Protein synthesis, bodily renewal and the sleep-wake cycle.

Clinicians with interests in endocrinology, and in nutrition, have been among those with a concern for how the body builds and renews itself. Growth and renewal depend upon protein synthesis, for which food is necessary, for food provides amino acids. The biochemical controls for cellular protein synthesis, however, are similar for all organisms, and not immediately dependent on diet. We ourselves have an interest in sleep and share the common man’s belief that sleep is in some way restorative. If the belief is correct, then one must ask what the link with restoration or renewal may be. Studies of cell and tissue kinetics c o n f m that there are circadian (i.e. about 24h) variations in protein synthesis and in cellular proliferation [ 11. Indeed, endogenous ‘clocks’ govern the function of every living tissue and in the whole body the clocks are co-ordinated by the brain, directly or indirectly. The chief human circadian rhythm is that of sleep-wakefulness. Entrained to it is, for example, a rhythm of plasma amino acids, the timing of the peaks and troughs being independent of feeding, and there are also 24h rhythms in intracellular amino acid levels that bear no simple relation to feeding or to plasma amino acid levels, which is not surprising, for amino acids are actively transported. As a feature of the sleep-wakefulness rhythm there are 24h variations too in bodily activity and in the concomitant degradation of body fuels. Since amino acids provide one source of fuel, it will be realized that if activity during