Dobowe zmiany stezenia melatoniny w osoczu krwi niedojrzalych plciowo loszek podczas dlugiego dnia swietlnego

The level of melatonin in plasma was investigated in gilts reared during long summer days (sunrise 430, sunset 2030). Lighting in the animal's rooms was provided by windows and fluorescent lamps, which were automatically turned on at 545 and turned off at 1945. The light intensity during photophase was 500 lux at the level of the animal's eyes. Blood samples were taken from twelve gilts over a 24 hour period and further sampling was continued in six pigs over the following 3 days. The effect of exposure to a 500 lux light during the night on plasma melatonin levels was studied in the remaining six gilts. The concentration of melatonin in the plasma was measured by direct radioimmunoassay employing an R/R/19540-16876 antibody and iodinated tracer. Concentrations of the investigated hormone were low during day and rapidly increased at the onset of night during which the plasma melatonin level remained at an elevated plateau and then declined at the onset of day. The mean concentration of plasma melatonin was about three times higher during the night compared to daytime. Monitoring of the pineal hormone level in blood plasma over four consecutive days indicated regular melatonin rhythms in 5 of the 6 investigated pigs. A 500 lux light (turned on for one night) did not prevent a nocturnal increase in plasma melatonin levels.