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Web End = Naunyn-Schmiedeberg's Arch Pharmacol (2017) 390:527533 DOI 10.1007/s00210-017-1349-4
http://crossmark.crossref.org/dialog/?doi=10.1007/s00210-017-1349-4&domain=pdf
Web End = ORIGINAL ARTICLE
Stimulation of 1- and 2-adrenoceptors dilates retinal blood vessels in rats
Asami Mori1 & Akane Sekito1 & Kenji Sakamoto1 & Kunio Ishii1 & Tsutomu Nakahara1
Received: 13 December 2016 /Accepted: 24 January 2017 /Published online: 3 February 2017 # Springer-Verlag Berlin Heidelberg 2017
Abstract Our previous studies have demonstrated that adrenaline dilates rat retinal arterioles by stimulating propranolol-sensitive -adrenoceptors and 3-adrenoceptors, and selective stimulation of 2- or 3-adrenoceptors causes retinal vasodilator responses. In the present study, we compared the effects of 1- and 2-adrenoceptor stimulation on rat retinal arterioles in vivo. Rat ocular fundus images were captured using an original high-resolution digital fundus camera. Diameters of retinal arterioles contained in the images were measured. Systemic blood pressure and heart rate were recorded continuously. Denopamine, a 1-adrenoceptor agonist, increased the diameter of retinal arterioles and heart rate, and produced a small but statistically insignificant decrease in mean arterial pressure. CGP20712A, a 1-adrenoceptor antagonist, but not ICI118551, a 2-adrenoceptor antagonist, significantly prevented denopamine-induced retinal vasodilator and heart rate responses. Salbutamol, a 2-adrenoceptor agonist, increased the diameter of retinal arterioles and decreased mean arterial pressure without significantly changing heart rate. The effects of salbutamol were significantly prevented by ICI118551, but not by CGP20712A. These results suggest that stimulation of 1- and 2-adrenoceptors dilates retinal blood vessels and indicate that all three -adrenoceptor subtypes (1, 2, and 3) may be involved in the retinal vasodilator response to adrenaline in rats.
Keywords 1-adrenoceptor agonist . 2-adrenoceptor agonist . Retinal circulation . Vasodilation
Introduction
Retinal blood vessels lack autonomic innervation (Delaey and Van De Voorde 2000), but activation of the sympathetic nervous system could increase retinal blood flow by elevating the level of circulating adrenaline in rats (Nakazawa et al. 2008; Mori et al. 2011). Adrenaline caused retinal vasodilator responses by stimulating propranolol-sensitive -adrenoceptors and 3-adrenoceptors (Nakazawa et al. 2008; Mori et al.
2011). Selective agonists for 2- or 3-adrenoceptors induced vasodilation of the rat retinal arteriole (Mori et al. 2010). Thus, 2- and 3-adrenoceptor-mediated pathways appear to act as an important vasodilatory mechanism in rat retinal circulation (Nakazawa et al. 2008; Mori et al. 2010). 1-adrenoceptors are also expressed in vascular cells, and...