5‐Methylurapidil may discriminate between α1‐adrenoceptors with a high affinity for WB4101 in rat lung

The α1‐adrenoceptors of rat lung with a high affinity for [3H]‐prazosin were subdivided into two populations (high and low affinity sites) by WB4101 and 5‐methylurapidil but the proportions were different between both drugs. After pretreatment with chlorethylclonidine, WB4101 recognized only high affinity sites, while 5‐methylurapidil still detected high and low affinity sites. These results indicate that α1‐adrenoceptors with a high affinity for WB4101 are not homogeneous in the rat lung, suggesting the possible existence of a new α1‐adrenoceptor subtype in addition to α1A and α1B subtypes.