Energy expenditure of rats subjected to long-term food restriction.

Food restriction, even when expressed per unit of metabolic mass, leads to energy conservation as seen by decreased oxygen consumption. The objective of the present study was to verify whether the energy conservation mechanism reduces energy expenditure for as long as food restriction lasts or whether a return to basal level may occur without realimentation, mainly in mildly food-restricted rats. Wistar rats were brought to the laboratory on weaning. They were then assigned to control group that received ad libitum food intake, R10 and R20 groups that received 90 and 80%, respectively, of the food eaten by control group and RM group that received an amount of food enough only to keep body weight. The food restriction period lasted for 3 months and was followed by another month during which all groups received ad libitum food intake. The results showed that even in animals subjected to mild food restriction (10%) there was a sustained decrease in oxygen consumption that lasted until refeeding of the animals. The results led to the conclusion that the energy conservation mechanism is active from little food restriction until more stronger levels of restriction, in a proportional manner, and the decreased energy expenditure is maintained during the whole food restriction period.

Fish mercury concentration in the Alto Pantanal, Brazil: influence of season and water parameters.

The tropical flood plain Pantanal is one of the world's largest wetlands and a wildlife sanctuary. Mercury (Hg) emissions from some upstream gold mining areas and recent findings of high natural Hg levels in tropical oxisols motivated studies on the Hg cycle in the Pantanal. A survey was made on total Hg in the most consumed piscivorous fish species from rivers and floodplain lakes in the north (Cáceres and Barão de Melgaço) and in the south part of Alto Pantanal (around the confluence of the Cuiabá and Paraguai rivers). Samples were collected in both the rainy and dry seasons (March and August 1998) and included piranha (Serrasalmus spp.), and catfish (Pseudoplatystoma coruscans, pintado, and Pseudoplatystoma fasciatum, cachara or surubim). There was only a small spatial variation in Hg concentration of the 185 analyzed fish samples from the 200 x 200 km large investigation area, and 90% contained total Hg concentration below the safety limit for regular fish consumption (500 ng g(-1)). Concentration above this limit was found in both Pseudoplatystoma and Serrasalmus samples from the Baia Siá Mariana, the only acid soft-water lake included in this study, during both the rainy and dry seasons. Concentration above this limit was also found in fish outside Baia Siá Mariana during the dry season, especially in Rio Cuiabá in the region of Barão de Melgaço. The seasonal effect may be connected with decreasing water volumes and changing habitat during the dry season. The results indicate that fertile women should restrict their consumption of piscivorous fishes from the Rio Cuiabá basin during the dry season. Measures should be implanted to avoid a further deterioration of fish Hg levels.

Effects of diet and thermal acclimation on oxygen consumption in rats.

The relationship between food intake and oxygen consumption was studied in a group of 60 rats acclimated at environmental temperatures of either 30 or 10 degrees C. Three separate experiments were performed. In the first, 28 rats were divided into two groups: control, which received 20 and 32 g of food/day at 30 and 10 degrees C, respectively, from 0800 to 1700 and experimental, which received 10 and 25 g of food/day at 30, and 10 degrees C, respectively. The experimental period lasted 6 weeks. Oxygen consumption was measured weekly at environmental temperatures of 5, 15, 25, 30, and 35 degrees C. In the second experiment, 16 rats were subjected to the same food intake as the animals in the first experiment. After 1 week, their oxygen consumption was measured at 25 degrees C over a period of 24 h. The third experiment was carried out with 16 other rats in which the control groups received the same amount of food as in the first experiment, and the experimental groups were fed 6 and 11 g/day at 30 and 10 degrees C, respectively, during 1 week. In the first experiment, no changes in oxygen consumption (per kilogram 0.67) were apparent in the experimental rats during 6 weeks. However, after 1 week on severe food restriction a significant decrease in oxygen consumption (per kilogram 0.67) was observed. A long-lasting thermic effect of food was observed in control rats from the second experiment and a rapid effect was apparent in restricted rats.(ABSTRACT TRUNCATED AT 250 WORDS)