Circulating levels and function of 1,25-(OH)2D3 in lactation.
During lactation in the rat, vitamin D is required for maintenance of a normal serum calcium level and maximal enhancement of active calcium transport in the duodenum. Vitamin D does not appear to be required for part of the adaptive increase in intestinal calcium transport or for calcium transport into the milk. The functions of vitamin D appear to be mediated by 1,25-(OH)2D3, the circulating level of which increases during lactation. Two days after sudden weaning, the serum level of 1,25-(OH)2D3 falls to levels below the pre-pregnant control level in parallel with a sharp increase in serum calcium; normal levels of calcium and 1,25-(OH)2D3 are observed one week after weaning. The initial stimulus for the increase in circulating 1,25-(OH)2D3 during lactation appears to be a small decrease in serum calcium which stimulates parathyroid hormone secretion, which in turn enhances synthesis of 1,25-(OH)2D3. Vitamin D is also required by the lactating rat to insure normal development of the suckling pup, since vitamin D deprivation during pregnancy and lactation causes significant decreases in body weight gain, in serum levels of 25-OHD3, calcium and phosphorus, in bone ash content and clear evidence of histological rickets by 20 days of age.
D000818:Animals; D002117:Calcitriol / Q000097:blood / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D005260:Female; D007408:Intestinal Absorption; D007774:Lactation; D008892:Milk / Q000032:analysis; D010280:Parathyroid Glands / Q000502:physiology; D011247:Pregnancy; D051381:Rats; D014808:Vitamin D Deficiency / Q000378:metabolism
D002117:Calcitriol; D002118:Calcium