Alteration of the circadian rhythm of intact parathyroid hormone following a 96-hour fast.
OBJECTIVE
PTH(1-84) secretion in normal male subjects follows a circadian rhythm. The control of this rhythm is multifactorial with both neuroendocrine and chemical influences. The aim of this study was to assess the effect of a 96-hour fast on the circadian rhythm of PTH(1-84), serum calcium, phosphate and nephrogenous cAMP (NcAMP), an index of PTH(1-84) bioactivity.


METHODS
Blood samples for estimation of all analytes were obtained over a 24-hour period at 30-minute intervals. Urine samples were obtained 4 hourly during the daytime and overnight. Each subject was studied on two occasions after being randomized to either (a) normal hospital diet or (b) a 96-hour fast with water freely available.


METHODS
Six healthy adult males aged between 28 and 40 years, mean 32 years.


METHODS
PTH(1-84) was measured by an in-house immunoradiometric assay. Serum calcium, phosphate, albumin, creatinine and urinary creatinine were measured by standard automated techniques. Calcium was adjusted for albumin. Plasma cAMP was estimated by a commercial method and urine cAMP by in-house radioimmunoassay and NcAMP obtained by calculation. Rhythm parameters were analysed by cosinor techniques.


RESULTS
There were alterations in the circadian rhythms of serum phosphate, PTH(1-84) and NcAMP following a 96-hour fast. Fasting abolished the nocturnal rise in phosphate, PTH(1-84) and NcAMP but had little effect on the pattern of adjusted calcium over a 24-hour period. The mean concentrations of serum phosphate, adjusted calcium and NcAMP decreased significantly following the fast and mean PTH(1-84) increased during day time.


CONCLUSIONS
Fasting for 96 hours significantly alters the circadian rhythm of PTH(1-84) secretion by lowering the mean calcium concentration and attenuating the circadian rhythm of serum phosphate.
Fraser
W D
WD
University Department of Clinical Chemistry, Royal Liverpool University Hospital, UK.
Logue
F C
FC
Christie
J P
JP
Cameron
D A
DA
O'Reilly
D S
DS
Beastall
G H
GH
D000328:Adult; D002118:Calcium / Q000097:blood; D002940:Circadian Rhythm; D000242:Cyclic AMP / Q000097:blood / Q000652:urine; D005215:Fasting / Q000097:blood* / Q000652:urine; D006801:Humans; D015592:Immunoradiometric Assay; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood / Q000378:metabolism*; D010710:Phosphates / Q000097:blood
D010281:Parathyroid Hormone; D010710:Phosphates; D000242:Cyclic AMP; D002118:Calcium