Retinoids exert their functions in the same way as classical hormones, as transcription factors acting via nuclear receptors. In addition, retinoids have been shown to have a key role in several other endocrine systems. It is therefore not surprising that tissue homeostasis of retinoids is well regulated.
Dioxins are widespread, highly toxic, environmental pollutants.
Their resistance to chemical and biological degradation, together with their lipophilicity, cause dioxins to be accumulated in the food chain. Humans are exposed to these substances mainly via food such as fatty fish, meat, and milk products. The fact that dioxins disturb retinoid homeostasis has been known for quite some time. A homeostasis is the critical one, resulting in the altered tissue levels of vitamin A and possibly also other effects. The lower levels of hepatic retinyl esters in TCDD-treated rats may be due to a combination of increased mobilization of hepatic stores of vitamin A, and a severely decreased LRAT activity in the hepatic stellate cells.