To study the relationship between Ca^2+ intake, Ca^2+ absorption and Ca^2+ retention.Methods; Thirty-six weaning rats were firstly fed with Ca-poor diet for a 3-week Ca^2+ depletion period, and then randmnly divided into 3 groups to receive diet with low,adequate and high Ca^2+ contents. The experiment lasted 12 weeks,with a 3-day metabolism experiment conducted in the 5th week. Resu/ts: Supplement with adequate amount of Ca^2+ increased bone Ca^2+ , bone mineral density(BMD), bone mineral content(BMC) and the weight,ht of femur(P < 0.05).Higher doses of Ca^2+ failed to further improve the efficiency.Analysis showed that Ca^2+ intake was positively correlated to bone Ca^2+ ,BND and BMC,and negatively correlated to the rates of Ca2~ absorption and retention. Dase-effect study revealed that the Ca^2+. absorption rate(Y)was a hyperbola function of Ca^2+ intake(X),i.e.Y = e^6.8068 X^-0.8821 + 20(F=47.3154,P < 0.0001).It was fonnd from the results that bone Ca2~ content( determined by atom absorptima spectzoldmtmneter)had a linear correlation to BMC( determined with tmi-photon bone minerdl densitmneter). Conclusion: The rate of Ca^2+ absorption is a hyperbola function of Ca^2+ intake. The incremnent of Ca^2+ absorption will be minimal when Ca^2+ intake exceeds 3d 250 mg in rats.BMC, better than BMD,may substitute for the ideal bone Ca^2+ content as the index to assess the efficacy of Ca^2+ supplement.
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