ABSTRACT Background: Interpretation of parathyroid hormone (PTH) measurements requires an understanding of its structural conformation. PTH reflects calcium intake and vitamin D status but is commonly measured in the fasted state using 2nd generation assays, known to cross-react with PTH 7-84 fragments, which is not observed with 3rd generation assays. The objective was to determine if plasma PTH in the fed and non-fed state differ while controlling for diurnal rhythm and the generation of PTH assay. Methods: Blood was sampled, 2 d apart, from Sprague-Dawley rats (30 males and 30 females) in both fed and non-fed states at 20 wk of age (weight: 470.2±23.2 g) for measurement of ionized calcium (iCa), total intact (INT) and bioactive 1-84 (BIO) PTH. Differences between groups were tested using a GLIMMIX model with sex and feeding state as fixed effects and individual rats as a random effect. Results: Females had a lower iCa than males (F: 1.43±0.01 vs M: 1.46±0.01 mmol/L, P=0.03). In males and females, there was no difference between fed and non-fed groups when PTH was assessed using the INT PTH assay (M Fed: 21.6±1.3 vs M Non-fed: 22.6±2.3 pmol/L, P=0.59; F Fed: 19.3±1.5 vs F Non-fed: 22.8±2.9 pmol/L, P=0.39). However, in females only, PTH measured using the BIO PTH, was significantly lower in the fed group versus the non-fed (Fed: 8.4±0.8 vs Non-fed: 16.7±3.4 pmol/L, P=0.05). Conclusions:
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DeGuire, J. and Weiler, H. (2013) Feeding Reduces Serum Concentration of Endogenous Bioactive (1-84), but Not Total Intact Parathyroid Hormone in Female Sprague-Dawley Rats. Open Journal of Nephrology, 3, 61-65. doi: 10.4236/ojneph.2013.31010.
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