A protein that plays an important regulatory role in heart failure in the heart also exerts powerful effects on the adrenal gland, Jefferson Medical College researchers have found. The protein, GRK2, is a potential drug target for heart failure.
Walter Koch, Ph.D., director of the Center for Translational Medicine in the Department of Medicine at Jefferson Medical College of Thomas Jefferson University in Philadelphia, and his co-workers had showed previously that GRK2, or G-protein coupled receptor kinase 2, is increased in the heart in heart failure, and shuts off certain receptors called beta-adrenergic receptors, desensitizing them. When the heart is failing, the body's sympathetic nervous system, which kicks into gear in the so-called fight or flight response, goes to work, releasing catecholamines - hormones such as epinephrine and norepinephrine in an ill-conceived attempt to stimulate the heart.
Catecholamines are released from two sources - nerve terminals and from the adrenal gland, from which they enter the circulation. Dr. Koch and his co-workers wondered if GRK2 and alpha 2-adrenergic receptor function were affected in the adrenal gland as well. They subsequently looked at adrenal glands from mice in heart failure, and found that GRK2 was increased. According to Dr. Koch, when neurons release catecholamines, a feedback system that works through alpha 2-adrenergic receptors "is the brake on the system." They found that mice in heart failure had high levels of GRK2 in the chromaffin cells in the adrenal gland, which caused the downregulation and desensitization of alpha 2 adrenergic receptors.