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Biomedical subjects

G Collier

Publications and source records attributed to G Collier.

At least 55 records · Page 3Linked to original sources
PubMed1986

Macronutrient selection by foraging rats.

Rats were studied in a laboratory simulation of foraging for separate sources of carbohydrate, fat, and protein. Fixed ratios of bar-presses were required to search for a cue signalling the availability of a meal and to procure each meal. In the first phase, the costs of procuring all three foods were raised equally for three rats. Meal frequency declined and meal size increased for all three foods. Protein opportunities were accepted more frequently than those for other foods, and the proportion of calories taken from protein remained low and constant. Two rats were studied in the remaining three phases. When protein meal cost was raised while the costs of energy foods were low, protein intake was gradually reduced and at the highest cost was dropped from the diet. There were individual differences in the preferred source of energy calories; when each animal's preferred energy source was made more costly, these preferences persisted over the range of costs studied in one rat, but shifted abruptly in the other rat. Finally, when search costs were raised, the animals became less selective in accepting meal opportunities and composing their diets. These results suggest that diet selection in the rat is flexible and responsive to changes in the costs of acquiring food. This ability is consistent with the foraging behaviors required by omnivorous generalized feeders.

Animals↗
PubMed1986

Time budgets in growing chicks.

The manner in which rapidly growing chicks distribute their time among diurnal activities was measured in two studies in which the amount of available light was varied to match seasonal extremes. The effectiveness of the chick's time budgets was assessed in terms of the impact on growth. In Experiment 1, 24-hr patterns of feeding, drinking, nesting, and wheel-running were recorded during successive photoperiods with 12, 6, 18, and 12 hr of light when access to a social partner was concurrently available. In Experiment 2, access to a social partner was an exclusive activity. In both studies, chicks' 24-hr behavioral patterns in response to temporal constraints on their diurnal activities were surprisingly plastic, permitting them to defend a normal and high rate of growth. This was accomplished by changes in feeding rate and by nocturnal feeding rather than by systematic elimination of other diurnal activities. When sociality and feeding were competing activities, feeding time decreased and feeding rate increased such that contact with a conspecific as well as rapid growth were defended. The absolute amount of time spent in measured activities was invariant within subjects irrespective of age, photoperiod, or the number and type of activities recorded, providing evidence of time budgets in immature organisms. In both studies, buffer time (the amount of time spent in no activity) emerged as a significant aspect of the daily time budget that is defended through a variety of environmental challenges.

Animals↗
PubMed1986

Twilight activity and antipredator behavior of young fowl housed in artificial or natural light.

Twenty-four-hr patterns of running wheel activity (Experiment 1) and death feigning, an antipredator behavior (Experiment 2), were studied in domestic chicks housed outside, in natural lighting, or indoors, with light onset and offset timed to coincide with the upper limbs of local sunrise and sunset, respectively. Although chicks housed outside were more active and displayed stronger death feigning reactions, the daily patterns of each activity were highly similar in the two groups. Activity peaked during the period corresponding to evening twilight and was negligible during the morning twilight period; in contrast, death feigning peaked during the morning twilight period. Activity measures indicated that chicks on the artificial light schedule had learned to anticipate dark by day 5, and subsequent ontogenetic changes in activity occurred exclusively in the evening twilight phase.

Aging↗
PubMed1984

Characteristics of selective activation of cyclic AMP-dependent protein kinase isoenzymes by calcitonin and prostaglandin E2 in human breast cancer cells.

The characteristics of the cyclic AMP-dependent protein kinase isoenzyme response to calcitonin stimulation have been studied in two human breast cancer cell lines, T47D and MCF 7. Both cell lines possess calcitonin receptors, a calcitonin-responsive adenylate cyclase and the two isoenzymes of the cyclic AMP-dependent protein kinase, types I and II. The adenylate cyclase also responds to prostaglandin E2. Acute activation of the cyclic AMP-dependent protein kinase isoenzymes was determined by using a modification of a multiple small anion exchange column method [Livesey, Kemp, Re, Partridge & Martin (1982) J. Biol. Chem. 257, 14983-14987]. Control experiments showed that post-extraction activation did not influence the data. Calcitonin caused a rapid, selective activation of isoenzyme II in the T 47D cells with half-maximal response at 10(-10)M, and persisting for at least 24h. In MCF 7 cells calcitonin also caused a highly selective activation of isoenzyme II with half-maximal response at 5 X 10(-11) M, but the response was transient with a return to basal isoenzyme activity by 4-6 h. At this time further addition of calcitonin did not restimulate the cyclic AMP-dependent kinase activity. In neither cell line did calcitonin treatment result in activation of isoenzyme I. Prostaglandin E2, on the other hand, the only significant alternative agonist of adenylate cyclase in T 47D cells, activated isoenzymes I and II to an equal extent in these cells, illustrating that two hormones activating adenylate cyclase in the one cell type might exert different effects by their selective actions upon protein kinase isoenzymes.

Breast Neoplasms↗
PubMed1984

Effect of co-ingestion of fat on the metabolic responses to slowly and rapidly absorbed carbohydrates.

The present study examined the acute effects of co-ingestion of fat (37.5 g) on the post-prandial metabolic responses to 75 g of carbohydrate which was either slowly absorbed (lentils) or rapidly absorbed (potatoes). Co-ingestion of fat resulted in a significant flattening of the post-prandial glucose curves, the effect being more pronounced for the rapidly absorbed potatoes. This was probably due to delayed gastric emptying. However, the post-prandial insulin responses to either carbohydrate were not significantly reduced by fat, suggesting that the insulin response to a given glucose concentration was potentiated in the presence of fat. The gastric inhibitory polypeptide (GIP) responses to both carbohydrates were greatly increased in the presence of fat. To investigate further the possible roles of GIP in the entero-insular axis, a 5-g bolus of glucose was injected intravenously 1 h after lentils +/- fat. This was sufficient to raise the glucose levels above the threshold reported for GIP to potentiate insulin secretion. However, despite the large differences in circulating GIP levels, the insulin response to glucose was not affected by the presence of fat. These results suggest that (1) the rate of absorption of carbohydrate is a major determinant of post-prandial metabolic responses even in the presence of fat, (2) fat-stimulated GIP secretion does not potentiate glucose-induced insulin secretion, and (3) the potentiation of the insulin response to glucose when carbohydrate is co-ingested with fat is consistent with the well-documented insulin resistance associated with high fat diets.

Absorption↗
PubMed1983

Cost and meal patterns in wild-caught rats.

The effect of domestication upon behavior is not clearly understood and thus generalizations from domesticated laboratory animals to nondomesticated animals must be made with caution. Laboratory free-feeding studies with a variety of domesticated species have demonstrated that these animals reduce meal frequency and increase meal size as the cost of procuring access to food increases. The present experiment was conducted to determine if the same relations would be obtained with wild-caught rats. The results showed that laboratory-tested, wild-caught rats respond to changes in the cost of obtaining food in the same manner as domesticated rats. Wild-caught rats did, however, take longer to train and were less efficient than domesticated rats have proven to be in earlier research. In general, the results affirm the validity of laboratory simulations as a means of exploring parameters associated with foraging in natural settings.

Animals↗
PubMed1983

Palatability and meal patterns.

Investigations of palatability have often been confounded by nutritional, pharmacological or methodological problems. The present experiment examined the free-feeding meal patterns of two differentially preferred yet nutritionally equivalent diets. When the two diets were offered sequentially (Experiment 1), no differences were found in meal frequency, meal size, or meal duration. However, when the diets were offered simultaneously in Experiment 2, the preferred diet was consumed more frequently, in larger meals, and at a faster feeding rate than the less preferred diet. Further, the meal patterns in Experiment 2 of the preferred diet were identical with those found for both diets in Experiment 1. Therefore, the meal patterns of two diets with differing palatability depend upon the method of presentation with differences appearing when the diets are offered simultaneously but not when they are offered sequentially.

Animals↗
PubMed1983

The effect of coingestion of fat on the glucose, insulin, and gastric inhibitory polypeptide responses to carbohydrate and protein.

In the present study we examined the effect of coingestion of 50 g fat (butter) on the postprandial glucose, insulin, and gastric inhibitory polypeptide responses to 50 g carbohydrate (potato) or 50 g protein (low fat veal) in eight normal subjects. The coingestion of fat with either carbohydrate or protein resulted in greatly increased gastric inhibitory polypeptide responses, the effect being more pronounced with carbohydrate. The addition of fat to a carbohydrate meal also reduced the postprandial glucose response. This could have been due to several factors including a delayed glucose absorption, secondary to a fat-induced inhibition of gastric emptying. However, despite the lower blood glucose levels in the presence of fat the insulin response was not reduced, suggesting a potentiation of insulin secretion in the presence of fat. Thus, despite the apparent improvement in glucose tolerance when carbohydrate is ingested together with fat, the accompanying potentiation of insulin secretion could form the basis of long-term changes in insulin sensitivity which accompany alterations in dietary fat intake.

Adult↗
PubMed1982

Effect of physical form of carbohydrate on the postprandial glucose, insulin, and gastric inhibitory polypeptide responses in type 2 diabetes.

In the present study we measured the postprandial glucose, insulin, and gastric inhibitory polypeptide responses to 75 g carbohydrate administered either as glucose, unpolished (brown) rice, or ground brown rice to six recently diagnosed type 2 diabetics and six healthy subjects. The diabetic and normal subjects responded in a qualitatively similar manner to the three meals although there were major quantitative differences. Brown rice elicited significantly lower postprandial glucose, insulin, and gastric inhibitory polypeptide responses than either ground brown rice or glucose in both groups. There were no significant differences in the metabolic responses to ground brown rice (complex carbohydrate) and glucose (simple carbohydrate) in either diabetic or normal subjects. These data highlight the role of the physical form of complex carbohydrate in determining metabolic responses to it in both diabetic and normal subjects, and provide a rationale for designing diabetic diets containing complex carbohydrate in a form which is slowly digested and absorbed.

Adult↗
PubMed1979

Patterns of eating as a function of the cost of the meal.

Rats were required to complete fixed ratio schedules (FR 20-FR 2560) of wheel turns to obtain access to food. By decreasing meal frequency and increasing meal size directly as functions of the fixed ratio requirement, animals controlled total daily food intake and body weight relatively constant until the highest ratio requirement was introduced. These functional changes in feeding patterns provide experimental support for theoretical models of optimal feeding strategies. At the highest ratio requirement, as animals lost weight, they increased running and therefore opportunities to feed, however, food intake continued to decrease with increasing exposure to this schedule. As rats on this schedule initiated feeding each time food became available, but did not eat large enough to this schedule. As rats on this schedule initiated feeding each time food became available, but did not eat large enough meals to maintain body weight, it is suggested that activity may interest with satiety mechanisms to produce termination of meals.

Animals↗