Diminished Internalization and Action of 1,25- Dihydroxyvitamin D3in Dermal Fibroblasts Cultured from New World Primates*

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Abstract
We investigated the occurrence of 1,25-dihydroxyvitamin D3 [l,25-(OH)2D3]-resistant osteomalacia in the New World primate colony of Saguinus imperator at the Los Angeles Zoo. The mean serum concentration of 1,25-(OH)2D3 was elevated 5-fold in the New World primates compared to that in their Old World counterparts. The specific internalization of 0.6 nM [3H]1,25-(OH)2D3 by cultured dermal fibrobalsts from New World primates was reduced 75% compared to that by cells from Old World primates or man. The decrease in hormone uptake resulted from a decrease in the number of high affinity intracellular binding sites for 1,25-(OH)2D3 and apparently caused a 90–95% reduction in l,25-(OH)2D3-induced 25-hydroxyvitamin- D3-24-hydroxylase activity. There was no alteration in the capacity or avidity of New World primate serum for 1,25-(OH)2D3 compared to that of serum from Old World primates. These data suggest that the occurrence of vitamin Dresistant osteomalacia in New World primates is the result of decreased high affinity, receptor-mediated uptake of 1,25- (OH)2D3 by the target cell. {Endocrinology116: 2523–2527, 1985)

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