Absorption, distribution and endogenous excretion of zinc by rats fed various dietary levels of inorganic tin and zinc.

Three studies were designed to determine the effects of various levels of tin (less than 1, approximately 100, approximately 200, approximately 500 and approximately 2000 micrograms tin/g diet) and zinc (approximately 15, approximately 30, approximately 52 micrograms zinc/g diet) on the metabolism of zinc by growing rats. Retention of zinc in tibia, kidney, liver and plasma was decreased significantly when rats consumed greater than or equal to 500 micrograms tin/g diet. Tibia zinc levels were also sensitive to lower levels of dietary tin, i.e., even 100 micrograms tin/g diet when rats were fed 51.8 micrograms zinc/g diet. Apparent absorption of zinc was significantly less when rats were fed approximately 200 or approximately 500 micrograms tin/g diet rather than a control diet containing 15.8 micrograms zinc/g diet and significantly less when rats were fed approximately 500 micrograms tin/g diet rather than approximately 200 micrograms tin/g diet with 29.7 micrograms zinc/g diet. The effect of dietary tin on fecal excretion of endogenous zinc and true absorption of zinc seemed to be dependent on the dose. Rats fed approximately 2000 micrograms tin/g diet lost significantly more zinc of endogenous origin in the feces than control animals. A significant decrease in true absorption of zinc was observed among those rats fed approximately 500 micrograms tin/g diet with 29.7 micrograms zinc/g diet. Increased consumption of zinc resulted in decreased apparent absorption of zinc, increased losses of endogenous zinc in the feces, and decreased true absorption of zinc.