Cardiac histamine receptors and cyclic AMP

Histamine directly acts on beta-adrenoceptors as well as H1-histaminergic receptors, and causes positive inotropic effects in isolated ventricular muscles of carp heart (Cyprinus carpio)

1. The mechanism for positive and negative inotropic effects of histamine was studied in electrically stimulated ventricular strips of carp heart. 2. A high concentration of histamine (1 mM) caused a transient negative, and subsequent positive inotropic effects. The positive effect was significantly reduced by pyrilamine, diphenhydramine or dl-propranolol, but was not affected by cimetidine or d-propranolol. 3. Prior treatment with reserpine significantly decreased epinephrine and norepinephrine contents in ventricular muscles, and also almost completely abolished the positive inotropic effect caused by tyramine; however, this treatment failed to affect the positive inotropic effect of histamine. 4. The transient negative inotropic effect was reduced by neither atropine, diphenhydramine, pyrilamine nor cimetidine, and potentiated by pyrilamine. 5. These results suggest that the positive inotropic effect of histamine observed in the ventricular muscle of carp heart is mediated by a direct stimulation of both H1-receptors and beta-adrenoceptors. The negative inotropic effect is unrelated to either cholinergic or histaminergic receptor stimulation.

Effects of promethazine on ischemic and reperfusion arrhythmias in rat heart

The effects of the H1-receptor antagonists promethazine, mepyramine, and chlorpheniramine on ischemic and reperfusion arrhythmias were studied in the isolated perfused rat heart. Promethazine reduced both ischemic and reperfusion arrhythmias (2 x 10(-6)M-7.5 x 10(-6)M). Mepyramine and chlorpheniramine decreased these arrhythmias but at concentrations about 10 times higher. The H2-blockers cimetidine and ranitidine had no antiarrhythmic effect. Promethazine also: (i) increased release of noradrenaline by the heart; and (ii) increased coronary flow in the reperfusion period and in some mildly ischemic zones. It is proposed that promethazine exerts most of its antiarrhythmic effects by a nonspecific mechanism, possibly membrane stabilization; in addition, enhanced coronary flow may play a role.

Characterization of the effects of histamine on the transmembrane electrical activity of guinea-pig and rabbit SA- and AV-node cells

The effects of histamine on the transmembrane electrical activity of cells of small preparations (0.5 X 0.5 mm) of guinea-pig and rabbit sinoatrial- and atrioventricular-nodes were studied. Histamine at concentrations above 10(-7) mol/l increased the firing rate, the rate of diastolic depolarization, the maximum diastolic potential, the amplitude and the maximum rate of depolarization of the action potential of pacemaker cells of rabbit and guinea-pig sinoatrial cells and rabbit atrioventricular cells. These effects were antagonized by the H2-receptor blocker cimetidine (2.5 X 10(-6)mol/l) but they were not modified by the H1-receptor blocker chlorphenamine (2.5 and 5 X 10(-6)mol/l). Small preparations of guinea-pig atrioventricular node did not exhibit spontaneous activity, but it was induced by histamine and blocked by cimetidine. Histamine increased the maximum upstroke velocity of propagated action potential of cells of the central part of complete atrioventricular node in both species studied. These effects were blocked by cimetidine, but not by chlorphenamine. It is concluded that the increase in automaticity induced by histamine in guinea-pig and rabbit sinoatrial and atrioventricular nodes was due to stimulation of H2-receptors. Histamine did not depress electrical activity of atrioventricular node cells, but rather increased it. This effect was due to H2-receptor stimulation.

The effects of histamine on contraction frequency, sodium influx, and cyclic AMP in cultured rat heart cells

Histamine has been shown to have both positive inotropic and chronotropic effects. To evaluate the chronotropic effects, spontaneously contracting monolayers of cultured rat myocardial cells were treated with histamine, 10(-7) M-10(-4) M. This resulted in a dose-dependent increase in contraction frequency reaching a maximum in 10(-5) M histamine. Contraction frequency (mean +/- SEM) increased from a control of 121 +/- 5 contractions per minute to 153 +/- 4.5, 181 +/- 9, 212 +/- 4, and 216 +/- 1 in 10(-7) M, 10(-6) M, 10(-5) M, and 10(-4) M histamine, respectively (for each n = 10, p less than 0.001). The effect was time-dependent, taking 30 minutes to develop fully. Changes in contraction frequency were accompanied by parallel dose- and time-dependent increases in the verapamil-sensitive sodium influx. Verapamil-sensitive sodium influx (pmol/cm2/sec) increased from a control of 10.45 +/- 1.44 (mean +/- SEM) to 24.34 +/- 2.41 and 32.57 +/- 2.35 at 10- and 30-minute treatment with 10(-6) M histamine (n = 5, p less than 0.001). These data fit the previously described relation between verapamil-sensitive sodium influx and contraction frequency in these cells. Cimetidine (10(-4) M) but not diphenhydramine (10(-4) M) abolished both the contraction frequency and sodium influx response to histamine. Subsequent studies showed a dose- and time-dependent elevation of cyclic adenosine monophosphate (cAMP) with histamine treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

H1- and H2-receptors in the guinea-pig heart: an electrophysiological study

The mechanical and electrophysiological effects of 2-pyridylethylamine (PEA) and 4-methylhistamine (4MeH) in different sections of guinea-pig heart were examined. 4MeH produced a dose-dependent increase in contractility in the right ventricle and the right atrium, and a decrease in functional refractory period (FRP) in all the sections studied; the action potential duration was decreased and the plateau phase was usually heightened in both atria and the ventricle. These effects were consistently antagonized by cimetidine. PEA-induced changes in contractility, FRP and the action potential profile were studied in the presence of cimetidine. Triprolidine antagonized PEA effects on FRP and the action potential profile only in the left atrium. The results obtained are discussed in terms of the functional role of both H1 and H2 receptors in the various guinea-pig heart sections.

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.

Chronotropic and dromotropic effects of histamine on the canine heart

The actions of 2-methylhistamine (H1 agonists), 4-methylhistamine (H2 agonist), and histamine were studied by selective perfusion of the sinus node artery and atrioventricular node artery in 75 dogs anesthetized with pentobarbital sodium. 2-Methylhistamine and histamine had variable and inconsistent effects on the sinus rate. 4-Methylhistamine (100 microgram/ml) produced acceleration of the sinus rate from 158 +/- 4 to 173 +/- 5 beats per minute (P less than 0.05) when perfused via the sinus node artery. The effects of the histamine agonists on atrioventricular junctional rhythms were similar to the effects on sinus rhythm. The response of the sinus node to vagal stimulation was attenuated by selective perfusion with histamine; however, the direct negatively chronotropic action of acetylcholine was not affected by histamine. Neither 2-methylhistamine nor 4-methylhistamine affected the response of the sinus node to vagal stimulations. Both 4-methylhistamine and histamine (but not 2-methylhistamine) attenuated (P less than 0.05) the response of the sinus node to stimulation of the right stellate ganglion. The positively chronotropic effects of directly perfused norepinephrine were unaffected by histamine or 4-methylhistamine. These results suggest a neural depressing action of histamine on autonomic efferent fibers. In the atrioventricular junction, both histamine and 2-methylhistamine (but not 4-methylhistamine) had negatively dromotropic effects. Cimetidine (an H2 antagonist) had no significant direct effects on the sinus rate or atrioventricular conduction and failed to prevent the acceleration of the sinus rate produced by local perfusion with 4-methylhistamine.