QUANTITATIVE ASSESSMENT OF THE EFFECTS OF VARIABILITY IN DIETARY ZINCDOSE-RATE IDIORRHYTHMS UPON ZINC DEPOSITION IN BONE OF WEANLING RATS BY USING A SLOPE-RATIO ASSAY

We quantitatively assessed the effect of the idiorrhythmic dose-rate v ariability in dietary zinc intake on zinc deposition in the femur and incisor of weanling rats by the slope-ratio analysis of analogous idio rrhythms. In idiorrhythmic feeding the dose (x) is viewed over the per iod of the entire experimental epoch as a dose-time equivalent modulo (Mx) that can be divided into a series of equal products of different doses with different frequency (idiorrhythm, I). Each I is administere d in a regularly recurring pattern to deliver the same dose as that fr om a standard daily regimen of zinc, albeit at a different rate; Ix = [d(nth)(Mx)]/d(nth), where d(nth) is the sequential number of zinc dos ing day separated by 1 to 7 days of feeding the diet without zinc when d(nth) > 1. Four different Mx were tested, M3, M6, M12, and M24 provi ding 3, 6, 12, and 24 mg Zn . kg(-1) diet.d(-1), respectively, over a 24 day epoch; each Mx had seven analogous Ix of different doses sizes, but the same dosing frequency (d(nth)). The slopes for the M3, M6 and M12 analogous idiorrhythms showed that zinc deposition in the femur a nd incisor, as a measure of metabolic availability, varied considerabl y with spacing of the dose with time. Metabolic availability of zinc p rogressively decreased by 50% from I = Mx/1 to I = 4Mx/4. Then it rose to approach the initial I = Mx/1 values of animals fed zinc daily for I = 5Mx/5 and I = 6Mx/6, before it finally dropped again to the botto m level for I = 8Mx/8. The results showed that the impact of zinc dose -rate in dietary zinc intake is an important determinant of a adequate supply of metabolic zinc. (C) Elsevier Science Inc. 1997.