Exercise enhances vasorelaxation in experimental obesity associated hypertension

Objective: Regular exercise is recommended for the non-pharmacological trea tment of hypertension, but the mechanisms underlying the lowering of blood pressure remain controversial. Therefore, we studied the effects of 22-week -long training on blood pressure, arterial reactivity, and metabolic abnorm alities in a model of genetic obesity and moderate hypertension. Methods: O bese and lean Zucker rats were subjected to treadmill exercise from 8 to 30 weeks of age. Blood pressures were measured by the tail-cuff method, and u rine was collected in metabolic cages. At the end of the study, the samples for biochemical determinations were taken, and reactivity of isolated mese nteric and carotid arterial rings was examined in standard organ chambers. Results: The exercise prevented the elevation of blood pressure which was o bserved in non-exercised obese Zucker rats, and also reduced blood pressure in the lean rats. The relaxations of norepinephrine-preconstricted mesente ric and carotid arterial rings to acetylcholine and nitroprusside were clea rly improved by exercise in the obese rats. In the lean rats exercise enhan ced vasorelaxation to nitroprusside in the mesenteric and carotid rings, an d to acetylcholine in the carotid preparations. The exercise-induced improv ement of endothelium-mediated dilatation to acetylcholine was abolished by nitric oxide synthesis inhibition with N-G-nitro-L-arginine methyl ester, b ut not by cyclooxygenase inhibition with diclofenac or functional inhibitio n of endothelium-dependent hyperpolarization by precontractions with KCl. T he urinary excretion of the systemic prostacyclin metabolite (2,3-dinor-6-k etoprostaglandin F-1 alpha) was increased two-fold by exercise in the obese and lean rats, whereas that of the thromboxane A(2) metabolite (11-dehydro thromboxane B-2) remained unaffected. Treadmill training reduced blood gluc ose, cholesterol, and triglycerides, but did not affect the high levels of insulin in obese Zucker rats. Conclusions: These results suggest that the a ntihypertensive effect of long-term exercise in experimental obesity relate d hypertension is associated with improved vasodilatation. This is expresse d as enhanced relaxation via endogenous and exogenous nitric oxide, and inc reased endothelial prostacyclin production. The improved control of arteria l tone after training could be attributed to the alleviation of hyperlipide mia and insulin resistance, whereas hyperinsulinaemia per se remained unaff ected. (C) 1999 Elsevier Science B.V. All rights reserved.