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Gastrointestinal Absorption of Lead in Chicks: Involvement of the Cholecalciferol Endocrine System¹

Department of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

The role of dietary calcium and phosphorus in modifying the intestinal absorption of lead and also the effect of lead ingestion on the metabolism of cholecalciferol were studied in chicks. The efficiency of absorption of ²⁰³Pb and ⁴⁷Ca was increased when the animals were fed a low calcium diet and treated with cholecalciferol. The synthesis of the vitamin D-induced calcium-binding protein (CaBP) was correspondingly increased. When the chicks were depleted of vitamin D and repleted with 1,25-dihydroxycholecalciferol [1,25(OH)₂D₃] as their only source of the vitamin, the absorption of both ⁴⁷Ca and ²⁰³Pb was unaffected by dietary calcium levels, and no change in CaBP levels occurred. Low dietary intake of phosphorus resulted in an increase in ⁴⁷Ca and ²⁰³Pb absorption and in CaBP synthesis when the animals were treated with cholecalciferol. However, when the birds were repleted with 1,25(OH)₂D₃, the intestinal absorption of ⁴⁷Ca and of ²⁰³Pb was increased, as well as the intestinal CaBP levels. Intracardial injection of increasing doses of 1,25(OH)₂D₃ to rachitic chicks resulted in a concomitant increase in ²⁰³Pb absorption in a manner that correlated with the degree of synthesis of CaBP. Ingestion of lead by the chicks was found to impair growth and renal production of 1,25(OH)₂D₃, resulting in lowered circulating and intestinal content of the hydroxylated metabolites of cholecalciferol.

KEY WORDS: • cholecalciferol • lead • calcium

¹ Supported by Department of Energy Contract DOE EV-S-2792 and by National Institutes of Health Grant AM-04652.

² On sabbatical leave from the Biochemistry Department: The Weizmann Institute of Science, Rebovot, Israel 76100.

Manuscript received 22 August 1983.

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