Vitamin A Intake and Status Influence Retinol Balance, Utilization and Dynamics in Rats ,

Abstract

To study effects of vitamin A status on retinol dynamics, male rats were fed purified diets varying in vitamin A concentration. Group 1 rats had marginal liver vitamin A levels (∼500 nmol) and were in a slight positive vitamin A balance; Group 2 had similar liver levels but were in a slight negative balance; Group 3 had lower liver levels (∼370 nmol) and were in a slight negative balance; Group 4 had depleted liver reserves (<10 nmol) and were in vitamin A balance. [3H]Retinollabeled plasma was injected intravenously, and serial plasma samples were collected for 41 d while rats (six per group) consumed ∼50 nmol retinol/d (Group 1) or ∼25 nmol/d (Groups 2–4). Plasma retinol was normal in Groups 1–3 (1.9–2.0 µmol/L) and lower in Group 4 (0.96 µmol/L). Plasma tracer data were fit to a three-compartment model. The central plasma retinol compartment (transit time, 1.5–1.7 h) exchanged with a fast turning-over extravascular vitamin A pool (transit time, 3–4.5 h; ∼40 nmol) and with a larger, slow turning-over extravascular pool (transit time, 5.5–10 d) that was the site of irreversible utilization of vitamin A. Irreversible utilization was 36 nmol/d (Group 1), 29 nmol/d (Groups 2 and 3) and 20 nmol/d (Group 4). The data indicate that in rats with low or marginal vitamin A status, vitamin A intake, vitamin A reserves and plasma retinol concentration all influence vitamin A utilization and other aspects of retinol dynamics.