Fig. 3.

Proposed multi-compartmental model for VA metabolism as viewed from plasma space in neonatal rats after administration of [³H]retinol. A: Compartments are represented as circles; interconnectivities between compartments correspond to L(I,J)s, or the fraction of retinol in compartment J transferred to compartment I per day. Components 3 and 15 are delay elements. Compartments/component 1–3 represent VA digestion and absorption. Compartments/component 10, 15, and 4 represent CM metabolism, the uptake of CM remnants, and the processing of VA in extravascular tissues. Compartment 5 represents plasma retinol bound to RBP; this retinol exchanges with VA in one extravascular pool (compartment 6). The asterisk represents the site of input of [³H]retinol in the oral dose and is also the site of input of dietary VA. B: Mean observed (symbols) and model-predicted fraction of administered dose (lines) in plasma versus time (days) after administration of [³H]retinol to neonatal rats. Each point represents the mean of n = 3 pups.