Catecholamines + Heart

Catecholamines and effects on heart

Epinephrine(beta>alfa) and Norepinephrine(alfa>beta) both has effect on Heart(beta 1 receptor) and blood vessels(alfa 1 receptors).Both of these catecholamines increase Heart rate(positive chronotropic action) and force of contraction(positive ionotropic action).However Epinephrine decrease total peripheral resistance and Norepinephrine increase total peripheral resistance.Because Norepinephrine causes vasoconstriction .

Due to vasoconstriction,Norepinephrine increase Blood prassure(both systolic & diastolic),which causes stimulation of Baroreceptors.As a result Reflex Bradycardia occurs.
           So Norepinephrine causes

• Decrease Heart rate and Cardiac Output
• Increase TPR
• Increase Blood pressure.

Again Epinephrine causes vasodilation so it decreases TPR and ultimately Diastolic pressure decrease but Systolic pressure increase(because its not directly depends on TPR).Due to low TPR its not stimulate Baroreceptors sufficiently.
So net effect of Epinephrine

• Increase Heart rate and Cardiac Output
• Decrease TPR
• Widening of pulse pressure(Difference between systolic and diastolic blood pressure,indicate cardiac output)

Collected & Concise only for postgraduate student