Hydrocortisone and Vitamin D₃ Stimulation of 32P_i-Phosphate Accumulation by Organ-Cultured Chick Embryo Duodenum

Abstract

Either vitamin D₃ (or 1α,25-(OH)₂-D₃) or hydrocortisone (HC) stimulated phosphate accumulation by organ-cultured embryonic chick duodenum. In combination, these two steroids stimulated phosphate uptake synergistically. Phosphate accumulation appeared to be independent of other vitamin D₃-stimulated processes: CaBP concentration, cAMP concentration, or alkaline phosphatase activity. L-phenylalanine, a reported alkaline phosphatase inhibitor, when added to the culture medium progressively inhibited either D₃- or HC-stimulated phosphate uptake subsequent to culture, but did not inhibit the synergistic action. Under these conditions L-phenylalanine had no consistent effect on alkaline phosphatase activity but unexpectedly, greatly inhibited vitamin D₃-stimulated CaBP concentration, but only in the absence of HC. Some limited suggestion of an intestinal phosphoprotein sensitive to either vitamin D₃ or HC was observed.

Key words

Organ-Cultured Duodenum - Vitamin D₃ - Hydrocortisone - Calcium-binding Protein - Phosphate Transport - L-Phenylalanine