Interactions between alinidine and responses to acetylcholine, dopamine and 5-hydroxytryptamine of specific Helix central neurones

Alinidine antagonizes the myocardial effects of adenosine

The bradycardiac drug alinidine (2.8-182.3 microM) antagonized the negative inotropic effect of adenosine in isolated left rat atria in a non-competitive fashion. A 50% reduction of the maximal adenosine effect was achieved with 64.6 microM alinidine. The shortening of the action potential duration and the suppression of slow action potentials in guinea pig atria by 1-10 microM adenosine could be abolished by 5.7 microM alinidine. Adenosine (1 mM) exerted a negative inotropic effect on isolated strips from the right ventricle of rat heart exposed to 0.36 microM isoproterenol, an effect which was fully antagonized by 91.1 microM alinidine. Addition of 1 mM adenosine to spontaneously beating isolated rat atria induced pronounced bradycardia. Under these conditions, the bradycardiac agent alinidine increased the contractile rate concentration dependently (11.4-182.3 microM), while the chemically unrelated bradycardiac compound UL-FS 49 did not accelerate the beat frequency. As alinidine antagonized all the cardiac actions of adenosine that we tested, it may be concluded that the drug interferes with A1-receptor-mediated effects.

Alinidine reverses the descending staircase of isolated rat atria by an antimuscarinic action

Contractile force of isolated atria from most mammalian species increases with the rate of electrical stimulation, resulting in an ascending staircase. In contrast, in the rat, contractile force decreases with increasing rate of stimulation (descending staircase). The bradycardic and antianginal drug alinidine (5.7-91.2 mumol/l) reversed the descending staircase to ascending by a positive inotropic effect at higher stimulation rates. Maximal positive inotropy was obtained with 45.6 mumol/l, a concentration which also caused maximal bradycardia in spontaneously beating atria. Concentrations of 1 mumol/l of the antimuscarinic compounds atropine as well as the quaternary salt ipratropium bromide also reversed the descending staircase of rat atria. Addition of alinidine did not cause any further increase in force of contraction under these conditions. Addition of 1 mumol/l physostigmine to isolated left atria from guinea pigs for blockade of acetylcholinesterase decreased contractility at all stimulation rates, but did not change the ascending character of the staircase. Alinidine antagonized the negative inotropic effect of physostigmine. The known antimuscarinic action of alinidine was quantified in electrically driven (0.25 Hz) left rat atria by antagonism of the negative inotropic effect of oxotremorine (0.01-10 mumol/l). Alinidine acted as a strictly competitive antagonist with a pA2 of 5.82. In isolated papillary muscle from guinea pigs, pretreated with reserpine for depletion of catecholamines, carbachol (0.1-3000 mumol/l) exerted positive inotropic effects. Alinidine antagonized also this effect in a competitive fashion with a pA2 value of 5.58.(ABSTRACT TRUNCATED AT 250 WORDS)