Quantitative assessment of the effects of variability in dietary zinc dose-rate idiorrhythms upon zinc deposition in bone of weanling rats by using a slope-ratio assay

Abstract

We quantitatively assessed the effect of the idiorrhythmic dose-rate variability in dietary zinc intake on zinc deposition in the femur and incisor of weanling rats by the slope-ratio analysis of analogous idiorrhythms. In idiorrhythmic feeding the dose (x) is viewed over the period 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 administered in a regularly recurring pattern to deliver the same dose as that from 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 dosing 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 providing 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 dose 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 and incisor, as a measure of metabolic availability, varied considerably with spacing of the dose with time. Metabolic availability of zinc progressively 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 bottom level for I = 8Mx 8 . The results showed that the impact of zinc dose-rate in dietary zinc intake is an important determinant of an adequate supply of metabolic zinc.