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Altered Regulation of Parathyroid Hormone Secretion by Calcium in Pregnant and Lactating Rats
Author(s) -
Schultz Vijitha L.,
Boass Agna,
Garner Sanford C.,
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.1997.12.6.903
Subject(s) - medicine , endocrinology , parathyroid hormone , immunoradiometric assay , parathyroid chief cell , calcium , extracellular , lactation , chemistry , secretion , hormone , radioimmunoassay , biology , pregnancy , biochemistry , genetics
We have previously shown that the serum parathyroid hormone (PTH) concentration in lactating (L) rats is not suppressed by high serum Ca 2+ to the same extent as in nonmated (NM) rats. To investigate further Ca 2+ regulation of PTH secretion, parathyroid cells from NM rats and rats in late pregnancy and at peak lactation were dispersed and incubated for 2 h in medium containing 0.52–2.05 mM Ca 2+ . Medium PTH was assayed with a homologous immunoradiometric assay (IRMA). At the two highest Ca 2+ levels (1.81 and 2.05 mM), medium PTH was significantly higher ( p = 0.031) for cells from L rats than for cells from NM rats. In contrast, significantly less ( p < 0.001) PTH was secreted for the L group versus the NM group at medium Ca 2+ values of 1.27 and 1.46 mM. Estimated set points for L and NM groups were 1.17 mM and 1.35 mM, respectively, corresponding closely to the prevailing serum Ca 2+ for these two groups. Consistent with the present in vitro data, high serum PTH (>40 pg/ml) in L rats occurred only at serum Ca 2+ values below 1.27 mM. Elevated serum PTH at lower serum Ca 2+ levels was also seen in pregnant rats. Dispersed parathyroid cells from 20− to 21‐day pregnant rats secreted significantly more PTH ( p = 0.028) than cells from NM rats at all Ca 2+ levels tested (1.1–1.6 mM). In conclusion, the relationship between extracellular Ca 2+ and PTH secretion is altered in rats during late pregnancy and at peak lactation, perhaps as part of the adaptation to the demands for calcium for pre‐ and postnatal growth.