Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
9-Hydroxyoctadecadienoic acid
9("S")-HODE and with progressively lesser potencies 9("S")-HpODE, a racemic mixture of 9-HODE, 13("S")-HpODE, and 13("S")-HODE directly activate human (but not mouse) GPR132 (i.e. G protein coupled receptor 132 or G2A) in Chinese hamster ovary cells made to express these receptors; 9("S")-HODE was also a more potent stimulator of human G2A than a series of mono-hydroxy arachidonic acid metabolites. GPR132 was initially described as a pH sensing receptor; the role(s) of 9-HODEs as well as other linoleic and arachidonic acid metabolites in activating GPR132 under the physiological and pathological conditions in which it is implicated to be involved(see (see GPR132 for a listing of these conditions) have not yet been determined. This determination, as it might apply to humans, is made difficult by the inability of these HODEs to activate rodent GPR132 and therefore to be analyzed in rodent models.