Correlation between body weight (epididymal fat) and permeation rate of serum leptin through the blood-brain barrier (BBB) in male rats aged 8 months.

In this study, in order to clarify the kinetics of leptin, we focused on the ratio of leptin concentrations in cerebrospinal fluid and serum in aged male rats, and examined the weight of epididymal fat, and the passage rate of leptin through the blood-brain barrier. In the lighter animals, the epididymal fat weight was low, while leptin concentrations in the serum and cerebrospinal fluid were also low. Conversely, in the heavier animals, the weight of epididymal fat and leptin concentrations in the serum and cerebrospinal fluid were higher. With regard to the ratio of leptin in the cerebrospinal fluid and serum, the passage rate of leptin through the blood-brain barrier was lower in the heavier animals than in the lighter animals.

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).

Effects of i.c.v. administration of leptin on copulatory and ingestive behavior in STZ-induced diabetic male rats.

It is well known that circulating leptin concentrations correlate with adiposity in both humans and rodents and decrease after fasting, energy restriction, or weight loss. The goal of the present study was to confirm whether the decreases of copulatory behavior and the increases of ingestive behavior in STZ-induced diabetic male rats could be reversed by i.c.v. administration of leptin. Adult male Wistar-Imamichi rats aged 9 weeks were used for the studies. Males received a single injection of STZ (60 mg/kg, i.p.) and vehicle. During the experiment, individual body weight, and food and water intake were measured. The copulatory and ingestive behaviors in STZ-induced diabetic males were observed at 2 and 4 weeks after STZ. At 6 weeks after STZ, leptin (10 microg/10 microl) or aCSF (artificial cerebrospinal fluid) was injected through a lateral ventricle cannula and the above two behaviors were observed again. The i.c.v. leptin injection to STZ-induced diabetic males resulted in a significant increase of ejaculation frequencies (3.6 +/- 0.26 vs. 2.9 +/- 0.30 times) and a significant decrease in amount of food ingested (36.2 +/- 1.93 vs. 23.2 +/- 3.76 g), compared with the aCSF-injected control (p<0.01). These findings suggest that the copulatory and ingestive behaviors in i.c.v. leptin-injected STZ diabetic males were restored to levels equivalent to those in control males.