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Factors Affecting Absorption and Excretion of ⁵⁴Mn in Rats

United States Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND 58202

The effects of different levels of dietary Mn and different modes of ⁵⁴Mn administration and the effect of sucrose and starch on absorption and excretion of the isotope were studied. Rats were fed diets containing between 1.3 and 82.4 mg Mn/kg for 7 or 14 d and administered ⁵⁴Mn by gavage or a test meal containing 5 or 20 µg Mn. Additional rats for each dietary treatment received ⁵⁴Mn by intramuscular or intraperitoneal injection. Amount of Mn in the oral dose did not affect ⁵⁴Mn absorption, but increasing dietary Mn reduced Mn absorption and enhanced ⁵⁴Mn excretion. Absorption of ⁵⁴Mn by fasted, gavaged rats was four times higher than in unfasted gavaged rats or in fasted rats fed test meals. Orally administered ⁵⁴Mn had a shorter biological half-life than injected ⁵⁴Mn and tissue distribution of ⁵⁴Mn differed in rats given ⁵⁴Mn by different routes. Rats fed between 1.4 and 2.8 mg Mn/kg diet grew as well as or better than those fed amounts similar to the recommended level (50 mg/kg). Sucrose-fed rats absorbed more than ⁵⁴Mn than starch-fed rats. Rats fed sucrose excreted injected ⁵⁴Mn faster than rats fed starch. Concentrations of liver Mn in sucrose-fed rats were higher than in starch-fed rats. Our results indicate that both absorption and excretion are important in maintaining Mn homeostasis in rats.

KEY WORDS: • Mn • absorption • excretion • rats • sucrose • starch • bioavailability

¹ Present Address: University of Michigan Medical School, Department of Human Genetics, Ann Arbor, MI 48109-0618.

Manuscript received 21 September 1987. Revision accepted 22 July 1988.