LIVER VITAMIN-A LEVELS IN RATS ARE PREDICTED BY A MODIFIED ISOTOPE-DILUTION TECHNIQUE

We tested the hypothesis that the fraction of an injected dose (FD(p)) of [H-3]retinol remaining in plasma could be used to predict liver vi tamin A mass. Rats (n = 36) with liver vitamin A ranging from 1.4 to 2 3,000 nmol received an intravenous dose of [H-3]retinol-labeled plasma . Plasma samples obtained at 4, 4.4, 5, 5.4, 6, 7 and 8 d were analyze d for radioactivity; liver vitamin A levels were determined at 8 d. Us ing a regression equation developed previously [liver vitamin A (nmol) = 7493-exp(-148.FD(p))], there was a log linear relationship between FD(p) and liver vitamin A mass from 1.4 to 5200 nmol retinol; the equa tion did not predict levels greater-than-or-equal-to 7500 nmol. By exp anding the regression equation [liver vitamin A (nmol) = 88,928.exp(-1 347.FD(p)) + 5606.exp(-120.FD(p))] and using the FD(p) at 4.4 d, liver vitamin A levels ranging from <4 to 23,000 nmol were well predicted. Satisfactory equations were also developed for data obtained at 4, 5 a nd 5.4 d. We conclude that this modified isotope dilution technique is a sensitive and reliable method for assessing vitamin A status in rat s over a wide range of vitamin A nutriture. It is likely that this met hod could be modified for use in humans.