脊髄におけるプロスタグランジン

In the spinal cord, prostaglandins participate in the pain transmission including hyperalgesia and allodynia. Prostaglandin D２ and E２ induce hyperalgesia, while prostaglandin E２ and F２α induce allodynia. PGF２α synthase （PGFS） produce two stereoisomers of PGF２, PGF２α and９α, １１β-PGF２ which are synthesized from PGH２ and PGD２, respectively, by the distinct reductions in the prostaglandin synthesis pathway. Because the two reduction are occurred in the different active sites, PGFS is a multifunctional enzyme. PGFS has at least two isozymes, namely, PGFSⅠ and Ⅱ with different Km values for PGD２ （１２０ and １０μM, respectively）. They belong to the aldo-keto reductase superfamily based on substrate specificity, molecular weight, and amino acid sequence. In vivo, PGFSs possibly reduce some steroids such as dihydrotestosterone and dihydroprogesterone by their enzymological characteristic. The morphological study of PGFSⅠ and Ⅱ in the rat spinal cord demonstrated their distinct localization. That is, PGFSⅠ existed in neuronal somata and dendrites, and PGFSⅡ existed in ependymal cells and tanycytes surrounding the central canal. Additionally, both PGFSⅠ and Ⅱ existed in endothelial cells of blood vessels. Furthermore, PGF２α receptor, namely FP, was also present in neuronal somata and dendrites. Immunoreactivity for PGFSⅠ and FP was relatively intense in the dorsal horn of the spinal cord that is a connection site of pain transmission. PGFSⅡ in the ependymal cells and tanycytes is not co-localized with FP, and may mainly metabolize PGD２ which is one of the sleep inducers and abundant in the cerebrospinal fluid. These findings suggest that PGFSⅠ and Ⅱ in the rat spinal cord has different biological actions such as neuronal active receptivity and fluid component control, via different cell groups.

四国医学雑誌 : http://www.tokushima-u.ac.jp/med/research/shikoku_acta_medica.html