Effects of linoleic acid on sweet, sour, salty, and bitter taste thresholds and intensity ratings of adults

Evidence supporting a taste component for dietary fat has prompted study of plausible transduction mechanisms. One hypothesizes that long-chain, unsaturated fatty acids block selected delayed-rectifying potassium channels, resulting in a sensitization of taste receptor cells to stimulation by other taste compounds. This was tested in 17 male and 17 female adult (mean +/- SE age = 23.4 +/- 0.7 yr) propylthiouracil tasters with normal resting triglyceride concentrations (87.3 +/- 5.6 mg/day) and body mass index (23.3 +/- 0.4 kg/m(2)). Participants were tested during two approximately 30-min test sessions per week for 8 wk. Eight stimuli were assessed in duplicate via an ascending, three-alternative, forced-choice procedure. Qualities were randomized over weeks. Stimuli were presented as room-temperature, 5-ml portions. They included 1% solutions of linoleic acid with added sodium chloride (salty), sucrose (sweet), citric acid (sour), and caffeine (bitter) as well as solutions of these taste compounds alone. Participants also rated the intensity of the five strongest concentrations using the general labeled magnitude scale. The suprathreshold samples were presented in random order with a rinse between each. Subjects made the ratings self-paced while wearing nose clips. It was hypothesized that taste thresholds would be lower and absolute intensity ratings or slopes of intensity functions would be higher for the stimuli mixed with the linoleic acid. Thresholds were compared by paired t-tests and intensity ratings by repeated measures analysis of variance. Thresholds were significantly higher (i.e., lower sensitivity) for the sodium chloride, citric acid, and caffeine solutions with added fatty acid. Sweet, sour, and salty intensity ratings were lower or unchanged by the addition of a fatty acid. The two highest concentrations of caffeine were rated as weaker in the presence of linoleic acid. These data do not support a mechanism for detecting dietary fats whereby fatty acids sensitize taste receptor cells to stimulation by taste compounds.     

Effects of pharmacologic reductions in salivary flow on judgments of suprathreshold taste stimuli

The effects of short term salivary flow reductions on suprathresholdjudgments of taste intensity were measured using both a seriesof taste solutions and a comparable series of tastants driedon a filter paper base. Decreases in salivary flow were producedby the oral administration of either Elavil^®, Benadryl^®or atropine. The pharmacologic agents produced a 25 –82% reduction in salivary flow during the period that tastetesting occurred but no measurable effects on perceived tasteintensity were found. The exponents of power functions describingmolar concentration and perceived intensity were unchanged aswas the spread in perceived intensity between aqueous and drystimuli. Significant relationships between individual differencesin salivary flow and suprathreshold taste parameters also failedto emerge.     

Direct magnitude estimation of salt taste intensity with continuous correction for salivary adaptation

Subjects sipped and expectorated NaCl solutions, estimatingintensities by direct magnitude estimation, with and withoutinterstimulus rinsing, while saliva samples were taken priorto each tasting and analysed for sodium. Interstimulus rinsingwas seen to reduce salivary sodium concentrations and elicithigher intensity estimates. Exponents for simple psychophysicalpower functions were seen to be higher in the no-rinsing condition,confirming earlier studies. When the functions were correctedfor adaptation level and chemical activity, the trend in exponentswas reversed; this can be interpreted in terms of context effects.It was also found that power functions only produced the bestfit for approximately half the functions; parabolic functionsproduced approximately half, while a few were best fitted byexponential, linear and logarithmic functions.     

The taste, odor and hedonic quality of polyglycerols

Twenty subjects judged the taste and odor intensity and thetaste and odor pleasantness/unpleasantness of five concentrationsof sucrose, glycerol, a commercial triglycerol, a syntheticlinear diglycerol and a synthetic linear triglycerol. Judgmentsof intensity were made using the method of magnitude estimation;judgments of pleasantness/unpleasantness were made using a graphicline scale. Only the two linear polyglycerols had appreciableodor intensity. Both were described as having an ‘acrid’or ‘burnt caramel’ quality. The odor exponent forthe linear triglycerol was extremely high (1.44) and may beattributed to its intensely unpleasant quality. Sucrose wascharacterized solely by sweet taste, glycerol and the commercialtriglycerol by sweet and bitter tastes, the linear diglycerolby sweet, bitter and sour tastes, and the linear triglycerolby bitter and sour tastes. The relationships between perceivedtaste intensity and concentration were well described by powerfunctions, although the slope of the psychophysical functionfor the linear triglycerol was markedly lower than that forthe other compounds. The relative order of taste intensitieswas: linear triglycerol > sucrose > glycerol = lineardiglycerol > commercial triglycerol. Judgments of taste (andodor) pleasantness/unpleasantness showed only sucrose and glycerolto have positive hedonic qualities. All the polyglycerols werejudged unpleasant at all concentrations. Differences in thetaste and odor characteristics of the commercial and synthetictriglycerols were attributed to the commercial product beinga mixture of over 20 compounds. Although the synthetic lineardi- and triglycerols are effective in lowering water activity,these data suggest that more purified crystalline forms mustbe synthesized before they can be used effectively as humectantsfor intermediate moisture foods.     

Use of perceived effort ratings to control exercise intensity in young healthy adults

The purpose of this study was to evaluate the use of the rating of perceived exertion (RPE) as a means of regulating the intensity of exercise during running. The subjects were healthy, relatively fit young adults (16 men and 12 women). Estimates of effort were recorded using the Borg 6-20 Scale whilst the maximal oxygen uptake of the subjects was measured as they ran on an electrically driven treadmill. In a further session, the same subjects were requested to run on the treadmill at constant exercise intensity based on their interpretation of levels 9, 13 and 17 of the Borg Scale. They regulated their running speed and the treadmill gradient but had no knowledge of performance from the equipment display panel. A linear regression analysis was carried out to examine the relationship between heart rate, perceived exertion and relative metabolic demand. This revealed that the rating of perceived exertion was at least as good a predictor of exercise intensity as heart rate in both the graded exercise test and effort production test. The results support the view that RPE may be used to predict relative metabolic demand, especially at higher workloads and could be a useful medium for controlling intensity of effort during vigorous exercise in such subjects.     

Intensity and hedonic judgments of taste mixtures: an information integration analysis

Anderson's (1981) information integration approach was usedto examine taste mixture integration for intensity and hedonicjudgments of sucrose/sodium chloride and sucrose/citnc acidsolutions. In Experiment I, total intensity and hedonic ratingswere made for factorial combinations of sucrose and sodium chlorideor citric acid. The total intensity judgments produced an integrationpattern characterized by extreme subadditivity at high soluteconcentrations. (Subadditivity refers to the tendency for totalmixture intensity to be rated as less than the sum of the unmixedcomponent intensities.) The intensity judgment integration patternswere essentially identical for the two mixture types. However,the pattern of integration for the sucrose/sodium chloride andsucrose/citric acid mixtures differed for the hedonic ratings.Sucrose tended to eliminate the unpleasantness associated withincreasing concentrations of citric acid, while it only modulatedthis trend for sodium chloride. In Experiment II, subjects ratedthe individual sweet, salty and sour components of the mixturesto determine whether mixture suppression of the component tastescould account for the subadditivity of the total intensity judgmentsand/or the pattern of results for the hedonic ratings. It wasfound that sucrose suppressed the sour component of the sucrose/citricacid mixtures more than the salty component of the sucrose/sodiumchloride solutions This difference in component suppressionseemed to account for the hedonic integration patterns of thetwo mixture types which suggests that mixture suppression isan important factor to consider when predicting the pleasantnessof simple taste mixtures.     

Contributions of Smell and taste to overall intensity

The integration of olfaction and gustation in producing thesensation of flavor was studied using an almond extract stimuluspresented with the Two-Module Delivery System. Almond in themouth was found to influence the scaling of smell. The datasugest that this background effect is due to the diffusion ofairborne molecules from the oral cavity to the olfactory receptorsarea. At least under some stimulation conditons, almond vaporin the nose was shown to afect the scaling of taste. When scalingoverall intensity, subjects apparently added together the sensationsof smell and taste to produce the sensation of overall intensity.However, for all combinations of odorants and tastants, theestimate of overall intensity was less than the sum of the estimateof the smell and the estimate of the taste. The data furthersuggest that when estimating the overall intensity, the magnitudeassigned to the olfactory or gustatory sensations was less thanthat which have been assigned when estimating just smell ortaste.     

Effects of cannabinoids on energy metabolism.

The present review summarizes the recent work carried out by our group on the link between signal transduction pathways and metabolic regulation systems as affected by cannabinoids. In cells such as astrocytes and lymphocytes, which express cannabinoid receptors, physiologically relevant doses of cannabinoids induce a remarkable metabolic stimulation as determined e.g. by enhanced glucose utilization. Studies performed in astrocytes show that the cannabinoid-evoked stimulation of glucose metabolism is independent of adenylyl cyclase inhibition, and seems to rely on the cascade CB1 cannabinoid receptor --> Sphingomyelin breakdown --> Ceramide --> Raf-1 --> Mitogen-activated protein kinase (MAPK) --> Glucose utilization. A role for phosphoinositide 3'-kinase in the stimulation of glucose utilization by cannabinoids is also put forward. In addition, ceramide generated upon CB1 cannabinoid receptor activation may enhance ketone body production by astrocytes independently of MAPK. Anandamide has also been shown to exert metabolic effects in hepatocytes, cells that do not express cannabinoid receptors. The biological role of cannabinoids as modulators of metabolism is as yet unclear.     

Effects and interactions of natural cannabinoids on the isolated heart

A Langendorff perfused rat heart preparation was designed to process dose-response effects of cardioactive drugs on rate, coronary flow, and supraaortic differential pressure (delta P; an index of cardiac performance). In this preparation, delta 9- -tetrahydrocannabinol (THC) 2 X 10(-6) M to 10(-5) M induces in the isolated perfused rat heart a biphasic increase in rate (maximal at 8 X 10(-6) M). Tachycardia is associated with decreases in (delta P) and no change or decreased coronary flow. Cardiac toxicity is observed with 3 X 10(-5) M. Cannabidiol (CBD) at concentrations of 9 X 10(-6) M to 10(-4) M has limited effect on rate while increasing delta P and coronary flow. Cannabinol (CBN) 8 X 10(-6) M to 3 X 10(-4) M depresses rate and delta P while coronary flow remains constant. Simultaneous equimolar administration of THC with CBD antagonizes or mitigates the cardiac effects of THC on rate, delta P, and coronary flow.     

Effects of therapeutic doses of amiloride and hydrochlorothiazide on taste, saliva and salt intake in normotensive adults

Tentative evidence suggests that hydrochlorothiazide (HCTZ)and amiloride may alter salivary function, taste sensitivityand dietary intake. The effects of these diuretics on salivaryflow and composition, taste attributes (i.e. recognition thresholds,perceived intensity ratings and preference) as well as sodiumintake were further examined in 73 normotensive adults in adouble-blind, placebo-controlled, cross-over study. Followingrandom assignments to one of three groups [5 mg twice per dayof amiloride (n = 24), 50 mg/day of HCTZ (n = 24) or placebo(n = 25)], subjects took appropriate placebos for 2 weeks, activedrug for 8 weeks and placebo for 3 weeks. Relative to baselinevalues, amiloride treatment resulted in a significant 39% decreasein stimulated salivary sodium levels and a 28% decline in NaClrecognition thresholds. HCTZ significantly stimulated sodiumintake as the sodium/creatinine ratio was {small tilde}50% higherfollowing 4 weeks of drug use relative to baseline values. Subjectswere subjectively unaware of these changes. Potential mechanismsand clinical implications of these findings are considered.     

Effects of horsefly (Tabanidae) salivary gland extracts on isolated perfused rat heart

The speed with which horseflies (Diptera: Tabanidae) obtain a bloodmeal suggests they have potent vasodilators. We used isolated perfused rat heart to examine the vasoactivity of salivary gland extracts (SGEs) of three horsefly species, Hybomitra bimaculata Macquart, Tabanus bromius Linnaeus and Tabanus glaucopis Meigen. Administration of horsefly SGEs to the heart produced biphasic coronary responses: a decrease and subsequent increase in coronary flow (CF), characterized by initial vasoconstriction followed by prolonged vasodilation of coronary vessels. However, although SGEs of H. bimaculata induced a significant decrease in left ventricular pressure (LVP), the effect on changes in CF was not significant except at the highest dose tested. The ability to reduce LVP without significantly lowering CF, or affecting heart rate and rhythm, represents a unique set of properties that have considerable therapeutic potential if they can be reproduced by a single molecule.     

Brain activation associated with ratings of the hedonic component of thermal sensation during whole-body warming and cooling

Thermal sensation has both discriminative and hedonic components. The neural network associated with thermal discrimination has been described, but the representation of the hedonic component of thermal sensation in the brain has yet to be demonstrated. This study measured regional cerebral blood flow (rCBF) with Positron Emission Tomography in human participants during whole-body cooling and warming. Ratings of the hedonic dimension of thermal sensation were correlated with rCBF and compared to brain activation maps of skin and core temperature changes. The hedonic dimension of thermal sensation was represented in a widely distributed network that included somatosensory, limbic, paralimbic, and associative cortices. Changes in rCBF associated with ratings of the hedonic dimension of thermal sensation were contrasted with changes in rCBF associated with skin and core temperature to identify brain regions that were uniquely activated by the hedonic dimension of thermal sensation. The contrast between the correlates of the hedonic dimension of thermal sensation and the correlates of skin and core temperatures identified a region in the posterior part of the mid cingulate cortex (pMCC). The independent relationship between rCBF changes in the pMCC with ratings of the hedonic dimension of thermal sensation may indicate an important role for the pMCC in the integration of temperature-related signals from receptors in the skin and core.     

Effects of marijuana on testosterone in male subjects

Clinical studies have given contradictory reports on the effect of smoking marijuana on the plasma levels of testosterone in males. A reanalysis of existing data established that testosterone levels are depressed both after smoking one marijuana cigarette and after intravenous infusion of delta-9-tetrahydrocannabinol, a pharmacologically active component of marijuana. Simulation of the marijuana interaction, under the assumption that delta-9-tetrahydrocannabinol inhibits testosterone production or secretion, suggests a minimum of 24 hours are required for testosterone to return to pre-smoking levels. A series of clinical studies are specified to clarify the nature of the interaction.     

Perception of everyday odors--correlation between intensity, familiarity and strength of hedonic judgement.

In this study, 40 Japanese, 44 German and 39 Mexican women were presented with 18 everyday odorants. They were asked to rate them for intensity on a six-point scale from not detectable to very strong, for pleasantness on an 11-point scale from -5, to neutral at 0, to +5, and for familiarity on a six-point scale from completely unknown to extremely familiar. Consistent positive correlations were found between paired rating scores for the three measures, and although they were not particularly strong (r(s) range, 0.19-0.60), for most odorants all three correlations were significant. Similar results were obtained whether the data were analyzed on an individual or a national basis. Most notable were the consistent positive correlations between perceived intensity and ratings of familiarity and hedonic strength. It is suggested that the perceived intensity of the odorants depended not only on stimulus concentration but probably also on experience-dependent factors.     

The effect of exercise intensity and duration on salivary immunoglobulin A.

Two experiments were performed to examine salivary immunoglobulin A (s-IgA) responses to varying levels of exercise intensity and duration. For experiment 1, 9 college men (mean age, SD = 23.56, 1.64 years) completed treadmill runs of 15, 30, and 45 min at approximately 60% of maximum oxygen consumption (VO2max). For experiment 2, 9 other college men (mean age, SD = 23.67, 2.0 years) ran for 20 min at approximately 50, 65 and 80% of VO2max. Unstimulated salivary samples were collected before, and immediately, 1 and 2 h after the exercise. Samples were assayed for s-IgA using an enzyme-linked immunosorbent assay. Mean s-IgA levels did not change significantly (P greater than 0.05) at any of the post-exercise collection times when compared to pre-exercise levels. The results of this investigation indicated that running at intensities of 50-80% of VO2max and for durations of 15-45 min did not affect s-IgA levels.     

The effect of cooling the tongue on the perceived intensity of taste

Two experiments were performed (i) to measure the effect ofcooling on the perceived intensity of taste, and (ii) to determinewhether the temperature of the tongue or the temperature ofthe solution was primarily responsible for the changes in perceivedintensity that were observed. The first experiment revealedthat cooling both the tongue and the taste solutions from 36to either 28 or 20°C produced measurable reductions in theperceived intensity of the sweetness of sucrose and the bitternessof caffeine. The saltiness of NaCl and the sourness of citricacid were unaffected by cooling. The second experiment demonstratedthat the temperature of the tongue was the critical factor forproducing the effects on sweetness and bitterness. The latterfinding implies that some of the inconsistencies in the literatureon taste–temperature interactions might have been avoidedif the temperature of the tongue had been routinely controlled.In addition, the importance of lingual temperature suggeststhat thermal effects on taste intensity may often be due tochanges in the sensitivity of the gustatory transduction processrather than to changes in the molecular properties of the tastesolutions.     

Effects of age and sex on taste sensitivity to phenylthiocarbamide (PTC) in the Berkeley Guidance sample

Using a modification of the Harris and Kalmus method for ascertainingthe taste threshold for phenylthiocarbamide (PTC), data werecollected on 424 Caucasian individuals from the three generationallongitudinal study of the Berkeley Guidance subjects in Berkeley,CA. Analysis of the data indicates the distribution of thresholdsis significantly different from that in the London sample ofHarris and Kalmus in that the frequency of nontasters is abouthalf that found in London. The difference is not attributedto the modifications made in the testing procedure but to areal difference in gene frequency. Both the PTC taster and nontasterphenotypes display a large amount of variation in expressionbetween individuals. They are differently expressed in malesand females, the latter being more sensitive. As people age,the expressions of their genotypes change. Neither age nor sexseem to affect the penetrance of the PTC genes which remainsthe same within each sex at all ages unless some other environmentalfactor, such as radiation, impinges. Consideration of theserelationships is necessary for the investigation of family relationships,the mechanisms responsible for maintaining this ancient geneticpolymorphism and the degree of polytypy present in the species.