title: Hypercalcemia fails to suppress elevated serum parathyroid hormone concentrations during lactation in rats.
abstract: We have previously reported that increased serum immunoreactive parathyroid hormone (iPTH) in the lactating (L) rat is generally accompanied by hypocalcemia when diets containing 0.4% calcium (Ca) or less are fed. However, instances were also observed in which elevated iPTH levels did not coincide with a hypocalcemic signal. To test the hypothesis that iPTH levels can remain elevated even in the presence of hypercalcemia in lactation, a diet containing 1.2% Ca and 0.4% phosphorus (P) was fed to lactating rats in three experiments (A, B, and C) to achieve serum ionized calcium (ICa) levels approximately 10% above levels for nonmated (NM) controls. The serum ICa of NM controls fed the 1.2% Ca diet was slightly, but significantly, elevated, and serum iPTH (determined by an N-terminal specific assay) was significantly suppressed compared with NM controls fed a 0.4% Ca diet. In experiment A, L rats fed a 1.2% Ca diet had 81% higher serum iPTH levels than NM controls fed the same diet in spite of a mean (+/- SEM) ICa level of 1.77 +/- 0.05 mM for L rats versus 1.46 +/- 0.01 mM for NM controls; NM controls fed a 0.4% Ca diet had serum ICa of 1.37 +/- 0.01 mM. This novel finding of significantly higher iPTH and ICa in L compared with NM rats fed a 1.2% Ca and 0.4% P diet was confirmed in experiment B with eight rats in each group of L or NM rats fed either the 1.2% or the 0.4% Ca diet.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology and Dental Research Center, University of North Carolina, Chapel Hill 27599.
authors.forename: S C
authors.initials: SC
authors.lastname: Garner
authors.forename: A
authors.initials: A
authors.lastname: Boass
authors.forename: S U
authors.initials: SU
authors.lastname: Toverud
mesh_terms: D000818:Animals; D001835:Body Weight; D002136:Calcium, Dietary / Q000494:pharmacology; D005260:Female; D006934:Hypercalcemia / Q000097:blood / Q000503:physiopathology*; D007700:Kinetics; D007774:Lactation / Q000097:blood*; D010281:Parathyroid Hormone / Q000097:blood*; D010758:Phosphorus / Q000097:blood; D011247:Pregnancy; D051381:Rats
chemical_list: D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D010758:Phosphorus