| Background and objective: Although the prevalence of clinical hypertension is of a far lesser magnitude in children than in adults, there is ample evidence to support the concept that the roots of essential hypertension extend back into childhood. Diet is an important factor influencing blood pressure. Precious studies showed increase in dietary simple sugars intake could raise blood pressure in adult rats. The blood pressure of the rats with high-sugar diet for 2~4 weeks is 5~20mmHg higher than that of control rats. Yet the mechanism involved is not clearly and different opinions exist. Some studies shows that the blood pressure elevation induced by high-sugar intake is associated with insulin resistance (IR) and hyperinsulinmia, while other articles support the view that this effect is caused by increased activity of renin-angiotensin system (RAS) and sympathetic nerve system. This study is aimed to investigate the effects of high-sucrose on blood pressure of developing Wistar rats, the role that sympathetic nerve system might play in this process and the change of vascular response to various vasoactive agents. Methods: Thirty-two male neonatal Wistar rats were included in the study. Sixteen of them underwent chemical sympathectomy, produced by intra-peritoneal administration of 6-hydroxydopamine (6-OHDA), while the others were treated with vehicle (0.1%VitC saline) alone. Then the rats weredivided into four groups after three weeks weaning: 0.1%VitC saline-normal chow group (VN), 0.1% VitC saline-high sucrose group (VS), 6-OHDA- normal chow group (OHN), 6-OHDA-high sucrose group (OHS). Body weight (BW) was observed for the following eight weeks. The tail-cuff method was used to measure systolic blood pressure (SBP) and heart rate (HR) from the fourth to the eighth week. Then hemodynamic measurements were performed, and the responses of blood pressure to tyramine and various vasoactive agents, i.e. angiotensinⅡ(AngⅡ), norepinephrine (NE), acetylcholine (ACh) and nitroglycerini (NTG), were recorded. The effectiveness of sympathectomy was tested by comparing the pressor and tachycardic responses to tyramine in rats treated with 6-OHDA with those in untreated rats. And then the thoracic aorta was dissected, carefully freed from connective tissue, and placed in phosphate buffer solution, pH 7.4 at 37℃. Isometric force of the aortic ring segments was measured according to established methods using a force transducer connected with a polygraph. Aorta ring segments were constricted with potassium chloride (KCl), AngⅡ and NE. Endothelial-dependent vasorelaxation was measured with ACh and endothelial-independent vasorelaxation was measured using NTG. Contractions were expressed as the percentage of contraction produced by KCl and relaxations were expressed as the percentage of contraction produced by NE. Morphological studies were performed in the heart, thoracic aorta and ren. Moreover, the level of blood glucose, plasma insulin and AngⅡ were measured. Expression of AngⅡ receptor 1 (AT1) mRNA was examined by RT-PCR assay.Results: 1. 6-OHDA treatment produced a subtotal sympathectomy (about 70%). 2. Weight gain was not affected by either high-sucrose diet or chemical sympathectomy.Higher blood pressure was observed in the VS group but not in the3. OHS group. 4. Morphological studies showed that no significant changes in the heart, aorta and ren were found in all groups.5. The pressor responses to AngⅡ and NE were significantly larger in sympathectomized rats in vivo than in control rats. The responses to ACh and NTG were similar in all groups. 6. Vasoconstriction of the aorta ring segments to AngⅡand NE increased in the VS group. Vasorelaxation to ACh and NTG were similar in all groups.7. The concentrations of blood glucose and plasma insulin were similar in all groups, as well as the insulin sensitivity index (ISI). The level of plasma AngⅡ increased significantly in the VS group and the OHS group.8. The expression of AT1 mRNA in the aorta increased in... |
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