Mammary gland 1,25-dihydroxyvitamin D3 receptor content during pregnancy and lactation.

The purpose of this study was to establish the time course and magnitude of changes in 1,25-dihydroxy-vitamin D receptor activity in rat mammary gland during pregnancy and lactation and to correlate these changes with casein production and alkaline phosphatase activity. Marked increases in both 1,25-dihydroxyvitamin D3 receptor and alkaline phosphatase activities were seen towards the end of pregnancy but the time course of these changes was not synchronous. Receptor activity was first detectable at 11 days of pregnancy with a marked rise in receptor levels at 3 days post-partum. Changes in alkaline phosphatase activity more closely correlated with casein production and peak activity was observed at the time of parturition. We conclude that 1,25-dihydroxyvitamin D3 receptor content increases during pregnancy and lactation and may be involved in maintaining milk calcium concentration.