Untersuchungen zur Melatoninrhythmik beim Hausschwein (Sus scrofa f. domestica) unter Anwendung einer neu entwickelten HPLC-Methode

The existence of a melatonin rhythm in the domestic pig with
respect to the light intensity has been discussed controversally.
These controversial results are caused in part by inappropriate RIA
methods. Until now, there are no published results describing
non-immunological identification of melatonin in the domestic pig.
Therefore, the main-objective of this study was to establish a HPLC
method for the determination of melatonin in plasma and saliva
samples of domestic pigs and to examine the correlation of the
melatonin concentration of these two specimens. A further aim of
this study was the possible replacement of blood sampling which
requires the restraint of the animal by minimally invasive saliva
sampling. The study was conducted on 12 domestic crossbred pigs
aged 14 weeks (6 gilts, 6 barrows), which were housed in single
pens under standardized conditions and under an equatorial
lightregime (LD 12:12). Photophase light intensities were set in
two groups with 250 lux and 470 lux, scotophase light intensities
were below 1,0 lux. Blood and saliva samples were collected over a
period of 24 hours on two non-successive days with sampling
intervalls of 3 hours. Following chloroform extraction, samples
were analyzed by a HPLC system. Identification and quantification
of melatonin were achieved by comparing the retention times with
those of authentical standards containing a known melatonin
concentration. Results of this study showed that the HPLC method is
appropriate for the determination of melatonin concentrations of
both plasma and saliva samples and comprises a remarkably high
sensitivity, which allows a reliable measurement of melatonin
concentrations even in photophase samples. Results revealed
identical concentrations of both photophase and scotophase
melatonin concentrations at a light intensity of 250 lux,
indicating a lack of suppression of pineal melatonin secretion
during photophase. This indicates that differences in hormone
concentrations driven by day/night-changeovers were not sufficient
for pigs to differenciate between day and night at a light
intensity of 250 lux. Results also showed significantly lower
photophase melatonin concentrations at a light intensity of 470
lux, compared to 250 lux. This indicates a stronger light-induced
melatonin supression, not being able to synchronize melatonin
secretion to the lightregimen completely and therefore may have
been assessed as insufficient by the animals. Furthermore, results
showed clear differences in the melatonin profiles of castrated
male and intact female pigs. There was no correlation of salivary
and plasma melatonin concentrations. Therefore blood samples cannot
be replaced by minimal-invasive saliva samples. Further studies
should be done to investigate the light intensity, which entrains
the synchronisation of the melatonin profile to the lightregime.
This could be done by using this highly sensitive HPLC method to
assess the photic demands of domestic pigs kept in indoor
piggeries. Particular attention should be given to the consequences
of a potential effect of a stress-load on the animals and its
stimulating effects on the synthesis of melatonin, as well as
potential sex differences.