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Effect of Dietary Picolinic Acid on the Metabolism of Exogenous and Endogenous Zinc in the Rat¹

Department of Biological Sciences, University of Lancaster, Lancaster LA1 4YQ England

The excretion of ⁶⁵Zn was compared by metabolic balance studies in adult male rats fed purified diets containing 0.8 mmol Zn/kg diet, with and without 40 mmol picolinic acid per kilogram diet, after single intragastric (i.g.) and intraperitoneal (i.p.) doses of the isotope. In a third experiment picolinic acid was introduced for 3 d into the diet of rats prelabeled with ⁶⁵Zn. The urinary excretion of total zinc was increased by the ingestion of picolinic acid in all three experiments. The urinary and fecal outputs of ⁶⁵Zn were both consistently greater in picolinic acid-fed rats than in the corresponding control animals. This was particularly marked after i.p. injection of the tracer, and the specific activities of urine and feces from the treated rats were both increased. When picolinic acid was introduced into the diet of prelabeled rats there was a delay of 24 h in the urinary response and 48 h in the fecal response. The residual ⁶⁵Zn levels were reduced in several tissues from the picolinic acid-fed rats, especially after i.p. administration of the isotope. These observations indicate that dietary picolinic acid increases the turnover of endogenous zinc in addition to enhancing the absorption and excretion of ingested metal, and this has implications for its use in cases of zinc deficiency.

KEY WORDS: • picolinic acid • endogenous zinc • zinc excretion • zinc absorption

¹ Supported jointly by the Science and Engineering Research Council of Great Britain and Farley Health Products Ltd., Plymouth, England.

² Present address: Department of Agricultural Biochemistry and Nutrition, Faculty of Agriculture, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU England.

Manuscript received 31 August 1984. Revision accepted 1 May 1985.