Physiologia Bohemoslovaca最新文献

The present results are a continuation of our experiments demonstrating the fact that the local action of a permanent magnetic field (PMF) with an intensity of 0.2 T on the rabbits carotid sinus area under pentobarbital anaesthesia has a hypotensive effect under normotonic conditions (Gmitrová et al. 1987). The aim of this paper was to investigate the PMF influence on the carotid sinus region during artificial hypotension in rabbits. The experiments were carried out in rabbits under pentobarbital anaesthesia under hypotonic conditions caused by electrostimulation of the right depressor nerve. Blood pressure, heart rate and respiration rate changes were monitored before the application of PMF (0.2 T intensity) on the sinocarotid region, during the "on" effect of PMF, under the PMF action, during the PMF "off" effect and after PMF application. PMF significantly decreased the depressor effect of depressor nerve electrostimulation in contrast to the condition of normotonia, where PMF had a hypotensive effect.

Patients with essential hypertension have 3.2 fold and patients with chronic uraemia 11.7 fold higher serum concentrations of endogenous digitalis-like activity than normotensives (76.3 +/- 9.3 nM). Upon haemodialysis this serum activity drops to almost normal values. A low molecular factor could be partially purified from 4000 l haemofiltrate.

The relation between blood pressure level and extracellular fluid volume and its distribution was studied in rats subjected to the following hypertensive stimuli--1K1C and 2K1C renal artery constriction, subtotal nephrectomy-salt and DOCA-salt. In all experimental groups the blood pressure increase was accompanied by increased extracellular fluid volume which was not always distributed proportionally between intravascular (PV) and interstitial (IFV) compartments. The blood pressure rise was further potentiated by plasma volume expansion so that the increased PV/IFV ratio was associated with a more pronounced hypertensive response (1K1C vs 2K1C, DOCA-salt vs subtotal nephrectomy-salt). However, adequate expansion of interstitial fluid is a necessary prerequisite for the hypertensive response. In DOCA-salt treated DI Brattleboro rats (lacking antidiuretic vasopressin action) plasma volume expansion per se was not accompanied by severe DOCA-salt hypertension. It is concluded that the expansion of both compartments of extracellular space, i.e. plasma volume and interstitial fluid volume, was necessary for a full development of severe hypertension. The expansion of only one of these compartments was accompanied by a mild blood pressure increase or blood pressure did not change significantly.

Detergents (Triton X-100, dodecyl sulphate, saponin) added in concentrations of 0.1-10 mg/ml to solution at the outer frog skin surface reversibly reduced potential difference (PD) and short-circuit current (Isc); when added at the inner surface. Triton X-100 initially induced a short increase in the PD and Isc followed by a pronounced decrease similarly as after the application of any of the detergents used. When added to either serosal or mucosal surface of frog urinary bladder, the detergents reversibly abolished the reactivity to vasopressin. Triton X-100 blocked foskolin and cAMP-induced effects on membrane water permeability. The results suggest that hydrophobic elements of membrane play a crucial role in the regulation of membrane permeability for ions and water and of the responsiveness of the cells to vasopressin. Differences in sensitivity to detergents could be observed between the apical and the basolateral cell membrane.

Bilateral paralysis of the diaphragm can result in normo or hypoventilation, according to the species studied. Our aim was to ascertain the results of bilateral phrenicotomy in the rat and, if hypoventilation should be present, to try to identify its pathophysiology. We used 33 male rats under urethane anaesthesia (1.3 g/kg i.p.). They were divided into three groups: control animals, rats with bilateral phrenicotomy and a group with two doses of pentobarbital (25 mg/kg i.p. each) on top of the urethane anaesthesia. We observed pronounced hypoventilation both in the rats after phrenicotomy and those with pentobarbital. At comparable levels of hypoventilation (PaCO2 = 5.61 +/- 0.28 kPa immediately after phrenicotomy and 5.91 +/- 0.25 kPa after the first dose of pentobarbital; and 7.21 +/- 0.47 kPa 4 hours after phrenicotomy and 7.38 +/- 0.39 kPa after the second dose of pentobarbital) the only difference was a longer relative duration of inspiration in phrenicotomized rats; (0.39 +/- 0.04 and 0.34 +/- 0.04 after phrenicotomy; 0.32 +/- 0.04 and 0.24 +/- 0.05 in rats after pentobarbital). Immediately after phrenicotomy and 2 and 4 hours later, and also after both doses of pentobarbital breathing was stimulated by hypoxia and hypercapnia due to the additional external dead space (0.5 ml) for 5 min. There was no pronounced differences in the ventilatory response to the dead space between the two groups; the response changed from an isocapnic (in control rats and before phrenicotomy or pentobarbital) to an isoventilatory one (four hours after phrenicotomy and after the second dose of pentobarbital). The rats after the second dose of pentobarbital did not, however, survive the added dead space.(ABSTRACT TRUNCATED AT 250 WORDS)

The micropuncture technique and X-ray microanalyses were used to evaluate Na, K, Ca, Mg, Cl and fluid transport in the early distal tubule mediated by low-molecular fractions isolated from the intestine of the hibernating ground squirrel (HSI). Perfusion of intertubular capillaries with a solution containing HSI with a molecular weight of 1-10 kD (0.1 mg.ml-1) decreased the relative reabsorption of fluid, Ca and Mg. The other low-molecular fraction 1-10 kD of m.v. (0.1 mg.ml-1) isolated from the intestine of alert ground squirrels (ASI 1-10) caused no significant changes of the ionic concentration and inulin concentration index in the distal tubule. Fraction 1 with molecular weight 1.2-4.5 kD (0.1 mg.ml-1) obtained by further division of HSI 1-10, decreased the reabsorption of fluid and ions under study. Fractions 2 (m.w. 0.98 kD) and 3 (m.w. 0.89 kD) had no effect on the ion and fluid transport in the same tubule. The addition of naloxone (0.4 mg.ml-1) blocked the action mediated by HSI 1-10 or fraction 1. Thus, the substance(s) capable of regulating Ca, Mg, and fluid transport in the distal tubule likely to be mediated by the opiate-dependent process has a molecular weight of 1.2-4.5 kD.

It has been shown previously that 3,4-diaminopyridine (3,4-DAP) facilitates synaptic transmission in the frog sympathetic ganglion inducing so-called stimulus-bound repetition (SBR), i.e. a brief burst of repetitive postganglionic discharges after a single orthodromic stimulus. In the present study we analyzed one of the possible mechanisms of the 3,4-DAP-induced SBR, namely changes in postsynaptic membrane excitability. We found that 3,4-DAP in concentration optimal for inducing SBR (2 X 10(-4) mol.l-1) had no direct effect on the excitability of the postsynaptic membrane of frog sympathetic neurones. The excitability was expressed as the threshold for action potentials elicited orthodromically, antidromically and directly, as well as the spike activity evoked by constant depolarizing current pulses. We also indirectly excluded the involvement of two other possible mechanisms of neuronal membrane excitability modulation in the 3,4-DAP-induced SBR, i.e. the M-current suppression by analyzing the participation of muscarinic receptor activation in the SBR, and inhibition of the Ca(2+)-activated K+ currents by measuring the duration of afterhyperpolarization of antidromic action potential. Our findings indicate that no remarkable changes in the properties of the postsynaptic membrane contribute to the generation of 3,4-DAP-induced SBR in the frog sympathetic ganglion. This strongly supports the hypothesis that the mechanism underlying SBR evoked by this drug is presynaptic.

Salt loads (0.17 or 0.34 mmol Na+; 6 M NaCl solution labelled with 24Na) were administered into the amnion of 7-day-old chick embryos. The 24Na distribution in embryonic blood, amniotic and allantoic fluids was measured in 1, 2, 4, 8, 12 and 24 h intervals to assess the kinetics of salt load movements in particular egg compartments. The aim was to estimate the efficiency of the embryonic homeostatic apparatus to maintain ionic balance in the internal environment of the embryonic body. The Na+ concentration in amniotic fluid was expected to rise after salt loading by about 275 and 400 mM, respectively. More than 10% of the salt dose per ml appeared in the embryonic blood 2 h after salt load administration while only 0.2% were found in the urine (collected as allantonic fluid). The maximal rise of 24Na activity in the blood of salt-loaded embryos reached 11%-12% of the dose which corresponded to an increase of Na+ concentration by 19 and 41 mM, respectively. The maximum of 24Na activity appeared in the allantoic fluid with a delay of several hours and indicated an increment of Na+ concentration by 6% and 9% of the dose per ml in the case of salt-loaded embryos. The Na+ concentration in the allantoic fluid (urine) never exceeded that in the blood. The final Na+ activity (estimated in the blood 24 h after salt loading) was equal to 5% of the dose per ml in both cases, indicating a persistent elevation of Na+ concentration by 8.6 and 17.2 mM, respectively.

Experiments were carried out on 16 anaesthetized, non-paralysed cats to determine the effects of unilateral, successive focal cooling of the nuclei of the dorsal and ventral respiratory groups (DRG, VRG) of the medulla oblongata on quiet breathing parameters. The results of cold block tests of the respiratory nuclei showed that: 1. Compared with the control state, cooling of the ventrolateral part of the nucleus solitarii (vl. NTS) and the rostral part of the nucleus retroambigualis (r. NRA) to 20 degrees C or 15 degrees C decreased the respiration rate (p less than 0.001), prolonged the inspiration time (p less than 0.01 and p less than 0.001 respectively) and the development of apneustic breathing. A decrease in the inspiratory pleural pressure values (p less than 0.01) was found after cooling the r. NRA region to 15 degrees C. In 45% of the cases of cooling of the vl. NTS and 66.7% of cooling of the r. NRA to 15 degrees C, an incidence of short inspiratory efforts was observed. 2. Focal cooling of the nucleus retrofacialis (nucl. RF) region to 20 degrees C always arrested rhythmic respiration. 3. The effects of unilateral focal cooling of the respiratory nuclei were always bilaterally symmetrical and, after discontinuing cooling, reversible. 4. The findings indicate that the inspiratory neurones of the r. NRA participate more in regulation of the intensity of inspiration than those of the vl. NTS, while the nucl. RF region may be a part of central regulatory mechanisms essential for the maintenance of rhythmic breathing in cats.