Evaluation of Y-27632, a Rho-kinase inhibitor, as a bronchodilator in guinea pigs

Abstract

To evaluate (+)-(R)-trans-4-(l-Aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride, monohydrate (Y-27632), a selective Rho-kinase inhibitor, as a novel bronchodilator in vivo and in vitro, we investigated the effect of Y-27632 on the acetylcholine- or ovalbumin-induced increase in lung resistance (R_L) in non-sensitized or passively sensitized guinea pigs, and the relaxant effects of salbutamol, Y-27632 and theophylline on acetylcholine- or ovalbumin-induced contraction of isolated trachea. Y-27632 inhalation (1 mM, 2 min) inhibited acetylcholine- or ovalbumin-induced increase in R_L without changes in mean blood pressure, and the effect persisted for at least 3 h. Salbutamol, Y-27632 and theophylline each completely reversed the acetylcholine- or ovalbumin-induced contraction of isolated trachea with rank order of potency, salbutamol>Y-27632>theophylline. The relaxant effect of Y-27632 was not affected by propranolol. We conclude that, although Y-27632 is not as potent as a β-adrenoceptor agonist, Y-27632 may become an alternative inhaled bronchodilator, because Y-27632 is more potent than theophylline, and the relaxant effect is independent of β-adrenoceptors.

Introduction

A small G protein, RhoAp21, and its target protein, Rho-kinase, contribute to Ca²⁺ sensitization of contraction in a variety of smooth muscles Gong et al., 1996, Hirata et al., 1992, Somlyo and Somlyo, 1994, Uehata et al., 1997. A highly selective Rho-kinase inhibitor, (+)-(R)-trans-4-(l-Aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride, monohydrate (Y-27632), reversed G protein-mediated Ca²⁺ sensitization in permeabilized mesenteric arteries, and Y-27632 decreased mean blood pressure in hypertensive rat models (Uehata et al., 1997). Similarly, receptor-dependent, G-protein-mediated Ca²⁺ sensitization occurs in canine, rabbit, and human airway smooth muscle in vitro Iizuka et al., 1997, Iizuka et al., 1999, Yoshii et al., 1999, and Y-27632 completely relaxes airway smooth muscle through inhibition of Ca²⁺ sensitization (Yoshii et al., 1999).

The Y-27632 effect is likely to be independent of contractile receptor agonists. Further, the Y-27632 effect is independent of 3-isobutyl-1-methylxanthine, a phosphodiesterase inhibitor (Yoshii et al., 1999). These results suggest that the site of Y-27632 action is distinct from those of conventional bronchodilators such as β-adrenoceptor agonists and xanthine derivatives. However, Y-27632 has not been fully characterized as a bronchodilator in vivo and in vitro.

To address this issue, first, we investigated whether Y-27632 inhalation may inhibit the acetylcholine- or antigen-induced increase in lung resistance (R_L) without cardiovascular side-effects. In some experiments, we measured plasma concentrations of Y-27632, which was given to normotensive guinea pigs either intravenously (i.v.) or by inhalation. Second, we compared the relaxing potency of Y-27632 with that of conventional bronchodilators, salbutamol and theophylline, in isolated trachea contracted with acetylcholine or antigen.