Clonidine-d₄is intended for use as an internal standard for the quantification of clonidine by GC- or LC-MS. Clonidine is an agonist of α₂-adrenergic receptors (α₂-ARs; K_is = 61.66, 69.18, and 134.9 nM for α_2A-, α_2B-, and α_2C-ARs, respectively).¹It stimulates [³⁵S]GTPγS binding to HEK293 cell membranes expressing the human receptors with EC₅₀values of 26.92, 56.23, and 912.01 nM for α_2A-, α_2B-, and α_2C-ARs, respectively. Clonidine also binds to I₁-imidazoline sites in a variety of cell and tissue types (K_ds = 4-15 nM).²It induces relaxation of isolated mesenteric artery rings precontracted with norepinephrine when used at a concentration of 10 μM.³Clonidine (10 μM) also induces membrane hyperpolarization and reduces norepinephrine-induced depolarization in isolated mesenteric artery rings. Clonidine (0.1 and 1 μg/kg) reduces mean blood pressure and heart rate when administeredviamicroinjection to the nucleus reticularis lateralis (NRL) of anesthetized normotensive cats.⁴Formulations containing clonidine have been used in the treatment of hypertension.

1.Jasper, J.R., Lesnick, J.D., Chang, L.K., et al.Ligand efficacy and potency at recombinant α2 adrenergic receptors: Agonist-mediated [35S]GTPγS bindingBiochem. Pharmacol.55(7)1035-1043(1998) 2.Ernsberger, P., Graves, M.E., Graff, L.M., et al.I1-imidazoline receptors. Definition, characterization, distribution, and transmembrane signalingAnn. N.Y. Acad. Sci. 763(1)22-42(1995) 3.Silva, E.G., Feres, T., Vianna, L.M., et al.Dual effect of clonidine on mesenteric artery adrenoceptors: Agonistic (alpha-2) and antagonistic (alpha-1)J. Pharmacol. Exp. Ther.277(2)872-876(1996) 4.Bousquet, P., Feldman, J., and Schwartz, J.Central cardiovascular effects of alpha adrenergic drugs: Differences between catecholamines and imidazolinesJ. Pharmacol. Exp. Ther.2301(1)232-236(1984)