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Intramuscular Relative Dose Response (RDR) Determination of Liver Vitamin A Stores in Rats¹

Departments of Pediatrics and Nutritional Sciences, University of Wisconsin, Madison, WI 53715

This study questioned whether the relative dose response (RDR) method to detect liver stores of vitamin A could be used by intramuscular administration of the vitamin. Vitamin A-deficient and reference rat serum retinol levels were determined by HPLC at zero time and then again 5 h after an intramuscular injection of 5.25 µmol/kg retinyl palmitate. The RDR percentage was calculated: [(A₅-A₀)/(A₅)] x 100. The 5-h RDR was determined in 20 deficient and 16 reference diet rats and a clear relationship to liver retinyl palmitate concentration was demonstrated. At a liver retinyl palmitate concentration of < 0.105 µmol/g, all RDR values were > 20%. When the liver retinyl palmitate was > 0.122 µmol/g the RDR was < 20%. This study suggests that the intramuscular RDR is a valid tool for estimating liver retinyl palmitate in populations in which the oral RDR cannot be administered.

KEY WORDS: • retinol • intramuscular • relative dose response (RDR) • liver • rats

¹ Supported by the Cooperative State Research Service, U.S. Department of Agriculture, under agreement 88-37200-3477.

Manuscript received 10 October 1989. Revision accepted 8 August 1990.