Evidence for alpha 2 adrenergic receptors in bovine cerebral arteries

Specific [3H]yohimbine binding to the homogenates of bovine cerebral arteries was saturable and of high affinity (KD = 21 nM) with a Bmax of 720 fmol/mg protein. On the other hand, there was no detectable specific [3H]prazosin binding to these tissues. Scatchard and Hill plot analyses of specific [3H]yohimbine binding indicated one class of binding sites. Specific binding of [3H]yohimbine was displaced effectively by alpha 2 adrenergic agents and less effectively by alpha 1 adrenergic agents. IC50 values for adrenergic drugs of [3H]yohimbine binding were as follows: yohimbine, 55 nM; tramazoline, 270 nM; clonidine, 580 nM; methoxamine, 15 microM; prazosin, 47 microM, phenylephrine, 49 microM; norepinephrine, 60 microM; epinephrine, 150 microM. These results suggest that alpha adrenergic receptors in bovine cerebral artery are mostly of the alpha 2 subtype.