Lactic acidosis: how is it possible?

Hello,

I understand that several diseases are characterized by the presence of lactic acidosis, with lowered blood pH supposedly due to lactate (as in diabetes for example).
My question is: how is it possible, since lactate coming out of the lactate dehydrogenase from pyruvate is... lactate, not lactic acid. So how does lactic acidosis occur when lactate is already ionized (thus unable to further dissociate to release a proton) when produced?

Thanks.

Reply 1

Cheesychips1

11

I was taught that lactate was used as a marker for tissue hypoxia in 'lactic acidosis', rather than causing the acidosis. So in 'lactic acidosis' the acidosis is caused by hydrogen ions from ATP hydrolysis I believe?, and the lactate also rises via the mechanism you mentioned, but no doesn't actually cause the acidosis. I hope that makes sense.

I'm sure an anaesthetist would be explain to explain it much better :smile:

Reply 2

nexttime

22

Original post by interprete

... lowered blood pH supposedly due to lactate (as in diabetes for example).

Original post by Cheesychips44

I was taught that lactate was used as a marker for tissue hypoxia in 'lactic acidosis', rather than causing the acidosis. So in 'lactic acidosis' the acidosis is caused by hydrogen ions from ATP hydrolysis I believe?, and the lactate also rises via the mechanism you mentioned, but no doesn't actually cause the acidosis. I hope that makes sense.

I'm sure an anaesthetist would be explain to explain it much better :smile:

Spot on.

Lactate production actually involves absorbing hydrogen ions - lactate is a good pH buffer. Its the result of a metabolic acidosis, not the cause. Its just a marker of metabolic stress.

That's why its a good global prognostic marker. One recent chinese study found that lactate was a better prognostic marker in pneumonia than all of CURB65 combined, for example.

This is in complete contrast to ketoacidosis as in DKA*, where the ketones produced actually are acidic and your kidney will need time to compensate if you are consistently producing them.

*Of course people with DKA will also get lactic acidosis if sick enough

Edit: also, not many doctors will be familiar with this in my experience - bear that in mind when they start talking about "lactic acid"!

(edited 6 years ago)

Reply 3

Jpw1097

19

Original post by interprete

Hello,

I understand that several diseases are characterized by the presence of lactic acidosis, with lowered blood pH supposedly due to lactate (as in diabetes for example).
My question is: how is it possible, since lactate coming out of the lactate dehydrogenase from pyruvate is... lactate, not lactic acid. So how does lactic acidosis occur when lactate is already ionized (thus unable to further dissociate to release a proton) when produced?

Thanks.

Just as everyone else has said, lactate is a marker of hypoxia and does not cause metabolic acidosis. In fact, the body does not produce lactic acid at all, it produces lactate which, as @nexttime said, accepts protons and actually retards metabolic acidosis.

ATP hydrolysis releases protons while ATP synthesis absorbs protons. However, in times of increased metabolic demand or hypoxia, ATP hydrolysis is greater than ATP synthesis because ATP supplied from non-mitochondrial sources (mainly glycolysis) is being used in addition to ATP generated via oxidative phosphorylation.

I recommend you read this article which explains the biochemistry of exercise-induced metabolic acidosis, it's a very good read. http://ajpregu.physiology.org/content/287/3/R502.long.

It is often taught that metabolic acidosis is caused by the increasing concentration of lactic acid - this is simply not true. As I mentioned earlier, lactic acid isn't even produced.

Lactic acidosis: how is it possible?

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