NEUROENDOCRINOLOGY
LETTERS
including
Psychoneuroimmunology, Neuropsychopharmacology,
Reproductive Medicine, Chronobiology
and Human Ethology, ISSN 0172–780X
The
relationship between the daily profile of chosen biochemical
markers of bone metabolism and melatonin and other hormone secretion
in rats under physiological conditions
Key
words: hormones, bone metabolism, daily rhythm, male rats
Abstract
BACKGROUND:
The mechanism of generating and synchronizing daily rhythms
of bone and mineral metabolism markers has not been entirely
explained. Most studies indicate that LD cycle and/or feeding
schedules provide important synchronizers of these rhythms.
It seems that endogenous factors, including systemic and local
hormones can be important in the mechanism of dependence of
bone and mineral metabolism parameters rhythms on LD cycle
and feeding schedule.
OBJECTIVE:
To assess the relationship between the daily profile of chosen
biochemical parameters of bone and mineral metabolism (serum
ALP, PICP, ICTP and iP and urinary excretion of HYP and total
calcium) and daily secretion of MEL, GH/IGF-I axis activity
and parathyroid, thyroid, adrenal cortex and gonads function
in 48 adult male rats.
METHODS:
Material for studies was collected every 3 hours within a
day. Hormones, PICP and ICTP concentrations were determined
with the use of RIA method and ALP, HYP, total calcium and
iP values – spectrophotometrically.
RESULTS:
Existence of a negative correlation between daily oscillations
of studied markers of osteogenesis (ALP and PICP) and daily
profile of MEL and PTH secretion and positive – with
daily fluctuations of GH and IGF-I was shown. Moreover, ALP
values correlated negatively with daily oscillations of CT.
Concentrations of bone resorption markers (ICTP, HYP and total
calcium) correlated negatively with daily fluctuations of
MEL and – positively with GH, IGF-I and thyroid hormones.
CONCLUSION:
The present results suggest that physiological daily rhythmicity
of PTH, MEL, GH, IGF-I and thyroid hormones most probably
play an important role in regulating the daily rhythm of biochemical
markers of bone metabolism.
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Abbreviations
ALP
-- alkaline phosphatase
B -- corticosterone
CT -- calcitonin
FT4 -- free thyroxine
FT3 -- free triiodothyronine
GH -- growth hormone
HYP -- hydroxyproline
ICTP -- cross-linked carboxyterminal telopeptide of type I collagen
IGF-I -- insulin-like growth factor-I
MEL -- melatonin
iP -- inorganic phosphorus
PICP -- carboxyterminal propeptide of type I procollagen
PTH -- parathormone
T -- testosterone
T4 -- total thyroxine
T3 -- total triiodothyronine
Introduction
Biochemical
parameters of bone and mineral metabolism show a daily rhythm
in experimental animals and humans [1–11], but the physiological
mechanisms underlying these rhythms have not been entirely explained.
In animal studies, the predominant mechanism underlying the
daily rhythms of bone and mineral metabolism parameters seems
to be exogenous and depends on intake of calcium and phosphorus
[12, 13]. Numerous investigators have reported the influence
of feeding schedules (meal timing) on the circadian changes
in biochemical parameters of bone and mineral metabolism [1,
6, 14–16]. Most of the data support the conception that
the feeding schedule is a powerful Zeitgeber that can override
the influence of the light:dark (LD) cycle. Nevertheless, the
LD cycle remained the predominant synchronizer for the bone
matrix formation rhythm [3]. There is some evidence that endogenous
mechanisms could also be important. Several published observations
suggest that parathormone (PTH) and glucocorticoids might play
a role in the synchronization of the bone metabolism periodicity
[4, 10, 17–20]. However, an effect of other hormones, including
melatonin (MEL), cannot be excluded.
The aim of the study was to investigate the influence of the
endogenous daily fluctuations of MEL and other hormones such
as growth hormone (GH), insulin-like growth factor-I (IGF-I),
total and free triiodothyronine (T3, FT3), total and free thyroxine
(T4, FT4), corticosterone (B), testosterone (T) in serum and
PTH and calcitonin (CT) in plasma on the daily rhythmicity of
chosen biochemical parameters of bone and mineral metabolism
(alkaline phosphatase – ALP, carboxyterminal propeptide
of type I procollagen – PICP, cross-linked carboxyterminal
telopeptide of type I collagen – ICTP, inorganic phosphorus
– iP levels in serum and urinary excretion of hydroxyproline
– HYP and total calcium) in rats under physiological conditions.
