"These results, it must be acknowledged, are confusing—indicating as they do that propionic acid can push blood pressure in either direction, depending on which receptor is involved. Almost certainly, other as-yet-unidentified receptors are part of the picture, too. It does look, though, as if something produced by gut bacteria, probably propionic acid or a related molecule, is acting like a hormone and regulating blood pressure. If the same were to prove true in people, it would add a new layer of complexity to the relationship between humans and their microbiomes."
The microbiome and health: Sniffing out hypertension | The Economist