title: Impaired insulin-induced attenuation of noradrenaline-mediated vasoconstriction in insulin-resistant obese Zucker rats.
abstract: 1. Insulin resistance is associated with hypertension but the underlying mechanism is unclear. We tested the hypothesis that insulin-induced vasodilatation is impaired in insulin-resistant obese Zucker rats. We studied mesenteric artery (approximately 220 microns diameter) function before the development of hypertension in 3-month old obese Zucker rats and age-matched lean rats. 2. In vessels from lean rats, insulin at concentrations of 50, 500 and 5000 m-units/l attenuated the constriction in response to noradrenaline (50 m-units/l: 8 +/- 3%, P < 0.05; 500 m-units/l: 13 +/- 3%, P < 0.02; 5000 m-units/l: 13 +/- 2%, P < 0.02). 3. Vessels from obese rats failed to show any such response to insulin (2 +/- 6% increase in maximal tension with 5000 m-units/l; not significant), both in the presence and absence of L-arginine (3 mmol/l). 4. Vessels from obese rats showed slight but significant impairment in the vasodilator response to acetylcholine (5 x 10(-8)-10(-4) mol/l) (obese: 64.1 +/- 3.7% relaxation; lean: 77.3 +/- 3.7% relaxation; P < 0.05); however, relaxation in response to A23187 was not significantly different between the phenotypes (obese: 81.3 +/- 10.6% relaxation; lean: 79.1 +/- 9.7% relaxation; not significant). 5. Systolic blood pressure was not significantly different in lean (126 +/- 8 mmHg) and obese (127 +/- 7 mmHg) rats at the time of study (not significant). 6. We conclude that insulin-induced attenuation of noradrenaline-mediated vasoconstriction is impaired in the obese Zucker rat and that this defect precedes and therefore could contribute to the development of hypertension in this insulin-resistant model. The defect in insulin action could reside in the endothelial generation of nitric oxide, as endothelial function is also abnormal.
authors.affiliation: Diabetes and Endocrinology Research Group, University Clinical Departments at Aintree, Fazakerley Hospital, Liverpool, U.K.
authors.forename: A B
authors.initials: AB
authors.lastname: Walker
authors.forename: J
authors.initials: J
authors.lastname: Dores
authors.forename: R E
authors.initials: RE
authors.lastname: Buckingham
authors.forename: M W
authors.initials: MW
authors.lastname: Savage
authors.forename: G
authors.initials: G
authors.lastname: Williams
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D007333:Insulin Resistance / Q000502:physiology*; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008638:Mesenteric Arteries; D009638:Norepinephrine / Q000494:pharmacology*; D009765:Obesity / Q000503:physiopathology*; D051381:Rats; D011924:Rats, Zucker; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D007328:Insulin; D007476:Ionophores; D000001:Calcimycin; D001120:Arginine; D000109:Acetylcholine; D009638:Norepinephrine