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The parathyroid hormone circadian rhythm is truly endogenous--a general clinical research center studyWhile circulating levels of PTH follow a diurnal pattern, it has been unclear whether these changes are truly endogenous or are dictated by external factors that themselves follow a diurnal pattern, such as sleep-wake cycles, light-dark cycles, meals, or posture. We evaluated the diurnal rhythm of PTH in 11 normal healthy male volunteers in our Intensive Physiologic Monitoring Unit. The first 36 h spent under baseline conditions were followed by 28-40 h of constant routine conditions (CR; enforced wakefulness in the strict semirecumbent position, with the consumption of hourly snacks). During baseline conditions, PTH levels followed a bimodal diurnal rhythm with an average amplitude of 4.2 pg/mL. A primary peak (t1max) occurred at 0314 h, and the secondary peak (t2max) occurred at 1726 h, whereas the primary and secondary nadirs (t1min and t2min) took place, on the average, at 1041 and 2103 h, respectively. This rhythm was preserved under CR conditions, albeit with different characteristics, thus confirming its endogenous nature. The serum ionized calcium (Cai) demonstrated a rhythm in 3 of the 5 subjects studied that varied widely between individuals and did not have any apparent relation to PTH. Urinary calcium/creatinine (UCa/Cr), phosphate/Cr (UPO4/Cr), and sodium/Cr (UNa/Cr) ratios all followed a diurnal rhythm during the baseline day. These rhythms persisted during the CR, although with different characteristics for the first two parameters, whereas that of UNa/Cr was unchanged. In general, the temporal pattern for the UCa/Cr curve was a mirror image of the PTH curve, whereas the UPO4/Cr pattern moved in parallel with the PTH curve. In conclusion, PTH levels exhibit a diurnal rhythm that persists during a CR, thereby confirming that a large component of this rhythm is an endogenous circadian rhythm. The clinical relevance of this rhythm is reflected in the associated rhythms of biological markers of PTH effect at the kidney, namely UCa/Cr and UPO4/Cr.
Document ID
20040173077
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
el-Hajj Fuleihan, G.
(Brigham and Women's Hospital, Harvard Medical School Boston Massachusetts 02115, United States)
Klerman, E. B.
Brown, E. N.
Choe, Y.
Brown, E. M.
Czeisler, C. A.
Date Acquired
August 22, 2013
Publication Date
January 1, 1997
Publication Information
Publication: The Journal of clinical endocrinology and metabolism
Volume: 82
Issue: 1
ISSN: 0021-972X
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: M01-RR-02635
CONTRACT_GRANT: R01-AG-06072
CONTRACT_GRANT: K01 AG-00666-01
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Musculoskeletal
NASA Discipline Regulatory Physiology
Non-NASA Center

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