Effects of light and food on plasma leptin concentrations in ewes

Plasma leptin concentration shows pulsatility and diurnal rhythm in humans. However, there are few reports concerning the 24-h profile of circulating leptin levels in ruminants. Five crossbred ewes were housed in metabolism c ages under a l-h light-dark cycle. The ewes were offered alfalfa hay daily to meet their energy requirement. Blood samples were collected at 15-min in tervals for 24 h. Plasma leptin concentrations were determined using a radi oimmunoassay and the profile of plasma leptin levels was analysed by the PU LSAR algorithmic program for detecting pulse. Plasma leptin concentration c hanged in a pulsatile fashion. The mean leptin concentration was 2.93 ng/ml . The mean pulse frequency was 4.8 pulses per day and the mean pulse amplit ude was 0.67 ng/ml with an average pulse length of 1:13 h. Plasma leptin le vel was not affected by feeding or lighting cycle. These results indicate t hat plasma leptin level in sheep shows pulsatility but diurnal rhythm is no t exhibited.