Stimulation of β1- and β2-adrenergic receptors at the heart leads to elevated heart rate and and contractility. At peripheral arterioles epinephrine interacts with α- and β2-receptors. β2-receptors are numerous in skeletal muscles and at arterioles of the splanchnic bed. High concentrations of epinephrine lead to vasodilatation in these areas. In organs which contain only α-receptors, such as skin, epinephrine causes vasoconstriction. In organs where both α- and β-adrenergic receptors are present, epinephrine mainly stimulates β-receptors. There is no vasoconstrictive effect as long as the concentration of epinephrine does not reach very high levels.
Norepinephrine interacts with a number of organs in a similar, but remote way. Organs containing α- and β-adrenoceptors show vasoconstrictive reactions, due to a lower affinity of β2-receptors to circulating norepinephrine [68].
© 2001 Alexander Binder