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

G-protein coupled receptors such as α -adrenergic receptors (AR) are linked via the G-protein G /G to both Ca entry and release of Ca from stores, but can also activate the small GTP binding protein RhoA and Rho kinase to produce contractions involving Ca sensitization. In rat portal vein, tonic but not phasic components of contractions to the α -AR agonist phenylephrine involve predominantly the α -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 α -AR in two further tissues to investigate the predominant α -AR subtype involved. We have examined the Rho kinase inhibitor fasudil in rat aorta and mouse spleen, tissues containing multiple α -AR subtypes. Male Wistar rats (250-300g) and C57 mice were killed by CO 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 37 C. Tissues were contracted with cumulative additions of norepinephrine (NE) in 0.5 log unit increments, over the concentration range 10 -10 M. Both α - and α -ARs mediate contractions of mouse spleen and the major α -AR involved is the α -adrenoceptor, and this receptor interacts with an α -AR at low, and an α -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 α -AR: α - and α -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 α -AR antagonist prazosin and the putative α -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 α -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 α -adrenoceptor are involved in contractions of both rat aorta and mouse spleen, the evidence suggests that, as previously reported in rat portal vein, α -adrenoceptors are most likely linked to the Rho kinase pathway Alsufyani 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.