The primary prostaglandin-inactivating enzyme of human placenta is a dimeric short-chain dehydrogenase.

The native form of NAD-dependent 15-hydroxyprostaglandin dehydrogenase of human placenta has a mol. wt. of about 50 000, while the subunit mol. wt. is around 28 000, suggesting a dimeric quaternary structure. These properties, the amino acid composition, insensitivity to EDTA, and inhibition patterns show general similarities to other short-chain dehydrogenases. Several hormones tested did not influence the activity of 15-hydroxyprostaglandin dehydrogenase, but an unusual activation by two anti-depressant drugs was found and may relate to the existence of a natural regulatory factor.