The metabolism of retinyl methyl ether in the rat in vivo.

1. Retinyl methyl ether was converted into vitamin A in vitamin A-deficient rats regardless of whether administered by oral, intraperitoneal, intramuscular or subcutaneous route; intramuscular administration seemed to be the best for conversion as well as storage. 2. Significantly, unchanged retinyl methyl ether was also found in the liver after oral administration but not after administration by other routes. 3. Oral administration of 1mg of retinyl methyl ether led to a progressive increase in liver vitamin A with time reaching a value of 16% of administered dose after 24h. No retinyl methyl ether was detectable in liver at any time-interval in this experiment. 4. Conversely, oral administration of 4mg of retinyl methyl ether/day for 4 days led to the accumulation of 25% of the dose as unchanged retinyl methyl ether in the liver 1 day after the last dose; however, it was gradually but completely converted into vitamin A over a period of 18 days. 5. The significance of these findings with special reference to the fundamental metabolism of vitamin A, the site of conversion of retinyl methyl ether into vitamin A, the relative efficiency of various routes of administration and its biological activity are discussed.