Characterization of β-adrenoceptors in urinary bladder: comparison between rat and rabbit
Research and Development Division, Hokuriku Seiyaku Co. Ltd., Katsuyama, Fukui 911, Japan.
- 1β-Adrenoceptor subtypes in rat and rabbit urinary bladder were investigated in functional experiments by use of several agonists and antagonists.
- 2All agonists tested produced concentration-dependent relaxation, but the relative potencies varied between both species: BRL 37344 (pD2:8.0)>isoprenaline (7.3)>adrenaline (6.7)=noradrenaline (6.6) in rat bladder, and isoprenaline (8.7)=adrenaline (8.5)>noradrenaline (7.7)=BRL 37344 (7.4) in rabbit bladder.
- 3The relaxation response to isoprenaline in rat bladder was relatively resistant to propranolol and ICI 118551, and the slopes of Schild plot for both antagonists were different from unity. The apparent pKB values estimated by single concentrations of propranolol (1, 10 μm) and ICI 118551(10 μm) were 6.6 and 5.4, respectively.
- 4On the other hand, the relaxation response to isoprenaline in rabbit bladder was antagonized by lower concentrations (1 nm–100 nm) of propranolol and ICI 118551 in a competitive manner, resulting in pA2 values of 8.7 and 8.6, respectively.
- 5These results suggest species-heterogeneity of β-adrenoceptors in urinary bladder; β3 and β2 subtypes in rat and β2 subtype in rabbit.