Intestinal interactions of lead and calcium.

The biological interactions between lead and calcium are complex and not well-understood, but can be demonstrated in virtually every tissue. High affinity lead-binding to intracellular calcium receptor and transport proteins as well as the involvement of lead in calcium-activated and calcium-regulating processes may provide a molecular basis for the broad spectrum cellular and systemic effects. The intestinal absorptive cells are responsible for transporting the entire body complement of calcium and most of the body lead burden. They represent, therefore, the first critical step in maintaining systemic and cellular calcium homeostasis, as well as the first line of defense against lead poisoning. Any interactions which occur at this level, either to enhance the body burden of lead or to diminish the transport of calcium, may have serious health-related repercussions. This article reviews research concerning those interactions involving calcium, lead and the vitamin D endocrine system which ultimately influence intestinal function, calcium homeostasis and body lead retention.