Different atypical beta-adrenoceptors mediate isoprenaline-induced relaxation in vascular and non-vascular smooth muscles
Abstract
Atypical beta-adrenoceptors mediating smooth muscle relaxation were compared in several rat tissues including the distal colon, fundic strip, thoracic aorta and common carotid artery. Isoprenaline, CGP 12177 and BRL 37344 concentration-dependently relaxed longitudinal strips of the distal colon and fundus precontracted with carbachol (10(-6)M) as well as ring segments of the aorta and carotid artery precontracted with noradrenaline (10(-7)M). The rank order of potency was isoprenaline = BRL 37344 > CGP 12177 in the distal colon, isoprenaline = CGP 12177 > BRL 37344 in the aorta and carotid artery segments and isoprenaline > BRL 37344 > CGP 12177 in the fundic strip. Pretreatment with BRL 37344 induced a marked desensitization of the distal colon and fundic strips but not the aorta and carotid artery to isoprenaline. In the fundus and distal colon, pretreatment with CGP 12177 (10(-4)M abolished the effect of isoprenaline. Cyanopindolol (10(-6)M) shifted the isoprenaline curve to the right, without reducing the maximum response, in the distal colon fundic strip. -logKB values were 7.44 +/- 0.08 and 7.53 +/- 0.10 in the distal colon and fundic strip respectively. The same concentration of cyanopindolol did not inhibit the relaxant...Continue Reading
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