Changes induced in rat plasma composition by lactation

Thermogenic effects of a "cafeteria" diet on the rat during its reproductive cycle

The heat production and oxygen consumption of intact virgin, pregnant, lactating and postlactating rats has been investigated both in groups fed a "cafeteria" diet as well as in controls. A third group of rats fed the cafeteria diet after parturition has been investigated. Pregnant rats fed a "cafeteria" diet increased their weight faster than controls. During lactation no increases in weight were observed, and in postlactation both "cafeteria" groups attained the same values higher than controls. The ingestion of a "cafeteria" diet resulted in higher heat production in all groups except lactating rats, which--in addition--showed higher heat outputs than all the other groups when the actual data were corrected by metabolic weight according to the surface law. The high lactation heat production (and oxygen consumption) can be a consequence of increased metabolic activity in the rat organism, devoted to milk production. It can be concluded that during lactation the dam energy output through the milk must absorb any increases in energy input due to the more densely-packed energy in the "cafeteria" diet, and this did not result in increased heat production.

Effects of lactation on circulating plasma metabolites in 'cafeteria-fed' rats

1. The effects of 'cafeteria feeding' on primiparous Wistar rats during lactation have been studied by measuring circulating levels of glucose, amino acids, lactate, urea and ammonia as well as glycogen levels in liver and muscle. 2. No significant changes in glucose levels were observed despite alterations in blood glucose compartmentation. 3. Compared with controls, the dams given the cafeteria diet had higher liver glycogen stores which were more easily mobilized at the peak of lactation. 4. Rats given the cafeteria diet showed a lower amino acid utilization than controls and adequately maintained circulating levels, as determined by the lower circulating levels of ammonia and urea. 5. No significant differences in body-weight were observed in the period studied despite increasing dam weight after weaning in the cafeteria-fed group. 6. The size of pups of cafeteria-fed dams was greater than that of controls, and the differences were marked after weaning, when the metabolic machinery of the cafeteria pup maintained high protein accretion and body build-up using fat as the main energy substrate characteristic of the preweaning stage. The controls, however, changed to greater utilization of amino acids as an energy substrate and adapted to high-protein (low-biological-quality) diets with a significantly different pattern of circulating nitrogen distribution.

Effects of 24-hour starvation period on metabolic parameters of 20-day-old rats

The effects of a 24-hour starvation period upon 20-day-old rat pups were studied both in animals kept in the presence of their starved dams and in their absence. The relative loss of body weight was more intense in the rats that received no milk, being however, severe in both groups. There was a significant maintenance of both plasma glucose levels and total amino acids, with differences in blood glucose compartmentation and a remarkable uniformity in the effects of starvation upon individual amino-acid concentrations. A significant increase in plasma urea was observed, higher in the rats kept in the presence of the dam. Ketone bodies increased with starvation but their final levels were lower than in adults. The general pattern of metabolic change observed suggests a situation, after 24-h food deprivation, similar to that of long term starvation in adults; with an active protein amino-acid catabolism but with a remarkable maintenance of circulating foodstuff levels.