Nitroglycerin????

[chillaxbro]

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Uworld 137

Nitroglycerin works mostly on veins. I knew that.

I also know that NO works via cGMP pathway.

This pathway should theoretically be able to work on arteries as well right? what about nitroglycerin makes it work mostly on veins? or is NO only for veins and not arteries like I thought?

 

[Ismet]

Nitro/NO work on both arteries and veins. At lower doses, it dilates veins more than arteries, but there is arterial dilation that increases with increasing dosage. The sublingual dose of nitro is a sizable dose. It primarily dilates veins to decrease preload and decrease O2 demand. At higher doses it will also dilate arteries to decrease afterload and reduce cardiac oxygen demand, as well as dilate the coronary arteries to improve blood flow to the heart itself.

 

[chillaxbro]

Well the question shows a pic of nitroglycerin and asks which components of the cardiovascular system is most susceptible to this drug. Answer was veins.

So it affects both veins and arterioles but why does it affect veins more?

 

[Ismet]

I believe there's more aldehyde dehydrogenase, which is what degrades nitro into NO.

 

[chillaxbro]

Woah that's cool. Does nitroglycerin not work as well in Asian people because they have asian glow?

 

[Ismet]

Woah that's cool. Does nitroglycerin not work as well in Asian people because they have asian glow?

Haha not sure, that would be interesting to find out. This is mitochondrial ALDH that degrades nitro, not sure if that makes a difference or if people with the mutation are down all forms of ALDH.

 

[Jabbed]

I believe there's more aldehyde dehydrogenase, which is what degrades nitro into NO.

Source? Genuinely curious.

 

[worldbeater]

Also, it's the order of what nitroglycerin acts on that's important, acts on the veins first and the arteries second (veno-vaso dilator), the question can go in that direction. I got yelled at when I didn't know that earlier in my prep..haha. You mentioned cGMP as well, so your probably familiar with it's contraindication with sildenafil for erectile dysfunction (MOA: PDE5 normally breaks down cGMP, sildenafil prevents degradation of PDE5), causing extreme hypotension (World Q).

 

[chillaxbro]

Also, it's the order of what nitroglycerin acts on that's important, acts on the veins first and the arteries second (veno-vaso dilator), the question can go in that direction. I got yelled at when I didn't know that earlier in my prep..haha. You mentioned cGMP as well, so your probably familiar with it's contraindication with sildenafil for erectile dysfunction (MOA: PDE5 normally breaks down cGMP, sildenafil prevents degradation of PDE5), causing extreme hypotension (World Q).

Have you taken STEP1 yet or are you still preparing? You know everything man

 

[chillaxbro]

Haha not sure, that would be interesting to find out. This is mitochondrial ALDH that degrades nitro, not sure if that makes a difference or if people with the mutation are down all forms of ALDH.

I googled it and it's true! http://www.medscape.com/viewarticle/788162

 

[Ismet]

Source? Genuinely curious.

Idk, I was just pimped on it once and this is what I was told. Did a brief lit search and this is apparently a theory but hasn't been proven, the mechanism isn't fully understood.

 

[worldbeater]

Have you taken STEP1 yet or are you still preparing? You know everything man

Thanks man, appreciate it! There is a lot I don't know, you would be surprised, but I am getting better everyday. I am still prepping, in the 2nd half of my prep though.

 

[jqueb29]

Nitro/NO work on both arteries and veins. At lower doses, it dilates veins more than arteries, but there is arterial dilation that increases with increasing dosage. The sublingual dose of nitro is a sizable dose. It primarily dilates veins to decrease preload and decrease O2 demand. At higher doses it will also dilate arteries to decrease afterload and reduce cardiac oxygen demand, as well as dilate the coronary arteries to improve blood flow to the heart itself.

We were taught that the arterial dilation is actually a bad thing in terms of coronary arteries. For instance, let's say you've got 80% occlusion of the LAD. The area distal to the obstruction will already be maximally dilated due to production of local vasodilatory metabolites, so nitro won't increase flow to the LAD. But it would be able to dilate other coronary arteries, resulting in the "coronary steal" that First Aid mentions. Basically, you can't dilate the LAD any further, but the nitro would be able to dilate the circumflex, RCA, etc; this is because these unoccluded arteries are not already maximally dilated, since there is no reason for them to be since the tissue they supply is adequately perfused.

So we give lower doses that affect veins more, as higher doses would result in coronary artery steal and actually have negative effects.