The endogenous retinoid metabolite S-4-oxo-9-cis-13,14-dihydro-retinoic acid activates retinoic acid receptor signalling both in vitro and in vivo.

Retinoic acid receptor (RAR) and retinoid X receptor are ligand-induced transcription factors that belong to the nuclear receptor family. The receptors are activated by small hydrophobic compounds, such as all-trans-retinoic acid and 9-cis-retinoic acid, respectively. Interestingly, these receptors are also targets for a number of exogenous compounds.

Retinoids and spermatogenesis: lessons from mutant mice lacking the plasma retinol binding protein.

Using Rbp4-null mice as models, we have established for the first time the kinetics of the spermatogenetic alterations during vitamin A deficiency (VAD). Our data demonstrate that the VAD-induced testicular degeneration arises through the normal maturation of germ cells in a context of spermatogonia differentiation arrest. They indicate that retinoic acid (RA) appears dispensable for the transition of premeiotic to meiotic spermatocytes, meiosis, and spermiogenesis.

Altered retinoid metabolism in female Long-Evans and Han/Wistar rats following long-term 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-treatment.

This study investigated the effects of long-term low-dose 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on retinoid, thyroid hormone, and vitamin D homeostasis in Long-Evans and Han/Wistar rats using a tumor promotion exposure protocol. Female rats (ten/group) were partially hepatectomized, initiated with nitrosodiethylamine (NDEA), and given TCDD once per week by sc injection for 20 weeks at calculated daily doses of 0, 1, 10, 100, or 1000 ng/kg bw/day. Groups of nonhepatectomized/uninitiated rats (five/group) were identically maintained.