Teenagers can make it seem as if hormones control the cycles of the heart. Now, scientists have proved it.
Researchers at the University of Pennsylvania in Philadelphia have shown that a molecular clock in the circulatory system oscillates in a 24-hour rhythm in step with cells in the brain. This heart cycle responds to a hormone derived from vitamin A.
Scientists have known for years about regions of the brain where cells cycle through a steady cadence of activity, called a circadian rhythm, that regulates sleep-wake cycles. The concentrations of molecules, called clock proteins, that drive this process also wax and wane over a 24-hour period.
Only in the past 3 years have scientists learned that the concentrations of such proteins also oscillate in organs beyond the brain, such as liver and kidneys. In the June 29 Cell, Garret A. FitzGerald, Peter McNamara, and their colleagues report that such clock proteins also cycle in the heart–and even in bl