This study was designed to determine whether combined treatments with genistein dosage and moderate resistance exercise would exhibit synergistically preventive effects on bone loss following the onset of menopause. Forty-one 12 wk-old female SD rats were assigned to five groups: 1) Sham operated (Sham); 2) ovariectomized (OVX-Cont); 3) OVX received genistein (OVX-GEN); 4) OVX exercised (OVX-EXE); and 5) OVX treated with both genistein and exercise (OVX-GEN-EXE). All rats were fed a low Ca (0.1%) diet ad libitum. Daily genistein dosage was 12 mg/kg body weight. Exercising rats took 40 sets of 1-min run interspersed with 1-min rest with a 100 g weight on the back on an uphill treadmill at 20 m/min. The experimental duration consisted of the adaptation and treatment periods of 4 weeks each. Uterine weight in OVX-Cont, OVX-GEN, OVX-EXE and OVX-GEN-EXE decreased to about 15% of that in Sham (p < 0.001). The femoral BMD (mg/cm2; mean +/- SE), assessed by DEXA (Lunar), of OVX-Cont was significantly lowered to 206 +/- 5 by -9%, as compared to 226 +/- 2 of Sham (p < 0.001). The BMD of OVX-GEN, OVX-EXE and OVX-GEN-EXE were 217 +/- 2, 217 +/- 2 and 222 +/- 2, respectively, and genistein dosage and resistance exercise equally increased the BMD of OVX rats by 5% (p < 0.01). Combined treatment of genistein and exercise more successfully recovered their decreased BMD by 8% (p < 0.001). BMD of the fourth lumbar vertebrae in OVX-Cont was declined to 191 +/- 7 by -15%, as compared to 225 +/- 4 in Sham (p < 0.001). OVX-EXE and OVX-GEN-EXE gained the BMD by 6% to 205 +/- 4 and 203 +/- 3, respectively, as compared to that of OVX-Cont (p < 0.01). These results suggest the possibility that the combined treatment of genistein dosage and resistance exercise have more beneficial effects by acting rather independently than their separate trials on the prevention of ovx-induced bone loss in femurs.

SummaryWe have demonstrated that the habitual intake of chitosan can decrease bone mass in ovariectomized (OVX) SHRSP rats fed a low-Ca diet (0.1%). In the present study, we examined both the etiology of bone loss induced by dietary chitosan and the preventive ef fect of vitamin C supplementation. Rats were OVX and maintained on one of the following diets for 6 wk: 10% cellulose (CE), 10% chitosan (CH) or 10% chitosan with sodium ascor bate (CHVC). CH caused a significant reduction in bone mineral density (BMD) and stiffness in femurs and the fourth lumbar vertebrae (L4). There was no significant difference in intes tinal Ca absorption between CH and CE, whereas CH intake significantly reduced intestinal P absorption. The bone loss in CH rats was accompanied with an increase in urinary Ca ex cretion and a decrease in serum Ca as well as a significant increment in serum PTH and 1,25(OH)2D3. The vitamin D receptor and calcium binding protein D9K mRNAs were also significantly increased in the duodenum of CH rats. Vitamin C supplementation to CH caused an increase in the Ca and P contents of femurs as well as BMD of the L4, with a de crease in urinary Ca excretion. These results indicate that dietary chitosan with low Ca in take possibly induces the loss of bone mass by enhancing urinary Ca excretion rather than by inhibiting Ca absorption, and that vitamin C supplementation could prevent bone loss caused by chitosan through the increment of retained Ca followed by suppression of urinary Ca excretion. Key Words dietary chitosan, OVX rats, bone loss, serum 1,25(OH)2D3, CaBP D9K mRNA Chitosan, a polymer of glucosamine and a type of water insoluble dietary fiber, is prepared by the deacety lation of chitin, which constitutes the exoskeletons of arthropods such as crabs, shrimp, lobsters and insects (1). Chitosan has been shown to have a hypocholes terolemic effect in humans and animals (2-5), and also an inhibitory effect on intestinal fat digestion and ab sorption in rats (6). It has also been reported to be of low toxicity (7), and has come to be widely used as a food supplement to lower blood cholesterol and prevent weight gain. However, in spite of a number of nutri tional advantages, chitosan may serve as a chelator of several minerals and hence impair their bioavailabili ties. Deuchi et al. discovered that decreased intestinal absorption of calcium (Ca) and bone mineral contents of femurs were induced in male rats when fed diets con taining 5% chitosan for 2 wk (8). Moreover, Wada et al., in an experiment using 47Ca, observed that there was no discriminatory difference in fecal Ca excretion in rats fed chitosan or cellulose, but a significant increase in urinary Ca excretion with chitosan intake (9). These studies suggested that dietary chitosan might influence calcium and bone metabolism through inhibiting Ca absorption and/or by accelerating its urinary excretion.The decrease in net Ca retention as a consequence of habitual intake of chitosan with a low-Ca diet may en hance the risk of osteopenia or osteoporosi...