Why there's polyuria in Cushing's Syndrome? - USMLE Forums
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  #1  
Old 12-04-2010
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Urine Sample Why there's polyuria in Cushing's Syndrome?

Hi friends
Please explain me
Why one of Cushing's syndrome characteristics is polyuria?!
Thanks a lot for answers!
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Old 12-04-2010
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Cushing's state is diabetogenic. Steroids are diabetogenic on the long run. One of the most important features of a high sugar state is polydipsia and polyuria.

I'm not sure if there's another explanation
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Old 12-04-2010
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Agree with Rasheed
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Old 12-04-2010
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i agree with rasheed..cortisol is gluconeogenic so it increases glucose in the body which leads to osmotic diuresis and therefore polyuria!
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Old 12-04-2010
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But in Cushing's syndrome mineralocorticoid effect of the high level of glucocorticoid and deoxycorticosteroid lead to salt and water retention (and so hypertension)
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Old 12-04-2010
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Default because of hyperglycemia and hypercalcemia(bone resorption)

because of hyperglycemia and hypercalcemia(bone resorption)
and catabolic state
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Old 12-04-2010
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I think since the osmolarity of plasma is decided as 2Na + Glucose/18 +..... the osmolarity is determined primarily by sodium levels .. in the urine in normal situations glucose is non detectable hence it would be completely sodium dependent...

with a diabetogenic situation such as cushings syndrome, urine osmolarity MIGHT similarly not be determined just by sodium concentration but instead by the high glucose concentration - note that there is NO WAY to absorb this glucose since all transporters are saturated. So there would still be diuresis no matter how much sodium one might absorb (under the action of aldosterone and whatever).

my two cents..
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Old 12-04-2010
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Quote:
Originally Posted by drarnab View Post
I think since the osmolarity of plasma is decided as 2Na + Glucose/18 +..... the osmolarity is determined primarily by sodium levels .. in the urine in normal situations glucose is non detectable hence it would be completely sodium dependent...

with a diabetogenic situation such as cushings syndrome, urine osmolarity MIGHT similarly not be determined just by sodium concentration but instead by the high glucose concentration - note that there is NO WAY to absorb this glucose since all transporters are saturated. So there would still be diuresis no matter how much sodium one might absorb (under the action of aldosterone and whatever).

my two cents..
I think this is the best explanation.
Glucose does contribute significantly to osmolarity when abnormally high. so the hypertension is contributed by retention of sodium and water, and polyuria because of the diabetogenic state.
then why dont the fluid levels balance?? Because it's a pathology!! Im sure the levels of fluid keep fluctuating in the body because of the correctional process, but the balancing mechanisms eventually become overwhelmed..
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Old 03-26-2012
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it is due to nephrogenic diabetes insipidis due to hypokalemia
cortison cause hypokalemia which cause polyurea due to
1- decrease expression os aquaporin 2 in collecting tubules( -- adenyle cyclase ) and that decrease sensitivity to ADH
2- decrease the action of Na/K pump in the ascending loop of henle.....so retaining Na and H2O in the tubules
3- stimulation of thrust center causing polydipsia
4- psychological polyurea

http://www.facebook.com/groups/marioclinic/

Last edited by dr mario; 03-26-2012 at 03:42 PM.
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Old 04-08-2012
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It's because cortisol can bind mineralcorticoid receptors, but in renal cells there is an enzyme (11-hsd) that convert cortisol into cortisone, which has no affinity for the receptor. However, if there is too much cortisol in the blood, like in cushing desease, this enzyme is saturated and cortisol can bind the receptor
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