Which subtype of adrenergic receptors generally promotes increased heart rate when stimulated?

The subtype of adrenergic receptors that promotes increased heart rate when stimulated is Beta 1. These receptors are primarily located in the heart where their activation leads to a series of physiological responses that enhance cardiac function.

When Beta 1 receptors are stimulated, they activate adenylate cyclase, which increases the production of cyclic AMP (cAMP). The rise in cAMP levels leads to increased calcium influx during cardiac myocyte depolarization, resulting in a stronger and faster contraction of the heart muscle, a positive chronotropic effect (increased heart rate), and increased conduction velocity through the atrioventricular node.

In contrast, Alpha 1 receptors are mainly associated with vasoconstriction, while Alpha 2 receptors inhibit neurotransmitter release, leading to decreased sympathetic outflow. Beta 2 receptors, located in peripheral tissues such as the lungs and vascular smooth muscle, primarily mediate vasodilation and bronchodilation, without a direct role in increasing heart rate.