Dynamic Changes in Circulating 1,25-Dihydroxyvitamin D During Reproduction in Rats

Abstract

The concentrations of 1,25-dihydroxyvitamin D [1,25-(OH)2D], calcium, and phosphorus were measured in the serum of rats during pregnancy and at various stages of lactation. The concentration of 1,25-(OH)2D hormone increased almost two-fold during pregnancy and the latter part of lactation, but decreased to control levels or very low values immediately after birth and weaning, respectively. Furthermore, the concentration of 1,25-(OH)2D was inversely correlated with the concentration of calcium, suggesting that circulating 1,25-(OH)2D fluctuates in concert with calcium demands during the reproductive cycle. Parathyroidectomy in lactating rats caused a 70 percent inhibition of the normally observed 1,25-(OH)2D increase, indicating that parathyroid hormone, in response to changes in serum calcium, is a primary modulator of 1,25-(OH)2D during lactation.

Maternal Mineral and Bone Metabolism During Pregnancy, Lactation, and Post-Weaning Recovery

“…Serum calcitriol concentrations increase two-to sevenfold during normal pregnancy in rats, mice, sheep, guinea pigs, and rabbits (90,92,358,477,478,502,512,718,735,775,1021). The vitamin D binding protein level increased slightly in mice and declined modestly in rats and guinea pigs (104,478,958).…”

“…Serum phosphorus remains normal during pregnancy in rats (117,314,718) and mice (477,478,580), but may be modestly reduced in guinea pigs (958), sheep (21,57), goats (21,55), and cows (21). It is especially low during milk fever of cows (613).…”

“…The serum calcium of lactating rats has been quite variable in published reports, and not clearly explained by the calcium content of the diet: hypercalcemia on 1.5 or 1.2% calcium (86,318); normocalcemia on 1.6% (568), 1% (991), 0.5% (114), 0.4% calcium (91,318,569), and an unspecified diet (337); low blood calcium on 1.2, 0.9, 0.8, and 0.4% calcium (76,90,320,321,568,718,920,927,989); and marked hypocalcemia on 0.1, 0.04, and 0.01% calcium (32,320,321,568,991). The ionized calcium has been low on a 1.6% calcium diet (568), high on a 1.2% calcium diet (318), low on a 0.8% calcium diet (989), normal (318) and low on a 0.4% calcium diet (90,568,569), and low on a 0.1% calcium diet (32, 568).…”

Fetal growth and 1,25-dihydroxyvitamin D3 injections into thyroparathyroidectomized pregnant rats

“…The requirements for 1,25-(OH),D, probably increase at the end of gestation ; the observation of elevated serum 1,25-(OH) 2 D a levels in pregnant rats at the end of gestation (Halloran, Barthell and de Luca, 1979 ;Pike et al, 1979 ;Garel et al, 1981) …”

ROLE OF 1,25‐(OH)2D3 DURING PREGNANCY; STUDIES WITH PIGS SUFFERING FROM PSEUDO‐ VITAMIN D‐DEFICIENCY RICKETS, TYPE I

“…In addition to being transported across the intestinal mucosa, Ca and Pi have to be transported across the placenta during pregnancy to provide adequate supply to the fetus and to ensure fetal Ca and Pi homeostasis. During pregnancy higher levels of circulating 1,25-(OH)2D3 and increasing amounts of duodenal Ca binding protein (CaBP) have been reported in humans and rats (Bruns, Fausto & Avioli, 1978;Marche, Delorme & Cuisinier-Gleizes, 1978;Pike, Parker, Haussler, Boass & Toverud, 1979).…”