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F Chytil

Publications and source records attributed to F Chytil.

At least 55 records · Page 3Linked to original sources
PubMed1988

Presence of novel retinoic acid-binding proteins in the lumen of rat epididymis.

The lumen of the rat epididymis was found to contain two binding activities for retinoic acid. The two proteins could be separated by chromatography on DEAE-cellulose but were essentially identical in binding specificity and molecular weight, as determined by gel filtration. The proteins were clearly distinct from cellular retinoic acid-binding protein and other known retinoid-binding proteins. The binding of various retinoids was examined by sucrose gradient centrifugation assay. The proteins were more discriminating than has been observed for cellular retinoic acid-binding protein. Of the retinoids examined, only 13-cis-retinoic acid showed appreciable ability to compete for binding of all-trans-retinoic acid. Retinol and retinal showed no ability to compete; various ring analogs of retinoic acid had little or no ability to compete. The presence of such binding activities in the lumen of the epididymis could mean that retinoic acid plays a role in sperm maturation and function, if retinoic acid proves to be the endogenous ligand.

Animals↗
PubMed1988

Effect of retinol on fetal lamb tracheal epithelium, with and without epidermal growth factor. A model for the effect of retinol on the healing lung of human premature infants.

Twelve pairs of fetal lambs were used to test the hypothesis that the necrotizing tracheobronchitis followed by squamous metaplasia seen in premature infants who develop chronic bronchopulmonary dysplasia might be related to low retinol stores and might, therefore, be reversed by retinol supplementation. Epidermal growth factor (EGF) was used to model the growth factor stimulus initiated by chronic wounding of the airways, and retinol was used as a differentiator of proliferating cells stimulated by EGF. Saline-treated animals were used as controls, as were fetal lambs receiving retinol alone or EGF alone. The effects of EGF on tracheal and bronchial epithelium consisted of proliferation of basal and intermediate cells, necrosis and slough of lining ciliated and mucous-producing cells, followed by squamous metaplasia. In fetal lambs given retinol, plasma, liver and lung retinol levels rose and mucous producing cells were increased in number. In the presence of EGF plus retinol, differentiation of mucous-producing cells was accelerated. We believe that this fetal lamb model with low initial levels of retinol in plasma, liver and lung, treated with EGF may mimic human premature infants with chronic bronchopulmonary dysplasia, and that the addition of retinol in amounts sufficient to raise their tissue levels produces a more normal surface epithelium in conducting airways.

Analysis of Variance↗
PubMed1987

Specificity of cellular retinol-binding protein in the transfer of retinol to nuclei and chromatin.

We have reported previously that cellular retinol-binding protein (CRBP) is able to transfer retinol to specific binding sites in nuclei and chromatin. In this report, we have examined the specificity of the interaction of the protein moiety of retinol-CRBP (R-CRBP) with chromatin and nuclei in the transfer process. We first determined the ability of apo-CRBP, apo-serum retinol-binding protein (RBP), and apo beta-lactoglobulin (BLG), all capable of retinol binding, to compete with R-CRBP in the transfer of retinol to chromatin and nuclei. Apo-CRBP was an effective competitor but apo-RBP and apo-BLG showed no competitive ability. On the other hand, cellular retinol-binding protein type II (CRBP(II], whose amino acid sequence shows a considerable similarity to CRBP, did compete for the transfer of retinol from the R-CRBP complex, but less effectively than CRBP. These results demonstrate that the interaction of the protein moiety of the R-CRBP complex with nuclei and chromatin is quite specific.

Animals↗
PubMed1987

Clinical trial of vitamin A supplementation in infants susceptible to bronchopulmonary dysplasia.

We conducted a randomized, double-blind, controlled trial to determine whether vitamin A supplementation from early postnatal life could reduce the morbidity associated with bronchopulmonary dysplasia in very low birth weight (VLBW) neonates. Forty VLBW neonates (700 to 1300 g birth weight, 26 to 30 weeks gestational age), who were oxygen dependent and required mechanical ventilation for at least 72 hours after birth, were given by the intramuscular route either supplemental vitamin A (retinyl palmitate 2000 IU) or 0.9% saline solution on postnatal day 4 and every other day thereafter for a total of 14 injections over 28 days. The study groups were comparable in gestational maturity, clinical characteristics, initial lung disease, and vitamin A status at entry into the trial. Vitamin A administration resulted in significantly higher mean plasma concentrations of vitamin A and retinol-binding protein in treated infants compared with controls. Bronchopulmonary dysplasia was diagnosed in nine of 20 infants given vitamin A supplement and in 17 of 20 control infants (P less than 0.008). Four of 19 infants in the vitamin A group and 11 of 20 in the control group required mechanical ventilation on study day 28 (P less than 0.029). The need for supplemental oxygen, mechanical ventilation, and intensive care was reduced in infants given vitamin A supplement compared with controls. Airway infection and retinopathy of prematurity were less frequent in the vitamin A group. We conclude that vitamin A supplementation at the dosage used in this trial in VLBW neonates not only improves their vitamin A status but also appears to promote regenerative healing from lung injury, as evidenced by a decrease in the morbidity associated with bronchopulmonary dysplasia.

Bronchopulmonary Dysplasia↗
PubMed1987

Rat cellular retinol-binding protein: cDNA sequence and rapid retinol-dependent accumulation of mRNA.

Cellular retinol-binding protein (CRBP) may be an important mediator of vitamin A action. We report here the identification of a cDNA clone corresponding to the rat CRBP gene. The cDNA is 695 nucleotides long, with an open reading frame corresponding to a protein of 134 amino acids. The deduced amino acid sequence is identical with that of rat CRBP. The nucleotide sequence shows 90.5% similarity with the human CRBP cDNA sequence. Genomic DNA analysis indicates that CRBP is present in one, or at most two, copies within the rat genome. Analysis of mRNA reveals a single species in every tissue tested and suggests that the isolated cDNA is full-length. Finally, when retinol-deficient rats are fed retinyl acetate for 4 hr, about 4-fold accumulation of CRBP-specific mRNA is observed in the lungs. This rapid effect suggests that the micronutrient retinol may directly influence the expression of its specific intracellular binding protein.

Amino Acid Sequence↗
PubMed1987

Cellular vitamin A-binding proteins in the testis.

Vitamin A plays an important role in the testis, being essential for the maintenance of spermatogenesis. Studies on CRBP and CRABP suggest that both retinol and retinoic acid are involved in maintaining testicular function. The cellular location of the two proteins suggests that retinoic acid may be particularly involved in the later stages of germ cell differentiation, but retinol may be the form of vitamin A that the Sertoli cell receives initially. The requirement for vitamin A may be to regulate gene expression in the testis by direct interaction with the chromosomal material. Specific distinct binding sites for retinol and retinoic acid can be demonstrated in testicular nuclei and chromatin. These sites are only revealed when the two ligands are present in complex with their specific binding proteins, suggesting that these proteins may be required for the action of retinol and retinoic acid in some cells of the testis.

Animals↗
PubMed1987

How do retinoids work?

The main physiological function of natural retinoids, i.e. the dietary micronutrient retinol and its metabolite retinoic acid, is in proper differentiation and maintenance of differentiated state of many if not all epithelia. Also, it appears that the metabolism of nonepithelial cells can be affected by these compounds. The effects are diverse. Although the exact molecular mechanism causing these effects remain to be elucidated, recent research indicates that both retinol and retinoic acid affect genomic expression by activating and simultaneously repressing specific genes. Such action results in the appearance and disappearance of more than 40 specific proteins. The effect on the genomic expression is time-dependent. Some of the genes are influenced very soon in a matter of a few hours. Effects on other genes require considerable time. Whether natural retinoids interact with the genome directly remains to be shown. How such interactions could occur is discussed.

Carrier Proteins↗
PubMed1986

Transfer of retinoic acid from its complex with cellular retinoic acid-binding protein to the nucleus.

Cellular retinoic acid-binding protein (CRABP), a potential mediator of retinoic acid action, enables retinoic acid to bind in a specific manner to nuclei and chromatin isolated from testes of control and vitamin A-deficient rats. The binding of retinoic acid was followed after complexing [3H]retinoic acid with CRABP purified from rat testes. The binding was specific, saturable, and temperature dependent. If CRABP charged with nonlabeled retinoic acid was included in the incubation, binding of radioactivity was diminished, whereas inclusion of free retinoic acid, or the complex of retinol with cellular retinol binding protein (CRBP) or serum retinol binding protein had no effect. Approximately 4.0 X 10(4) specific binding sites for retinoic acid were detected per nucleus from deficient animals. The number of binding sites observed was influenced by vitamin A status. Refeeding vitamin A-deficient rats (4 h) with retinoic acid lowered the amount of detectable binding sites in the nucleus. CRABP itself did not remain bound to these sites, indicating a transfer of retinoic acid from its complex with CRABP to the nuclear sites. Further, CRBP, the putative mediator of retinol action, was found to enable retinol to be bound to testicular nuclei, in an interaction similar to the binding of retinol to liver nuclei described previously.

Animals↗
PubMed1986

Retinoic acid: biochemistry and metabolism.

Retinoic acid, unlike the naturally occurring vitamin A (retinol), is a minor component of the human diet. It is formed in vivo from retinol and has many metabolites. The biological activity of the metabolites is not higher than that of retinoic acid itself, indicating that the metabolites must be products of retinoic acid catabolism. Little is known about the enzymatic systems responsible for forming retinoic acid or about how it enters the cell. Discovering the molecular mechanism(s) of retinoic acid activity in cellular metabolism is important to understanding its physiologic role. The pharmacologic effects of high doses of retinoic acid may be caused by its action on cellular membranes. Conversely, low concentrations appear to produce physiologic effects. Results of experiments with animals and with cell cultures indicate that the primary physiologic role of retinoic acid is in cellular differentiation. Retinoic acid influences genomic expression, inducing the appearance of some proteins while suppressing the expression of others. The existence of an intracellular retinoic acid-binding protein suggests that it may mediate the physiologic effects of retinoic acid on cellular differentiation.

Animals↗
PubMed1986

Vitamin A status affects chromatin structure.

We have examined RNA synthesis by nuclei isolated from testes of rats of varying vitamin A status. Nuclei from retinol-deficient animals showed substantially decreased RNA synthesis by polymerase II when compared to nuclei from normal animals. Within 4 hours after oral administration of retinyl acetate (as the source of retinol) to deficient animals, RNA synthesis by polymerase II had significantly increased. Administration of retinoic acid had a similar but lesser effect. Nucleoside analysis after alkaline hydrolysis of the RNA synthesized by the endogenous polymerase II suggested that the increased activity was due to a greater number of actively transcribing polymerase II molecules on the DNA. Further, when the template capacity of testicular chromatin isolated from deficient and retinyl acetate refed animals was compared, the number of sites recognized by E. coli RNA polymerase was increased twofold after retinyl acetate administration. We conclude that these retinol-induced changes in transcription are due at least in part to changes in chromatin structure.

Animals↗
PubMed1985

Partial characterization of nuclear binding sites for retinol delivered by cellular retinol binding protein.

Retinol (vitamin A alcohol), which plays an important role in the differentiation of epithelia, can be transferred to chromatin in vitro. Rat liver chromatin can accept retinol in a specific and saturable manner only when the retinol is presented as a complex with cellular retinol-binding protein (CRBP). A partial characterization of the nuclear components responsible for accepting retinol is reported here. A preparation of solubilized chromatin isolated from liver nuclei was able to accept retinol from its complex with CRBP as described previously for nuclei and chromatin. The binding of retinol to chromatin was noncovalent. However, chromatin prepared from nuclei which were incubated with DNase I or micrococcal nuclease did not accept retinol specifically. Chromatin in the form of mono and dinucleosomes also did not accept retinol. However, treatment of nuclei with RNase did not affect the specific binding of retinol. Furthermore, it has been found that retinol was not transferred to purified double or single stranded DNA. These results are interpreted to indicate that the transfer of retinol to specific nuclear binding sites requires a higher order of chromatin structure than that occurring in nucleosome preparations.

Animals↗
PubMed1985

Vitamin A status of neonates with bronchopulmonary dysplasia.

We prospectively assessed and compared the vitamin A status of two groups of preterm neonates (less than 1500 g birth weight, less than 32 wk gestation), one who developed clinical and radiographic evidence of bronchopulmonary dysplasia (BPD) (n = 10), and the other (control) who developed no significant lung disease (n = 8). The infants with BPD in this study required prolonged mechanical ventilation and supplemental O2 therapy, and had a higher incidence of cardiorespiratory complications when compared to controls. Their mean plasma vitamin A concentrations were significantly lower than those of controls at four sampling times in the 1st postnatal month. In contrast to the controls, infants with BPD showed a substantial decline in their plasma vitamin A concentrations from the initial values, and a high percentage of individual values of plasma vitamin A concentration in these infants were less than 10 micrograms/dl during the 8-wk postnatal period of observation. Delayed establishment of gastrointestinal feeding and a lower vitamin A intake in these infants relative to controls may have accounted for this decline. Our data show that preterm neonates who develop BPD have suboptimal plasma vitamin A concentrations for extended periods of time postnatally. We speculate that the necrotizing bronchiolitis and squamous metaplasia of conducting airways associated with vitamin A deficiency could influence the orderly repair of lung injury in susceptible neonates who are mechanically ventilated and could contribute to the pathophysiology of BPD in these infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchopulmonary Dysplasia↗
PubMed1985

Liver vitamin A reserves of very low birth weight neonates.

This study assessed the liver vitamin A concentrations at birth in a group of very low birth weight neonates (n = 25) (less than 1500 g birth weight, less than 32 wk gestation), dying within 24 h of birth, prior to possible changes in vitamin A status induced by postnatal intervention. Serum concentrations of vitamin A and retinol-binding protein were also measured in 16 of these neonates. The mean (+/- SD) liver vitamin A concentration was 30.0 +/- 12.9 micrograms/g (range 2.0-49.0 micrograms/g). The mean (+/- SD) serum vitamin A concentration was 13.0 +/- 4.7 micrograms/dl (range 6.7-22.8 micrograms/dl). The mean (+/- SD) serum retinol-binding protein concentration was 2.2 +/- 0.8 mg/dl (range 1.5-4.8 mg/dl). Liver vitamin A, serum vitamin A, and serum retinol-binding protein concentrations did not correlate significantly with gestational age or birth weight. Linear regression analysis did not show a significant correlation between liver vitamin A, and serum vitamin A or retinol-binding protein concentrations. This study provides reference values for vitamin A concentrations at birth in very low birth weight neonates, which may be helpful in future studies designed to evaluate postnatal changes in the vitamin A status of these high-risk neonates.

Female↗
PubMed1985

Function of vitamin A in the respiratory tract.

Solid old and more recent evidence reviewed here suggests strongly that vitamin A (retinol) functions as a necessary factor for the initiation and maintenance of proper differentiation of tracheal and bronchopulmonary epithelium. Recent examinations of the vitamin A status of children born prematurely may help to design an improved nutritional management of these patients.

Bronchi↗
PubMed1984

Perinatal rat lung retinol (vitamin A) and retinyl palmitate.

The potential role for retinol (vitamin A alcohol) in the differentiation of the developing lung prompted this study in the perinatal rat. High performance liquid chromatography was used to separate, detect, and quantitate retinol and retinyl palmitate in lipid extracts of tissue and serum. Fetal and maternal blood showed the presence of retinol, whereas no retinyl palmitate was detected. On the other hand, fetal and postnatal lungs contained retinyl palmitate as well as retinol. Considerable changes in the content of lung retinyl palmitate were found during lung development. Fetal lungs (17-21 days of gestation) contained 2.3 +/- 0.36 micrograms/g wet weight (mean +/- SD) of retinyl palmitate and 0.14 +/- 0.05 micrograms/g of retinol. Lungs of pups (1-10 days old) contained much less retinyl palmitate, 0.63 +/- 0.20 micrograms/g, whereas the amount of retinol was the same as in fetal lungs. The surprisingly high content of retinyl palmitate in fetal lung and its depletion after birth may be functionally related to retinol action in the developing lung.

Animals↗