Homeostatic reactions of quantitative Zn metabolism on deficiency and subsequent repletion with Zn in ⁶⁵Zn-labeled adult rats

The objective of the present study was to investigate the homeostatic control of Zn fluxes (absorption, excretion) and changes of tissue Zn storage (depletion, refilling) during Zn deficiency and subsequent Zn repletion. Methods: Thirty-six ⁶⁵Zn-labeled female rats weighing 217 g were fed either a purified diet with sufficient Zn (21 μg/g, control) for 26 days, or with deficient Zn (2 μg/g) for 12 days followed by 14 days repletion with the control diet. The animals were killed at the onset of the study (4 reference), at the end of the Zn deficiency episode (4 controls and 4 deficiency), and at repletion days 2, 4, 7, 10 (each 4 of repletion), and day 14 (4 control, 4 repletion). Feed supply was restricted (7.8 g/head and day). Results: Control animals were in slightly positive Zn balance and tissue Zn distribution remained unchanged along the whole study. Zn retention was negative in Zn-deficient animals (-16 μg/d). Mobilization of whole body Zn originated mainly from the skeleton, which lost 21% of normal bone Zn quantity (8% of whole body Zn). At the onset of repletion (day 2), Zn retention was highly positive (112 μg/d) due to a significant increase in true absorption and a low excretion rate of endogenous fecal Zn. Until day 10 of repletion, Zn fluxes returned continuously to normal values. Skeleton Zn quantity was restored for about half of the previously mobilized amount of Zn within 2 days of repletion and reached the control level at the end of the study. The contributions of other tissues to chances in whole body Zn were of minor quantitative relevance. Conclusions: The primary Zn store of whole body Zn is localized in the skeleton. It is under control of Zn homeostasis and its depletion and repletion corresponds to adaptations of intestinal Zn exchange (true absorption, endogenous fecal excretion).