Protein-Energy Relationship in Adult Rats

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Abstract
During ad libitum feeding for 20 days, adult female rats were given isocaloric diets supplying either 5 or 15% of the total calories as protein from lactalbumin; average nitrogen intakes per 5 days were 464 mg for group L and 1159 mg for group A, respectively. Then food intake was restricted to two-thirds of ad libitum amounts for 30 days; groups maintained previously with 464 mg N received 266, 450, 835 or 1279 mg N, and groups maintained previously with 1159 mg N received 434, 762, 1144 or 1492 mg N/5 days. Although ad libitum food intake of group L was higher than that of group A, gains in body weight were similar. Nitrogen retention, hepatic nitrogen concentration and activities of hepatic succinic dehydrogenase and xanthine oxidase were greater and hepatic fat concentration lower in group A than in group L. Increments in nitrogen intake during restriction minimized losses in body weight and increased the unit activities of 2 hepatic enzymes studied. Liver weights were reduced markedly in all restricted groups, hepatic nitrogen concentrations increased and percentage of hepatic fat decreased. Concentrations of carcass nitrogen and body fat were similar for both ad libitum and restricted groups.