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.