Inhibitory effects of female sex hormones on urinary stone formation in rats

Background. The effects of female sex hormones on urinary stone formation a re not known. This study was conducted to investigate the effects of these hormones on stone formation by using an ethylene glycol (EG) and vitamin D- induced rat urolithiasis model. Methods. Adult female Wistar rats were fed the same diet for four weeks and were then divided into four groups (N = 10 each). One group was administer ed 0.5 mi of olive oil three times per week for four weeks as a control. Th e other three groups were administered 0.5 mu g of vitamin D-3 and 0.5 mi o f 5% EG three times per week for four weeks. The rats in two of these three groups were oophorectomized, and the rats of the remaining group underwent a sham operation on the day before the start of the four-week treatment pe riod. One of the two oophorectomized groups was then administered a supplem entation of female sex hormones (0.1 mg of estrogen and 2.5 mg of progester one 3 times per week for 4 weeks). On the first day of the fifth week of th e experimental period, the degree of crystal deposition was determined hist ologically, and the calcium content in renal tissue was measured. We also i nvestigated the level of osteopontin (OPN) mRNA in renal tissues by Norther n blot analysis. OPN is a matrix protein thought to be a promoter of stone formation. Results. The urinary oxalate excretion, crystal deposition and calcium cont ent in renal tissue and the expression of OPN-mRNA were greater in the ooph orectomized rats compared with the controls, and the same parameters were i nhibited by the female sex hormone supplementation. Conclusions. These results suggest that female sex hormones can inhibit ren al crystal deposition in EG-treated rats by suppressing the urinary oxalate excretion and the expression of OPN.