Arterial blood pressure and aortic responses in obese, age-grouped Zucker rats

Endothelial dysfunction is one of the many proposed mechanisms of hypertension and it may justify, at least in part, the increased blood pressure of hypertensive subjects. Nevertheless, the exact mechanisms involved in the hypertensive condition of obese Zucker rats are unclear. In this study, we measured the arterial blood pressure (tail cuff method) of four groups of seven, female, obese Zucker rats each. The rats of groups 1-4 were 9-12, 15-18, 21-24 and 27-30 weeks old respectively. We also evaluated the responses of aortic rings to KCl, methoxamine and acetylcholine, in these animals. Aortic rings were successively exposed to 80 mM KCl and to methoxamine (10(-8)-10(-5) M). The endothelium-dependent relaxation to acetylcholine (10(-9)-10(-5) M) was also established in the methoxamine-precontracted tissue (precontraction close to 80% of the maximum effect of methoxamine). A clear increase in the arterial blood pressure was observed when the age of these animals increased. The contractile responses to KCl and methoxamine were lower in the aortic rings of rats with increased arterial blood pressure. The response to acetylcholine was lower in the rings from 15-18, 21-24 and 27-30 weeks old rats, than in the younger groups. In conclusion, obese Zucker rats develop hypertension and endothelial dysfunction. Nevertheless, the arterial contractions elicited by depolarization or by α(1)-adrenoceptor stimulation decrease in aged, obese Zucker rats.