Adrenoceptor subtypes and their cholinoceptor-induced blockades in mammalian atria

Abstract

1. In the presence of pilocarpine, the concentration-effect curve of isoprenaline consisted of two curves with widely different pD 2 values. 2. Between 0.1-10 μM pilocarpine, the low pD 2 curve was unaltered; but the other curve was shifted parallely rightward to a fixed position at which gradual decrease in amplitude ensued. 3. Atropine abolished all effects of pilocarpine. But phentolamine prevented only the decrease in amplitude of isoprenaline curve. 4. Similar results occurred in various mammalian atria and when (-) isoprenaline was used. The positions of the high pD 2 curves of (-) and racemic isoprenalines were different; but those of the low pD 2 ones were the same. © 1979.