Fetal Cardiac Muscle Research Articles

Enhanced myocardial adenylate cyclase activity in spontaneously hypertensive rats.

This study was designed to clarify the state of beta-adrenergic signal transduction and the disordered level of its transduction in hypertensive hearts, using myocardium from spontaneously hypertensive rats (SHR) as a generic model of essential hypertension. Beta-adrenergic receptor binding sites and dissociation constants in the extracted membranes of adult (70-100 days of age) SHR heart were not significantly different from those of Wistar-Kyoto (WKY) rats, the non-hypertensive control. The adenylate cyclase activities stimulated by isoproterenol with GTP, NaF and forskolin were significantly higher in SHR compared to those in WKY. To determine whether differences in signal transduction are natural or are a result of hypertension, we evaluated chronotropic responses in cultured cells of fetal hearts which had not been exposed to hypertension. Fetal cardiac muscle cells of SHR were more sensitive than WKY to isoproterenol stimulation over a wide concentration range. However, there were no statistically significant differences between these two strains with respect to the density of binding sites. These results suggest that in the transduction of adrenergic signals, alterations distal to the beta-receptors are present in the adult hearts of hypertensive rats, and, that the adrenergic signal transduction is already exaggerated in the pre-hypertensive fetal stage.

Duchenne and Becker Muscular Dystrophies: Genetics, Prenatal Diagnosis, and Future Prospects

DMD and BMD are now understood at the genetic, biochemical, and molecular levels. At the genetic level, both disorders result from mutations of the X-linked gene encoding dystrophin. At the biochemical level, DMD results from the deficiency of a large protein called dystrophin, whereas BMD results when dystrophin is present, though abnormal in either amount or molecular structure. To date, thousands of patients have been analyzed for mutations of the dystrophin gene in peripheral blood DNA or alterations of the dystrophin protein in muscle tissue. The severity of the clinical phenotype of these patients has been compared with their dystrophin gene mutations and corresponding dystrophin protein alterations, revealing an unexpectedly high degree of correlation. Thus, information derived from the molecular analysis (DNA or protein) of a particular patient provides a "molecular diagnosis," which is highly predictive of the clinical course that patient can be expected to follow. Because molecular diagnoses are independent of the patient's age, they provide a prognosis for the large majority of muscular dystrophy patients even before clinical symptoms of their disease become apparent. Such prognostic molecular diagnoses have proven particularly valuable when the patient is an isolated case, with no family history for the disorder. Prenatal genetic diagnosis of DMD or BMD may involve use of Southern blot or PCR techniques to search for a deletion in the DNA of at-risk fetuses or more complicated family linkage studies using intragenic and flanking RFLPs. More recently, assay of dystrophin content in fetal skeletal or cardiac muscle from at-risk abortuses has been accomplished, allowing definitive discrimination of affected and normal fetuses in cases in which deletion analyses and family DNA studies were equivocal. In utero fetal skeletal muscle biopsy for dystrophin protein assay has actually been accomplished in at least one at-risk pregnancy in which family DNA studies were uninformative. Dystrophin was present in skeletal muscle from this 20-week-old male fetus, and the pregnancy continued, resulting in the term birth of a healthy male infant. The future holds exciting opportunities for neonatal screening and treatment of these devastating neuromuscular diseases.

Isolation of fetal mouse motor neurons on discontinuous percoll density gradients

The spinal cords of fetal NIH:CR mice, gestational age Day 12 to 14, were dissected free of meninges and dorsal root ganglia, chemically dissociated, and layered onto discontinuous Percoll gradients at densities 1.040, 1.050, and 1.060 g/ml. After centrifugation (800 Xg for 15 min at 4 degrees C), three morphologically, biochemically, and immunohistologically distinct cell populations were collected from the gradient interfaces. The first interface, located at a density of 1.040 g/ml, was choline acetyltransferase enriched (0.86 +/- 0.08) compared to the second and third fractions (0.42 +/- 0.01 and 0 pmol acetylcholine synthesized/microgram protein, respectively). When simultaneously cultured with fetal mouse cardiac muscle on a gelatin-polylysine-laminin substrate in serum-free medium, these cells developed the characteristics of motor neurons.

Molecular genetic characterization of a developmentally regulated human perinatal myosin heavy chain.

We have isolated a human cDNA which corresponds to a developmentally regulated sarcomeric myosin heavy chain. RNA hybridization and DNA sequence analysis indicate that this cDNA, called SMHCP, encodes a perinatal myosin heavy chain isoform. The nucleotide and deduced amino acid sequences of the 3.4-kb cDNA insert show strong homology with other sarcomeric myosin heavy chains. The strongest homology is to a previously described 970-bp cDNA encoding a rat perinatal isoform (Periasamy, M., D. F. Wieczorek, and B. Nadal-Ginard. 1984. J. Biol. Chem. 259:13573-13578). The homology between the analogous human and rat perinatal myosin heavy chain cDNAs is maintained through the highly isoform-specific final 20 carboxyl-terminal amino acids, as well as the 3' untranslated region. Ribonuclease protection studies show that the mRNA encoding this isoform is expressed at high levels in 21-wk fetal skeletal tissue and not in fetal cardiac muscle. In contrast to the rat perinatal isoform, which was not found to be expressed in adult hind-leg tissue, the gene encoding SMHCP continues to be expressed in adult human skeletal tissue, but at lower levels relative to fetal skeletal tissue.

Cloning and characterization of a cDNA encoding transformation-sensitive tropomyosin isoform 3 from tumorigenic human fibroblasts.

We isolated a cDNA clone from the tumorigenic human fibroblast cell line HuT-14 that contains the entire protein coding region of tropomyosin isoform 3 (Tm3) and 781 base pairs of 5'- and 3'-untranslated sequences. Tm3, despite its apparent smaller molecular weight than Tm1 in two-dimensional gels, has the same peptide length as Tm1 (284 amino acids) and shares 83% homology with Tm1. Tm3 cDNA hybridized to an abundant mRNA of 1.3 kilobases in fetal muscle and cardiac muscle, suggesting that Tm3 is related to an alpha fast-tropomyosin. The first 188 amino acids of Tm3 are identical to those of rat or rabbit skeletal muscle alpha-tropomyosin, and the last 71 amino acids differ from those of rat smooth muscle alpha-tropomyosin by only 1 residue. Tm3 therefore appears to be encoded by the same gene that encodes the fast skeletal muscle alpha-tropomyosin and the smooth muscle alpha-tropomyosin via an alternative RNA-splicing mechanism. In contrast to Tm4 and Tm5, Tm3 has a small gene family, with, at best, only one pseudogene.

Cloning and characterization of a cDNA encoding transformation-sensitive tropomyosin isoform 3 from tumorigenic human fibroblasts.

We isolated a cDNA clone from the tumorigenic human fibroblast cell line HuT-14 that contains the entire protein coding region of tropomyosin isoform 3 (Tm3) and 781 base pairs of 5'- and 3'-untranslated sequences. Tm3, despite its apparent smaller molecular weight than Tm1 in two-dimensional gels, has the same peptide length as Tm1 (284 amino acids) and shares 83% homology with Tm1. Tm3 cDNA hybridized to an abundant mRNA of 1.3 kilobases in fetal muscle and cardiac muscle, suggesting that Tm3 is related to an alpha fast-tropomyosin. The first 188 amino acids of Tm3 are identical to those of rat or rabbit skeletal muscle alpha-tropomyosin, and the last 71 amino acids differ from those of rat smooth muscle alpha-tropomyosin by only 1 residue. Tm3 therefore appears to be encoded by the same gene that encodes the fast skeletal muscle alpha-tropomyosin and the smooth muscle alpha-tropomyosin via an alternative RNA-splicing mechanism. In contrast to Tm4 and Tm5, Tm3 has a small gene family, with, at best, only one pseudogene.

Effect of maternal fasting on ovine fetal and maternal branched-chain amino acid transaminase activities.

Activities of branched-chain amino acid transaminase were assayed in maternal skeletal muscle, liver and fetal skeletal muscle, cardiac muscle, liver, kidney and placenta obtained from fed and 5-day-fasted late gestation ewes. Very high activities were found in placenta; fetal skeletal muscle also had high activity. Fetal brain had intermediate activity, followed by cardiac muscle and kidney. Fetal liver possessed negligible activity. Activities were low in both maternal liver and skeletal muscle. Trends were seen for fasting to increase activities in fetal placenta, skeletal muscle, brain, kidney, heart and maternal liver, but these changes were statistically significant only for fetal brain and placental tissue. Fetal skeletal muscle activity was 100 times that of maternal skeletal muscle. These data imply differences in the metabolism of the branched-chain amino acids by fetal and adult ruminants and expand the thesis that branched-chain amino acids are important to the metabolism of the ovine fetus.

Myosin from fetal hearts contains the skeletal muscle embryonic light chain.

The contractile proteins of adult skeletal and cardiac muscle tissue are very similar. Some of these proteins are identical in amino acid sequence or differ only slightly. Various structural studies have shown that the heavy and light chains of myosin are also homologous in skeletal and cardiac muscles. In developing skeletal muscles, certain myosin subunits are present which are not found in the corresponding adult muscle. Whether fetal cardiac muscle also contains myosin subunits homologous to these early forms is not known. We now report that ventricular myosin of fetal rats has a light chain polypeptide corresponding to the skeletal muscle embryonic light chain. This result provides further evidence that a form of myosin light chain, not detectable in adult skeletal or ventricular myosin, is characteristic of the early stages of striated muscle development.

Cardiac parameters of the newborn after tocolysis (author's transl)

Since 1971 premature labor has been treated with Fenoterol and Verapamil in the Department of Obstetrics and Gynecology of the University in Mannheim. In animal experiments as well as in the isolated fetal cardiac muscle elective myocardial necroses were observed following stimulation with beta-sympathomimetics. These lesions are prevented by additional application of Ca++-antagonists. Fenoterol and Verapamil are capable of passing through the placenta. To evaluate the question whether a possible cardiac lesion of the infant is caused by tocolysis, 31 newborns of mothers after tocolysis were compared to a group of 19 infants without tocolysis. At the first day of life as well as at the age of 2 and 4 weeks ECG was registered, and the serum electrolytes K+, Ca++ and Mg++ were determined. At day 1 and day 4 as well as during the 2nd and 5th week CK and CK-MB were measured, and during the 2nd week the size of heart was registered. We were unable to demonstrate pathological cardiac findings in newborns following tocolysis which were related to the preceding medication.

The passage of thiamine across the rat placenta and its uptake by the fetal organs. II. The uptake of thiamine by fetal organs.

Having injected 3H-thiamine into the maternal bloodstream of rats in their 15th day of pregnancy, the uptake by the fetal organs (liver and cardiac muscle) of the 3H-thiamine which had been transported across the placenta was studied by electron microscope autoradiography and by measuring the radio-activity of the tissues, using the same methods reported in the first paper of this series. In the fetal liver both developed silver grains and radioactivity were found in greates amounts in specimens collected 5 hrs after injection. Developed silver grains were abundant in the mitochrondria, Golgi apparatus, rough-surfaced endoplasmic reticulum, glycogen area, and nucleus, indicating that these cell organelles take up thiamine and utilize it for the cell metabolism. In the fetal cardiac muscle, the developed silver grains and radioactivity were found in greatest amounts 2 hrs after injection. The silver grains were abundant in the glycogen area, Golgi apparatus, and myofibrils, but they were especially abundant in the mitochondria. This indicates that thiamine is taken up by these organelles and employed in the cell metabolism.

A Comparison of the Active Stiffness of Fetal and Adult Cardiac Muscle

A Comparison of the Active Stiffness of Fetal and Adult Cardiac Muscle

Comparison of the responses of fetal and adult cardiac muscle to hypoxia.

Comparison of the responses of fetal and adult cardiac muscle to hypoxia.

The Actions of Cardioactive Drugs on Developing Myocardium

Clinicians have long recognized age related differences in cardiac pharmacology. These phenomena may reflect altered drug metabolism or disposition in the immature organism and/or an altered sensitivity of fetal and neonatal myocardium per se. The latter possibility was examined by studying the responsiveness to cardioactive drugs of heart muscle isolated from a total of 100 fetal, newborn, and adult sheep and swine. The enhancement of cardiac contractility produced by digitalis was significantly greater in newborn than adult heart. However, newborn myocardium required significantly more digitalis to achieve a peal inotropic effect or to demonstrate evidence of toxicity when compared to the adult. Fetal and adult cardiac muscle was equally responsive to isoproterenol, and acetylcholine. Fetal heart was supersensitive to the positive inotropic effects of norepinephrine. At all ages acidosis attenuated the augmentation of contractility produced by norepinephrine. Propranolol exerted a morc profound negative inotropic action on fetal than adult heart, although the effectiveness of beta adrenergic receptor blockade by propranolol was equal in fetal and adult myocardium. Glucagon exerted a negative inotropic effect on fetal cardiac muscle, a small positive inotropic effect in newborns, and a marked augmentation of contractility in the adult. Thus, a marked agedependency of the myocardial resonses to many cardioactive drugs exists that must be considered in any clinical evaluation of cardiac pharmacology in the perinatal period.