Identification and characterization of 3H-prazosin binding to alpha 1-adrenoceptors in bovine teat muscles.

The highly specific alpha 1-adrenoceptor antagonist 3H-prazosin was used to characterize alpha 1-adrenoceptors in smooth muscles of the cistern wall of teats of lactating cows. Binding was rapid, readily reversible, stereospecific and saturable. Scatchard analysis of saturation binding data on bovine teat membranes revealed that 3H-prazosin bound to a single class (Bmax = 128 +/- 13 fmol/mg of membrane protein) of noncooperative sites (Hill coefficient = 0.95 +/- 0.02) with high affinity (KD = 0.47 +/- 0.05 nM). Competition binding studies with 9 antagonists and 8 agonists, indicated that 3H-prazosin labeled the alpha 1-receptor.