Regulation of the intestinal 1,25-dihydroxyvitamin D3 receptor during neonatal development in the rat

Monoclonal antibodies have been used to examine the regulation of expression of the rat intestinal receptor for 1,25-dihydroxyvitamin D3 during neonatal development. 1,25-Dihydroxyvitamin D3 binding activity increases dramatically between Days 15 and 28 postpartum in normal neonatal rats. Immunoprecipitation and combined immunoprecipitation-immunoblotting experiments demonstrate that this increase in hormone binding activity is caused by an increase in the amount of receptor protein present in rat intestine between Days 18 and 28 of age. Very little receptor protein, if any, appears to be present in rat intestine prior to Day 18 of life. These results suggest that the expression of the gene for 1,25-dihydroxyvitamin D3 receptor is regulated during neonatal development in the rat.