Search PubMed⌕ Search

Biomedical subjects

L P Mercer

Publications and source records attributed to L P Mercer.

32 records · Page 2Linked to original sources
PubMed1982

The ability to predict weight gain, individual organ weight, and corresponding food intake in the rat by the four-parameter model for physiological responses.

The applicability of the four-parameter model for physiological responses to the prediction of food intake and corresponding weight gain and individual organ weight gain was studied further in 40-day postpartum male rats. Seven groups of animals were maintained on diets in which protein content ranged from 0 to 23.54% casein. Food intake and weight gain were recorded every other day for each animal for 21 days. At the termination of the experiment the following organs were removed and weighed: liver, heart, lungs, spleen, kidneys, adrenals, and testes. When these weight values are fitted by use of the four-parameter model, food intake and total animal and organ weight gains can be predicted in relation to the amount of protein in the diet. It was found that liver, heart, lungs, spleen, and whole animal had similar K(0.5) values. However, it was also shown that there is variation in response of organs when relating organ weight as a percentage of body weight. For example, heart, lungs, and testes show an increased ratio on low protein diet while liver, kidneys, and adrenals maintain a fairly constant ratio and the spleen shows a decreased ratio. Additionally, it was noted that the animals on low protein diet consumed more food per gram body weight but did so at a slower rate. Possible future applications of the four-parameter model for physiological reponses are discussed.

Animals↗
PubMed1982

The quantitative nutrient-response relationship.

A quantitative mathematical model for the description of nutrientresponse relationships can be derived by the application of the concepts of a) specific nutrient-macromolecular interaction, b) response proportional to the extent of this interaction, c) law of mass action and d) saturation kinetics. This model can be used to produce the four-parameter mathematical model for physiological responses. The possible uses of the model are discussed, an idealized example is given, and the model is applied to the interpretation and description of a growth experiment in which male, weanling Sprague-Dawley rats are fed diets varying in concentration of an amino acid mixture.

Animals↗
PubMed1982

Kinetics of specific food intake and weight gain in rat.

We report the expanded application of a recently developed time-invariant analytic function that relates food intake, growth (weight gain), and dietary nutrient concentration in the laboratory rat. Data from seven experiments were utilized, providing analysis of three stages of rat (Sprague-Dawley) growth (weanling, adult, and pregnant) and a variety of nutrients: casein, lactalbumin, amino acid mix, thiamin, and pyridoxine. For each experiment the rats were fed graded levels of a nutrient, ranging from 0% to a percentage well above the recommended amount, in an otherwise nutritionally adequate diet. Weight-specific weight gains and food intakes were calculated for each dietary group and fitted to the Gompertz equation. The resulting rate constants for each group were identical for weight gain and food intake. The rate constants were then fitted as functions of dietary nutrient concentration by the four-parameter mathematical model for physiological responses. Kinetic rate constants could be characterized as functions of the dietary concentration of each nutrient tested. This approach offers new possibilities for the determination and optimization of dietary requirements. With this approach, one may characterize food intake and growth in a single rate constant, which varies as a function of dietary nutrient concentration.

Aging↗
PubMed1981

Control of food intake in the rat by dietary protein concentration.

Male, weanling Sprague-Dawley rats were fed isocaloric diets containing graded levels of protein or amino acid mixtures. Food intakes and weight gains were recorded daily or every other day. Both short-term and long-term (64 days) experiments were carried out. Linear regressions of food intake versus time and weight gain versus time were used to establish daily weight gains and food intakes. The four-parameter mathematical model for physiological responses was used to predict daily food intake, daily weight gain, daily food intake per 100 g weight and efficiency of food conversion (daily weight gain/daily food intake) as functions of dietary protein concentration. The changes in the four parameters generated from the four-parameter model were examined as a function of time. Several aspects of food intake, weight gain and efficiency were shown to be functions of concentration of dietary protein.

Amino Acids↗
PubMed1981

Prediction of food intakes, weight gains, organ weights, and tumor size in tumor-bearing rats by the four-parameter mathematical model for physiological responses.

Groups of male weanling rats bearing the transplantable Novikoff ascites hepatoma were fed diets containing graded levels of protein. The food intakes and weight gains were recorded daily. Seven days after inoculation of the rats with the tumor (6 days in Experiment 2), the rats were sacrificed, their organs were weighed, and the tumor and ascites fluid volumes were determined. These results were analyzed by the four-parameter mathematical model for physiological responses. It was found that tumor-bearing rats eat and gain weight at the same rates as control rats fed identical diets, implying that this rapidly growing tumor does not interfere with the normal food intake and growth control mechanisms and that food intakes and weight gains are predictable by the four-parameter model. Organ growth was regulated in both normal and tumor-bearing rats but some actual organ weights in tumor-bearing rats were smaller than in control rats due to the presence of the tumor. However, other organs (spleen, lung, kidneys, and small intestine) of the tumor-bearing rats showed significant differences (p less than 0.01, Student's t test) from control rats. It was also possible to predict the growth of the tumor on the basis of the casein content of the diet.

Animals↗
PubMed1978

New methods for comparing the biological efficiency of alternate nutrient sources.

The objective of this study is to propose new methods for the determination of biological efficiency (the ability of a nutrient to produce a response) and for comparison of the efficiencies of alternate nutrient sources. The proposed methods are based on a four-parameter kinetic model which describes response as a function of intake. The comparison of the abilities of two proteins (casein and soybean protein concentrate) to promote weight gain in weanling rats is presented as an example; however, the model is also useful for other nutrients (proteins, amino acids, vitamins, minerals, etc.) and other responses (blood enzyme or protein levels, tissue enzyme levels, etc.). Application of the method leads to useful comparisons of nutrient sources as well as information concerning the maximum efficiencies and rates of nutrient utilization from different sources.

Animals↗
PubMed1975

General model for nutritional responses of higher organisms.

A general saturation equation is derived which is shown to describe a wide variety of nutrient-response relationships in higher organisms. Iterative multiple linear regression analysis is used to obtain least squares estimates of the constants defining theoretical nutrient-response curves. Curves thus generated accurately predict experimentally observed responses. From this treatment, response parameters are developed which are analogous to Vmax and Km of enzyme kinetics. It is proposed that this model be applied in evaluating nutritional requirements and in assessing the relative biological efficiency of nutrient sources.

Animals↗
PubMedDate not supplied

The problem of human protein requirements: some kinetic and metabolic considerations.

Estimated human protein requirements have been substantially lowered by FAO/WHO expert committees over the past two decades. The estimates and methods of calculation are considered in the light of the kinetics of response to protein intake, body protein turnover, amino acid flows in the body, and the concept of nitrogen (N) steady state. Whereas traditional methods of estimation have assumed an essentially linear (first order) response of N retention to absorbed N, animal studies show that response to graded protein intakes obeys saturation kinetics. Corrections for protein quality have also assumed a linear relation between response and supply of limiting amino acid, while animal experiments indicate that this response likewise follows saturation kinetics. Evidence is lacking that the present minimum protein standards for humans can support acceptable internal nitrogen steady states at any age above infancy or foster normal growth in the child. New research approaches to determination of protein requirements are suggested , including study of the kinetics of human response to graded protein intakes and graded variations of quality; development of indicators of nitrogen steady state and correlation with clinical status; and determination of optimum protein-energy ratios by age and sex.

Amino Acids↗
PubMedDate not supplied

Histidine, histamine, and the neuroregulation of food intake: a review and hypothesis.

Feeding, a behavior regulated by the central nervous system (CNS), includes the acquisition of specific essential nutrients and the maintenance of energy balance. Modulation of feeding behavior is a normal part of survival, but certain pathological conditions interrupt or modify regulatory aspects of feeding, thereby leading to inappropriate intake. This review examines aspects of metabolism associated with the anorexia seen in animals suffering from protein-energy malnutrition (PEM). The main focus is the indispensable amino acid histidine (His), the biosynthetic precursor of the neurotransmitter histamine (HA). In kwashiorkor-like PEM, His is elevated in plasma and brain, whereas all other indispensable amino acids are decreased. The elevation of His in the brain is to concentrations five times normal. Because the rate of HA synthesis in the brain is a function of the His concentration, His elevation raises the possibility of a profound direct effect of CNS function. In children, PEM consistently produces the symptoms of depressed food intake, edema, growth failure, and psychomotor changes. One known central effect of HA is the stimulation of ACTH and corticosteroid release. Based on these observations, the hypothesis being examined is as follows: one component of the pathophysiological neuroregulation of food intake involved the His-induced variation of HA concentration in the hypothalamus and the subsequently altered neurochemical activity at the corticotropin-releasing factor (CRF) neurons o the paraventricular nucleus (PVN).

Animals↗