Feeding elevates plasma concentration of endogenous bioactive (1‐84) but not total intact parathyroid hormone in Sprague‐Dawley rats

Parathyroid hormone (PTH) is an endocrine regulator of bone metabolism and mineralization in addition to maintaining calcium homeostasis. In monkeys, feeding caused reduced PTH, suggesting that fed and non‐fed states should be considered when interpreting PTH values. The objective of this study was to determine if such effects are seen in rats. Blood samples were taken from 44 Sprague‐Dawley rats (22 male and 22 female) in both the fed and non‐fed states at 20 wk of age (mean weight: 470.2±23.2 g). Both total intact (TI) and bioactive 1‐84 (BA) PTH were measured using ELISA (Alpco Diagnostics, USA). Differences between groups were calculated using a two‐way ANOVA with repeated measures and significance p<0.05. Non‐fed BA PTH concentration (14.8±2.2 pmol/L) was significantly higher than in the fed state (9.0±0.7 pmol/L, p=0.02). BA PTH in the non‐fed state versus fed state was significantly elevated in females (p=0.04), but not in males (p=0.26). Values in female rats (12.9±2.2 pmol/L) were on average 19% higher than males (10.9±1.0 pmol/L) but not significantly different (p=0.39). These differences were not observed in TI PTH, which detects fragments of PTH, that potentially mask the effect (fed: 20.9±1.6 vs. non‐fed: 24.8±3.5; p=0.13). These results suggest that fasting can elevate BA PTH. Studies related to PTH should consider standardization of fast duration, gender effects, and measure BA PTH. Grant Funding Source : NSERC