Tissue levels of retinoids in human embryos/fetuses

In nonhuman vertebrate embryos, two endogenous retinoids with significant morphogenic activities have been identified thus far: all-trans retinoic acid and 3, 4-didehydroretinoic acid. To date, no information is available concerning endogenous retinoid levels in developing human embryos or fetuses. The purpose of the present study was to provide data relating to normal levels of retinoids in various human embryonic and fetal tissues at various stages of gestation measurable with HPLC techniques. Our investigations show that all-trans-retinoic acid, 13-cis-retinoic acid, retinol, all-trans-retinoyl-beta-glucuronide, and one unidentified metabolite were all present and quantifiable in several human embryos and fetuses investigated. Tissue levels of retinol were consistently much higher than those of the other three detected metabolites; 4-oxo metabolites were below the levels of detection in all samples studied.