title: Imidazoline receptors in the heart: characterization, distribution, and regulation.
abstract: Imidazoline receptors were identified in cardiac tissues of various species. Imidazoline receptors were immunolocalized in the rat heart. Membrane binding and autoradiography on frozen heart sections using 0.5 nM para-iodoclonidine (125I-PIC) revealed that binding was equally and concentration-dependently inhibited by epinephrine and imidazole-4-acetic acid (IAA), implying 125I-PIC binding to cardiac alpha2-adrenergic and I1-receptors, respectively. After irreversible blockade of alpha2-adrenergic receptors, binding was inhibited by the selective I1-agonist, moxonidine, and the I1-antagonist, efaroxan, in a concentration-dependent (10-12 to 10-5 M) manner. Calculation of kinetic parameters revealed that in canine left and right atria, I1-receptor Bmax was 13.4 +/- 1.7 and 20.1 +/- 3.0 fmol/mg protein, respectively. Compared to age-matched normotensive Wistar Kyoto rats, I1-receptors were increased in 12-week-old hypertensive rat (SHR) right (22.6 +/- 0.3 to 43.7 +/- 4.4 fmol/unit area, p < 0.01) and left atria (13.3 +/- 0.6 to 30.2 +/- 4.1 fmol/unit area, p < 0.01). Also, compared to corresponding normal controls, Bmax was increased in hearts of hamsters with advanced cardiomyopathy (13.9 +/- 0.4 to. 26.0 +/- 2.3 fmol/unit area, p < 0.01) and in human ventricles with heart failure (12.6 +/- 1.3 to 35.5 +/- 2.9 fmol/mg protein, p < 0.003). These studies demonstrate that the heart possesses imidazoline I1-receptors that are up-regulated in the presence of hypertension or heart failure, which would suggest their involvement in cardiovascular regulation.
authors.affiliation: Laboratory of Cardiovascular Biochemistry, Center Hospitalier de L'Université de Montréal Research Center, Campus Hotel-Dieu, Quebec, Canada.
authors.forename: Rouwayda
authors.initials: R
authors.lastname: El-Ayoubi
authors.forename: Jolanta
authors.initials: J
authors.lastname: Gutkowska
authors.forename: Soundar
authors.initials: S
authors.lastname: Regunathan
authors.forename: Suhayla
authors.initials: S
authors.lastname: Mukaddam-Daher
mesh_terms: D000818:Animals; D009202:Cardiomyopathies / Q000378:metabolism; D006224:Cricetinae; D004285:Dogs; D006801:Humans; D054755:Imidazoline Receptors; D008647:Mesocricetus; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism*; D009928:Organ Specificity; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D011955:Receptors, Drug / Q000032:analysis / Q000378:metabolism*; D012756:Sheep
chemical_list: D054755:Imidazoline Receptors; D011955:Receptors, Drug