LEPTIN CIRCADIAN RHYTHM EXPRESSION IN GOATS

Abstract

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 17β-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<0.10) in 5/8 goats. BMI tended to influence the expression of leptin circadian rhythms (P=0.13); 50% (4/8) vs. 12.5% (1/8) of goats w/leptin circadian rhythm in HBMI vs. LBMI. Season did not affect (P=0.36) the expression of leptin circadian rhythm; 37.5% (3/8) and 25% (2/8) goats w/leptin circadian rhythm in BS and TS. Goats w/leptin circadian rhythm showed a diurnal ACROPHASE between 11:30 to 15:30 h. Frequency of leptin circadian rhythm in TS was low and similar in BMI groups (1/4 for HBMI and LBMI). There was a differential response between BMI groups during the BS with HBMI goats showing the highest frequency of leptin circadian rhythm (3/4 and 0/4 for HBMI and LBMI, P<0.001). The LBMI group had higher MESOR (P<0.05) and basal leptin concentrations (1.9 vs. 1.4 and 1.2 vs. 0.5 ng/ml in LBMI vs. HBMI). There were no differences (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.