1,25-DIHYDROXYVITAMIN D-3 AND OSTEOCALCIN IN MATERNAL AND FETAL GUINEA-PIGS

Maternal and fetal 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) and oste ocalcin were measured in guinea pigs, to examine their potential use a s animal models for fetal bone development and calcium homeostasis. Me asurements were performed on days 42, 57 and 63 of gestation. Maternal serum total 1,25(OH)(2)D-3 concentrations were increased only at the end of gestation (day 63). However, because the vitamin D binding prot ein (DBP) and albumin levels were decreased by 35-50% from day 42 onwa rds, the unbound 1,25(OH)(2)D-3, calculated as the 1,25(OH)(2)D-3/DBP molar ratio, was increased before day 63. Osteocalcin concentrations d uring gestation were 50-54% of levels found in nongravid animals. Feta l serum total 1,25(OH)(2)D-3 concentrations were 20% of those in mater nal guinea pigs. Since DBP levels were only 9-15% of maternal levels, the unbound 1,25(OH)(2)D-3 was consistently higher in fetuses, from da y 42 onwards. There was a rise in total and unbound 1,25(OH)(2)D-3 bet ween days 57 and 63 of fetal life. Osteocalcin concentrations were hig her in fetal than in adult guinea pigs, and reached peak values on day 57 (1023 mu g/l, i.e. 4.2 times higher than in adult female guinea pi gs). Fetuses of guinea pigs that had received a restricted food supply for 14 days (days 49-63) had normal 1,25(OH)(2)D-3 concentrations, bu t decreased osteocalcin concentrations compared with normal fetuses. T he data obtained in fetal guinea pigs are comparable with those found in human fetuses, and suggest that the guinea pig may be a suitable mo del for studies on fetal bone and mineral development.