FIGURE 1.

Stable-isotope infusion protocol and sampling schedule. A priming dose of [¹³C¹⁸O]urea, [5-¹⁵N]glutamine, [2,3,3,4,4 d₅]glutamine, [ring-d₅]phenylalanine, and [ring 3,5-d₂]tyrosine was given at time zero followed by a 10-h continuous infusion of the same tracers. For the first 3 h of the infusion (A), Na¹³CHO₃ was infused to determine the production rate of CO₂. After discontinuing the bicarbonate infusion, a primed-continuous infusion of [¹³C]leucine was given for the remaining 7 h of the infusion protocol (B).