Morley R. Kare

Effects of oral stimulation on the cephalic phase of pancreatic exocrine secretion in dogs

Abstract In dogs with cannulated gastric and duodenal fistulas, gustatory receptors were stimulated by swab application of taste stimulus solutions. The experiments were performed with fistulas open. A single taste stimulus of either 0.29 M sucrose, 0.1 M critic acid or 0.001 M quinine sulfate produced a large increase in pancreatic secretion of both volume and protein output. Sucrose was a better stimulant than citric acid or quinine sulfate for pancreatic output. After only one or two trials with each stimulant, the secretory response was no longer seen in any of the dogs. Following this extinction of the secretory response, the same dogs were given orally 100 ml of taste stimulus solution mixed with 25 g cellulose. Pancreatic secretory response occurring within 40 min following administration was gradually restored primarily for sucrose-cellulose. Oral administrations of the unpalatable citric or quinine-cellulose mixtures resulted in low pancreatic output, similar to the control water-cellulose. In contrast to oral administrations, intragastric administrations of these taste stimulus-cellulose mixtures resulted in low pancreatic output within 40 min after administration. The results suggest that taste stimulation alone does not affect pancreatic secretion. However, when coupled with swallowing, there is a greater effect by palatable than unpalatable taste stimuli on the cephalic phase of pancreatic secretion.

Interaction of MSG taste with nutrition: Perspectives in consummatory behavior and digestion

Studies in the taste system of mammals indicate that monosodium glutamate (MSG) produces a unique taste sensation termed umami. As a derivative of glutamic acid, MSG is a naturally occurring nutrient in many foods; its commercial use to improve food palatability for humans is well documented. Behavioral studies with experimental animals have revealed that preference for MSG in solutions and selection of MSG-flavored diets can be explained by sensory means with no appreciable effects on preference by postingestive consequences. However, preference for umami-flavored fluids is reduced by feeding rats low-protein diets or low quality protein. MSG-flavored diets, initially unpreferred, were subsequently highly selected. However, the adulteration of diets by MSG either did not or only slightly increased food intake. In light of the significant contribution of MSG to diet taste, apparently as a signal coupled to dietary proteins, physiological studies have been initiated to reveal its role as a stimulator of the cephalic phase of pancreatic exocrine secretion. Modified sham-feeding experiments with dogs have shown that oral stimulation by MSG produced significant stimulation of both pancreatic flow and protein output in conscious dogs.

The preference-aversion behavior of rats for nutritionally-controlled diets containing oil or fat

The preference-aversion behavior of Sprague-Dawley rats for semi-purified diets containing various levels of either corn oil, animal fat (lard) or hydrogenated vegetable oil (Crisco) was determined in brief and long-term, two-choice preference tests. After the first day of exposure, rats selected more calories from the control-unadulterated diet than from experimental diets containing either oil or fat. Only in the first hour of exposure (with diets containing either 5% Crisco, 15 or 25% lard) or in the first day (with diets containing 5% Crisco, 5 or 15% lard) was a preference for experimental diets observed. There were significant effects of oil and fat concentration and of exposure time upon preference for experimental diets, such that preference for the experimental diets was reduced as levels of oil or fat and as the time of experiment increased. Changes in diet selection had no major effect on total caloric intake measured as the sum of both experimental and control dietary choices, although total intake on a daily basis tended to decrease during the middle portion (2-4 days) of the study, then recover by the end of the study. The results suggest that postingestional factors related to the dietary oil and fat (rather than the sensory properties of the diets) directed the long-term preference behavior of rats for semi-purified diets adulterated with various levels of either corn oil, animal fat (lard) or hydrogenated vegetable oil (Crisco).

Preference of rats for food flavors and texture in nutritionally controlled semi-purified diets

Preference for nutritionally controlled, semi-purified diets modified by the addition of potent food flavors was determined for Sprague Dawley rats using two-choice diet preference tests. Intake of each food cup was monitored after 1 hr and for each 24 hr period thereafter up to 5 days. Preference was also determined for the flavored diets prepared in three forms differing in texture: powdered, and pellets of two sizes. Rats easily detected minor amounts of the food flavors, and the tests provided a catalog of 12 preferred flavors. Exposure time to the diets altered preference for a minority of flavors; diets initially avoided in the first hour test were likely to become less aversive upon continued exposure. Whether or not a specific flavored diet was preferred, total food intake was not affected during the 5 day period monitored. Rats displayed strong preference for diets of a pelleted texture compared to the same diets in a powdered form.

Diet palatability and growth efficiency: Evidence for a physiological interrelationship in rats

Abstract The total food intake and growth efficiency of growing rats were not affected by the feeding of a mild protein restricted (10%) diet containing an aversive taste stimulus. However, growing rats fed the same diet for a period of 18 days, suffered an inhibition of growth efficiency if the taste character of the diet was changed daily by the addition of a single but different aversive stimulus. For a period of time (9 days), these changes in diet palatability did not affect the total food intake. Rats fed diets containing a combination of the aversive taste changes and commercial soybean trypsin inhibitors, suffered an additional inhibition of growth efficiency. It is postulated that these manipulations in diet palatability interfered with digestive or metabolic processes.

Feeding low iron diets affects fluid preference in growing rats

Abstract The effect of dietary iron (ferrous sulfate) concentration on the intake of solutions of sodium saccharin, hydrochloric acid, quinine sulfate, sodium chloride, and potassium chloride was studied. Male Charles River CD weanling rats were divided into four groups and fed semi-synthetic iron-free diets supplemented with either 0, 10, 20 or 40 ppm ferrous sulfate. Using a 48 hour, two-bottle preference test, the rats fed the diet with 0 ppm (added) iron showed significantly higher preferences for sodium chloride and potassium chloride solutions compared with the other three groups. Total fluid intake also increased in rats given the unsupplemented diet. Water intake was not increased in this 0 ppm group when sodium was offered. Blood hemoglobin and hematocrit, serum iron and body weight were lowest in the group with 0 ppm added iron, yet neither adrenal weights nor serum zinc was affected by the dietary iron levels.

Gustatory Sequelae of Alimentary Disorders

Disorders in different regions of the alimentary tract have been associated with alterations in gustatory function. Current understanding of mechanisms underlying the taste disturbances and their impact on the physical and emotional well-being of patients is incomplete. Indeed, in most instances, present knowledge remains at a descriptive level. Accumulating evidence that profound interactions occur between the sense of taste and alimentary function poses a challenge to apply this knowledge in the clinic setting.

A Consideration of Some Psychological and Physiological Mechanisms of Odour Perception

Those to whom it falls to summarize the progress of a scientific discipline are often tempted to interpret an accelerating publication rate as a positive indicator of intellectual advance. Were we to subscribe to this approach we should be able to give a very rosy picture indeed of scientific achievement in odour perception and its attendant psychological and physiological mechanisms. Examination of the MEDLINE database of medical and life sciences research literature reveals a substantial increase in the annual scientific output having to do with the nose, odour, chemoreception and related topics (Fig. 1).1 From 1966 to 1987 the yearly figure rose from 750 to over 2500 papers. The somewhat broader BIOSIS database shows olfactory research pouring forth at the numbing rate of 4000 papers a year in 1987. Sceptics might view these figures as reflecting inflation in scientific publishing in general. Yet the same analysis1 showed that as a proportion of the total, olfactory papers grew from 0·4% in 1965 to 0·8% by 1987.