Primed constant infusion

Determination of the oxidation of a substrate by a constant infusion of tracer quantities of a carbon-labeled isotope of the substrate require the determination of the equilibrium enrichment of COp in expired air. In humans this necessitates a constant infusion of the tracer for 7 or 8 hours (2). The necessary asymp-ototic value in COp enrichment can be obtained more rapidly if the bicarbonate pool is primed in addition to the priming of the substrate pool. The rationale for determining the appropriate priming dose for the bicarbonate pool is precisely the same as described above. The additional Information that is necessary to calculate the aopropriate bicarbonate prime when a primed-constant infusion of a -labeled substrate is given is the percent of substrate uptake that is oxidized to COp. In steady-state conditions and at... 

Thus, the primed-constant infusion technique is easEy administered, an experiment can be completed in a couple of hours, and valid kinetic data. Because of these attributes, we have applied this technique in a variety of physiological settings. 

The primed-constant infusion technique was used in aE experiments. In order to quantitate both the rate of cose production and glucose oxidation, it was necessary to determine the enrichment of plasma glucose and of expired COp. 

In an independent study, glucose flux was measured in 5 severely malnourished infants of 1 to 2 yr old using the primed constant infusion technique with [U- C]glucose as tracer [307]. Glucose flux was estimated at 3.0 mg kg" min" (range 1.8-4.4) in the malnourished state and not signiflcantly different in the same infants after recovery, 2.7 mg kg" min" (range 2.4-3.2). 

After adaptation to each diet, sows were individually housed in respiration chambers for the measurement of indicator amino acid oxidation during a primed, constant infusion of L-[1- C] pheiylalanine and, simultaneously, heat production (HP) over 4 h. The gas exchange was recorded for Oj, COj, and CH,j (Brouwer, 1%5) in 1 min intervals. Expired CO2 and blood plasma were collected in 30 min intervals for determination of enrichment. 

In practice, estimation of hepatic blood flow usually involves the infusion of dye, but measurements have also been made using a single injection of dye. In the former method, a dye is infused at a constant rate after a priming dose until the plasma concentration is steady. Hepatic venous blood is obtained by catheterization. The rate of uptake of dye by the liver is usually taken to be the rate of infusion of dye without allowing for urinary excretion. BSP (B42, C9, S22, W27, W30), indocyanine green (L9, R3, W18, W27, W28), and isotopically labeled rose bengal (L4, W27) have been used in this way. 

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