Intramuscular relative dose response (RDR) determination of liver vitamin A stores in rats

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 mumol/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 less than 0.105 mumol/g, all RDR values were greater than 20%. When the liver retinyl palmitate was greater than 0.122 mumol/g the RDR was less than 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.