6-n-propylthiouracil
compound / compound-prop
プロピルチオウラシル（PROP）
6-n-propylthiouracil is a thiourea-class antithyroid drug used as a standard probe in psychophysical studies of PTC/PROP taster status. An agonist of the TAS2R38 bitter taste receptor.
Photographs (captions in Japanese)
プロピルチオウラシル製剤 Propycil（50mg錠）の写真。6-n-プロピルチオウラシル（PROP）は精神物理学で味覚テイスター状態の標準プローブとして用いられる。
写っているもの: 該当なし（生物ではなく医薬品）部位・状態: 錠剤(製剤名 Propycil、50mg)
写真: Tomino de WS／ CC BY-SA 4.0／ 原画像／ 台帳の原画像
写真の範囲と来歴
被写体の確認: 原典の記載による同定。製剤名がファイルページで特定されている実在の医薬品写真。
掲載画像: Wikimedia Commons の原寸ファイル。苦味研究所では切り抜き・色調変更なし。 表示用には幅1200px上限のWebPを配信し、台帳の原画像は上のリンクから確認できます。
On this page (6 sections)
Reading the bitterness
PROP (6-n-propylthiouracil) is a thiourea-class compound that has been used as an antithyroid drug and, in psychophysical experiments investigating individual differences in taste perception, has been used as a standard reference substance alongside PTC (phenylthiocarbamide). Both are compounds that activate a bitter taste receptor called TAS2R38, but their responses differ. In a study of 32 subjects with known TAS2R38 haplotypes, when comparing detection thresholds, the fold difference between PAV and AVI homozygotes exceeded 400-fold for PTC, whereas for PROP it remained at 40-fold. There are also observations of 2 AVI homozygotes responding strongly to PROP and 2 PAV homozygotes showing little response, suggesting that genetic and environmental factors beyond TAS2R38 haplotype are involved in PROP taste sensitivity.
Regarding PROP bitterness perception, there is a well-known concept of a 「スーパーテイスター」 (in translation: "supertaster") that associates this sensitivity with the density of fungiform papillae and taste buds on the front of the tongue. A 1994 report that became the basis for this concept stated that papilla density correlated significantly with perceived PROP bitterness. However, a 2014 replication study in 394 subjects found no association between papilla density and PROP response (R-squared = 0.003). Even when stratified by TAS2R38 haplotype, papilla density lacked predictive power. The authors of this study caution against using papilla density as an indicator of taste sensitivity and against casual use of the term 「スーパーテイスター」 (in translation: "supertaster").
In an experiment where L-arginine was added to a PROP (3.2 mM) solution at stepwise concentrations of 0.8-5.2 mM, bitterness intensity increased and latency decreased significantly in AVI/AVI homozygous (non-responder) subjects in a dose-dependent manner. Of 8 non-responders who did not detect PROP at all, 6 first detected PROP bitterness at the lowest concentration of 0.8 mM, and all detected bitterness at the highest concentration of 5.2 mM.
Electrogustometry (ETG) recordings showed that the depolarization amplitude during PROP stimulation correlated significantly with perceived bitterness intensity (r = 0.741, P < 0.00001, n = 43). This amplitude also correlated with fungiform papilla density (r = 0.504, P = 0.00057). The maximum depolarization rate also correlated with both bitterness intensity (r = 0.511, P = 0.00053) and papilla density (r = 0.518, P = 0.00037).
Sources for this overview
Checked for this overview: Confirmed the finding that threshold separation ratios between PTC and PROP differed across haplotypes.
PTC/PROP tasting: anatomy, psychophysics, and sex effects
Checked for this overview: Confirmed the initial report linking papilla density to PROP bitterness.
Checked for this overview: Confirmed the finding in a 394-subject replication study that papilla density and PROP response lacked association.
Checked for this overview: Arginine addition enabled PROP bitterness detection in non-responders.
Checked for this overview: Correlation coefficient between electrophysiological amplitude and perceived bitterness intensity.
Follow the connections
6-n-propylthiouracil →is not perceptually interch…→ phenylthiocarbamide
6-n-propylthiouracil →— perceived bitterness is a…→ L-arginine
Structured claims — open a section to read each claim's confidence, evidence and limits
Sensory (4)
Scope: 32 subjects with known TAS2R38 diplotypes were tested with concentration series of both compounds. Threshold was defined as the 75% point on the psychometric function
Note: A mechanistic caveat about the practice of using PROP as a substitute for PTC. The direct basis is that 2 AVI/AVI subjects responded strongly to PROP while 2 PAV/PAV subjects showed almost no response.
Show data
compound-prop —is_not_perceptually_interchangeable_with→ compound-ptcScope: Human psychophysics with papilla counts on the tongue surface. Originally reported as a significant correlation supporting the supertaster concept
Note: The correlation that had been the anatomical pillar of the supertaster concept was not reproduced in a direct n=394 verification (Garneau 2014) (R-sq = 0.003). Not significant within diplotype groups either.
Show data
compound-prop —has_perceived_bitterness_associated_with→ "The density of fungiform papillae and taste buds on the front of the tongue"Scope: Layer: solution. Bitterness intensity and latency were measured repeatedly using the Labeled Magnitude Scale (LMS) in 51 healthy adults (already TAS2R38-genotyped and PROP taster-status classified).
Show data
compound-prop —has_perceived_bitterness_affected_by→ compound-arginineScope: Layer: solution. Electrophysiological recording (electrogustometry) from 43 healthy adults during application of PROP (3.2 mM) solution to the tongue, with linear regression analysis against TAS2R38 genotype, PROP taster classification, and LMS bitterness intensity ratings.
Show data
compound-prop —has_perceived_bitterness_associated_with→ "The depolarization amplitude during PROP stimulation, recorded from the tongue by electrogustometry (ETG), correlated significantly with perceived bitterness intensity (r=0.741, P<0.00001, n=43). The same amplitude also correlated with fungiform papillae density (r=0.504, P=0.00057). The maximum rate of depolarization also correlated with bitterness intensity (r=0.511, P=0.00053) and papillae density (r=0.518, P=0.00037)."