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Regulation of Serum Calcitriol by Serum Ionized Calcium in Rats During Pregnancy and Lactation
Author(s) -
Boass Agna,
Garner Sanford C.,
Schultz Vijitha L.,
Toverud Svein U.
Publication year - 1997
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.1997.12.6.909
Subject(s) - calcitriol , endocrinology , medicine , lactation , pregnancy , parathyroid hormone , chemistry , calcium , biology , genetics
Serum calcitriol concentrations in rats follow a biphasic pattern during reproduction, with elevated levels during late pregnancy, a decline after parturition, and a rise to even higher levels during peak lactation. We have previously shown that serum calcitriol in rats at peak lactation correlates significantly with, and appears to be regulated by, serum ionized Ca (Ca 2+ ), with parathyroid hormone (PTH) serving a permissive role. We have extended this study by determining if serum calcitriol also correlates with serum Ca 2+ during late pregnancy, when calcitriol levels are clearly elevated, and during early lactation, when only modest increases in serum calcitriol are observed. Analyses of data combined from nonmated, 21‐day pregnant (P), and 1‐day lactating rats (L) revealed a significant regression ( p < 0.001) of calcitriol on Ca 2+ , but a nonsignificant regression ( p = 0.34) of calcitriol on serum PTH. An even stronger correlation ( p < 0.001) between calcitriol and Ca 2+ was found for the combined data for 5−, 8−, and 14‐day L rats. The partial correlation coefficient for calcitriol versus Ca 2+ , with PTH as the independent variable, was highly significant ( p < 0.01) for the data from both combined groups. However, the coefficient for calcitriol versus PTH, with Ca 2+ as the independent variable, was not significant ( p > 0.05). Fetal weights (uterus and contents) correlated significantly with both maternal calcitriol and Ca 2+ concentrations ( p < 0.01), but not with maternal PTH levels. Litter weights for 14‐day‐old pups likewise correlated significantly with maternal calcitriol and Ca 2+ ( p < 0.001). We conclude that hypocalcemia, induced by the demands for Ca for fetal calcification and milk production, appears to be a controlling factor in serum calcitriol elevation in late pregnancy and throughout lactation, whereas PTH may be important for calcitriol synthesis without playing a direct regulatory role.