The effect of hypertension on bone decrease in hypertensive rats

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1. The effect of high salt intake on the mandibular bone in Dahl-Iwai salt-sensitive (DS) ratsTwenty-eight 11-week-old male DS rats were divided into four groups. The control groups received a normal (0.2% NaCl) diet while the experimental groups received a diet supplemented with 8.0% NaCl. The systolic blood pressure was significantly increased in the experimental groups compared to the control groups. The animals were sacrificed under ether anesthesia at the 8th week or the 22nd week of the experiment. The biochemical data in plasma and urine suggested negative calcium balance in the experimental groups compared to the control groups. The bone mineral density was significantly reduced at the 22nd week of high salt loading. The histomorphometric analysis suggested that the reduction of the mandibular bone volume had already started by the 8th week of high salt loading along with the increased bone resorption and the decreased bone formation, and that the improper bone remodeling balance became normalized by the 22nd week of high salt loading. In conclusion, these results indicate that a high salt intake causes not only severe hypertension but also a mandibular bone reduction in the DS rats.2. The effect of hypertension on bone mineral density in spontaneously hypertensive rats (SHR)The systolic-blood pressure was significantly increased in SHR compared to their normotensive genetic control Wistar Kyoto rats (WKY). There was no difference in bone mineral density of tibia and mandible between 7-week-old SHR and WKY.However, bone mineral density of tibia was significantly lower in 34-week-old SHR than in 34-week-old WKY.There was no difference in cortical bone but significant difference in cancellous bone. These results indicate that hypertension may not significantly reduce total mineral density of mandible because there is smaller amount of cancellous bone in mandible than in tibia.