<Originals>The inhibitory effects of female sex hormones on urinary stone formation in rats

There is no sex difference in the incidence of urolithiasis in childhood or climacterium, but the male to female ratio has been reported to be approximately 3 : 1 during the reproductive stage. This suggests that female sex hormones inhibit stone formation. Based on this observation, the influences of female sex hormones on stone formation were investigated in female rats with experimentally induced stones. Oophorectomized groups (A and C) and non-oophorectomized groups (B and D) were prepared. Stones were induced by administering vitamin D_3 and ethylene glycol for 12 weeks in Groups A and B, and for 4 weeks in Groups C and D. Groups E and G were prepared in a similar manner to Group C, and Group F was prepared in a similar manner to Group D. To supply the female sex hormones, estrogen and progesterone were also given to Group G. The degree of stone formation was determined histologically ; simultaneously, bone mineral content was determined with microdensitometry. The levels of various other stone-related substances, estradiol and hydroxyproline, as well as calcium content in renal tissue were measured. Osteopontin m-RNA in renal tissues was also determined by Northern blot technique. The urinary excretion of citric acid and bone mineral content were decreased and the incidence of stone formation was increased in oophrectomized rats. Stone formation in renal tissue and the appearance of osteopontin, a component of stone matrix, were inhibited by female sex hormones supplements. These results suggest that the low incidence of urolithiasis in women of reproductive age is attributable to female sex hormones.