Effects of amino acid imbalance and protein content of diets on food intake and preference of young, adult, and diabetic rats

Amino acid profiles, disease activity, and protein intake in adult patients with Crohn's disease

Introduction

Crohn's disease (CD) is an immune-mediated inflammatory disorder of the gastrointestinal tract with a relapsing-remitting course. Amino acids (AAs) may play critical roles in the intestinal manifestations of disease, due to their involvement in many metabolic and immune functions. The present study aimed to explore serum AA concentrations in adult patients with CD, looking into their variations due to disease activity, surgery and protein content of diet. Eventually, the link between AAs and inflammatory markers was also assessed.

Methods

Consecutive adult patients aged 18-65 years with diagnosis of CD were recruited. All participants underwent anthropometry and were instructed to fill in a 3-day food record to assess protein intake. Disease activity was clinically defined using the Crohn's Disease Activity Index (CDAI), while blood samples were taken to analyze serum AA profile and inflammatory markers.

Results

A total of 103 patients with CD (61 men and 42 women; age:39.9 ± 13.9 years, BMI: 23.4 ± 3.51 kg/m2) were included. Tryptophan levels were found to be remarkably decreased in most subjects, unrelated to disease activity. On the contrary, concentration of lysine, leucine, valine and glutamine decreased in active versus quiescent CD patients, while aspartic acid, glutamate and glycine increased. The latter AAs were also directly correlated with CDAI and serum interleukin (IL)- 1β concentration. Considering the total protein intake, expressed as g/kg/body weight, we observed a reduction in some essential AAs in patients with unmet protein requirements compared to patients who met the recommendation.

Discussion

In conclusion, specific AAs varied according to disease activity and protein intake, adjusted to body weight and disease status. Glu and Asp concentrations raised with increasing IL-1β. However, extensive research is needed to understand the mechanisms underpinning the link between variation in serum AAs, disease activity and protein intake in patients with CD.

Effects of Intraperitoneal Infusion of Dextrose and Amino Acids on the Appetite of Rabbits

We studied the effect of Intraperitoneal Infusion of various volumes and concentrations of dextrose (D) and amino acid (AA) solutions, In a variety of peritoneal dialysis schedules on food Intake and biochemical profile in normal and uremic rabbits.

Following omentectomy, a peritoneal catheter was implanted. Animals had free access to food, and consumption was measured daily by weight of the remaining food in the cage.

We studied the effect of volume (30-50-100 mL/kg), dextrose concentration (0.5-1.5-2.5-4.25-6.6 g/dL) and AA (Travasol based) (2% in Dianeal or glucose-free solution).

Dialysis schedules Included once/day, twice/day, or four-daily exchanges similar to CAPD.

The durations of the exchanges were 4–6 weeks and in certain groups, amino acid exchanges for a week alternated with dextrose exchanges.

Our results Indicate the following: omentectomy and catheter implantation significantly decrease food Intake. There is a significant decrease In food Intake after initiation of dialysis that returns to baseline after 2–4 weeks while dialysis continues. Higher volumes (100 mL/kg) decrease food Intake significantly, especially with hypertonic solution of either D or AA. There was no difference in food Intake between D and AA Infusion In any amount of infused volumes.

Amino acids do not seem to have a suppressing effect on appetite. However, large volumes and hypertonicity reduce food Intake.

Heating Has No Effect on the Net Protein Utilisation from Egg Whites in Rats

Egg whites (EW) are a good source of protein; however, they are typically heated prior to consumption. Therefore, we investigated the effects of different heating conditions on the protein utilisation rate of EW. Male Sprague-Dawley rats (n = 36, 198 ± 1 g) were divided into six groups and fed American Institute of Nutrition-76 chow containing unheated EW, soft-boiled EW, boiled EW, milk whey protein, soybean protein, or no protein over a 10-day period using pair-feeding. Urine and faeces were sampled daily beginning on day 5 to measure nitrogen content and the net protein utilisation (NPU) rate. The soybean protein group had a significantly lower level of food intake and was thus excluded from subsequent analyses. The NPU value was similar among the unheated, soft-boiled, and boiled EW groups (97.5 ± 0.4, 96.5 ± 0.1, and 96.5 ± 0.7, resp.). The EW group values were significantly higher than the whey group values (90.5 ± 1.0). These results show that EW serve as a good source of protein, irrespective of heating.

A low protein diet alters gene expression in rat pancreatic islets

Insulin secretion is regulated mainly by circulating nutrients, particularly glucose, and is also modulated by hormonal and neuronal inputs. Nutritional alterations during fetal and early postnatal periods, induced by either low protein or energy-restricted diets, produce beta-cell dysfunction. As a consequence, insulin secretion in response to different secretagogues is reduced, as is the number of beta-cells and the size and vascularization of islets. In this study, we used a cDNA macroarray technique and RT-PCR to assess the pattern of gene expression in pancreatic islets from rats fed isocaloric low (6 g/100 g, LP) and normal (17 g/100 g, NP) protein diets, after weaning. Thirty-two genes related to metabolism, neurotransmitter receptors, protein trafficking and targeting, intracellular kinase network members and hormones had altered expression (up- or down-regulated). RT-PCR confirmed the macroarray results for five selected genes, i.e., clusterin, secretogranin II precursor, eukaryotic translation initiation factor 2, phospholipase A(2) and glucose transporter. Thus, cDNA macroarray analysis revealed significant changes in the gene expression pattern in rats fed a low protein diet after weaning. The range of proteins affected indicated that numerous mechanisms are involved in the intracellular alterations in the endocrine pancreas, including impaired glucose-induced insulin secretion.

Time course and pattern of compensatory ingestive behavioral adjustments to lysine deficiency in rats

We and others have demonstrated that rats deficient in an essential amino acid (EAA) will consume sufficient quantities of the lacking nutrient to produce repletion when it is made available in solution. In the current series of experiments, we made rats deficient in lysine (LYS) by limiting the level of this EAA in the diet. We then examined licking behavior during approximately 23-h two-bottle intake tests over 4 consecutive days. In three separate experiments, rats were presented with the following: 1) 0.1 mol/L LYS and water, 2) 0.2 mol/L threonine (THR) and water and 3) 0.1 mol/L LYS and 0.2 mol/L THR. Lysine-deficient (LYS-DEF) rats drink significantly more LYS than did nondepleted controls (CON) when this amino acid was available. Meal pattern analysis revealed that the enhanced intake of LYS occurred as a function of a greater number of ingestive bouts, not changes in bout size. A cumulative analysis of LYS intake between CON and LYS-DEF rats revealed that a potentiation of intake developed within 30 min of sampling the solution when LYS and water were available and within 90 min when LYS and THR were the contrasting choices. In conclusion, increased LYS intake in the deficient rats occurs relatively rapidly and appears to be at least somewhat specific. Moreover, LYS deficiency does not seem to enhance the palatability of the limiting amino acid as judged by behaviors such as lick rate and bout size. Instead, LYS-DEF rats relieve the deficiency by increasing the number of drinking episodes initiated.

Protein selection by rats adapted to high or moderately low levels of dietary protein

After preliminary studies on flavor acceptability, patterns and indices of subsequent feeding behavior were monitored by computer in young rats which were adapted to 15% or 70% casein diets before being offered, sequentially, choices between flavored diet pairs in which the proportions of percentage casein were 5/65, 5/55, 5/45, 5/35 and 5/25. Similarly adapted rats received these choices in the reverse sequence. Rats adapted to 15% casein usually ate randomly from the diet pairs and selected approximately 15-30% casein; individual behaviors were prominent. The 70% casein groups avoided the higher casein diet, often within minutes (except for the first-offered 5/25 choice), and seldom selected more than 10% casein; individual differences were infrequent. Such rats also distinguished between flavored 70% and 65% casein diets. Sizes and numbers of meals and rates of eating differed for the paired diets, especially for rats adapted to 70% casein. A flavor added to the 70% casein adaptation diet was not avoided when present only in the 5% casein diet of a 5/65 choice. Rats adapted to 70% soy protein before receiving flavored 5/65 to 5/25 choices selected 20-28% soy protein, a level far above those of casein selections by rats adapted to 70% casein. Dietary adaptation and type of protein thus affect subsequent diet selection and feeding patterns and indices.

Sparrows discriminate between diets differing in valine or lysine concentrations

White-crowned Sparrows (WCS) were given free access to pairs of semisynthetic diets that were either adequate or subadequate (25% of requirement) in valine or lysine. Within 2 to 4 days WCS chose a ratio of the paired diets that allowed them to maintain body mass or restore any losses quickly. On the initial choice days the birds transiently reduced total daily food intake (TDFI) roughly in proportion to their intake of the subadequate diet. The initial decrease of TDFI was greater and the latency in choosing an effective ratio of the paired diets was 2-3 days longer with valine than with lysine diets in well-nourished test birds. In malnourished birds fed only the subadequate test diet for 3 days, valine-deficient birds increased TDFI and body mass more promptly than did lysine-deficient birds when offered a choice of adequate and subadequate diets. The form of the test amino acid (CAA = crystalline, PB = protein-bound) had little effect on choice behavior, but sudden transfer of WCS from a PB acclimation diet to test diets with a large total CAA concentration increased the latency of effective choice by 2-3 days. A brief acclimation (2-3 days) to a CAA diet precludes any bias between nutritionally equivalent CAA and PB diets. The small differences in choice dynamics between valine and lysine and between dietary forms may help to identify mechanisms involved in food choice but are probably ecologically insignificant to free-living WCS. These birds are very adept at selecting diets that satisfy their amino acid requirements.

The influence of a high-protein, low-carbohydrate diet on bone development in the fetuses of rat dams with streptozotocin-induced diabetes

1. The purpose of the present study was to determine the effects of diet on the mandibles and growth centres of the long bones in the fetuses of diabetic rat dams given a normal diet compared with those given a high-protein, low-carbohydrate diet. 2. On the 9th day of gestation, the controls, groups 1 and 3, were injected with citrate buffer and given 200 and 600 g protein/kg diets respectively. Groups 2 and 4 were injected with 40 mg streptozotocin/kg body-weight and pair-fed with groups 1 and 3 respectively on the 200 and 600 g protein/kg diets. 3. On day 22, some dams were injected with either 45Ca or [14C]proline. Mandibles and long bones were removed and weighed and analysed for Ca content, 45Ca uptake, collagen and collagen synthesis. 4. The body-weights, and mandibular and long-bone weights of the fetuses in the diabetic 200 g protein/kg group were smaller than those of the non-diabetic 200 g protein/kg group, whereas those of the diabetic 600 g protein/kg group showed no difference from the non-diabetic 600 g protein/kg group. 5. The rate of collagen synthesis was higher in the fetuses of the diabetic 600 g protein/kg group than those of the non-diabetic group. Bones of the diabetic 200 g protein/kg group were lower in collagen content when compared with the non-diabetic group, whereas there was no difference between the diabetic and non-diabetic 600 g protein/kg groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of protein intake in the young rat

Both adult and weanling rats are able to control their dietary intake of protein. The purposes of the current study were to determine: the precision of this ability in the weanling rat and when this ability makes its ontogenic appearance. We studied three overlapping age groups spanning the third, fourth and fifth postnatal weeks. Animals chose between two isocaloric liquid diets, one protein-free and the other composed of 50% protein. The intake volume of each diet was measured daily. Three days after introduction to the diets, pups were subjected to short-term tests designed to determine their ability to distinguish between the two diets. All three age groups responded to the protein conditions. However, the youngest group displayed comparatively weaker responses characterized by a prolonged period of reduced protein intake and weaker responses to the protein conditions of the short-term test. We conclude that young rats control protein intake by the end of the third postnatal week and that this ability strengthens throughout the remainder of the weaning period.

Self-selection of dietary casein and soy-protein by the cat

Growing specific-pathogen-free kittens were fed for two weeks a choice between two complete diets differing only in protein content. When casein diets containing 18, 36 and 54% protein were offered in the three possible combinations, the kittens consistently avoided the higher casein diets and kittens offered the two highest levels of casein significantly reduced their total food intake. In one soy-protein choice study, 16, 31 and 63% protein diets were each offered with a protein-free (PF) diet. When diets were similar in physical consistency, kittens selected similar amounts of both diets with the result that the PF:16% group consumed below their requirement of protein. In another soy-protein experiment the 16, 31 and 63% protein diets were offered in their three possible combinations. Kittens in all three groups selected similar amounts of both diets. Except for their avoidance of casein, the kittens did not regulate in a consistent manner their intake of protein and therefore, behaved very differently from the rat in the self-selection of dietary protein.

Strategies of protein selection by weanling and adult rats

Weanling and adult male rats were offered pairs of diets containing either 0 and 20%, 0 and 40%, 0 and 60%, or 10 and 40% casein. Initially they preferred the lower protein diets, and then after one to ten days abruptly switched to adequate levels of protein choice. After 14 days, the diets were changed so that the first group received 10 and 40%, the second 20 and 60%, the third 10 and 40%, and the fourth 0 and 60% casein. Following the change, all weanling rats showed significant and systematic shifts in percentage of total energy chosen as protein (%P-E); most adults did not. Within each group, the variability in %P-E selected between different rats was higher than the day-to-day variability of individuals. In the adults no significant correlations were observed between protein selection and brain serotonin metabolism. We conclude that protein intake in rats is regulated in the sense that all animals learnt to eat sufficient protein to maintain growth, and most animals ate a constant amount of protein each day. On the other hand, the range of protein intake between individuals, and the shifts in selection among the weanlings when diet choices were changed seem to preclude the existence of a mechanism which precisely regulates protein intake.