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Epinephrine in the presence of propranolol

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This is the fourth example in a 4-part series showing the effects of autonomic drugs on BP and HR.

In this example we’re going to give an iv bolus of high-dose epinephrine in the presence of an iv infusion of propranolol so remember that epinephrine is an agonist of alpha 1 alpha 2 beta 1 and beta 2 adrene acceptors with greater beta activity than alpha activity but at this high dose we will see both alpha and beta receptors having effects propranolol is a beta

1 beta 2 non selective audrina scepter antagonist so now let’s draw out the diastolic and the systolic and the mean arterial pressure and the heart rate and so we’re going to look at the effect of epinephrine when propranolol is on board so propranolol is a beta 1 beta 2 receptor antagonist so now both of these receptors are going to be blocked and therefore when

We give epinephrine it will only have an effect on the alpha 1 and alpha 2 receptors so let’s give epinephrine right here at the arrow and then the effect of epinephrine via alpha 1 agonism on diastolic pressure won’t be to increase it okay the effect of alpha 2 agonism is going to be to decrease the magnitude of sympathetic outflow so this will kind of attenuate

Any response you see to alpha 1 mediated vasoconstriction because it will have kind of a counteracting effect to sympathetic activity but the direction of the response is going to be the same so don’t worry about these minor variations in magnitude of responses due to alpha 2 effects just worry about the overall direction of the effects that you’re going to see

Okay now let’s look at systolic pressure since the beta receptors are blocked there’s no effect of beta stimulation by epinephrine on the cardiac output so the systolic pressure just increases in parallel to the diastolic pressure so there is no increase in pulse pressure it’s the same as it was before administering the drug and this is because there is no beta one

Effect now the mean arterial pressure is going to increase as well and this is going to cause activation of the baroreceptor reflex so this mean arterial pressure will activate the baroreceptor which will decrease sympathetic outflow and increase parasympathetic outflow and so the result of this is going to be to decrease the heart rate so you’ll see this decrease

In heart rate as a result of this increased parasympathetic activity the result of the decrease in sympathetic activity again they kind of modulate the magnitude of these systolic and diastolic curves but it’s not going to change the direction of them okay so now what single drug could produce a response that looks like this what we’re looking for is something that

Is an alpha-1 and alpha-2 agonist and the closest that we can come in the drug world is going to be fan phenol efrain phenol efrain is going to actually be an alpha 1 agonist it’s going to lack that alpha 2 agonism so just remembering that the function of the alpha 2 organism is to kind of tone down the magnitude of the sympathetic activity in the absence of alpha

2 agonism the sympathetic nervous system would not be experiencing that feedback inhibition and so the magnitude of the response for phenol efrain would be greater than that of epinephrine when they’re both being given in the presence of propranolol but the overall shape would be the same

Transcribed from video
Epinephrine in the presence of propranolol By Five Minute Pharmacology