Comparison of beta-adrenoceptor populations in cat and guinea-pig left atria

The subtypes of beta-adrenoceptor present in left atrial preparations from the guinea-pig and cat have been assessed using both responses obtained in organ bath experiments and radioligand binding studies. From the positive inotropic responses to procaterol, the pKB values for practolol using a variety of agonists, and from displacement of [125I]cyanopindolol from left atrial membrane homogenates by the selective beta 1- and beta 2-adrenoceptor antagonists L643,717-01J10 and ICI 118,551, it was concluded that guinea-pig left atria possess only beta 1-adrenoceptors, whilst cat left atria possess both beta 1- and beta 2-adrenoceptor subtypes.