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Old 04-08-2015
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Default Mg and PTH

can anyone please explain why a slight decrease in Mg increases PTH while a severe decrease in Mg decreases PTH?

thanks.
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Old 04-08-2015
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Quote:
Originally Posted by yagoy View Post
can anyone please explain why a slight decrease in Mg increases PTH while a severe decrease in Mg decreases PTH?

thanks.
im not entirely sure but basically mg is required as a cofactor for adenylate cyclase which makes camp n thats needed for pth activation and apparently mg also helps pth exocytose from the cell.. so severe decrease in mg will cause hypoparathyroidism...

i dont know how slight dec in mg increases pth
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Old 04-08-2015
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this is what I understood from different resources:

Chief cells of the parathyroid have calcium sensing receptors that respond to high levels of calcium, thus inhibiting PTH, and when calcium is low, nothing is bound to the receptor so PTH is released.

MOA of the above:

calcium sensing receptor + calcium --> Gq pathway; activating of phospholipase with an eventual increase in intracellular calcium, and so if calcium levels are high there is a negative feedback inhibition to not release PTH. Also, Gq pathway inhibits cAMP (which functions to activate PTH)

now that I introduced the basic mechanism, lets move on to magnesium.
magnesium is a cofactor for adenylate cyclase (Gs pathway) which produces cAMP (and we said cAMP activates PTH) also magnesium is a partial agonist for calcium sensing receptor.
when magnesium decreases mildly, it means more cAMP is produced because the agonistic effect is lost, so PTH increases.

When magnesium decreases too much, PTH is no longer exocytosed (since magnesium is responsible for the exocytosis of PTH)

I could be wrong, so if anyone agrees or disagrees please let me know.
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