Effects of the H1-antagonist promethazine and the H2-antagonist burimamide on chronotropic, inotropic and coronary vascular responses to histamine in isolated perfused guinea-pig hearts

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

Highlights in cardiovascular effects of histamine and H1-receptor antagonists

Despite numerous studies, the cardiac actions of histamine are still obscure. Yet, histamine could probably be clinically relevant. It is stored in large amounts in human cardiac tissue, where it is contained in the cytoplasmatic granules of mast cells. Mast cells are present in normal human heart tissue; they are more abundant in diseased human heart tissue where they lie in close proximity to blood vessels and between myocytes. The histamine content of human heart mast cells is comparable to the histamine content of lung parenchymal and skin mast cells. Ultrastructural studies confirmed the presence of mast cells around vessels and between myocytes. Consequently, these cells are easily accessible to circulating antigens, drugs and stimuli that activate the cells to release vasoactive mediators which in turn can exert significant cardiovascular effects. Histamine possesses arrhythmogenic effects and once locally released, may enhance automaticity and induce triggering activity resulting in severe tachyarrhythmias. The major arrhythmogenic effects of histamine consist in increasing sinus rate and ventricular automaticity, and in slowing atrioventricular conduction. In addition, histamine may interfere with depolarization and repolarization through its effects on calcium and potassium currents. These effects are mediated by H2-receptor. Therefore direct activation of histamine receptor can induce cardiac arrhythmias. Consequently, the interference of these histaminergic effects may explain, at least in part, the arrhythmogenic effects described for some second-generation antihistamines, such as terfenadine and astemizole. In this brief review we will discuss the cardiac effects of histamine in experimental animal models and in man, and will review data on the safety of the new second-generation antihistamines, focusing on their cardiotoxic effects.

Relevance of mediators to cardiac parameters of isolated anaphylactic guinea-pig heart

The release of histamine, eicosanoids and catecholamines were measured after induction of anaphylaxis in isolated guinea-pig hearts. The concentration-time profile of these mediators was compared with changes of cardiac parameters. The histamine and catecholamine levels of the coronary effluent were determined at 10 s intervals; thromboxane and prostacyclin levels at 60 s intervals. The release of histamine and norepinephrine were maximum between 20 and 30 s after the antigen challenge and decreased rapidly within 60 s. Thromboxane and prostacyclin increased to a maximum after 3 min and declined slowly within 10 min. The rise in histamine release was correlated with tachycardia. The release of thromboxane was correlated with the increase of coronary perfusion pressure. Cimetidine inhibited the tachycardia and clemastine reduced bradyarrhythmia. The inhibition of lipoxygenase and cyclooxygenase also reduced the rise in the perfusion pressure. These data suggest that different mediators are time-dependently involved in anaphylaxis-induced cardiac changes.

Indirect evidence for a role of phosphatidylinositol turnover in the cardiac response to H1-receptor stimulation

The influence of lithium on the positive inotropic effect of the H1-agonist 2-pyridyl-ethylamine (PEA) and of the H2-receptor agonist 4-methylhistamine was studied in isolated guinea-pig ventricular strips electrically stimulated at 1 Hz. Lithium (1-10 mM) was devoid of any effect on cardiac contraction; the positive inotropic effect of 4-methylhistamine was unaffected in the presence of 10 mM lithium. On the other hand, lithium (1-10 mM) dose-dependently shifted the dose-inotropic effect curve for PEA to the right; an antagonistic effect, qualitatively similar to that of lithium, was induced by the myoinositol antagonist 2-2'-anhydro-2-C-hydroxymethyl-myoinositol, at a concentration of 100 microM. Moreover the antagonistic effect of the higher lithium concentration (10 mM) was almost completely prevented in preparations superfused with 10 mM myoinositol. Since it is known that lithium is able to reduce the cellular availability of myoinositol by an interference with the phosphatidylinositol (PI) cycle, these results suggest that the H1-receptor-mediated increase in contractility may be linked to an increased turnover of PI, while the H2-receptor-mediated one is not.

Effect of Ni2+ on the multiphasic positive inotropic responses to histamine mediated by H1-receptors in left atria of guinea pigs

Effects of calcium antagonists and Ni2+ on the positive inotropic responses to histamine mediated by H1-receptors were investigated in left atria of guinea pigs. The preparations were electrically driven at 0.5 Hz in Krebs-Henseleit solution at a temperature of 30 degrees C unless stated otherwise. Histamine in low concentrations of 10 and 100 nmol/1 produced a monophasic positive inotropic effect, whereas in concentrations higher than 1 mumol/1 it exerted a multiphasic inotropic response composed of an initial increasing phase (initial component) and a second and late developing, greater positive inotropic phase (second component). These two components were sometimes separated by a transient decrease in developed tension. Both positive inotropic components caused by 3 mumol/1 histamine were inhibited by the H1-antagonists mepyramine, D-chlorpheniramine and diphenhydramine in a concentration-dependent manner, but not by the H2-antagonist cimetidine. Pretreatment with Ni2+ in concentrations of 0.2 and 0.5 mmol/1 preferentially suppressed the second component of the inotropic effect produced by 3 mumol/1 histamine without significantly affecting the initial component. On the other hand, the monophasic positive inotropic effect of 30 nmol/1 histamine was almost unaffected by this cation. The concentration-response curves for the positive inotropic effect of histamine were hardly influenced by Ni2+ in the range of lower concentrations of histamine, but significantly suppressed in the range of higher concentrations of the agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of histamine and the histamine antagonists mepyramine and cimetidine on human coronary arteries in vitro

The effects of histamine have been studied on human isolated coronary artery preparations taken from hearts ranging in age from 9 to 73 years. Histamine in large concentrations (100 microM) contracted arteries which were without tone or spontaneous activity and sometimes induced rhythmic contractile activity. If spontaneous rhythmic activity was present it was enhanced by histamine. The contractile effects of histamine were inhibited by mepyramine but not by cimetidine. Arteries which were contracted by depolarization responded with relaxation to histamine concentrations lower than those required to evoke a contraction; arteries from younger hearts were more sensitive than those from older hearts. Mepyramine potentiated the maximal relaxant effect of histamine in arteries from hearts of all ages but cimetidine had very little effect. In the presence of mepyramine, cimetidine antagonized the relaxant effect of histamine, shifting the concentration-effect curve to the right. It is concluded that human coronary arteries contain both H1- and H2-type receptors, the H1-receptors mediating contraction. The relaxant effects of histamine can only be inhibited by a combination of both H1- and H2-receptor antagonists.

Some characteristics of the inotropic effects of histamine H1- and H2-receptor agonists in comparison with those of alpha- and beta-adrenoceptor agonists

The positive inotropic effects of 2-pyridyl-ethylamine (PEA) and of 4-methylhistamine (4MeH) were studied in isolated guinea-pig ventricular strips electrically stimulated at a rate of 60 and 150/min. The increase in contractile tension induced by PEA (10(-7)-3 X 10(-4) M) in the presence of cimetidine (10(-5) M) was associated with a slight increase in time to peak tension and with a lengthening of the relaxation phase; the positive inotropic effect of PEA was significantly higher at a frequency of 60/min than at 150/min. Conversely, the inotropic response to 4MeH (10(-8)-3 X 10(-6) M) was not frequency dependent, and was associated with an evident decrease in relaxation time. Moreover, 4MeH consistently antagonized, in dose-dependent manner, the negative inotropic effects induced by the calcium antagonistic drug D600 and by lowering calcium concentration in the medium, and was able to restore the contractility abolished by treatment of preparations with a high K+ medium. On the other hand PEA, in the presence of cimetidine, scarcely antagonized the negative inotropic effects induced either by D600 or by low calcium solution, and was unable to restore the contractility of K+-depolarized preparations. The characteristics of the inotropic response of the H1-receptor agonist were very similar to those of the alpha-adrenoceptor agonist phenylephrine. This observation suggests that a common mechanism is probably involved in the inotropic effects mediated by H1 and by alpha receptors, and that this mechanism does not include a stimulation of the calcium transmembrane influx.

A question of the specificity of rabbit atrial chronotropic histamine receptors and agents which affect their activity

The histamine chronotropic response of rabbit atria appears to be controlled by both H1 and H2 receptors and can be blocked in part by either metiamide (an H2 antagonist) or diphenhydramine (an H1 antagonist), while both 2- and 4-methylhistamine (H1 and H2 agonists, respectively) stimulated the chronotropic response. At low agonist concentrations, the simultaneous presence of both H1 and H2 blockers results in considerably less inhibition than could be expected from calculations of individual inhibition data, suggesting that some sites behave as if they have both H1 and H2 properties. Additional compounds were tested for specific action on H1 and H2 receptors: 2-(2-pyridyl) ethylamine, reported to be an H1 agonist, appears to stimulate rabbit atria by releasing norepinephrine and guinea pig atria by releasing both norepinephrine and histamine; while dimaprit, reported to be an H2 agonist, may stimulate histamine receptors directly but has a nonspecific depressant action on rabbit atria which interferes with its use as an agonist in this species.

Chronotropic effect of histamine on cultured neonatal rat heart cells

The positive chronotropic effect (PCE) of histamine in cultured neonatal rat heart cells was monitored using a microscopic method as well as an electro-optically recording device. The action potential frequency was also measured (by means of microelectrodes). An increase in PCE was noted when histamine (from 1 X 10(-6) M to 1 X 10(-5) M) was added to the cells. However, higher concentrations (from 1 X 10(-5) M to 1 X 10(-4) M) were less effective. The PCE of histamine was reduced by pretreating the cells with antihistaminic drugs. H1-blocking agents (promethazine and mepyramine) were more potent than H2-blocking drugs (metiamide and cimetidine). In addition, the PCE of histamine was abolished when the cells were in presence of high K+ medium (26 mEq) but contraction and action potential amplitudes were increased. Our results demonstrate that these cultures respond to histamine and that this response is abolished by antihistaminic drugs thus suggesting the H1 and/or H2 receptors may be present in the neonatal rat heart cell cultures.