title: Altered regulation of parathyroid hormone secretion by calcium in pregnant and lactating rats.
abstract: We have previously shown that the serum parathyroid hormone (PTH) concentration in lactating (L) rats is not suppressed by high serum Ca2+ to the same extent as in nonmated (NM) rats. To investigate further Ca2+ 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 Ca2+. Medium PTH was assayed with a homologous immunoradiometric assay (IRMA). At the two highest Ca2+ 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 Ca2+ 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 Ca2+ for these two groups. Consistent with the present in vitro data, high serum PTH (> 40 pg/ml) in L rats occurred only at serum Ca2+ values below 1.27 mM. Elevated serum PTH at lower serum Ca2+ 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 Ca2+ levels tested (1.1-1.6 mM). In conclusion, the relationship between extracellular Ca2+ 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.
authors.affiliation: Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill, USA.
authors.forename: V L
authors.initials: VL
authors.lastname: Schultz
authors.forename: A
authors.initials: A
authors.lastname: Boass
authors.forename: S C
authors.initials: SC
authors.lastname: Garner
authors.forename: S U
authors.initials: SU
authors.lastname: Toverud
mesh_terms: D000818:Animals; D001810:Blood Volume; D002118:Calcium / Q000097:blood / Q000494:pharmacology*; D002136:Calcium, Dietary / Q000008:administration & dosage; D005260:Female; D066298:In Vitro Techniques; D007774:Lactation / Q000097:blood / Q000502:physiology*; D010280:Parathyroid Glands / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010281:Parathyroid Hormone / Q000097:blood / Q000378:metabolism*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000097:blood / Q000502:physiology*; D051381:Rats
chemical_list: D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D002118:Calcium