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

¹ Department of Physiology, School of Veterinary Medicine, Bischofsholer Damm 15, D-3000 Hannover, FRG
² Institute of Animal Nutrition, Federal Agricultural Research Center, Bundesallee 50, D-3300 Braunschweig, FRG

Biochemical parameters of Ca homeostasis in fetal and maternal plasma and placental transfer of Ca, P_i and vitamin D metabolites were measured during pregnancy and at parturition. Control pigs and pigs with inherited pseudo-vitamin D-deficiency rickets, type I (PVDR), which are devoid of renal calcitriol production, were used. Although sows with PVDR normally require treatment with massive doses of vitamin D at intervals of 4 weeks to stabilize Ca and P_i concentrations in plasma, these plasma parameters tended to normalize during the first 3 months of pregnancy when the vitamin D treatment was discontinued about 4 weeks before conception. In homozygote sows plasma calcitriol concentrations remained unphysio-logically low and the 25OHD₃ concentrations increased steadily during pregnancy reaching higher levels than those found in control sows. Despite hypocalcaemia and hypophosphataemia of the homozygote sows at term, fetal Ca and P_i concentrations were normal. This demonstrated a higher feto-maternal concentration gradient in PVDR pigs than in control pigs. It is concluded that maintenance of Ca and P_i homeostasis of the feto-maternal system, including active transplacental transport in pigs, is at least partly independant from calcitriol.

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