The responses of rats to various combinations of energy and protein. I. Diets made from purified ingredients

Male and female weanling rats were fed ad libitum for 28 days on purified diets with metabolizable energy levels of 8.0, 9.5, 11.0 or 12.5 MJ/kg and protein:energy ratios of 1:1, 1.33:1, 1.67:1 or 2:1 %:MJ/kg at each energy level. Major nutrients were balanced in proportion to energy and protein. The following parameters were measured: food intake, bodyweight, body length, abdominal fat, liver and kidney weights. Increasing dietary energy level reduced food intake but the reduction was not sufficient to prevent an increase in energy intake. This was reflected by increases in bodyweight, body length, abdominal fat, and relative liver and kidney weights, especially in male rats. Higher energy intake increased weight gain and food conversion efficiency to a greater extent than higher protein intake. The response to protein intake at different energy levels was not consistent. There was no common protein:energy ratio for overall good performance. It is concluded that rat growth and other features can be controlled by the alteration of dietary energy and protein levels.     

The availability to the rat of energy from various diet ingredients

The digestible and metabolizable energy values of 8 ingredients commonly used in laboratory animal diets were determined using the growing male rat, by the total collection method. Each ingredient was incorporated into a basal diet of maize, wheat, soyabean meal and fishmeal. The metabolizable energy values, on a dry matter basis, corrected to the nitrogen retention of the basal diet for rats per 100 g bodyweight were as follows: maize 15.23 MJ/kg, extracted soyabean meal 14.11 MJ/kg, barley 12.31 MJ/kg, wheat 14.09 MJ/kg, oatfeed 1.36 MJ/kg, white fishmeal 11.61 MJ/kg, dried skimmed milk 14.32 MJ/kg, casein 17.91 MJ/kg. Additional analytical data for the 8 ingredients are also given.     

Sparrows and a brushpile: Foraging responses to different combinations of predation risk and energy cost

Our observations of wintering house sparrows (Passer domesticus) feeding on cracked corn at feeders placed at different distances from a brushpile and in positions differentially exposed to the wind supported the hypothesis that where food patches are equal in net energy return, foragers use the one furnishing the most protection from predation. Results reinforced the hypothesis that when food sources furnish equal protection from predators, homeotherms below their lower critical temperature use the one providing the largest net energy return. When the sparrows had available both a colder, safer feeding site and a warmer, riskier one, they frequented both over the course of the winter and, as predicted, their use of the colder, safer site was negatively correlated with wind velocity and positively related to temperature and solar radiation. In this last case, it appeared the birds decided where to feed on the basis of some threshold difference between metabolic rates at the colder, safer site and the warmer, riskier location.     

Urotensin II induces hypertrophic responses in cultured cardiomyocytes from neonatal rats.

Urotensin II (UII), a cyclic neuropeptide, functions not only in the central nervous system but also in non-neural systems including cardiovascular systems. In the present study we examined whether UII regulates hypertrophy in cardiomyocytes. The exposure of cultured cardiomyocytes from neonatal rats to UII dose-dependently activated extracellular signal-regulated kinases (ERKs), important molecules in the development of cardiac hypertrophy. ERK activation by UII at 100 nM peaked at 8 min after stimulation. UII markedly induced expression of specific genes encoding atrial natriuretic peptide and brain natriuretic peptide, and significantly increased amino acid incorporation into proteins. Incubation of cardiomyocytes with UII increased cell size and myofibril organisation. UII, then, might participate in cardiomyocyte hypertrophy.     

Establishment and characteristics of four sub-strains of F344 rats reared on various low protein and low energy diets.

Four sub-strains, reared by sib-mating and having for their origin the F344/DuCrj strain of rats, were established by feeding with different levels of low protein and low energy diets, and their characteristics investigated. The amounts of crude protein (CP) and digestible energy (DE) in the four diets were 17.6%-3.0 kcal, 10.5%-2.5 kcal, 8.4%-2.0 kcal, and 10.5%-2.5 kcal, respectively, and the four sub-strains established here were provisionally designated as F344/Tig1, F344/Tig2, F344/Tig3 and F344/Tig4, respectively. Intakes of nitrogen-corrected metabolizable energy (MEn) did not differ, and a large intake of digestible crude protein (DCP) was observed in F344/Tig1 rats. The body weight of rats provided with lower-nutrient diets showed a tendency to decrease until the F2 generation, but no change among the generations was seen subsequently, and the same compiled differences in protein content were maintained. Similar transitions were observed in the lifetime rearing test. Though F344/Tig3 rats, which were reared on minimum nutrients, showed a tendency to delayed puberty, we were easily able to breed four pairs in every generation using procedures similar to those used for other strains of rats. There were no differences among the F344/Tig1 to -3 strains of rats in body length, digestive tract length, or organ weight per body weight, and all the rats had a normal range of biochemical values. But the F344/Tig4 showed a high glutamic-oxaloacetic transaminase (GOT), and a tendency to decreased liver function and a shorter lifespan. These sub-strains of F344 rats clarified differences in fatty acid compositions, such as docosahexaenoic acid (DHA) in serum, liver and the brain. The rats were intended to be useful animal models for the study of nutritional environments and their influence on the memory and learning.     

Influence of added microbial enzymes on energy and protein availability of selected feed ingredients

Addition of enzymes to feed ingredients results in an improved energy availability that reduces the difference between gross and metabolisable energy of the raw material. The level of improvement seen is related to enzyme type and to dosage, and correlates well with the substrate specificity of the various enzymes present. Thus the values found in this study are specific for the enzymes and dosages used. Nitrogen retention is also improved by enzyme addition but this did not show a clear dosage response with all materials. An improved nitrogen retention cannot be directly correlated with protein digestibility but an improved retention of protein may offer the possibility to reduce protein levels in the diet.     

The non-nutritional performance characteristics of peptones made from rendered protein

Economic considerations require the use of inexpensive feedstocks for the fermentative production of moderate-value products. Our previous work has shown that peptones capable of supporting the growth of various microorganisms can be produced from inexpensive animal proteins, including meat and bone meal, feather meal, and blood meal, through alkaline or enzymatic hydrolysis. In this work, we explore how these experimental peptones compare to commercial peptones in terms of performance characteristics other than chemical make-up; these characteristics can impact fermentation operating cost. It is shown that experimental peptone powders produced through enzymatic hydrolysis are highly hygroscopic and that their physical form is not stable to humid storage conditions; those produced through alkaline hydrolysis and commercial peptones are less hygroscopic. When used in growth medium, all peptones contribute haze to the solution; experiments show that the source of haze is different when using enzyme- versus alkali-hydrolyzed peptones. Alkali-hydrolyzed peptones and all peptones made from blood meal are stronger promoters of media foaming than the commercial peptones; some enzyme-hydrolyzed peptones support very little foam formation and are superior to the commercial peptones in this sense. Alkali-hydrolyzed peptones are roughly equivalent to commercial peptones in the coloration they contribute to media, while enzyme-hydrolyzed peptones contribute intense coloration to media. No peptone caused a significant change in the viscosity of media. The experimental peptones studied here may be acceptable low-cost substitutes for commercial peptones, but none is equivalent to the commercial products in all respects.     

Rates of protein synthesis by hepatocytes isolated from rats of various ages

The rate of total protein synthesis in isolated hepatocytes was determined. The incorporation of L-[³H]valine into protein is linear for at least two hours of incubation and is affected by the concentration of amino acids in the medium. Uptake of valine by hepatocytes from 1.5- and 18-month-old rats was identical and appears to occur by simple passive diffusion. Within five minutes, the specific activities of the intracellular and extracellular valine pools are equivalent. The specific activities of these pools are saturated by 1.6 mM valine and remain constant for 60 minutes of incubation. The rates of protein synthesis by hepatocytes from 1- to 2-month-old rats is 96.8 pmoles of valine per minute per milligram protein. This is comparable to rates of protein synthesis reported for perfused liver and liver in vivo and is approximately 64% higher than the rate of protein synthesis by hepatocytes from 18-month-old rats.     

Human responses to propionic acid. II. Quantification of breathing responses and their relationship to perception

In 20 normal and four anosmic participants, instantaneous inhalation and exhalation flow rates were recorded in response to 15 s stimulations with clean air or propionic acid concentrations (0.16, 1.14, 8.22 and 59.15 p.p.m., v/v) that ranged from peri-threshold for normals to clearly supra-threshold for anosmics. Each odorant/irritant delivery to the face-mask began with an exhalation. This allowed concentration to reach full value before stimulus onset, defined as the point where the participant began to bring the stimulus into the nose by inhalation. Two seconds after this stimulus onset, normals exhibited cumulative inhaled volume (CIV) declines of 39 and 14%, and latencies of 500 and 710 ms, with presentations of 59.15 and 8.22 p.p.m., respectively. With anosmics, 59.15 p.p.m. caused a 19% decline in CIV that began at 730 ms. Examination of the first inhalation after stimulus onset shows that the CIV declines in normals were achieved by a progressive decline in volume (InVol), beginning with a slight drop at 1.14 p.p.m., and a marked decline in duration (InDur) with only the highest concentration. Anosmics exhibited declines in InDur and InVol with only the 59.15 p.p.m. stimulus, and these declines were much more modest than the changes seen in normals. Comparison of these breathing results with perceptual responses from this same experiment demonstrates that: (i) in normals, odor perception rises slightly, but breathing does not change, with the lowest concentration; (ii) the higher breathing sensitivity (declines in InVol) of normals is paralleled by both the higher nasal irritation of these individuals and the presence of odor sensation; (iii) InDur declines in normals only with a stimulus concentration sufficient to cause marked nasal irritation in anosmics; and iv) in anosmics, modest but reliable declines in both InDur and InVol mirror the marked elevation in nasal irritation magnitude seen with only the highest concentration. In view of the failure of prior work to provide evidence that olfactory activation alone can cause any of the breathing changes we observed, we conclude that some breathing parameters are quite useful as rapid and sensitive measures of nasal irritation that arises from activation of nasal trigeminal afferents alone or in combination with the olfactory nerve.     

Sexual behaviour of female rats subjected to early protein energy malnutrition

Young rats (left with the mother until weaned) were exposed from birth to the age of 49 days to a low protein (malnutritional) diet. At 80 days the young females were ovariectomized and were subjected to standard long-term treatment with oestradiol and progesterone. The females' sexual behaviour was studied in interaction tests with an intact male. It was evaluated according to a scale of sexual responsiveness comprising copulatory (a lordosis posture) and precopulatory (a presenting posture, hopping, ritualized darting) patterns. All the experimental females displayed a high copulatory readiness and precopulatory behaviour; a tendency to lower sexual responsiveness, interpreted as diminished sensitivity to the given doses of the hormones, was manifested only after their repeated administration. Compared with the control females, the number of experimental animals in which the given doses of the hormones induced complete precopulatory behaviour--ritualized darting--was smaller. The results contrast with findings on the sexual behaviour of males subjected to malnutrition from an early age.