Untersuchungen zur Melatoninrhythmik beim Hausschwein (Sus scrofa f. domestica) unter Anwendung einer neu entwickelten HPLC-Methode Tierärztliche Fakultät - Digitale Hochschulschriften der LMU - Teil 01/07

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.