The primrose way

Space-filling model of the hydrogen sulfide molecule (Ben Mills)

Hydrogen sulfide (H₂S) is a signaling molecule in the brain and cardiovascular system. The antihypertensive effect of garlic has been attributed to the generation of H₂S from its contained polysulphides (reviewed here).

A recent study (here) indicates that H₂S may play a role in regulating blood flow on the fetal side of human placenta. One of the enzymes that generates H₂S (CSE) is found in the smooth muscle layer of stem villus arteries. Moreover it was shown using the H₂S donor NaHS that the molecule is able to dilate the fetal placental circulation. Because the placenta lacks innervation, signaling molecules like H₂S are likely to be important in the regulation of blood flow. The study found evidence that CSE expression is decreased in pathological pregnancies such as preeclampsia and fetal growth restriction.

H₂S is involved in oxygen sensing in the carotid body (here) and one wonders if it might perform a similar role in the placenta.