Phosphate Transport Adaptation in Rat Jejunum and Plasma Level of 1,25-Dihydroxyvitamin D₃

Abstract

Intestinal absorption of inorganic phosphate (Pi) increases in response to a reduction in the dietary supply of Pi. In this work this adaptive response has been characterized in jejunal brush border membrane vesicles and studied in temporal relationship with the change in the plasma level of 1,25(OH)2D₃. The results indicate that in rat jejunal brush border membrane vesicles the activity of the sodium-dependent Pi transport system is stimulated by a low Pi diet. This adaptive response was the result of an increase in the V_max and a reduction in the K_m of the cotransport system. This change in Pi transport was correlated with an increase in the circulating level of 1,25(OH)2D₃ in a time-related fashion. In conclusion, these results are consistent with the notion that Pi restriction leads to an increase in Pi transport activity in the luminal membrane of the intestine. A time course study suggests that the elevation in plasma 1,25(OH)2D₃ might be involved in the adaptation of the intestinal Pi transport system to Pi restriction.

Key words:

• Brush border membrane vesicles
• intestine
• phosphate absorption
• Pi adaptation
• plasma 1,25-dihydroxyvitamin D₃