Stimulation of specific 1,25-dihydroxyvitamin D3 binding protein in cultured postnatal rat intestine by hydrocortisone.

Abstract

During the third postnatal week, 1,25-dihydroxyvitamin D3 specific binding activity begins to rise in intestine and increases to adult levels by the time of weaning.To determine factors directly involved in stimulating the appearance of the specific binding protein for 1,25-dihydroxyvitamin D3, we have developed an organ culture system for postnatal rat intestine.Specific 1,25-dihydroxyvitamin D3 binding activity was successfully maintained in explants cultured for 24 h in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, insulin, and antibiotics.The influence of hydrocortisone on the appearance of 1,25-dihydroxyvitamin D3 binding activity was examined in intestines from rats 14 and 16 days postpartum.Minimal binding activity was observed in intestines from rats 14 days postpartum and in explants thereof cultured in control medium for 24 h.Explants from rats 14 days postpartum cultured in medium supplemented with low5 M hydrocortisone exhibited a 5-fold increase in 1,25-dihydroxyvitamin D3 specific binding activity.Specific 1,25-&hydroxyvitamin D3 binding activity significantly increased in intestines from rats 16 days postpartum when cultured in control medium for 24 h.Binding activity was further elevated by exposure of explants to hydrocortisone-supplemented medium.These studies suggest that the appearance of 1,25-dihydroxyvitamin D3 binding activity in postnatal rat intestine is initiated by glucocorticoids but also depends on intrinsic timing mechanisms.