Effects of the Rho Kinase Inhibitor Fasudil on Adrenergic Contractions of Rat Aorta and Mouse Spleen

Abstract

G‐protein coupled receptors such as α1‐adrenergic receptors (AR) are linked via the G‐protein Gq/G11 to both Ca2+ entry and release of Ca2+ from stores, but can also activate the small GTP binding protein RhoA and Rho kinase to produce contractions involving Ca2+ sensitization. In rat portal vein, tonic but not phasic components of contractions to the α1‐AR agonist phenylephrine involve predominantly the α1B‐AR subtype, and are at least partly mediated by mechanisms involving Rho kinase sensitive to fasudil (Alsufyani & Docherty, 2021). In this study we examined the involvement of Rho Kinase in contractions involving α1‐AR in two further tissues to investigate the predominant α1‐AR subtype involved. We have examined the Rho kinase inhibitor fasudil in rat aorta and mouse spleen, tissues containing multiple α1‐AR subtypes. Male Wistar rats (250‐300g) and C57 mice were killed by CO2 overdose and cervical dislocation, and rat aortic rings and mouse spleens were mounted in organ baths under 0.5 g tension, and bathed with Krebs‐Henseleit solution at 37oC. Tissues were contracted with cumulative additions of norepinephrine (NE) in 0.5 log unit increments, over the concentration range 10‐8‐10‐3M. Both α2‐ and α1‐ARs mediate contractions of mouse spleen and the major α1‐AR involved is the α1B‐adrenoceptor, and this receptor interacts with an α1D‐AR at low, and an α1A‐AR at high, NE concentrations (Alsufyani et al., 2021). In mouse spleen, fasudil (3 μM) reduced contractions to both low and high concentrations of NE. In rat aorta, contractions to NE are reported to be mediated by two subtypes of α1‐AR: α1B‐ and α1D‐ARs, with responses to low but not high concentrations of NE being sensitive to the antagonist BMY7378. Responses to high concentrations of NE in rat aorta are sensitive to the non‐selective α1‐AR antagonist prazosin and the putative α1B‐AR antagonist cyclazosin. Fasudil (3 and 10 μM) significantly reduced contractions to both low and high concentrations of NE in rat aorta in a dose dependent manner in terms of maximum response. It is concluded that α1‐AR mediated contractions to NE in both rat aorta and mouse spleen are sensitive to non‐competitive block by the Rho kinase inhibitor fasudil in concentrations of 3‐10 μM. Although multiple subtypes of α1‐adrenoceptor are involved in contractions of both rat aorta and mouse spleen, the evidence suggests that, as previously reported in rat portal vein, α1B‐adrenoceptors are most likely linked to the Rho kinase pathwayAlsufyani HA & Docherty, J.R. Can J Physiol Pharmacol. 2021 Jun;99(6):654‐659. Alsufyani HA, et al. Basic Clin Pharmacol Toxicol. 2021 Dec;129(6):416‐426.