Intestinal lead and calcium absorption: effect of 1,25-dihydroxycholecalciferol and lead status.

This study was designed to investigate, in some detail, the relative effects of the hormonal form of vitamin D (1,25-dihydroxycholecalciferol) on duodenal Pb and Ca absorption as a function of dietary Pb level. When cholecalciferol-deficient chicks were chronically repleted with physiologic levels of 1,25-dihydroxycholecalciferol (1,25(OH)2D3), as the sole source of the vitamin, 203Pb and 47Ca absorption were enhanced over 4- and 8-fold, respectively. Ingestion of Pb during the repletion period had no significant effect on the intestinal Ca absorption response to 1,25-(OH)2D3 even at a very high dietary Pb level. The efficiency of intestinal 203Pb absorption was, however, significantly diminished by dietary Pb, in an apparent dose-dependent fashion. The results indicate that the extent to which systemic Ca homeostatic mechanisms influence intestinal Pb absorption is dependent, in large part, on Pb status.