Influence
of pinealectomy and long-term melatonin administration on
GH-IGF-I axis function in male rats
by Zofia Ostrowska, Beata Kos-Kudla, Elzbieta Swietochowska,
Bogdan Marek, Dariusz Kajdaniuk & Nelly Ciesielska-Kopacz
Keywords:
MEL, GH-IGF-I axis, Circadian oscillations,
Male rats
Submitted:
March 15, 2001
Accepted: May 30, 2001
Abstract:
BACKGROUND: A relationship between circadian GH-IGF-I
axis activity and pineal gland function in rats is not sufficiently
elucidated, particularly in the aspect of melatonin (MEL)
participation with relation to a possible mechanism of these
dependencies.
OBJECTIVE:
Influence of pinealectomy and long-term MEL administration
on circadian GH-IGF-I axis function in male rats was evaluated.
An attempt was also made to determine whether the effect of
exogenous MEL is dependent on the pineal gland presence. METHODS:
Studies were performed in 192 sexually mature male Wistar
rats, which were subjected to pinealectomy or sham operation.
In half of the animals from each group MEL (Sigma, USA) in
dose of 50 µg/ 100g b.m. was administrated intraperitoneally
(daily between 5 and 6 pm during a 4-week period). Blood for
RIA assays of MEL, GH and IGF-I concentrations was collected
every 3 hours during a day-beginning at 8 am (rats killed
by decapitation).
RESULTS:
Significant influence of pinealectomy and exogenous MEL on
a daily profile of endogenous MEL in rats was confirmed. Distinct,
dependent on the time of the day anomalies in circadian oscillations
of GH and IGF-I showing positive correlation with changes
in endogenous MEL concentrations were also shown. GH rhythm
was suppressed in a group of rats with removed pineal gland;
after pinealectomy distinct decrease and after MEL use - distinct
increase of GH and IGF-I concentrations during the day were
observed. It had influenced mean daily concentrations and
values of amplitude of circadian GH and IGF-I oscillations
in all studied groups of animals. In rats with preserved pineal
gland the effect of exogenous MEL action was more intensified.
CONCLUSIONS:
Pineal gland can influence circadian function of GH-IGF-I
axis, and in mechanism of this dependence, changes in endogenous
MEL concentrations seem to play an important role. Administration
of MEL in rats after pinealectomy only partly prevents changes
of GH-IGF-I axis function caused by gland removal, which can
indicate participation of other pineal gland substances in
generating disturbances. Influence of exogenous MEL on GH-IGF-I
axis function during the day is dependent on the presence
of pineal gland, which can be connected with indirect and/or
direct influence of administrated hormone on this gland.
