Acta physiologica Academiae Scientiarum Hungaricae最新文献

Effects of intraperitoneal administration of cholecystokinin (CCK)-related peptides were studied on retention of single-trial learning passive avoidance behaviour. The COOH-terminal octapeptide of CCK (CCK-1-8-SE), the unsulfated octapeptide (CCK-1-8-NS), as well as the COOH-terminal tetrapeptide of CCK (CCK-5-8), administered immediately after the learning trial, facilitated passive avoidance behaviour. The data indicate that these peptides may influence memory consolidation processes.

Computer modelling technique is proposed to assist in physiological research on invertebrate neuronal membranes. The firing mechanism of a single patch of invertebrate neuronal membrane has been studied in dependence on maximum Ca++ conductance. The calculations are based on modification of Hodgkin-Huxley's data completed by a straight line approximation between experimental points of the kinetic parameters of Ca++ current and early transient potassium current. The time course of conductance changes is assumed to be proportional to m2h for Ca++ current. Three distinct potassium currents are involved into the model, viz. transient potassium current, delayed potassium current and Ca++-dependent potassium current. The modified Euler method run on a digital computer has been used for numerical integration of kinetic equations. Significant effects of Ca++ conductance on spike broadening, plateau development and spike afterhyperpolarization are represented. In the range of small Ca++ conductance an infinite spontaneous activity can be triggered by a short (suprathreshold) current pulse which may be considered a model of pacemaker activity. Plateau development resulting from potassium blocking or decreasing potassium equilibrium is facilitated by Ca++ conductance in the range of greater Ca++ conductance. The effects of voltage sensitivity of the coupling coefficient describing the current of Ca++-dependent K+ channels were studied and compared to the voltage independent case. The coupling coefficient seems to be a crucial factor in broadening the range of Ca++ conductance responsible for pacemaker activity. For greater values of Ca++ conductance, a decrease of the coupling coefficient leads to a transition from prolonged bursting to interruption of burst activity by burst-afterhyperpolarization. The blocking effect of 4-aminopyridine on fast outward current has been studied by the model which has a practical significance considering that aminopyridine is known as a convulsive agent. We suppose that it is reasonable to study the convulsive effects of aminopyridine by the model based on the kinetics of the isolated neuronal membrane. The model may help in understanding the ionic background underlying abnormal network activity during epileptic discharges of mammalian neurones.

The coronary vascular effect of various divalent cations and of sodium-metavanadate was compared in isolated perfused rat hearts. Their order of activity was as follows (the concentrations (microM) evoking a half-maximum increase of coronary resistance are indicated (in parentheses): Ni2+ (0.03) greater than Co2+ (0.1) greater than Hg2+ (0.16) greater than VO-3 (0.2) greater than Cu2+ (15) greater than Zn (50). Iron (Fe2+) and cadmium (Cd2+) were ineffective. The order of coronary vasoconstrictor potency of these metal ions differs from the order of their other physico-chemical properties indicating that their coronary action cannot be explained as being singly a consequence of ion-membrane interaction. In contrast to Ni2+, the effect of Hg2+ was totally inhibited by phenoxybenzamine (10(-5)M) indicating that coronary vasoconstriction induced by mercury ions is mediated by alpha-receptors. Coronary vasoconstriction induced by sodium-meta-vanadate was resistant to verapamil while removal of external Ca2+ potentiated its effect. These data suggest that in contrast to Ni2+ and Hg2+, vanadate increases coronary resistance by mobilizing intracellular Ca2+ in vascular smooth muscle cells.

In control and capsaicin-treated (300 mg/kg) rats tail skin vasodilatation was studied while the body temperature was raised to 38 degrees C, 39 degrees C or 40 degrees C and held at these levels. In the capsaicin-treated rats, at 38 degrees C vasodilatation was weaker than in the controls but at temperatures of 39 degrees C and 40 degrees C a delayed increase in tail vasodilatation occurred to the level observed in the controls. It is concluded that the threshold of vasodilatation response to heat is elevated after capsaicin treatment.

Differential distribution of gross, particulate and soluble forms of hexokinase in the cerebrum, cerebellum, pituitary, hypothalamus and thalamus and medulla oblongata was studied in 9 inland teleosts of different phylogenetic age to clarify the compartmentation of glucose metabolism. Enzyme activity (gross) was maximum in the cerebrum and minimum in the medulla oblongata, suggesting that glucose metabolism is more intensive in the former structure. The activity in the particulate fraction was highest in the cerebellum followed by the cerebrum, midbrain and medulla oblongata. Gross, particulate and soluble fraction of the enzyme was higher in major carp species than in cat fish or snake head species. Total particular and soluble fraction was highest in the cerebrum, cerebellum and midbrain. The distributional trend of the enzyme was similar in the 9 fishes.

The purpose of the present study was to investigate the changes of characteristic parameters of myocardial reactive hyperaemia that follow coronary artery occlusion for 10 sec and of the coronary vascular response to hypoxia during constant verapamil infusion (0.01 mg. kg-1 X min-1) in anaesthetized open-chest dogs. Reactive hyperaemia was significantly reduced by the specific Ca-antagonist verapamil, while augmentation of coronary blood flow by 100% N2 inhalation for 30 sec was not significantly influenced by the drug. The experimental results indicate that, similar to myocardial cells, verapamil reduces the oxygen requirement of vascular smooth muscle cells as well. The possibility exist that verapamil excludes factor(s) responsible for the disproportional overpayment of flow debt.

The possibility of local recording of the electrical activity of the sinus node was investigated on 22 dogs. Using a small unipolar electrode positioned at the proximity of the sinus node and applying a 2-4-fold electric amplification, an early, slow and low-amplitude wave could be recorded 20-40 ms before the P wave. This early wave gradually decreased when the electrode was moved away from the sinus node and finally fused into the local P wave. Temporary arrest of sinus node activity by injection of adenosine into the sinus node artery, electrical stimulation of the vagal nerve by infiltration with phenol of the sinus node region made the local P wave to disappear. Similarly, no early action before the P wave could be seen if the sinus node was driven electrically. The early wave recorded in the proximity of the sinus node represents the depolarization of the sinus node, and it is suitable to study the pacemaker activity of the sinus node together with sinoauricular conduction.

Amniotic fluid was collected from women in the 2nd trimester of their gravidity by amniocentesis and its effect on the isolated pregnant rat uterine preparation investigated. It was demonstrated that some of the amniotic fluid components partially purified by using the combination of various separation techniques stimulated, while others inhibited the contractions of the isolated rat uterine preparation. The inhibitory component, called utero-inhibin also inhibited the spontaneous contractions as well as the basal tone of the isolated rat intestinal preparation and those of the isolated human pregnant myometrium preparation. It is speculated that the inhibitory factor might play a physiological role in maintaining the resting state of human uterus during pregnancy.

The effect of mazindol on feeding behaviour was investigated in rats fasted for 24 hours. They were then given mazindol i.p. and placed in a new environment. The effect of the drug on the disappearance of 3H-noradrenaline (3H-NA) from various parts of the brain after injection into the cerebral ventricles was also investigated. Mazindol was more potent in suppressing feeding behaviour than in reducing food intake, indicating that a number of aspects of feeding behaviour may be more sensitive indices of the anorectic effect of a drug than food intake per se. Mazindol, in a dose of 30 mg/kg, accelerated the disappearance of 3H-NA from the medial hypothalamus but not from other areas of the brain, suggesting that the drug has a locus-specific action on cerebral noradrenaline metabolism.