γ-Glutamyl-Valyl-Glycine (γ-Glu-Val-Gly) and Glutathione (γ-Glu-Cys-Gly) as Kokumi Substances in Rodents

γ-Glu-Val-Gly (EVG), a potent agonist of the calcium-sensing receptor (CaSR), enhances preferences for umami, fat, and sweet taste solutions in rats at low concentrations that do not elicit a taste of its own. Increased preference for inosine monophosphate (IMP) and intralipos (a soybean–oil emulsion) was the most dominant effect. NPS-2143, an antagonist of CaSR, abolished these additive effects, which are considered to occur in the oral cavity, because the effects of EVG were confirmed in a brief exposure test. The additive effects of EVG and the effect of NPS-2143 were verified via electrophysiological taste nerve responses from the chorda tympani innervating the taste buds on the anterior part of the tongue. The additive effects on IMP and intralipos remained after transection of the chorda tympani, indicating that these effects also occur in the palate, the posterior part of the tongue, or both. Similar results were obtained for glutathione in mice. The results obtained in rodents may partially provide the underlying mechanisms through which kokumi substances induce thickness, mouthfulness, and lingeringness (continuity) in humans.