Dissociation constants and relative efficacies estimated from the functional antagonism of β-adrenoceptor agonists on transmural stimulation in rat vas deferens

Different mechanisms of action of agents acting on β‐adrenoceptors in barium‐stimulated and electrically‐stimulated rat vas deferens

“…The results obtained either in field-stimulated vas deferens or in organs contracted by barium chloride, support previous findings that the relaxation induced by f-adrenoceptor agonists are mediated by 12-adrenoceptors (Ganguly & Bhattacharya, 1969;Vohra, 1979;Lotti et al, 1980;Diaz-Toledo & Jurkiewicz, 1980;1990). This was indicated, according to Lands et al (1967), by the rank order of potencies for the agonists (Iso > Ad > NA), when the organ was electrically stimulated (Table 1) increase for isoprenaline and adrenaline potencies but the overall hierarchy was not substantially modified.…”

“…In the latter case, Iso, Ad, and NA elicited a dose-dependent decrease of the amplitude of twitches, without affecting the baseline (Diaz-Toledo & Jurkiewicz, 1980;1990). However, if the concentrations of these agonists were further increased, an undesirable rise in the baseline occurred, due to a well-known concentrationdependent interaction with postsynaptic a-adrenoceptors (Jurkiewicz & Jurkiewicz, 1976); the minimum concentrations of these agonists to start such an increase in the baseline were about 3 x 10-7M for Ad and NA, and 3 x 10-5M for Iso (Diaz-Toledo, 1983).…”

“…Almost all the results are based on functional antagonism against electrically-induced twitches (Ganguly & Bhattacharya, 1969;Vohra, 1979;Lotti et al, 1980;Diaz-Toledo & Jurkiewicz, 1980;1990).…”

Thermodynamic study of the interaction between terbutaline and salbutamol with an immobilized β2-adrenoceptor by high-performance liquid chromatography

“…The association constants obtained in this study showed good agreement with previous values reported for binding regions of terbutaline oň expressed in the membrane of Escherichia coli [31]. Diaz-Toledo et al determined a dissociation constant of 6.3 × 10 −6 M for terbutaline binding to theˇ2-AR expressed in rat vas deferens [32]. For salbutamol, similar conclusion that it had two kinds of major binding sites was also reported in the literature [29,33].…”