Acetylcholine and catecholamine modulation The vagus nerve, which is parasympathetic, releases acetylcholine onto the sa node and slows the intrinsic pacemaker activity and onto the av node and slows conduction velocity Sympathetic innervation to the heart releases norepinephrine and adrenal medulla releases epinephrine into the circulation Both of norepinephrine and epinephrine act through B1 adrenergic receptor and increase heart rate Both of norepinephrine and epinephrine cause an increase in the strength of contractionAcetylcholine and catecholamine modulation • The vagus nerve, which is parasympathetic, releases acetylcholine onto the SA node and slows the intrinsic pacemaker activity and onto the AV node and slows conduction velocity. • Sympathetic innervation to the heart releases norepinephrine and adrenal medulla releases epinephrine into the circulation. • Both of norepinephrine and epinephrine act through β1— adrenergic receptor and increase heart rate. • Both of norepinephrine and epinephrine cause an increase in the strength of contraction 28