A quantitative determination of physiological levels of all-trans-retinoic acid (vitamin A acid) in human serum has been developed. A double-phase extraction of 3.5 ml of serum followed by a specific and sensitive high performance liquid chromatography procedure allowed measurement of levels down to 1 ng/ml. Serum concentrations in 37 fasting volunteers ranged from 2.7 to 4.2 ng/ml and fitted a...

Structure-activity relationships are summarized for 87 retinoids, using reversal of keratinization in the hamster tracheal organ culture system to measure biological activity. Classes of compounds evaluated include all-trans-retinoic acid and its esters, ring-modified analogs of all-trans-retinoic acid and its esters, side-chain-modified analogs of all-trans-retinoic acid and its esters, analog...

Retinoic acid constantly undergoes structural inter-conversions among the geometrical isomers (all-trans-retinoic acid, 9-cis-retinoic acid, 11-cis-retinoic acid, 13-cis-retinoic acid and 9-13-di-cis-retinoic acid) by photoisomerization under natural light. Geometric isomers of retinoic acid thus formed showed different effects on human epidermal keratinocyte growth and differentiation. The abi...