Kahn says he is not sure whether type A behavior stimulates alpha receptors, whether alpha-receptor
stimulation causes type A behavior, or whether something else causes both reactions.
Increased tone and frequency of contractions are believed to result from stimulation of beta-receptors, and reduced activity from stimulation of alpha-receptors.
Women who experience anxiety during labor and have high adrenaline levels that stimulate the alpha-receptors, might present with dysfunctional labor.
Nerves to the penis release the neurotransmitter noradrenaline (a catecholamine), causing stimulation of alpha-receptors on the surface of adjacent smooth muscle cells.
To complicate matters further, different types of alpha-receptors (alpha-1 and alpha-2-subtypes) are located not only on the smooth muscle cells, but also directly adjacent on the nerve-buds, from where catecholamines and other neurotransmitters are released.