888 THE EFFECTS OF GLUCOCORTICOIDS AND VITAMIN A (VA) ON LEAD-203 (²⁰³Pb) TRANSPORT IN BONE ORGAN CULTURE

Abstract

A mobile compartment of bone Pb, regulated like bone mineral, has been demonstrated in vitro. Since the activation of lysosomal enzymes plays an important role in parathyroid hormone (PTH) effecting bone resorption, the importance of lysosomal labilizers (PTH, VA, CaNa₂EDTA[EDTA]) and stabilizers (glucocorticoids = cortisol[COR]) were assessed on the transport of bone Pb. Pregnant rats on day #18 of pregnancy were injected with 500μCi of ²⁰³Pb and 200 μCi of ⁴⁵Ca. On day #19, fetal bones were cultured in a chemically defined medium to which lysosomal labilizers and stabilizers were added. After 5 days in culture, ²⁰³Pb and ⁴⁵Ca released from bones into the above experimental medium (EM) were compared to that released from bones into the appropriate control medium (CM). The ²⁰³Pb results (*= p< .01, different from 1.00) were expressed as cpm EM/CM ratios:

Significant release of ⁴⁵Ca occured in #1 and #5; and significant increases in medium levels of hydroxyproline and acid phosphatase were measured in #1, 3 and 5, but not in #2, 4 and 6.

These data indicate that: 1) lysosomal mechanisms play an important role in the release of ²⁰³Pb from bone explants in vitro; 2) other agents, besides calcium-regulating hormones, control, in part, bone Pb metabolism in vitro, and 3) such agents (COR, VA) may well modify Pb's toxic effects in vivo.

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