Responses mediated via beta-1 adrenoceptors but not beta-2 adrenoceptors exhibit supersensitivity after chronic reserpine pretreatment

Abstract

The purpose of this study was to examine whether reserpine pretreatment induces supersensitivity of both beta-1 and beta-2 adrenoceptor-mediated responses. Guinea pigs received reserpine (0.5 mg kg-1 s.c. or i.p.) daily for 7 days. Isolated tissues were set up in the presence of phentolamine (5 microM) and metanephrine (10 microM) and the sensitivity to isoproterenol and, where possible, a partial agonist (ritodrine, salbutamol or prenalterol) was determined. The beta adrenoceptor-mediated responses were recorded as the increase in rate and tension of right and left atria, inhibition of carbachol-induced contractions of ileum, relaxation of aortic spirals contracted with histamine, inhibition of transmurally stimulated vas deferens and relaxation of tracheal spirals and lung strips with intrinsic tone. The atria exhibited supersensitivity after reserpine pretreatment (s.c. and i.p.) as a leftwards shift of the isoproterenol concentration-response curve and elevation of the prenalterol maximum response. The ileum was also supersensitive, but only when tissues from animals receiving i.p. reserpine were compared with shams, which themselves were subsensitive or when reserpine was administered s.c. The trachea was also supersensitive, but not the aorta, lung and vas deferens, the responses of which are mediated via beta-2 adrenoceptors. In contrast, beta-1 adrenoceptors are involved in the atrial, ileal and tracheal responses. Therefore, only responses mediated via beta-1 adrenoceptors exhibited reserpine-induced supersensitivity which supports the hypothesis that beta-1 but not beta-2 adrenoceptors receive a sympathetic innervation.