Plasma Leptin Concentrations In Rats Research Articles

Effect of Food Restriction and Intense Physical Training on Estrous Cyclicity and Plasma Leptin Concentrations in Rats

Intense physical training and dietary energy restriction have been associated with consequences such as nutritional amenorrhea. We investigated the effects of intense physical training, food restriction or the combination of both strategies on estrous cyclicity in female rats, and the relationship between leptin ad these effects. Twenty-seven female Wistar rats were distributed into four groups: SF: sedentary, fed ad libitum; SR: sedentary subjected to 50% food restriction (based on the food intake of their fed counterparts); TF: trained (physical training on a motor treadmill with a gradual increase in speed and time), fed ad libitum; TR: trained with 50% food restriction. We analysed estrous cyclicity, plasma leptin and estradiol as well as chemical composition of the carcass, body weight variation, and weight of ovaries and perirenal adipose tissue. Data demonstrate that physical training alone was not responsible for significant modifications in either carcass chemical composition or reproductive function. Food restriction reduced leptin levels in all animals and interrupted the estrous cyclicity in some animals, but only the combination of food restriction and physical training was capable of interrupting the estrous cyclicity in all animals. Leptin was not directly related to estrous cyclicity. From our findings, it may be concluded that there is an additive or synergistic effect of energy intake restriction and energy expenditure by intense physical training on estrous cyclicity. Leptin appears to be one among others factors related to estrous cycle, but it probably acts indirectly.

High-fat diet feeding reduces the diurnal variation of plasma leptin concentration in rats

To investigate the response of plasma leptin and its diurnal variation to graded levels of dietary fat intake, adult (486.8+/-10.8 g), male rats (N = 52) were fed diets containing 12%, 28%, 44%, and 60% fat for 4 weeks. The body weight gain and abdominal fat pad weight were higher (P < .05) in groups fed diets containing 44% and 60% fat compared with the two diets containing less fat. There were no significant differences in terms of body weight or fat pad weight between animals fed the two diets with higher fat content or between animals fed the two lower-fat diets. Twenty-four-hour energy expenditure was not different among the dietary fat groups. After 3 days on the experimental diets, plasma leptin increased (P < .03) in all dietary groups. The increases in leptin in animals fed 12% and 28% fat diets occurred primarily in the morning. In contrast, in groups fed the two diets containing higher fat content, leptin levels increased mainly in the afternoon. As a result, the daily variation in leptin increased (P < .05) in the two groups fed lower-fat diets, but decreased (P < .04) in animals fed the two higher-fat diets. These data demonstrate that short-term high-fat diet feeding abolished the diurnal fluctuation of plasma leptin levels, which may prevent proper leptin function and eventually contribute to the development of obesity.

Dietary fat type and energy restriction interactively influence plasma leptin concentration in rats

To investigate whether dietary fat source and energy restriction interactively influence plasma leptin levels and its association of leptin with insulin action, rats were fed diets containing either fish, safflower oil, or beef tallow (20% wt/wt) for 10 weeks. Groups of rats consumed each diet ad libitum or at 85% or 70% of ad libitum energy intake in a design that held fat intake constant. Graded levels of energy restriction caused body weight to decrease (P < 0.001) differently according to the dietary fat provided. Plasma leptin concentrations were 60% higher (P < 0.05) in the groups fed fish oil and safflower oil ad libitum compared with those in the beef tallow group, despite smaller perirenal fat mass and fat cell size in the fish oil-fed animals. Energy restriction resulted in a 62% decrease (P < 0.05) in leptin levels in fish oil- and safflower oil-fed rats, whereas no changes were observed in beef tallow-fed animals. Plasma insulin levels were lower (P < 0.05) in the fish oil group fed ad libitum compared with those in the two other diet groups.▪ These data demonstrate a hyperleptinemic effect in animals consuming diets rich in polyunsaturated fatty acid, which can be normalized to the level of saturated fat consumption by mild energy restriction. Thus, dietary fatty acid composition, independent of adipose tissue mass, is an important determinant of circulating leptin level in diet-induced obesity.—Cha, M. C., and P. J. H. Jones. Dietary fat type and energy restriction interactively influence plasma leptin concentration in rats.