for whole body whole body bc youre collecting excreta which is a conglom

For whole body whole body bc youre collecting excreta

This preview shows page 15 - 17 out of 70 pages.

for whole body (whole body b/c you’re collecting excreta which is a conglom eration of all the N being released by all the tissues in the body used to make 15 N-urea or 15 N-NH 3 ) o But this doesn’t tell you what’s happening in individual organs S in individual organs can be obtained if you take a sample of that tissue and measure incorporation of that labeled AA into the protein Done a lot in SM of human - Another way to get an idea of C of muscle without using isotopes or giving any label is looking at 3-methylhistidine (3MH) in actin-myosin. o This is done during injury, and helps corroborate the data from protein Q. B/c you can get S from doing a muscle biopsy but it’s harder to measure catabolism More is known about factors that go into S vs. C. Catab is harder to measure - 3MH: o Post-translational step: NRG req’ d-addition of methyl after actin-myosin peptide syn o Found in 3 muscle pools in the body: studied in terms of how much each contributes to total amounts of 3MH (listed in descending order) 1. Skeletal muscle 2. GI tract- carry out peristalsis 3. Skin - When you catabolize muscle and free the AAs, you cant reutilize His, it s cleared by the kidney and ends up in the urine o 3MH released from muscle ends up in urine b/c you can’t de -methylate So when you re-synthesize that muscle you have to use an intact His molecule and then at some point some of them get methylated I f you collect someone’s urine for 24hrs, and measure 3MH you can plug that into an equation ( how many 3MH there are/ muscle protein) and get an idea of muscle C rate And it’s the trend that counts, not absolute numbers - If an individual is doing a study measuring 3MH, researchers have to acclimate the individual first b/c anyone who eats meat gets 3MH from the meat. o It takes ~4-5d on a 3MH diet (meat free) for 3MH to stabilize to normal amount and then study can start 23. CRITICISM OF 3MH AS MARKER OF SM CATABOLISM - As you in size, there’s more SM and SM makes a more predominant input into overall body Q compared to a smaller animal in which the liver plays a larger role o So whatever happens to muscles affects the overall Q equation
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SFLORES_2/27/2014 16 - When it was first proposed to use 3MH excretion as an index for SM catabolism, there was a lot of uproar b/c you have to account for 1) GI tract which has a lot of muscle and 2) skin. Both are rapidly turning over. o So as you break GI and skin down, a lot of 3MH is released in the urine and you really can’t say that the 3M H in urine is due to changes in SM protein metabolism To answer this problem: Studies measured 3MH people with short bowl syndrome who had to remove a large part of their SI, before and after the surgery. Then you can see the role of the small gut, and found it played a very little role in overall 3MH excretion - Now, it’s well accepted that 90 -95% of 3MH is from SM turnover o § Clinicians can use this as a marker for SM catabolism and there has to be a corresponding change in S to balance that out 24. MEASURING Q IN DIFFERENT BODY SIZES -
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  • Spring '14
  • Knutson,MitchellD
  • NRG

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