Effects of (-)-(R)-1-(p-hydroxyphenyl)-2-[3,4-dimethoxyphenethyl)amino]ethanol (TA-064), a new cardiotonic agent, on circulating parameters of carbohydrate and lipid metabolism in the rat

Effect of denopamine on the phosphorylation of cardiac muscle proteins in the perfused guinea-pig heart. Comparison with isoproterenol

Effects of the new selectively beta 1-adrenergic cardiotonic drug denopamine (TA-064) on the phosphorylation of cardiac muscle proteins in the perfused guinea-pig heart were investigated in comparison with isoproterenol. Denopamine at 3 X 10(-6) M and isoproterenol at 10(-7) M were equipotent in their effects on the contractile force and + (dF/dt). Under these conditions, the increases in heart rate and tissue c-AMP levels by denopamine were significantly less than those by isoproterenol. Isoproterenol exerted a greater effect on -(dF/dt) than on +(dF/dt), whereas denopamine influenced both to the same extent. Denopamine (3 X 10(-6) M) and isoproterenol (10(-7) M) both stimulated 32P incorporation into the proteins of molecular weights of 150,000, 30,000, 19,000, 15,000 and 11,000 daltons. Among these proteins, the 30,000 and 11,000 dalton proteins, probably troponin-I and phospholamban, were phosphorylated to significantly lesser extents by denopamine than by isoproterenol. The above differences in the effects on c-AMP levels and protein phosphorylation between denopamine and isoproterenol may be causally related to the differences in their pharmacological properties such as the weaker arrhythmogenicity and comparatively less marked relaxation effect of denopamine compared with isoproterenol in the presence of similar cardiotonic effects.

Beta 1-adrenergic selectivity of the new cardiotonic agent denopamine in its stimulating effects on adenylate cyclase

Effects of the new selectively beta 1-adrenergic cardiotonic drug denopamine (TA-064), (-)-(R)-1-(p-hydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino]ethanol, on the adenylate cyclase-adenosine-3',5'-monophosphate (c-AMP) system of various tissues and cells in rats and guinea pigs were investigated in comparison with those of isoproterenol. Denopamine at concentrations above 10(-6) M stimulated lipolysis in vitro, and, above 10(-5) M, elevated the c-AMP level in isolated rat fat cells. The c-AMP level of guinea-pig heart ventricular muscle was also elevated when the heart was perfused with 3 X 10(-6) M denopamine or when slices of ventricular muscle were incubated with 10(-6) M denopamine. These changes were abolished in the presence of beta-adrenergic antagonists. Incubation with denopamine did not cause substantial elevation of c-AMP levels in rat reticulocytes and diaphragm. Denopamine activated adenylate cyclase of the rat cell membranes in a concentration-dependent manner. Although dose dependence was less apparent, denopamine also activated adenylate cyclase of the membrane fraction from guinea pig cardiac muscle, but it hardly activated the same enzyme from rat reticulocytes. Isoproterenol, on the other hand, showed marked concentration-dependent activation of adenylate cyclase in all these preparations. Denopamine did not inhibit c-AMP phosphodiesterase of both particulate and supernatant fractions of guinea-pig cardiac muscle. The stimulation of lipolysis by denopamine was observed even when elevation of the c-AMP level was not detected, while the stimulation of lipolysis by isoproterenol was always accompanied with an elevation of c-AMP. When guinea-pig hearts were perfused with 3 X 10(-6) M denopamine or 10(-7) M isoproterenol, their cardiotonic effects were of the same magnitude whereas the degree of c-AMP elevation in the ventricular tissue by denopamine was significantly less than that by isoproterenol. It was concluded that stimulation of the adenylate cyclase-c-AMP system by denopamine was restricted to the tissues whose receptors were predominantly of the beta 1-type, and that the elevation of c-AMP levels in these tissues by denopamine was less marked than by isoproterenol, suggesting that the stimulation of lipolysis and heart by denopamine may be mediated by a special pool of c-AMP or some other unknown factor(s).

Studies on the affinity and selectivity of denopamine (TA-064), a new cardiotonic agent, for beta-adrenergic receptors

Denopamine is a new orally active cardiotonic agent. The present experiment was carried out to characterize the binding affinity and selectivity of this drug for beta-adrenergic receptor subtypes. Binding studies were performed using 3H-dihydroalprenolol as the radioligand. Binding affinities of denopamine and some beta-agonists for rat heart membranes (KiH), which contain predominantly the beta 1-subtype, were in the order of isoproterenol (Iso, 14.1 nM) greater than prenalterol (158) greater than norepinephrine (Nor, 227) greater than or equal to epinephrine (Epi, 248) greater than denopamine (545) greater than or equal to dobutamine (645) greater than procaterol (1440) greater than terbutaline (6420). In rat lung membranes (predominantly beta 2-subtype), the order of potency (KiL) was Iso (20.6 nM) greater than procaterol (70.2) greater than Epi (136) greater than prenalterol (412) greater than dobutamine (735) greater than or equal to Nor (744) greater than denopamine (2205) greater than terbutaline (2500). The beta 1/beta 2-selectivity as judged from the KiL/KiH values was in the order of denopamine (4.1) greater than Nor (3.3) greater than prenalterol (2.6) greater than Iso (1.5) greater than dobutamine (1.1) greater than Epi (0.55) greater than terbutaline (0.39) greater than procaterol (0.05). Practolol, a beta 1-antagonist, showed a high beta 1-selectivity (KiL/KiH = 15.3). In the presence of guanine nucleotide (GTP), the denopamine radioligand competition curve showed a rightward shift, and its Hill coefficient increased like other agonists, although the degree of the shift was less than that observed with full agonists such as Iso. These results essentially correspond with the pharmacological and biochemical properties of denopamine and confirm the beta 1-selectivity and the agonist property of this compound.