Biomedical subjects

M R Yeomans

Publications and source records attributed to M R Yeomans.

28 records · Page 2Linked to original sources

PubMed1996

Palatability and the micro-structure of feeding in humans: the appetizer effect.

The effects of manipulated palatability on eating were assessed in 54 human volunteers eating pasta with a tomato sauce, with palatability adjusted by the addition of three levels of oregano. Meals were divided into 2 min eating episodes separated by brief pauses during which subjects rated aspects of appetite. Both intake and eating rate were greatest in the most palatable condition (0.27% oregano), whereas the addition of 0.54% reduced intake and eating rate. Hunger ratings increased during the initial stages of the meal with 0.27% oregano, but fell throughout the meal in the other conditions, whereas fullness ratings increased similarly in all three conditions. Rated food attractiveness was greatest with 0.27% oregano, and least with 0.54% oregano, but declined similarly through the meal with all three foods. Initial ratings of palatability were similar to those for food attractiveness, but changes in palatability across meals varied between subjects. Male subjects consistently ate more and faster than females, but similar effects of manipulated palatability on intake and subjective appetite were seen in both sexes. These data are consistent with the idea that palatability increases intake through a positive-feedback reward mechanism, and offers a novel method for measuring these effects.

Adolescent↗

PubMed1996

Selective effects of naltrexone on food pleasantness and intake.

The effects of 50 mg naltrexone on both pleasantness and intake of 10 common food items were investigated using a double-blind placebo-controlled study with 16 male volunteers. Rated food pleasantness was reduced significantly in the naltrexone condition compared with both controls (placebo and baseline). However, pleasantness ratings were not affected uniformly across foods, with sweetened, fatty, and high-protein foods being most affected. Changes in rated unpleasantness generally mirrored those for pleasantness, but evaluations of saltiness and sweetness were unaffected by naltrexone. Although total intake was reduced in the naltrexone condition, this was not significant compared with placebo. However, fat and protein intakes were significantly less following naltrexone. The effect of naltrexone on intake was also food dependent, but in this case intake of sweet foods was spared relative to other food categories. The apparent discrepancy between liking and intake data with sweet foods could be interpreted in terms of the likely influence of normal eating styles on food selection during a buffet-style meal, and may explain some contradictions in previous studies of this kind. The implications for understanding opioid involvement in food acceptability are discussed.

Adolescent↗

PubMed1995

Does exposure enhance liking for the chilli burn?

It has been suggested that merely being exposed to a novel stimulus can enhance liking for it. Two experiments explored this hypothesis in relation to the development of liking for the chilli burn in a two-course meal. In the first experiment there was a linear increase in rated liking for the burning sensation produced by 2.5 and 5.0 ppm capsaicin between the first and the fifth exposure to an experimental meal, whereas no significant change was seen for the vehicle food or the preceding non-chilli flavoured food. In the second experiment a similar linear trend was observed with the 5.0 ppm stimulus. However, liking and sensory ratings for an ascending capsaicin concentration series in a tomato juice vehicle tested before and after the exposure period were unaffected by any change in liking for the chilli burn in food. This experiment also suggested that increases in liking were not dependent on initial unfamiliarity with the chilli burn or on changes in rated burn intensity or arousal. Potential explanations for the observed effects are considered.

Adult↗

PubMed1993

Prior exposure to low or high fat milk enhances naloxone anorexia in rats.

Opioid peptides have been implicated in reward-related components of eating, especially with fatty and sweetened foods. This study examined the effect of pre-exposure of rats to milk on the subsequent anorexic effect of naloxone in a separate daily mash intake test. Rats were given constant access to either skimmed or whole milk for 15 days, in addition to normal diet. A third (control) group received only the normal diet. Subsequently, all groups received 0, 0.125, 0.5 and 1.0 mg/kg naloxone prior to their daily mash intake test. Naloxone caused dose-dependent reductions in mash intake in all groups, but this effect was significantly greater in the group with whole milk than in controls, with the group with skimmed milk intermediate. Daily intakes of milk were similar with skimmed and whole milk, and milk intake in separate two-bottle choice tests provided no evidence for overall preferences for either solution. These results suggest that prior exposure to milk enhances opioid involvement in feeding, and possible mechanisms for this are discussed.

Animals↗

PubMed1991

Lower pleasantness of palatable foods in nalmefene-treated human volunteers.

The involvement of endogenous opioids in control of human food intake and appetite was investigated in a double-blind placebo-controlled study using a single, 2.5 mg oral dose of the opioid receptor antagonist, nalmefene. Ratings of the pleasantness of the smell and the taste, but not the appearance, of a number of foods was significantly lower in nalmefene-treated subjects. The magnitude of this effect was greater in food items independently rated as highly palatable. Caloric intake of a buffet-style meal was 20% lower in nalmefene-treated subjects, with the proportional reduction in intake of individual food items also depending on their palatability. These results lend further support to recent suggestions that opioids are involved in reward-related aspects of ingestion.

Adult↗

PubMed1990

Effects of nalmefene on feeding in humans. Dissociation of hunger and palatability.

Effects of nalmefene on eating were investigated in two groups of ten male volunteers, in a double-blind placebo-controlled study. The nalmefene treated group ate 22% less, both in terms of absolute weight and caloric intake, of a standardised buffet-meal than did the placebo group. No differences in subjective ratings of hunger or satiety were found between the groups, suggesting that the reduced feeding was not a consequence of any change in motivation to eat. When analysed by nutrient content, nalmefene was found to reduce fat and protein, but not carbohydrate, intakes. Analyses of intakes of individual foods showed a differential effect of nalmefene on foods rated as highly palatable. Thus the apparent nutrient specificity of nalmefene appeared to be an indirect consequence of its effect on palatability. Nalmefene also caused slight increases in self-rated alertness, and decreases in ratings of tiredness and elation, although it was thought unlikely that these accounted for observed changes in eating behaviour. No other side-effects were detected, and performance on a choice reaction time task was unaffected. These results add weight to suggestions that endogenous opioids are involved in reward-related aspects of feeding associated with food palatability.

Adolescent↗

PubMed1989

Altered spontaneous and osmotically induced drinking for fowls with permanent access to dilute quinine.

Fowls were given a dilute quinine solution as their sole source of fluid, and effects on normal ingestion and on drinking responses to dipsogenic stimuli were examined. Compared to controls with water, daily fluid intakes were depressed by 25% with quinine. There was no significant effect of quinine on food intake, but growth was suppressed slightly. Drinking in response to hypertonic NaCl injections was attenuated with quinine, and whereas an initial peak in water intake was seen directly after hypertonic NaCl injection, this was absent with quinine. Moreover, increases in quinine intake after hypertonic NaCl injections were insufficient to restore normal osmolality. Plasma analyses indicated that birds drinking quinine were permanently dehydrated and, unlike birds with water, they appeared to reduce the hyperosmolality induced by hypertonic NaCl injections in the absence of drinking. In contrast, drinking responses to angiotensin were generally similar with quinine and water, although birds drinking quinine tended to stop sooner with the highest dose of angiotensin. These results support previous suggestions that osmotic thirst is of primary importance in control of normal drinking, but also demonstrate that birds tolerate a degree of dehydration if a suitable fluid source is unavailable.

Angiotensin II↗

PubMed1989

Opioid modulation of feeding and drinking in fowls.

1. D-ala2-methionine enkephalinamide (DME), the stable analogue of met-enkephalin (an opioid agonist), stimulated food intake of immature hens in the first 30 min after intracerebroventricular injection (2 and 8 micrograms/kg), but had no effect on either food or water intake when injected intravenously (15 and 60 micrograms/kg). 2. Naloxone (an opioid antagonist) had no effect on food intake after either intracerebroventricular (50 and 200 micrograms/kg) or intravenous (1 and 4 mg/kg) injection, but inhibited water intake in the second 30 min after intravenous injection. 3. Water intake was not measured after the intracerebroventricular injections of DME and naloxone. 4. Both feeding and drinking were inhibited in a dose-related way in the 7 h after intramuscular injection of nalmefene (0.2, 0.4, 0.8 and 1.6 mg/kg), a more potent and longer-lasting antagonist than naloxone. 5. These data are compared with published results from similar work with birds and mammals. It is concluded that central release of endogenous opioids may reinforce both feeding and drinking in fowls, but whereas opioid blockage affects feeding more than drinking in pigeons and quail, the opposite appears to be the case in fowls.

Animals↗

PubMed1988

Preloads of water, but not isotonic saline, reduce drinking in domestic fowls.

Fowls were deprived of water for 2 or 6 hr, and then given graded intravenous (IV) injections of water or isotonic saline. With both levels of deprivation, water preloads caused dose-dependent reductions in water intake which matched closely the volumes of preload given, whereas isotonic saline preloads had no effect on drinking, and feeding was unaffected in both cases. These results imply that drinking elicited by short periods of water deprivation is a response to increased plasma osmolality rather than to a loss of extracellular fluid volume. In further experiments, water intakes were reduced by at least as much as the volume administered when undeprived fowls were given 6 hr continuous IV infusions or IV injections of water, and food intakes were also suppressed. Plasma analyses taken at the end of continuous infusions of water indicated a fall in osmolality during this time. It was concluded that whereas increases in plasma osmolality increase drinking in fowls, a fall in osmolality below normal inhibits both drinking and feeding. It is suggested that spontaneous drinking may be regulated mainly by changes in plasma osmolality, rather than in extracellular volume.

Animals↗

PubMed1988

Intravenous hypertonic saline injections and drinking in domestic fowls.

Fowls were given intravenous (IV) injections of hypertonic solutions of NaCl, and subsequent water intakes were recorded. All concentrations of hypertonic NaCl increased drinking in the 90 min after injection, compared with control treatments. Increments in drinking in this time agreed closely with calculated amounts required to restore normal osmolality. In further experiments, delaying access to water by periods of 60-360 min after injection failed to reduce drinking elicited by hypertonic NaCl. Injections of 2.0 M NaCl caused increases in plasma osmolality and sodium concentration which were maintained throughout 360 min water deprivation, and caused prolonged reductions in hematocrit and plasma protein concentrations. These results demonstrate that cellular dehydration is a potent thirst stimulus in fowls, and imply that fowls do not reduce hyperosmolality by excretion of salt when water is unavailable.

Animals↗