groups were noted on day 13. On day 14, the oligodactylous hind limb buds were more spiky than normal and had well-developed preaxial necrotic site (foyer preaxial primaire) which was normally observed only on day 15. This area of programmed cell death was severely attenuated in polydactylous limb buds. Pollex triphalangy manifested as increased hand plate width from day 15. Also hind limb buds width differed by this stage between groups. No acceleration or retardation of skeletogenesis was observed in abnormal limbs. The data confirm the crucial role of spatial and temporal patterns of morphogenetic programmed cell death in control of digital pattern.

Alleles↗
PubMed1997

Developmental changes in the myocardial architecture of the chick.

BACKGROUND: Numerous studies describing myocardial architecture have been performed on the adult heart but considerably fewer have been made during embryonic or fetal development. To serve as a basis for interspecies comparison of ventricular morphology, and as a reference for studying the effects of experimental perturbations, we examined the development of chick throughout the entire incubation period. METHODS: Chick hearts from stage 14 (day 2) to stage 46 (day 21) were perfusion-fixed, and sectioned in transverse, frontal and sagittal planes. The ventricular myocardial architecture was examined and photographed in the scanning electron microscope. RESULTS: At embryonic stage 16 and earlier, the smooth-walled heart loop had an outer myocardial mantle, cardiac jelly, and endocardium. From stage 18, there was an outer compact and inner trabeculated myocardium. Trabeculated myocardium could be subdivided into the outer (basal) portion adjacent to the compact layer and the central (luminal) part. The outer basal layer could be distinguished from the inner luminal by shorter and finer trabeculae with small, round intertrabecular spaces. From stage 24, the patterns of trabeculae and intertrabecular spaces were ventricle-specific. Between stages 24 to 31, abundant trabeculations were present throughout both ventricular cavities. The trabeculae were initially radially arranged, but later adopted a spiral course, which persisted in a simplified form into adulthood. CONCLUSIONS: The ventricular myocardium undergoes distinctive morphogenesis, characterized by changes in trabecular patterning and orientation. We speculate that the embryonic trabecular architecture reflects the directions of the main stresses. Unlike fetal and adult hearts, which rely mostly on the compact myocardial layer, the trabeculae play a crucial role in the contractile function of the embryonic heart.

Animals↗
PubMed1997

On the development of Cetacean extremities: I. Hind limb rudimentation in the Spotted dolphin (Stenella attenuata).

The Cetacea are group of animals which have completely lost their hind limbs during the course of evolution as a result of their entirely aquatic mode of life. It is known, however, that during their embryonal period, the hind limb buds are temporarily present. The control mechanisms of this regression are not yet understood, and vestigial limbs can sometimes be found in adults. The aim of the present study is to describe the course of hind limb rudimentation during prenatal development of Stenella attenuata (Spotted dolphin) at tissue and cell levels and compare the results with other natural or experimentally induced amelias. Hind limb buds of dolphin embryos, CRL 10-30 mm, were examined histologically. Before total disappearance, they show histodifferentiation comparable with other mammals. Initially, they form the apical ectodermal ridge, which soon regresses. The mesenchyme undergoes the process of condensation to form anlagens of prospective skeletal elements. These condensations are surrounded by vascular plexuses. During the course of rudimentation, some mesenchymal cells die, while the others are incorporated into the body wall. Nerve ingrowth into rudimentary limb buds was also detected. The temporary presence of hind limb rudiments in cetacean embryos can be regarded as a good example of recapitulation of phylogenesis in ontogenesis.

Animals↗
PubMed1997

On the development of Cetacean extremities: II. Morphogenesis and histogenesis of the flippers in the spotted dolphin (Stenella attenuata).

Externally, the flippers of Cetacea resemble fish fins, but their internal structure is entirely mammalian. They show, however, some adaptative deviations from the typical pattern of the mammalian extremities, the most striking of which is an increased number of phalanges. The aim of this study is to describe the course of the development of flippers in the spotted dolphin (Stenella attenuata) and compare its features with other similar species from an evolutionary perspective. Early stages of flipper development were studied histologically. Differentiation of cartilaginous anlagens of the skeleton progresses proximodistally, condensation in digital rays being evident sooner than chondrogenesis in the carpal region. In one specimen, the temporary presence of cartilaginous rudiments of two carpal elements, which are not found in adults, was observed. At all examined stages, phalangeal number progressively increases up to (radial to ulnar) 3, 7, 7, 5, 3 in the most advanced stage. The reason for this condition is the specialised function of these limb-like structures. It is a classical example of convergence, in which mammalian extremities change their form to emulate the fin function. A similar condition is found in another group of originally terrestrial animals secondarily fully adapted to the aquatic mode of life-Ichyosauria (Reptilia).

Adaptation, Physiological↗