Heterogeneity of imidazoline binding sites revealed by a cirazoline derivative.

The affinity of AMPI (2-[3-aminophenoxy]methyl imidazoline) for [3H]clonidine and [3H]idazoxan imidazoline binding sites was determined in various rabbit and human tissues. Although cirazoline showed a high affinity (nM range) in all the tested tissues, its derivative, AMPI, had a high affinity (nM range) in rabbit brain and kidney but a low affinity (microM range) in the human brain. These differences in affinities were very similar to those obtained with amiloride. The same results were obtained when considering [3H]clonidine or [3H]idazoxan specific imidazoline binding sites.