Regional distribution of rat brain alpha 1-adrenergic receptors: correlation between (125I)-heat membrane binding and in vitro autoradiography

125I]-HEAT has proven useful for in vitro autoradiography as a specific alpha 1-adrenergic radioligand. We compared the binding of 125I]-HEAT to membranes from ten brain regions with the densitometric readings of these regions in autoradiographs. There was an excellent correlation between receptor numbers from membrane binding and relative optical densities from the autoradiography. The affinity of HEAT for binding to membranes from various regions was similar. The results of this direct comparison are further evidence that HEAT binds to alpha 1-adrenergic receptors in lightly fixed tissue sections. A further interesting observation is that in regions with a heterogeneous distribution of binding sites, membrane binding may not reflect the presence of a dense local population of receptors.