Characterization and quantitation of alpha-adrenergic receptor subtypes in rat hypothalamus
The binding of [3H]dihydroergocryptine ([3H]-DHE) to rat hypothalamic membranes was examined. Displacement of [3H]-DHE by 100 nM phentolamine, prazosin and clonidine can be used to assay for total α-, α1- and α2-adrenergic receptor sites respectively. The α1-adrenergic receptor content of the hypothalamus is 4.1 pmoles/g tissue whereas the α2-level is 6.5 pmoles/g tissue. [3H]-WB 4101 (α1 selective) and [3H]clonidine (α2 selective) binding yielded similar levels of 3.2 and 5.8 pmoles/g tissue. It is concluded that [3H]-DHE is a suitable ligand for the assay of α-adrenergic receptor subtypes under the conditions determined in this study.