Harmane produces hypotension following microinjection into the RVLM:: possible role of I1-imidazoline receptors

The beta-carboline, harmane (0.1-1.0 nmol) produces dose dependent hypotension when microinjected unilaterally into the rostral ventrolateral medulla (RVLM) of the anaesthetized rat. The potency of harmane on blood pressure is similar to that of the imidazoline, clonidine. The hypotensive effects of both clonidine and harmane are reversed by microinjection of the relatively I-1-receptor selective antagonist efaroxan (20 nmol). These results are consistent with harmane acting at an I-1-receptor in the RVLM. This is the first report of an endogenous ligand for I-1-receptors that has central effects on blood pressure.