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Biomedical subjects

J Nedvídek

Publications and source records attributed to J Nedvídek.

At least 19 recordsLinked to original sources
PubMed2003

[Use of the in vivo microdialysis technique in basic and clinical research].

Microdialysis is in vivo technique that permits monitoring of local concentrations of metabolites and drugs at specific sites in the body that makes it an attractive tool for the basic and clinical research. Microdialysis entered the experimental studies of the brain, and later also of the peripheral tissues such as adipose and muscle tissues, kidney, lung, eye, skin, and blood. There are several critical factors in the experimental implementations of microdialysis: the probe, the perfusion solution, tissue integrity, and the sensitivity of microdialysate analysis method. When the experimental conditions are optimised to give valid results, microdialysis can provide numerous data from the relatively small number of individual subjects. It can bring about detailed clinical information reflecting free metabolite and drug concentrations in studied tissues and/or in plasma. With the progress of analytical methods, applications and importance of the microdialysis technique in clinical and pharmacokinetic research and diagnostics will increase.

Humans↗
PubMed2001

The role of dopamine in methylene blue-mediated inhibition of estradiol benzoate-induced anterior pituitary hyperplasia in rats.

Recently, we demonstrated that methylene blue partially inhibited estradiol-benzoate-induced anterior pituitary hyperplasia in rats. Since central dopaminergic systems participate in the regulation of estrogen-induced anterior pituitary growth and tumor transformation, this study examined whether a 3-week treatment with methylene blue could affect anterior pituitary levels of dopamine (DA), dihydroxyphenylalanine (DOPA), and dihydroxyphenylacetic acid and dopamine (D-2) receptors in male rats. Compared to controls, methylene blue significantly decreased anterior pituitary weight, increased basal anterior pituitary DA levels, and inhibited estradiol benzoate-induced decreases in anterior pituitary DA concentrations. Furthermore, we found that methylene blue alone decreased anterior pituitary D-2 receptor number. Methylene blue given in combination with estradiol benzoate partially inhibited estradiol benzoate-induced anterior pituitary growth and estradiol benzoate-induced increases in D-2 receptor number. Estradiol benzoate-treated rats had significantly lower anterior pituitary DOPA accumulation after intraperitoneal administration of 3,4-hydroxybenzyl-hydrazine dihydrochloride (NSD-1015), an irreversible inhibitor of L-aromatic amino acid decarboxylase whereas methylene blue did not affect anterior pituitary DOPA accumulation when compared to controls. Methylene blue decreased anterior pituitary prolactin levels and inhibited increases in anterior pituitary prolactin after estradiol benzoate administration. The present results suggest that anterior pituitary DA may play an important role in estrogen-induced anterior pituitary hyperplasia and tumor formation and that antioxidant drugs such as methylene blue may attenuate estrogen-induced pituitary growth. This may occur via increases in anterior pituitary DA levels associated with down-regulation of anterior pituitary D-2 receptors.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2000

The regulation of adenohypophyseal prolactin secretion: effect of triiodothyronine and methylene blue on estrogenized rat adenohypophysis.

Estrogens and thyroid hormones contribute importantly to cell proliferation and tumor transformation in the pituitary gland. We found that methylene blue antagonized estrogen-promoted adenohypophyseal enlargement and the enhancement of prolactin secretion. The purpose of the present article is to provide a review about neurotransmitters and their receptors involved in estrogen-induced anterior pituitary growth and in the antagonistic effects of triiodothyronine (T3) and methylene blue (MB). Central dopaminergic and noradrenergic systems are the most important factors regulating pituitary growth and function. Recently nitric oxide (NO) was added to the list of the neurotransmitters and neuropeptides involved in the control of the anterior pituitary secretion. Our data suggest that estrogen-induced anterior pituitary growth is associated with decreased synthesis and metabolism of central catecholamines, reduction of adenohypophyseal beta-adrenergic receptors and increase of dopamine DA-2 receptors. We found that the treatment with T3 or MB prevented both estrogen-induced catecholaminergic inhibition and dopamine DA-2 receptor increment in the anterior pituitary. In contrast to T3, MB given alone also slightly decreased the anterior pituitary weight. Serum levels and anterior pituitary content of prolactin were increased after treatment with estradiol benzoate (EB), whereas T3 or MB partially attenuated prolactin hypersecretion after estrogen administration. This is in accord with the attenuation of EB-induced inhibition of dopaminergic system by T3 and MB. MB given in combination with EB also partially attenuated EB-promoted rise of adenohypohyseal NO synthase activity which plays an important role in the regulation of prolactin secretion. Further studies on central catecholaminergic systems, pituitary receptors, the nitrergic system and mechanisms of intracellular signal transduction are necessary for better understanding of pituitary tumor transformation and possibly for the discovery of new approaches towards treating patients with these diseases.

Adrenergic beta-Agonists↗
PubMed2000

Baroreflex control of heart rate in young and adult salt hypertensive inbred Dahl rats.

Baroreflex control of heart rate was studied in inbred salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) Dahl rats that were subjected to chronic dietary sodium chloride loading (for 4 weeks) either in youth or only in adulthood, i.e. from the age of 4 or 12 weeks. Using phenylephrine administration to pentobarbital-anesthetized male rats we have demonstrated the decreased baroreflex sensitivity (lower slope for reflex bradycardia) in young prehypertensive SS/Jr rats fed a low-salt diet as compared to age-matched SR/Jr animals. High salt intake further suppressed baroreflex sensitivity in young SS/Jr but not in SR/Jr rats. Baroreflex sensitivity decreased with age in SR/Jr rats, whereas it increased in SS/Jr rats fed a low-salt diet. Thus at the age of 16 weeks baroreflex sensitivity was much higher in SS/Jr than in SR/Jr animals. High salt intake lowered baroreflex sensitivity even in adult SS/Jr rats without affecting it in adult SR/Jr rats. Nevertheless, baroreflex sensitivity was significantly lower in young SS/Jr rats with a severe salt hypertension than in adult ones with a moderate blood pressure elevation. It is concluded that the alterations of baroreflex sensitivity in young inbred SS/Jr rats (including the response to high salt intake) are similar to those described earlier for outbred salt-sensitive Dahl rats. We have, however, disclosed contrasting age-dependent changes of baroreflex sensitivity in both inbred substrains of Dahl rats.

Age Factors↗
PubMed1996

Triiodothyronine attenuates estradiol-induced increases in dopamine D-2 receptor number in rat anterior pituitary.

Estrogens promote adenohypophyseal enlargement and tumor transformation, and thyroid hormones antagonize these effects. Hormone-induced pituitary enlargement may be mediated by alterations in pituitary dopaminergic function. The present study examined the effects of chronic (20 days) administration of estradiol benzoate (EB), triiodothyronine (T3), or EB and T3 (T3 + EB) on dopamine (D-2) receptors in rat anterior pituitary. D-2 receptor number increased after EB without altered receptor affinity. T3 alone did not affect D-2 receptor number in the anterior pituitary but significantly attenuated the effect of EB. T3 administration also inhibited EB-induced anterior pituitary hyperplasia. D-2 receptor upregulation by EB more likely could reflect a compensatory response to decreased receptor occupation. The present results suggest that D-2 receptors could play an important role in estrogen-induced adenohypophyseal tumor formation and hyperprolactinemia and that thyroid hormones may inhibit estrogen-induced pituitary tumor development via adenohypophyseal D-2 receptors.

Animals↗
PubMed1994

An analog of MIF, alaptide: effect on serum prolactin, dopamine receptors and growth of rat adenohypophysis.

Alaptide is a drug chemically derived from prolyl-leucyl-glycin amide (PLG) which is effective after oral administration. We studied the effect of long term treatment with alaptide and estradiol-benzoate on serum prolactin, growth reactivity and dopamine DA-2 receptors in the anterior pituitary of male rats. Alaptide reduced adenohypophyseal weight when given alone, but only nonsignificantly reduced growth reactivity of the anterior pituitary (AP) raised by estradiol-benzoate (EB). Alaptide significantly decreased the serum level of prolactin but, on the other hand, significantly increased the binding of 3H-spiperone to dopamine DA-2 receptors in AP membrane preparations, without affecting affinity. The administration of alaptide plus EB together resulted in an additional increase of dopamine DA-2 binding sites. We assume that alaptide has a weak dopaminergic activity on the AP of male rats.

Animals↗
PubMed1993

Adrenergic overactivity and insulin resistance in nonobese hereditary hypertriglyceridemic rats.

Nonobese, hereditary hypertriglyceridemic (HTG) rats provide an interesting model of hypertriglyceridemia, glucose intolerance, and hypertension. In age-matched 15 HTG and 16 control Wistar rats fed on a high sucrose diet (70 cal%) for 6 weeks, we measured insulin sensitivity in vivo and some parameters of sympatoadrenal system. Using euglycemic clamps with administration of 2-deoxy[1-3H]glucose, we found whole body insulin resistance and decreased glucose metabolic index Rg' in soleus muscle, epitrochlearis muscle, diaphragm, and white adipose tissue in HTG rats. We found higher levels of plasma epinephrine and higher excretion of vanilmandelic and homovanilic acids in HTG rats. The binding of [3H]-dihydroalprenol to the heart membrane fraction was similar in both groups, but the dissociation constant Kd was increased by 75% in the heart of HTG rats.

Adipose Tissue↗
PubMed1993

Age-dependent changes of baroreflex efficiency in Dahl rats: effects of high salt intake.

The age-dependent changes in baroreflex control of heart rate were studied in inbred Dahl rats. At the age of 8 weeks the baroreflex slope was significantly greater in salt-resistant (R/Jr) than in salt-sensitive (S/Jr) rats fed a low-salt diet. The reverse was true in 16-week-old animals. High salt intake (8% NaCl diet for 4 weeks) suppressed baroreflex efficiency in both age groups of S/Jr animals whereas no effects occurred in R/Jr rats. Baroreflex slope was, however, significantly lower in young S/Jr rats with a severe form of salt hypertension than in adult salt-loaded S/Jr rats in which only a moderate blood pressure elevation was observed.

Aging↗
PubMed1993

Age-dependent changes of baroreflex efficiency in Dahl rats: effects of high salt intake.

The age-dependent changes in baroreflex control of heart rate were studied in inbred Dahl rats. At the age of 8 weeks the baroreflex slope was significantly greater in salt-resistant (R/Jr) than in salt-sensitive (S/Jr) rats fed a low-salt diet. The reverse was true in 16-week-old animals. High salt intake (8% NaCl diet for 4 weeks) suppressed baroreflex efficiency in both age groups of S/Jr animals whereas no effects occurred in R/Jr rats. Baroreflex slope was, however, significantly lower in young S/Jr rats with a severe form of salt hypertension than in adult salt-loaded S/Jr rats in which only a moderate blood pressure elevation was observed.

Aging↗
PubMed1989

Vasopressin and water distribution in rats with DOCA-salt hypertension.

The role of vasopressin in the regulation of body water volume and its distribution to intravascular, interstitial and intracellular compartments, and the importance of particular body water compartments in the pathogenesis of DOCA-salt hypertension were studied in young Brattleboro rats. Vasopressin-deficient, vasopressin-synthesizing and vasopressin-deficient rats chronically supplemented with deamino-8-D-arginine vasopressin (dDAVP) were compared with water-drinking controls. The chronic DOCA-salt treatment caused a marked hypertension in vasopressin-synthesizing animals; in these animals body water was slightly increased due to the expansion of extra-cellular fluid volume whereas intracellular water tended to decrease, so that the ratio of extracellular fluid volume to intracellular water rose significantly. The development of DOCA-salt hypertension was attenuated in the vasopressin-deficient rats, which had a similar level of total body water, slightly increased intracellular water and significantly decreased extracellular fluid volume compared with the hypertensive vasopressin-synthesizing rats. Consequently, in the vasopressin-deficient rats, the ratio of extracellular fluid volume to intracellular water did not differ from that of controls. A vasopressin deficiency was associated with a failure to expand the interstitial fluid volume although plasma volume was increased. Unaltered total body water together with elevated plasma osmolality indicated an extracellular water deficiency in DOCA-salt-treated vasopressin-deficient rats. Chronic dDAVP supplementation restored the body fluid pattern and the hypertensive response of the DOCA-salt-treated vasopressin-deficient rats. In conclusion, the antidiuretic effects of vasopressin are necessary for the interstitial fluid volume expansion that is essential for a full development of DOCA-salt hypertension.

Animals↗
PubMed1985

[Use of colloidal gold in ultrastructural cytochemistry].

Colloid gold stabilized by macromolecules with various binding characteristics proved to be usable in transmission electron microscopy: Nucleic acids localization was studied in tissue cultures after embedding by techniques autoimmune serum-protein A--gold and RNase--gold. Technique with serum autoantibodies against double-stranded DNA resulted in marking condensed chromatin. Further experiments with ultrastructural localization of other autoimmune components seemed to be perspective and of diagnostic importance. Technique with RNase--gold complex marked especially ribosomes, nucleolus and interchromatin nuclear spaces. Herpes virus, rotavirus and enterovirus were identified in negative contrast by the technique antivirus serum--protein A--gold. A higher warrant of evidence achieved by the method may be used in virologic diagnosis. A small amount of tubulin was found in isolated permeabilized nuclei of Xenopus laevis by a direct immunocytochemical method with complex monoclonal IgG against tubulin-gold. Binding of complex of triiodothyronine-bovine serum albumin--gold on the cytoplasmic membrane of LEP cells in a short term tissue culture showed a possibility of tracing non-peptidic hormones binding on specific receptors.

Animals↗
PubMed1985

Dynamics of tubulin structures in Xenopus laevis oogenesis.

The distribution of tubulin and/or tubulin-containing structures was examined in separate classes of Xenopus laevis oocytes and in germinal vesicles isolated from them. Although a monoclonal antibody has been used, the technique applied on paraffin sections does not allow clear-cut definition of the state of tubulin present (monomeric, dimeric or polymerized form); however, the probable existence of assembled microtubules is indicated by supplementary techniques, i.e. histology and immunoperoxidase staining. Immunofluorescence reveals maximum tubulin concentration in the Balbiani body and in a ring-shaped formation around the nucleus in young oocytes. The Balbiani body disintegrates in the course of vitellogenesis, granules formed from its periphery migrate into the cytoplasm and gradually fill the entire cytoplasm as radial cords. In the ring-shaped formation around the nucleus strongly fluorescent cords and fibres are formed, particularly on the future vegetal-half-facing part of the nucleus. Reorganization of tubulin may be related to the establishment of a structure directing two-way shifts (1) of cytoplasmic organelles from the Balbiani body to the cytoplasm, and (2) of yolk proteins containing endosomes derived from the endocytically active oolemma to the yolk platelets. A distinct fluorescent fibrillar network is found inside the isolated germinal vesicles, near the nucleus membrane. Peripheral nucleoli, often present in nuclear membrane protuberances, seem to be surrounded by this material, which is oriented along the surface, and as a basket towards the inside of the nucleus. It is assumed that the structures may participate in the transport of nucleoli from the nucleus to the cytoplasm via the nuclear envelope.

Animals↗