Inhibition of rat colon motility by stimulation of atypical beta-adrenoceptors with new gut-specific agents.

The new putative beta-adrenergic agonists SR 58306A, 2-[(7-hydroxy-1,2,3,4-tetrahydronaphth-2-yl)amino]-1-phenylethanol hydrochloride and SR 58339A, 2-[(7-hydroxy-1,2,3,4-tetrahydronaphth-2-yl)amino]-1- (3-chlorphenyl) ethanol hydrochloride, were studied in vitro in comparison with reference compounds. SR 58306A and SR 58339A, unlike isoprenaline and the beta2 selective adrenergic agonists salbutamol and ritodrine, potently inhibited rat colon spontaneous contractions (EC50 5.9 and 1.1 x 10(-7) M) without increasing guinea-pig atrium frequency or relaxing guinea-pig trachea. The nonselective beta-adrenergic antagonists alprenolol, pindolol and propranolol competitively antagonized the action of SR 58306A on the colon, which was not prevented by either of the selective antagonists atenolol (beta 1) and ICI 118551 (beta 2). In the same preparation only alprenolol competitively antagonized isoprenaline; antagonism by either pindolol or propranolol was not competitive. These results suggest that in the rat colon isoprenaline interacts with different beta-receptor subclasses, whereas our new gut-specific compounds such as SR 58306A inhibit colonic motility by selectively stimulating atypical beta-adrenoceptors.