5-Methyl-urapidil discriminates between subtypes of the alpha 1-adrenoceptor.

The affinity of 5-methyl-urapidil for alpha 1-adrenoceptors was determined from the inhibition of [3H]prazosin binding on membrane of different rat tissues. In hippocampus, vas deferens and heart 5-methyl-urapidil displaced [3H]prazosin in a biphasic manner with mean pKI values between 9.1 and 9.4 for the high-affinity site and 7.2 to 7.8 for the low-affinity site. Only the low affinity site was found in spleen and liver. At present, 5-methyl-urapidil is the antagonist which most clearly discriminates between alpha 1-adrenoceptor subtypes.