Effect of Parathyroid Hormone on Left Ventricular Hypertrophy in Aged Ovariectomized Rats

Background：It has been well known that the bone and kidney are the principle organs of parathyroid hormine (PTH) actions. Although patients with primary hyperparathyroidism show a high incidence of LVH and trophic effects of PTH on adult rat ventricular cardiomyocytes were investigated in vitro, effect of PTH on the cardiac tissue in vivo is unknown. Methods：We examined the effects of PTH on the cardiomyocyte and interstitial tissue using adult rat heart. Twenty-two female Sprague-Dawley rats were ovariectomized bilaterally at three months old and weighing in 250-300 gm in order to exclude the trophic effect of estrogen. We administrated human parathyroid hormone (20 ug subcutaneously 5 times per week) to 12 rats for 4 weeks after raising for 8 weeks (PTH group)；the remaining 10 rats received only normal saline (control). We measured left ventricular thickness [IVS＋LVPW]/2] and number of cardiomyocytes and interstitial fibrosis on LM (H & E and Masson’s trochrome stain) and EM. Results：1) LV wall thickeness tended to increase in PTH group as compared with control (2.16±0.31 vs 1.12±0.21 mm, p＝0.099). 2) The number of cardiomyocyte in PTH group was significantly less than that of control (61.2±13.1 vs 70.5±14.9, p＝0.003, Magnification ×400). 3) There was no significant change of interstitial fibrosis between PTH group and control. Conclusion：These results shggest that PTH may produce left ventricular hypertrophic effects i