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ARS Home » Plains Area » Houston, Texas » Children's Nutrition Research Center » Research » Publications at this Location » Publication #102934
Title: THEORETICAL INVESTIGATION OF FRACTIONAL SYNTHETIC RATE IN NON-STEADY STATE

Author
item COHEN, DAVID - BAYLOR COLL OF MEDICINE
item DEMAR, JAMES - BAYLOR COLL OF MEDICINE
item Heird, William

Submitted to: American Diabetes Association Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/7/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: An interpretive summary is not required for this abstract.

Technical Abstract: Theoretical approaches to estimation of lipid synthesis in vivo have emphasized the utility of the fractional synthetic rate (FSR) of the product molecular species from a given immediate precursor (defined as the conversion rate of precursor to product divided by the mass of the product (Foster et al, J. Lipid Res. 34:2193-2205, 1993)). In the context of the stable isotope administration to estimate the rate of synthesis of a given lipid, calculation of the FSR requires the assumptions of (1) metabolic steady state, i.e., the rate of conversion (v) of precursor to product, the mass of precursor (MassA), the mass of product (MassB), and hence the value of FSR do not change; and (2) the product is unlabeled at the beginning of the experiment. We derive a formula for FSR at time t (FSR(t)), without requiring either assumption (1) or (2): FSR(t) = (d(fB)/dt)/(fA-fB), where fA (fB) is the fractional enrichment of the precursor (product), assumed to be time-dependent. This formula can be derived from two equations describing conservation of mass: d(MassB)/dt = v-w and d(fB.MassB)/dt = fA.v-fB, where v(t) and w(t) are the rate of conversion of precursor to product and the rate of disappearance of product, respectively, at time t. This formula has applications to experiments in which samples are limited and metabolic steady state does not hold. If assumptions (1) and (2) are satisfied, it gives the same value as the conventional formula for FSR.