Study: Clock Inside Our Blood Vessels

June 28, 2001 -- There may be a clock in our blood vessels that helps our body keep time.

University of Pennsylvania researchers have found what they say is the first evidence of a biological clock inside our circulatory system that resets in response to hormones and vitamins.

Although scientists have known there is a place in brain — called the superchiasmatic nucleus — that maintains circadian or biorhythms in our body, the new findings may help explain how some messages from the brain get communicated to the other organs in the body.

Blood Pressure is Rhythmic

The results of this study ultimately might help doctors develop new treatments based on this timing mechanism.

Blood pressure, for example, varies throughout the day with the highest levels in the morning. Heart attacks and strokes often occur in the morning, when pressure is highest.

"We know that the response to certain drugs varies as a function of clock time and metabolic enzymes are under circadian control," says Dr. Garret FitzGerald, chair of the Penn department of pharmacology, in Philadelphia, and lead author of the study appearing in the June 29 issue of the peer-reviewed scientific journal Cell.

"With these findings, perhaps we can begin to adjust the time of the clock to obtain greater sensitivity to drugs."

Understanding the clock inside the body's blood vessels would also be helpful for the treatment of jet lag and sleep problems shift workers can have, he says.

Looked for Protein-Protein Interactions

Researchers looked for substances in the body that interacted with the carrier or receptor for vitamin A on smooth muscle cells inside blood vessels. Hormones and vitamins bind to certain structures inside cells called receptors that allow the chemicals to exert their action inside the nucleus.

The scientists found a protein, called MOP4, which was similar to one that had been identified as a switch for the brain's master clock.

They then showed that vitamin A was able to change the rhythm of how this clock protein acted in the blood vessels in test tube experiments of human vessels cells and in mice.

Commenting on the findings, Jay Hirsh, a professor of biology at the University of Virginia with expertise in circadian rhythms, says the finding may help elucidate one of many signals that could be used in synchronizing molecular clocks throughout the body.

The finding in the blood vessels is particularly important, he says, because of the implications for blood pressure research.

Hirsh says circadian rhythm research has been picking up steam, recently.A recent finding identified another hormone in maintaining the rhythms of another common cell type in the body called fibroblasts, Hirsh says.

Earlier this year, other researchers identified a gene involved in a rare disorder called Familial Advanced Sleep-Phase syndrome, in which people have completely altered biological clocks. They wake up at 2 a.m. and go to sleep at 4 p.m.