Autonomics Question form UWORLD

[docjohn101]

The question ID is Q Id 1367 (351594).

It basically wants you to distinguish between the different receptors that norepi works on (alpha1, alpha2, and beta1) and the downstream effects (cAMP, DAG, IP3).

My question: According to the question, you would give norepi to someone who is hypotensive (that makes sense), but how do we distinguish between the Gq receptor and Gs receptor.

I know alpha1 is Gq, increasing IP3, and that beta1 receptor would increase vascular smooth muscle contractility (which would increase blood pressure, solving hypotension, right?)

Also, alpha1 is Gs, increasing cAMP, and that alpha1 receptor would increase contracility (which would increase blood pressure, solving hypotension, right?)

So, now back to the uworld question, there were two choices, one said increased IP3 and one said increased cAMP, how to tell the difference between the two?

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[AndyRSC]

Just to get the two straight:
Alpha1 is Gq, which increases IP3 and DAG. It increases vascular SM contractility.
Beta1 is Gs, which increases cAMP, and increases myocardial contractility and rate.

You probably already know the FA mnemonic "qiss qiq siq sqs," which is very high-yield, and I guarantee you'll see something pertaining to these receptors or their secondary messengers on the boards - probably more than once.

As for the question, I would guess it emphasizes the predominant effect of NE; it acts primarily on alpha1, increasing peripheral resistance. Was there anymore to the question?

 

[MrBeauregard]

alpha-1: Gq --> PIP2 --> IP3 and DAG --> DAG activates PLC and IP3 increases Ca to aid PLC in activating Protein kinase C and lead to smooth muscle contraction

alpha-2: Gi --> decreases cAMP concentrations (these are located presynaptically and decrease sympathetic output)

beta-1: Gs --> activate AC --> increase cAMP --> activate Protein kinase A which increases HR and contractility

beta-2: same mechanism as beta-1 but present on vascular smooth muscle

It seems as though we're missing some information from the question. As AndyRSC said, the qiss qiq siq sqs mnemonic is extremely high yield.

 

[docjohn101]

dont think there was anything else important in the question, but here it is:

85 year old man...altered mental status and fever diagnosed with septic shock, given antibiotics...has had fever for the past few days..past history of cardiovascular disease, diverticulitis, and dementia. His blood pressure is 60/40 despite aggressive IV hydration. Norepinephrine is given in response to hypotension. Which of the following cellular changes occurs directly in response to norepinephrine therapy?

a. cAMP increase in vascular smooth muscle cells
b. DAG decrease in vascualr smooth muscle cells
c. cAMP increase in cardiac muscle cells
d. cAMP decrease in bronchial smooth muscle cells
e. IP3 increase in cardiac muscle cells.

 

[AndyRSC]

The question hinges on where the receptors are located. In this case, the only one that fits is C.

 

[docjohn101]

can someone really quickly type up where each of the receptors are located?

 

[MrBeauregard]

can someone really quickly type up where each of the receptors are located?

Some are in multiple locations. First Aid lays them all out for you really well.