EFFECTS OF ESTROGEN REPLACEMENT ON INSULIN-LIKE GROWTH FACTOR-I CONCENTRATIONS IN SERUM AND BONE TISSUE AND ON INTERLEUKIN-1 SECRETION FROM SPLEEN MACROPHAGES IN OOPHORECTOMIZED RATS

Oophorectomy (OOX) has been known to increase bone turnover, but its precise mechanism is not fully understood. In order to further investigate the mechanism, we determined insulinlike growth factor I (IGF-I) concentrations in serum and bone tissue and interleukin 1 (IL-1) release from spleen macrophages in oophorectomized rats because it has been demonstrated that IGF-I stimulates bone formation and IL-1 stimulates bone resorption. Female 8-week-old Wistar rats were divided into four groups: (1) control, (2) OOX, (3) OOX given estradiol, and (4) control given estradiol. Ten mug/kg of 17beta-estradiol was given daily by subcutaneous injection. After 5 weeks of treatment, IGF-I concentrations in the extract from right femur and in serum were determined by specific radioimmunoassay. IL-1 activity released from lipopolysaccharide (LPS)-stimulated spleen macrophages was determined by bioassay. IGF-I contents in the femur and IGF-I concentrations in serum in oophorectomized rats were significantly higher than those in control rats. Treatment by estradiol inhibited the increase in IGF-I concentrations both in femur and in serum. IL-1 release from LPS-stimulated spleen macrophages in oophorectomized rats was increased, and treatment by estradiol also inhibited the stimulated IL-1 release. The ash weights and the calcium contents of left femur in oophorectomized rats were lower than those in control rats. These results suggest that both IGF-I and IL-1 may be involved in the mechanism of the regulation of bone turnover in oophorectomized rats.