Multiple clocks in our body?

Many travelers have experienced jet lag that groggy realization that while your day is beginning in Hawaii, the night you just left in Canada is hardly over. Jet lag is an inconvenient reminder that the body is set to a 24-hour clock, known as a circadian rhythm.

An internal biological clock is fundamental to all living organisms, influencing hormones that play a role in sleep and wakefulness, metabolic rate, and body temperature. Early studies pointed to an area of the brain, the hypothalamus, as the location of the master clock in mammals.

Recent research suggests, however, that this "master" clock may co-exist with other body clocks that regulate different body functions.

Researchers at the Oregon National Primate Research Center investigated circadian rhythm regulations and the adrenal gland in rhesus macaque monkeys, a gland which functions similarly in humans. This study identified in their adrenal gland 322 genes with functions that varied over a 24-hour period, ebbing and flowing at the same times each day. Researchers suggest that the adrenal gland may have its own timing mechanism apart from the body's master clock.

This study also shows that the core molecular circadian clock genes are expressed in most if not all of the cells in the body, both within and outside the brain. These clocks time the expression of other genes within the cells.

The importance of such biological timing under local control, and its implications for health and disease at the cell, tissue, and organ level represent new frontiers for biomedical research.

Therapies that target specific times of the day for specific parts of the body to achieve optimal results may be developed one day. Also, a better understanding of our body's various circadian rhythms may help us cope better with disrupted sleep patterns.

References:

Lemos DR et al. (2006) Twenty-Four-Hour Rhythmic Gene Expression in the Rhesus Macaque Adrenal Gland. Molecular Endocrinology 20:11064-76.

Okamura, H. (2004) Clock genes in cell clocks: roles, actions, and mysteries. J Biol Rhythms 19:388-399

Reepert SM, Weaver DR (2001) Molecular analysis of mammalian circadian rhythms. Annu Rev Physiol 63:647-676.

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