Relative dose-response

During the development of vitamin A deficiency in experimental animals, the plasma concentration of RBP falls, while the liver content rises. The administration of retinol to deficient animals results in a considerable release of holo-RBP from the liver. This is a rapid effect on the release of preformed apo-RBP in response to the availability of retinol, rather than an increase in the synthesis of the protein. There is no evidence that retinol controls the synthesis of RB P (Soprano et al., 1982). This provides the basis of the relative dose response (RDR) test for liver stores of vitamin A (Section 2.4.1.3) administration of a test dose of retinol gives a considerably greater increase in plasma retinol, bound to RBP, in deficient subjects than in those with adequate liver reserves, because of the accumulation of apo-RBP in the liver. 

The Relative Dose Response (RDR) Test The RDR test is a test of the ahUity of a dose of vitamin A to raise the plasma concentration of retinol several hours later, after chylomicrons have heen cleared from the circulation. What is being tested is the ahUity of the liver to release retinol into the circulation. In subjects who are retinol deficient, a test dose will produce a large increase in plasma retinol, because of the accumulation of apo-RBP in the liver in deficiency (Section 2.2.3). In those whose problem is due to lack of RBP, then little of the dose will be released into the circulation. An RDR greater than 20% indicates depletion of liver reserves of retinol to less than 70 /rmol per kg (Underwood, 1990). 

Tanumihardjo SA, Koellner PG, Olson JA. The modified relative-dose-response assay as an indicator of vitamin A status in a population of well-nourished American children. Am J Clin Nutr 1990 52 1064-7. 

Tanumihardjo SA, Muhilal, Yuniar Y, Permaesih D, Sulaiman Z, Karyadi D, Olson JA. Vitamin A status in preschool-age Indonesian children as assessed by the modified relative-dose-response assay. Am J Clin Nutr 1990 52 1068-72. 

Dark adaption test Pupillary response test Plasma retinol concentration Relative dose response... 

Van Jaarsveld, P. J., Faber, M., Tanumihardjo, S. A., Nestel, P., Lombard, C. J., and Spinnler Benade, A. J. (2005). 3-carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose response test. Am. ]. Clin. Nutr. 81, 1080-1087. 

The plasma concentration of vitamin A falls only when the liver reserves are nearly depleted. In deficiency there is accumulation of apo-RBP in the liver, which can only be secreted when vitamin A is available. This provides the basis for the relative dose-response test for vitamin A status — the ability of a dose of retinol to raise the plasma concentration several hours later, after chylomicrons have been cleared from the circulation. 

SA Tanumihardjo, HC Furr, JW Erdman Jr, JA Olson. Use of the modified relative dose response (MRDR) assay in rats and its application to humans for the measurement of vitamin A status. Eur J Clin Nutr 44 219-224, 1990. 

Duitsman PK, Cook LR, Tanumihardjo SA, Olson JA (1995) Vitamin A inadequacy in socioeconomically disadvantaged pregnant Iowan women as assessed by the modified relative dose response (MRDR) test. Nutr Res 15 1263-1276... 

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