Effect of GTP on the affinity of denopamine, a new cardiotonic agent, for beta-adrenergic receptors of turkey erythrocytes and rat reticulocyte membranes

Primary alkylboronic acids as highly active catalysts for the dehydrative amide condensation of α-hydroxycarboxylic acids

Primary alkylboronic acids such as methylboronic acid and butylboronic acid are highly active catalysts for the dehydrative amide condensation of α-hydroxycarboxylic acids. The catalytic activities of these primary alkylboronic acids are much higher than those of the previously reported arylboronic acids. The present method was easily applied to a large-scale synthesis, and 14 g of an amide was obtained in a single reaction.

Circulatory effects of denopamine in newborn piglets

Denopamine is an orally active beta 1 agonist whose cardiovascular action in the newborn is unknown. We evaluated its circulatory effects during normoxia in newborn piglets less than 7 days of age. The piglets were acutely instrumented under general anesthesia with an electromagnetic flow probe around the main pulmonary artery and catheters in the main pulmonary artery, aorta, left ventricle, and the right and left atria. A Millar high-fidelity catheter was used to measure left ventricular dp/dt. The ductus arteriosus was ligated. Denopamine was administered in the right atrium as a continuous infusion of 2, 4, and 8 micrograms/kg per min for 10 min each. Although cardiac index, heart rate and left ventricular dp/dt increased dose-dependently by 46.0 +/- 18.2%, 87.1 +/- 34.9% and 159.9 +/- 42.4%, respectively, stroke index was not significantly altered. Unlike pulmonary artery pressure (which increased dose-dependently), aortic pressure increased with 2 and 4 micrograms/kg per min denopamine, respectively, it fell with 8 micrograms/kg per min denopamine. Similarly, the systemic vascular resistance decreased with the high dose (8 micrograms/kg per min). There was no significant change in pulmonary vascular resistance. Denopamine is potently inotropic in the adult. However, its circulatory effect in the neonate is dependent on its chronotropic action. Furthermore, denopamine is a systemic vasodilator at high doses in the neonatal circulation.

Tracheal relaxing effects and beta 2-selectivity of TA-2005, a newly developed bronchodilating agent, in isolated guinea pig tissues

Tracheal relaxing effects and beta 2-selectivity of TA-2005 were investigated by functional experiments and radioligand binding assay in guinea pigs in comparison with those of other beta-agonists, isoproterenol, procaterol, formoterol and salbutamol. The relaxing activity of TA-2005 on histamine-induced contraction in the isolated trachea was most potent among the five agonists, and it was blocked by a beta 2-selective antagonist (ICI 118,551) but not by a beta 1-selective antagonist (bisoprolol). The potency of the relaxing effect was in the order of TA-2005 (pD2 = 9.79) greater than formoterol greater than procaterol greater than isoproterenol greater than or equal to salbutamol. The positive chronotropic effect of TA-2005 was similar to that of isoproterenol; and it was more potent than those of formoterol, procaterol and salbutamol in the isolated atria. The selectivity for tracheal muscle to atria of these agonists were in the order of procaterol greater than greater than or equal to formoterol greater than TA-2005 greater than salbutamol much greater than isoproterenol. A radioligand binding experiment using guinea pig lung and cardiac ventricle as beta 2- and beta 1-adrenoceptor sources, respectively, has also demonstrated that TA-2005 possesses extremely high affinity (IC50 = 1.04 nM) and selectivity (38-fold) to beta 2-adrenoceptors. By addition of GTP, the competition curve of [125I]iodocyanopindolol shifted rightward, indicating the agonist property. These results confirmed that TA-2005 is a highly beta 2-selective agonist that exerts a potent tracheal relaxing effect.

Effect of chronic administration of denopamine (TA-064), a new positive inotropic agent, on cardiac response of rats to denopamine

Effects of chronic administration of denopamine on acute cardiovascular response to denopamine were studied in anesthetized rats. Effects of repeated treatment with isoproterenol was also investigated. The dose of denopamine to increase LV dp/dtmax by 50% of the control (ED50) was 0.77 mg/kg, p.o. Following chronic administration of denopamine once daily at 10 or 20 mg/kg, p.o., for 14 days, the effect of denopamine (i.v.) on LV dp/dtmax was similar to that in the control group. In the 40 mg/kg-group, however, the positive inotropic effect of denopamine (i.v.) was attenuated significantly at lower doses without a decrease in the maximal response and the ED50 was increased 1.8-fold. Chronic treatment with denopamine in the diet at 20 or 40 mg/kg/day for 14 days did not influence the response to the drug. By subcutaneous administration of 50 micrograms/kg isoproterenol, thrice daily for 3 days, the ED50 of isoproterenol (i.v.) for positive inotropy were increased 6.8-fold. In addition, the maximal response to isoproterenol was depressed to about 70% of that obtained in the control. In the preparation desensitized by isoproterenol (50 micrograms/kg), the inotropic response to denopamine was attenuated at lower doses, but the maximal response was not altered. In the groups desensitized by the two drugs, the positive chronotropic effect of the drugs (i.v.) tended to decrease and the effects on blood pressure was not changed. By Scatchard analysis, the specific 3H-dihydroalprenolol binding to the cardiac membranes (Bmax) was reduced in the 40 mg/kg denopamine (p.o.) group as well as in the isoproterenol-treated groups. In the 10 mg/kg denopamine and 20 mg/kg denopamine groups, however, Bmax was not changed. These results suggest that chronic administration of denopamine hardly results in desensitization of its positive inotropy at the effective doses.