Food intake and leptin concentrations of lactating rats nursing various sized litters

Purpose:   Leptin, the obesity (ob) gene product, has been proposed as an adipose-related satiety factor. It might act as a signal, from peripheral adipose stores to the central nervous system, to decrease food intake and increase energy expenditure. Conversely, low leptin concentrations after fasting or energy restriction might act to increase food intake. The present study investigated the role of the suckling stimulus in the mechanisms regulating body weight, food consumption and leptin concentration in lactating rats nursing different sized litters. Methods:   The day of parturition was designated as day 0 of lactation. The rats were allocated randomly to three groups and the number of pups per litter was adjusted within one day of birth to eight (Group A), four (Group B) and two (Group C), with equal numbers of both sexes. From day 1 to day 10 of lactation, the separate weights of the mothers and pups, and the mothers' food intake were measured daily. On day 10, the rats were decapitated and blood was collected from the mothers for measurement of serum concentrations of leptin by ELISA. Results:   Food intake by the mothers in Groups B and C decreased by about 20% and 30%, respectively, by day 10 of lactation, compared with Group A, but the serum leptin concentrations of those in Group C increased by about 80%, compared with Groups A and B. There was a high positive correlation between leptin concentration and fat pad weight. Conclusion:   The findings suggest that the smaller litter in Group C reduced the energy cost of lactation, which induced an increase in the serum leptin concentration. (Reprod Med Biol 2005; 4: 203-206).