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Effect of Vitamin D on the Intestinal Absorption of ²⁰³Pb and ⁴⁷Ca in Chicks

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

The transfer of ²⁰³Pb and/or ⁴⁷Ca across the intestinal epithelium of the chick was investigated, with emphasis given to the functional role of cholecalciferol (vitamin D-3). ²⁰³Pb, after introduction in the intestinal lumen, is rapidly accumulated by the intestinal tissue, and only a fraction of ²⁰³Pb is translocated parenterally (absorbed). Cholecalciferol did not significantly affect the accumulation of ²⁰³Pb by intestinal tissue but did accelerate ²⁰³Pb movement across the basal-lateral membrane. In contrast, cholecalciferol both decreased ⁴⁷Ca tissue levels and increased ⁴⁷Ca absorption. In rachitic chicks, the rate of absorption of ²⁰³Pb was greater in the distal than in the proximal segments of the intestine; after cholecalciferol repletion, the degree of absorption in all segments was similar, indicating the order of cholecalciferol effectiveness as duodenum jejunum > ileum. An acute dose of 1.25(OH)₂D₃ to rachitic chicks also enhanced both ²⁰³Pb and ⁴⁷Ca absorption, but the time course and pattern of absorption of these metal cations differed. The time at which the absorption of ²⁰³Pb peaked and returned to base-line occurred sooner than for ⁴⁷Ca. Also the back-flux (blood intestinal lumen) of ⁴⁷Ca was enhanced by cholecalciferol, whereas no effect on the back-flux of ²⁰³Pb was noted. These studies show that cholecalciferol and 1,25(OH)₂D₃ affects both the ²⁰³Pb and ⁴⁷Ca absorptive processes, but the nature of these responses are not identical, suggesting differences in the transport path or the macromolecular interactions of these metal ions during the course of absorption, or both.

KEY WORDS: • cholecalciferol • lead • calcium

Manuscript received 5 June 1981.