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Biomedical subjects

R Dabrowski

Publications and source records attributed to R Dabrowski.

At least 19 recordsLinked to original sources
PubMed2005

Dielectric spectroscopy of a binary mixture of liquid crystals showing wide temperature range twisted grain boundary phase with re-entrant cholesteric phase.

There are only few materials, which have shown long temperature range twisted grain boundary (TGB) phases. One such material is the chiral binary mixture of 7OCB and 5* CBB (mole ratio 0.8 and 0.2) which shows unique phase sequence of cholesteric ( N*) , a wide temperature range TGBA (approximately 31 degrees C) and reentrant cholesteric (N*re) phases. In the present work we are reporting the dielectric spectroscopy of the above mixture with a chiral analog of earlier reported nematic (N) , smectic- A (SmA) , and reentrant nematic (Nre) phase sequences [Phys. Rev. A 46, 7733 (1992)] for different conditions of molecular orientations. Two modes of dielectric relaxations have been detected in a homeotropically aligned sample with unusually low relaxation frequencies for one of them. Planar oriented molecules in the TGBA phase show a soft mode of relaxation and support the recently proposed theory for the soft mode relaxation of the TGBA phase [Phys. Rev. E 65, 11701 (2001)]. By applying the dc electric field on planar oriented molecules in the TGBA phase, it has been possible to obtain a helix free homeotropically aligned TGBA phase.

Journal Article↗
PubMed2004

Working women are better responders to beta-blocker monotherapy of mild hypertension than men.

The aim of this single-blind study was to compare the efficacy of betaxolol treatment (20 mg/day) on 24-h blood pressure profiles in working men and women with mild hypertension (grade 1 acc. ESH/ESC/JNC 2003), A group of 11 men and 11 women with a mean age 47+/-5 years underwent 24-h blood pressure monitoring after 8 days of placebo and after 20 days of treatment. A significant reduction (p < 0.05) in blood pressure was found for 11 h in men and 15 h in women (systolic) and 9 h in men and 13 h in women (diastolic). There was a tendency for a greater mean reduction in women (9.6/8.0 mmHg in men versus 12.9/7.4 mmHg in women). Diastolic blood pressure variability was significantly reduced in women (9.9 versus 13.1, respectively, p < 0.002) with a tendency for systolic blood pressure variability reduction (13.0 versus 15.1). The smoothness index for systolic blood pressure was higher in women (1.0/0.74 versus 0.64/0.61). A better response for betaxolol treatment 20 mg/day was observed in women in terms of target organ damage: a longer period of significant blood pressure reduction, lower variability and a tendency toward a greater reduction.

Adrenergic beta-Antagonists↗
PubMed2003

Complex dielectric relaxation in supercooling and superpressing liquid-crystalline chiral isopentylcyanobiphenyl.

Results of broadband dielectric studies in glass-forming liquid crystalline chiral isopentylcyanobiphenyl (5(*)CB) are presented. Tests conducted as a function of temperature and pressure revealed the coexistence of glassy and critical properties. The latter are associated with the isotropic-cholesteric phase transition at T(I-Ch) approximately 250 K under atmospheric pressure. Dielectric loss curves in the isotropic liquid and in the cholesteric phase are clearly broadened on cooling and pressuring towards the glass transition. Although in the isotropic phase there is a single stretched loss curve, in the mesophase an additional relaxation process can be distinguished. The evolution of relaxation times is non-Arrhenius and can be portrayed by the Vogel-Fulcher-Tamman relation or its pressure counterpart. The glassy dynamics coexists with the critical-like behavior for the static dielectric permittivity and for the maxima of the dielectric loss curves. Their temperature and pressure dependences are associated with the critical exponent phi=1-alpha approximately 1/2, where alpha approximately 1/2 is the specific heat critical exponent. This behavior is associated with the continuous phase transition placed at DeltaT approximately 1.5 K below the clearing temperature for P=0.1 MPa. It has been found that 5(*)CB shows a unique pressure-temperature phase diagram. Pressure and temperature changes which begin in the isotropic liquid below at ca. T approximately 265 K always result in the transition to the cholesteric phase which can be supercooled or superpressed. For T>265 K the phase transition to another phase, presumably a solid one, always occurs. However, a cholesteric-solid phase border seems to exist only in isothermal pressure tests. It does not appear in the temperature studies.

Journal Article↗
PubMed2003

Galanin affects vasopressin and oxytocin release from the hypothalamo-neurohypophysial system in haemorrahaged rats.

The effect of centrally administered galanin (Gal; 100 pM i.c.v.) on the hypothalamo-neurohypophysial storage as well as blood plasma level of vasopressin and oxytocin was estimated in haemorrhaged (1 ml per 100 g b.w.) male Wistar rats. Gal i.c.v. treatment did not alter vasopressin and oxytocin content both in the hypothalamus and neurohypophysis as well as their concentration in blood plasma of not haemorrhaged rats. Haemorrhage decreased the hypothalamic and neurohypophysial vasopressin and oxytocin storage but increased the neurohormones plasma level in animals injected with vehicle solution. During the haemorrhage, the increase in plasma vasopressin and oxytocin was inhibited in rats previously treated i.c.v. with galanin. The hypothalamic and neurohypophysial vasopressin as well as oxytocin content significantly increased in animals treated with galanin and subsequently haemorrhaged. These results suggest that galanin may have a regulatory role in the hypothalamo-neurohypophysial function especially under condition of hypovolemia.

Animals↗
PubMed2002

Enantiomeric excess dependence of the phase diagram of antiferroelectric liquid crystals.

The phase diagram of the prototype antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl-4'-octyloxybiphengl-4-carboxylate (MHPOBC) in dependence of enantiomeric excess was measured. It was shown that the Sm-C*beta phase in very pure samples is the Sm-C*(FI2) phase with a four-layer structure, and only after small racemization it transforms into the ferroelectric Sm-C* phase. The phase diagram was theoretically explained by taking into account longer range bilinear and short range biquadratic interlayer interactions, that lead to the distorted clock structures and first-order transitions between them.

Journal Article↗
PubMed2000

Luteinizing hormone-releasing hormone and oxytocin response to hyperosmotic stimulation: in vitro study.

It was shown previously that luteinizing hormone-releasing hormone (LHRH) affects the neurohypophysial oxytocin release in water-deprived rats. However, the detailed mechanisms by which LHRH modifies the oxytocin response to hyperosmotic stimulation have not been explained so far. Using the isolated hypothalamo-neurohypophysial explants obtained from euhydrated rats, the effect of LHRH on the oxytocin secretion was studied under conditions of direct osmotic (i.e., Na(+)- evoked) as well as nonosmotic (i.e., K(+)-evoked) stimulation. Additionally, the oxytocin response to LHRH was investigated using the explants obtained from animals drinking 2% saline for eight days (systemic, i. e., both direct and indirect, osmotic stimulation). LHRH significantly enhanced Na(+)- and K(+)-evoked oxytocin release from explants taken from rats drinking tap water, indicating that LHRH could affect the Na(+)/K(+)-dependent depolarization of perikarya of oxytocin neurones. In contrast, LHRH significantly diminished the K(+)-stimulated hormone release when the neurohypophysial complex was obtained from previously salt-loaded rats, suggesting that peripheral osmotic stimulation somehow modifies the sensitivity of oxytocinergic neurones to LHRH (possible mechanisms are discussed). It is concluded that LHRH may participate in the regulation of oxytocin secretion via both direct and indirect impact on magnocellular oxytocinergic neurones depending on the current functional status of the hypothalamo-neurohypophysial complex.

Animals↗
PubMed2000

Melatonin and the synthesis of vasopressin in pinealectomized male rats.

The pineal hormone, melatonin, is known to modify, under different experimental conditions, neurohypophysial hormone secretion in the rat. The aim of this study was to investigate the effect of melatonin on the vasopressin biosynthesis rate in the hypothalamus of either pinealectomized or sham-operated rats, using the colchicine method. To estimate whether colchicine affects the function of the neurohypophysis in these animals, the neurohypophysial and plasma vasopressin levels were also measured. The vasopressin synthesis rate was increased after pineal removal, when compared with sham-operated animals, and melatonin strongly inhibited the rise in the hormone synthesis due to pinealectomy. After pineal removal plasma vasopressin concentration was significantly elevated, and melatonin attenuated this effect. On the contrary, the neurohypophysial vasopressin content was significantly decreased after pinealectomy, but it was not further modified by melatonin.Thus, melatonin suppresses the synthesis and secretion of vasopressin in pinealectomized rats. The present results confirm our previous reports as to the inhibitory impact of the pineal on both vasopressin synthesis and release and suggest that melatonin may mediate the effect of the pineal gland on vasopressinergic neuron activity.

Animals↗
PubMed2000

Response of aorta connective tissue matrix to injury caused by vassopressin-induced hypertension or hypercholesterolemia.

The aim of the study was to investigate the effect of two various atherogenic stimuli (vasopressin-induced hypertension or hypercholesterolemia) on the collagen and glycosaminoglycan (GAG) content in the internal or external part of both thoracic and abdominal aorta, which are differently susceptible to atherosclerosis. Experimental rabbits were divided into four groups: controls, animals injected with physiological saline or vasopressin at the dose of 1 IU/kg from the 1 st to the 25 th day of experiment, respectively. The animals from group 4 were maintained on food, containing 0.25% cholesterol. Only in the vasopressin-treated group, the systolic blood pressure was elevated from 110 mmHg at the beginning, to 166 mmHg at the end of the study. After 14 weeks the aorta was dissected into internal and external parts. GAG fractions were separated and estimated as uronic acids. Collagen was evaluated as the hydroxyproline content in the tissue. Augmented total GAG and heparan sulphate (HS) level, plus no changes in the collagen content were seen in the internal part of the thoracic aorta in rabbits with hypercholesterolemia or hypertension. In the hypertensive animals, the changes were extended to the external part of the aorta and, additionally, comprised the elevation of the chondroitin-4 sulphate (C-4S) content. The two atherogenic stimuli increased the collagen level with no elevation of the GAG content in the abdominal aorta. A convergent effect of the injury, caused by hypertension or hypercholesterolemia on the collagen, total GAG and HS content was shown in the respective parts of the rabbit aortas. The common GAG, increased in the thoracic aorta, stand for the HS, in both hypertensive and hypercholesterolemic rabbits. As the sensitivity to atherosclerosis development in different segments of the aorta varies, they express various responses of the connective tissue matrix to injuries, caused by hypertension or hypercholesterolemia.

Animals↗
PubMed1999

The effect of captopril on histamine release from purified rat mast cells.

OBJECTIVE: Captopril as inhibitor of angiotensin-converting enzyme is widely used in cardiovascular therapy, however, in some patients this drug causes allergic side effects. This fact suggests that captopril may release histamine from mast cells. MATERIALS AND METHODS: Peritoneal mast cells were obtained from rats. The cells were purified by Percoll. Aliquots of mast cells were incubated with captopril or with vehicle. Histamine was determined by the spectrofluorimetric assay. RESULTS: The results were analyzed with the Kruskall-Wallis (ANOVA) test. The study has shown that captopril releases histamine from mast cells. The process depends on Ca2+ presence in the incubation environment. Sodium cromoglycate, as mast cell membrane stabilizer, inhibits the effect of captopril. CONCLUSIONS: Our results suggest that allergic side effects of captopril may be linked to histamine release from mast cells.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1999

Luteinizing hormone-releasing hormone and function of the magnocellular vasopressinergic system.

Mechanisms by which luteinizing hormone-releasing hormone (LHRH) affects vasopressin secretion were investigated using the isolated rat hypothalamo-neurohypophysial explants. LHRH in a concentration of 4 x 10(-7)M inhibited both the basal and K(+)-stimulated vasopressin release from explants isolated from euhydrated rats. When, however, the tissue was obtained from animals previously salt-loaded, the inhibitory effect of LHRH was completely abolished, thus implying a decrease in the sensitivity to LHRH. LHRH did not affect vasopressin secretion under conditions of generalized blockade of synaptic inputs by 15 mM MgSO(4), suggesting the indirect action of this neurohormone on the hypothalamic magnocellular system. It is concluded that LHRH may play the role of a neuromodulator of vasopressinergic neurones in the rat.

Angiotensin II↗
PubMed1999

The pineal and oxytocin synthesis.

The aim of this study was to investigate the effect of pineal removal on oxytocin synthesis in the hypothalamus using the colchicine method. To this end, rats were injected intracerebroventricularly (i.c.v.) with colchicine solution (5 microg/5 microl) or normal saline and decapitated 20 h later. The animals were either pinealectomized or sham-operated two or eight weeks before i.c.v. injection. The oxytocin content in the hypothalamus was significantly higher in colchicine-treated rats whereas no significant differences were seen in the neurohypophysial hormone level between saline- or colchicine-injected animals. Thus, colchicine inhibited the hormonal transport but probably did not affect the function of the neurohypophysis. Two weeks after pinealectomy neither the oxytocin synthesis rate nor its neurohypophysial content were significantly different from control values. The oxytocin synthesis rate was increased markedly eight weeks after pineal removal. At that time, the neurohypophysial oxytocin content was reduced suggesting the increased secretion of the hormone. It is concluded that the pineal has an inhibitory impact on both oxytocin synthesis and release.

Animals↗
PubMed1999

Pinealectomy-induced elevation of collagen content in the intact skin is suppressed by melatonin application.

The pineal gland is involved in wound repair and collagen deposition in sponge-induced granulomas. The aim of this investigation was to discover whether the pineal gland was able to regulate collagen accumulation in the intact skin. Wistar rats were divided into five groups: control, sham-operated with vehicle application, sham-operated with melatonin injections (30 micrograms/100 g body wt), pinealectomized with vehicle, and pinealectomized with melatonin supplementation. After 8 weeks, the collagen content was estimated as hydroxyproline concentration in the dry tissue of the skin. The results showed that melatonin markedly (p < 0.001) reduced collagen accumulation in the skin. Pinealectomy enhanced collagen deposition in the skin (p < 0.02) and melatonin application reduced the pinealectomy-induced elevation of collagen content (p < 0.001). Results clearly indicate that collagen accumulation in the intact skin is under the control of the pineal gland, and that melatonin, the pineal hormone, is responsible for this control.

Animals↗
PubMed1998

[Evaluation of the rate for reaching steady state during oral propafenone therapy in patients with ventricular arrhythmias].

UNLABELLED: We prospectively evaluated reaching of steady state and clinical efficacy of propafenone (PPF), class Ic antiarrhythmic agent, in 16 patients (pts) (age 46-69, mean 57 years) with symptomatic ventricular arrhythmias (Low class II and IV). The majority (13 pts) had coronary artery disease. Drug was administered for 7 days (daily dose: 3 x 150 mg). Efficacy was defined as > 80% reduction of ventricular premature complexes (VPC) and class IV elimination in 24-hours Holter recording. Responders were continued on PPF for 3 weeks, in non-responders dose was titrated to 900 mg a day for the next 7 days. After second Holter evaluation the treatment was continued for 2 weeks in responders group. The non-responders were switched to other drug. After 4 weeks final Holter monitoring was performed. Serum concentration of PPF and its 2 metabolites: 5-hydroxy PPF and N-depropyl PPF were determined in 2, 3, 4, 5, 6, 7th day, just before the morning dose (3 x 150 mg/day) in 9 pts. RESULTS: Trough serum concentrations of PPF differed in high degree: 0-226 ng/ml (2nd day), 22-438 ng/ml (4th day), 42-614 ng/ml (6-7 day). An increasing tendency of serum concentrations of PPF was observed, so steady-state was not reached. This great dispersion of concentration values is because of non-linear metabolism and individual differences. Defined efficacy critetion was achieved in 62% pts, 56% for lower dose. Mean frequency of VPC was reduced by 86% in 24-hour Holter recording and per hour (p = 0.0011). Reduction of couplets/24 h was 87% (p = 0.0175). Significant prolongation of PQ (14%, p = 0.009) and QRS (13%, p = 0.0052) were observed. Changes of QT interval were not significant. One case of proarrhythmia was the cause of stopping the treatment. CONCLUSIONS: Serum concentrations' values undermine common opinion, that steady state can be reached after 1-2 days of treatment. High dispersion of serum levels is the result of nonlinear metabolism of PPF and individual differences. In spite of this the study showed defined antiarrhythmic efficacy in 62.5% pts. In this group 90% success rate was achieved after lower dose 3 x 150 mg.

Administration, Oral↗
PubMed1997

[Evaluation of antiarrhythmic efficacy of sotalol in various doses in patients with ventricular tachyarrhythmias].

UNLABELLED: Antiarrhythmic efficacy of sotalol--noncardioselective beta-adrenergic blocking agent with class III antiarrhythmic action was evaluated in 34 patients [pts] (mean age 55 +/- 11) with chronic ventricular arrhythmias and coronary artery disease, 38% with previous myocardial infarction. Two schedules of dosing were tested: 3 x 80 mg and 2 x 160 mg during 28 days of therapy. Pts with Lown class II and IV arrhythmia derived from 24-hours Holter recording were assigned. Ventricular premature complexes [VPCs] and couplets reduction by 80% and total elimination of runs defined antiarrhythmic efficacy. Proarrhythmia was defined by four times increase in VPCs, ten times increase in couplets and runs or sustained VT episodes. RESULTS: Antiarrhythmic efficacy of two doses of sotalol according to study criterion was: 31% for lower dose (3 x 80 mg) and 24% for higher dose (2 x 160 mg). Overall efficacy for both doses was 55%. According to Morganroth criterion, lower dose was effective in 29% pts and both doses, lower and higher, in 41% pts. According to other commonly used criterion: 70% VPCs reduction, 90% couplets reduction and total elimination of runs, lower dose of sotalol was effective in 32% pts and both doses in 47% pts. Significant reduction of heart rate and prolongation of QT and QTc were observed. In 3 pts QT was prolonged over 500 ms. Proarrhythmia according to Velebit criterion was suspected in one patient after one week of 3 x 80 mg teratment which caused premature cessation of therapy. No significant abnormalities in laboratory values were observed. CONCLUSIONS: Antiarrhythmic efficacy of sotalol was comparable to other studies. Its value in pts with malignant ventricular tachyarrhythmias: sustained ventricular tachycardia and ventricular fibrillation requires further studies with higher number of patients.

Adult↗
PubMed1996

Phase space evolution distribution functions for high energy electron beams.

The phase space evolution (PSE) model is a 3D electron beam dose calculation model for radiation oncology. The PSE model is based upon the transport of electrons with a specific energy and direction over short distances (typically 0.3-1 cm). The result of the transport of these electrons is described by an energy and direction distribution of the electrons, which is stored in a database. The database is used by the PSE model at the time of the actual electron transport simulation. A good agreement between dose distributions calculated by the PSE model and EGS4 Monte Carlo code for mono-energetic, mono-directional electron beams was found. The differences in point dose are within 1-2% of the maximum dose. These differences can be caused by errors in the database used, or by assumptions made in the PSE model. The aim of this paper is to get more insight into the possible errors introduced by the database. Results show that the data in the database are in good agreement with EGS4 calculated data. Also the influence of the database on a PSE calculated dose distribution has been investigated. The differences between a PSE calculated dose distribution and an EGS4 calculated dose distribution can be reduced to < 0.5% if the database is replaced by a database partly created by EGS4. This shows that small errors in the database have a distinct effect on the dose distribution, and that this dose distribution can be calculated accurately by the PSE model if the right database is used.

Computer Simulation↗
PubMed1996

Melatonin suppresses the pinealectomy-induced elevation of collagen content in a wound.

The pineal gland hormone was shown to be involved in the regulation of repair and connective tissue accumulation in a wound. The hypothesis that melatonin injection could reverse the pinealectomy-induced elevation of the collagen content in scar tissue was verified. The effect of various melatonin doses (3, 30 and 100 micrograms/100 g body wt) on soluble, insoluble and total collagen content in the granulation tissue of a wound was investigated. The collagen level was estimated in pinealectomized rats, as well as in pinealectomized animals treated with melatonin. Ivalon sponges inserted subcutaneously were applied as a wound model. After 4 weeks the collagen content was measured as a hydroxyproline concentration in the dry tissue of the wound. The results showed that melatonin at the dose of 30 micrograms/100 g body wt significantly decreased both total and insoluble collagen content in the wounded tissue (p < 0.05), but other doses were ineffective. Pinealectomy increased the total (p = 0.05) and insoluble collagen level (p < 0.05) in the granulation tissue. Melatonin suppressed pinealectomy-induced elevation of the total and insoluble collagen content in the wounds (p < 0.05). No influence of the pineal gland on the soluble collagen content was observed. The results showed that melatonin was involved in the inhibitory control of the collagen content.

Animals↗
PubMed1994

The effect of platelet activating factor antagonist (BN 52021) on pregnancy duration and collagen content in the pregnant rat uterus and cervix.

In order to study the role of Platelet Activating Factor (PAF) in the mechanism of parturition and connective tissue metabolism in the pregnant rat uterus, we investigated the influence of the Platelet Activating Factor Receptor Antagonist (BN 52021) on gestation duration and collagen concentration in pregnant rat uterus and cervix at term. Total and soluble collagen as well as dry tissue/wet tissue ratio were measured in the BN 52021 treated group (n = 9) and in the control group (n = 13). Gestation duration was evaluated in a group receiving BN 52021 (n = 10) and in a control group (n = 19) receiving pure solvent. There were no significant differences in water content. The total and soluble collagen concentration was also similar to the control in both the uterus and the cervix. The only significant difference was observed in the soluble collagen/total collagen ratio in the uterus. BN 52021 administration did not alter the gestational period. Basing on this experiment we suggest that not all the phospholipid metabolites activated by phospholipase A2 significantly influence the duration of pregnancy and connective tissue metabolism in the pregnant rat uterus.

Animals↗