ALPHA-1-ADRENERGIC RECEPTORS IN GUINEA-PIG MYOCARDIUM - IDENTIFICATION BY BINDING OF A NEW RADIOLIGAND, (PRAZOSIN-H-3

Binding of (3H)-prazosin to adrenoceptors in guinea pig myocardial membranes was rapid, readily reversible, stereospecific and saturable. By Scatchard analysis (n = 6) Bmax was 58 fmol of (3H)-prazosin bound/mg protein and the KD was 0.58 nm. The Hill number was 1.05. Adrenergic agonists competed with (3H)-prazosin as follows: (-)adrenaline > (-)noradrenaline > (-)phenylephrine ≫ (+)isoprenaline > (+)noradrenaline; antagonists competed in the order: non-radioactive prazosin > phentolamine ≫ piperoxan > yohimbine > sulpiride > propranolol. The KD for beta-adrenoceptors assessed by (-3H)-dihydroalprenolol was 0.86 nM and the Bmax (96 fmol/mg protein) was almost twice that of alpha-adrenoceptors. (3H)-prazosin appears to be a useful radioligand for the study of post-synaptic (alpha1) adrenoceptors in myocardial tissue. © 1979.