Adaptation of mammalian protein metabolism to amino acid supply

Abstract

The metabolism of the animal is equipped to adapt to changes in both the internal and the external environment. Among internal factors are activity versus rest and sleep, and the menstrual cycle in the case of the female. Metabolism must also respond to variations in the external environment, such as heat and cold, and notably the availability of food. Metabolic adaptation to nutrient supply is of two kinds. First, there are transient physiological adaptations to the intermittent intake of nutritionally adequate meals. These short-lived adaptations account for a large part of the diurnal variations that have been observed in the protein metabolism of mammals (Wurtman, 1969). Secondly, long-term adaptive reactions occur when there is a decrease in availability of an essential nutrient in the diet. Under such circumstances, tissue constituents are lost to varying degrees from different parts of the body. It is proposed to discuss here mainly short-term physiological adaptations to variations in amino acid supply and their relevance to the needs of the body for dietary protein. Adaptive changes resulting from long-term protein deficiency are considered in the paper by Waterlow & Stephen (1969).