Rilmenidine (hemifumarate)

Rilmenidine is an antihypertensive agent that has been shown to lower arterial pressure in various animal models by inhibiting the tonic activity of sympathoexcitatory neurons in the rostral ventrolateral medulla [1].

In vitro: Bilateral microinjection of rilmenidine into the C1 area of the rostral ventrolateral medulla (RVL) elicited dose-dependent falls in arterial pressure and heart rate. In RVL, rilmenidine competed with binding to imidazole and α2-adrenergic binding sites with a 30-fold selectivity for the imidazole binding sites [2]. Rilmenidine, a new antihypertensive agent, appeared 2.5 and 3.5 times more selective than clonidine and guanfacine, respectively, for medullary IPR sites than for cortical α-adrenoceptors [3]. Rilmenidine targeted the nonadrenergic imidazoline-binding site I1 receptor with the Ki value of 7.1 nM and demonstrated weaker affinity for the I2 receptor with the Ki value of 5.2 μM [4].

In vivo: In rat model of hypertension associated with insulin resistance, rilmenidine ameliorated the deleterious effects of a high-fructose diet, such as weight gain, hypertension, and resistance to the effects of insulin [5]. In a mouse model of Huntington's disease, rilmenidine induced autophagy, attenuated toxicity of polyglutamine expansions and the signs of disease, reduced the mutant huntingtin fragment levels [6].

References:
[1] Reis, D. J. and Piletz, J.E. The imidazoline receptor in control of blood pressure by clonidine and allied drugs. American Journal of Physiology 273(5 Pt 2), R1569-R1571 (1997).
[2] Gomez R E, Ernsberger P, Feinland G, et al.  Rilmenidine lowers arterial pressure via imidazole receptors in brainstem C1 area[J]. European journal of pharmacology, 1991, 195(2): 181-191.
[3] Bricca G, Dontenwill M, Molines A, et al.  Rilmenidine selectivity for imidazoline receptors in human brain[J]. European journal of pharmacology, 1989, 163(2): 373-377.
[4] Guyenet P G.  Is the hypotensive effect of clonidine and related drugs due to imidazoline binding sites [J]. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 1997, 273(5): R1580-R1584.
[5] Penicaud L, Berthault M F, Morin J, et al.  Rilmenidine normalizes fructose-induced insulin resistance and hypertension in rats[J]. Journal of hypertension. Supplement: official journal of the International Society of Hypertension, 1998, 16(3): S45-9.
[6] Rose C, Menzies F M, Renna M, et al.  Rilmenidine attenuates toxicity of polyglutamine expansions in a mouse model of Huntington's disease[J]. Human molecular genetics, 2010, 19(11): 2144-2153.