Mon Apr 22, 2002
By E. J. Mundell
NEW ORLEANS (Reuters Health) - The cells that drive the human heart appear to have their own internal clock, helping them to anticipate periods of activity and rest. Now, researchers are beginning to learn that chronic illnesses like diabetes may set that clock off-kilter, potentially raising the risk of a heart attack.
"The heart clock is particularly important in situations where people have heart disease, because there's a greater incidence of death first thing in the morning when people have this increased pressure on the heart cells," explained researcher Dr. Martin E. Young, of the University of Texas-Houston Medical School. He speculates that diabetes may set normal heart cycles awry, leaving it unprepared for that early morning surge in demand.
Presenting his findings Sunday at the annual Experimental Biology 2002 conference, Young explained that most of the body's major organs have their own circadian rhythms, independent of the 'master clock' located in the brain.
The heart's cellular timekeeper allows it to roughly keep track of the time of day. "Within the heart cell, there's this molecular clock that's constantly going in a nice phase of 24 hours," Young told Reuters Health. In healthy hearts, the clock lets the organ slow down as we go to sleep, then signals it to rev up again as we begin to wake up in the morning. It also regulates the heart around meals, anticipating periods of either abundant or low energy.
But what about the cellular clocks of unhealthy hearts? Diabetes is a known cardiovascular risk factor. In their study, Young, his colleague Dr. Heinrich Taegtmeyer and others used a toxic drug to induce diabetes in rats.
Examining the animals' hearts in the lab, the researchers discovered that their circadian mechanisms were set about 3 hours behind those of healthy, nondiabetic rats. "So if the heart is expecting a stimulus (such as awakening) 3 hours early and the stimulus doesn't come, then of course there's a loss of synchronization," Young explained. "And 3 hours later when the stimulus does come--when the rats wake up--the heart might not be able to anticipate it."
Young believes that aberrations in the circadian cycles of diseased hearts could help explain the early-morning peak in heart attacks seen in human populations. "The heart isn't able to anticipate that there's going to be a surge in the morning, and it could malfunction."
More study is needed to confirm that theory, of course. In the meantime, Young said, "One area that we're getting into is 'how is the clock reset?' Once we understand that then we could potentially develop drugs to artificially reset it."
SOURCE: Annual Experimental Biology 2002 conference