LEPTIN CIRCADIAN RHYTHM EXPRESSION IN GOATS WITH DIFFERENT BODY MASS INDEX AND DURING DIFFERENT SEASONS

摘要

The objective was to determine if serum leptin expresses a circadian rhythm in goats, and the effect of body mass index (BMI) and season of the year on such expression. Eight mature, ovariectomized, female goats with s.c. sylastic implants containing 17?-estradiol were maintained in a high (HBMI, n=4) or low (LBMI, n=4) BMI during the breeding (BS-december, n=8) and transition into anestrous (TS-february, n=8) seasons. Blood samples were obtained every hour throughout a 48 h period and serum leptin determined (Linco Res. Inc.). Results were analyzed by COSINOR program (fit of data to a cosine curve) obtaining the MESOR (mean leptin concentration), AMPLITUDE (half difference between highest and lowest leptin concentration) and ACROPHASE (time of highest leptin concentration). Frequency of occurrence of a circadian rhythm was analyzed by Fisher?s exact test. A leptin circadian rhythm was evident (P 0.05) in AMPLITUDE for any effect or their interaction. Evidence of a serum leptin circadian rhythm in female goats, with a diurnal increase in serum leptin was found and reported for the first time. Moreover, an effect of interaction between BMI and season in the expression of such rhythm was observed. Studies involving serum leptin in goats should take into account its circadian variation; otherwise under- or over-estimations might occur.