Bousquet et al., Coupry et al., and Ernsberger et al. in the 1980s. 1 Recently, agmatine (1, Figure 1) has been proposed to be the endogenous ligand for the I receptors. 2 There is some question whether agmatine is the sole endogenous agent. 3 These receptors do not interact with catecholamines including norepinephrine (2), the natural ligand for adrenoceptors. The imidazoline family of receptors does, however, recognize many ...
