Peak bone strength is influenced by calcium intake in growing rats.

In this study we investigated the effect of supplementing the diet of the growing male rat with different levels of calcium (from low to higher than recommended intakes at constant Ca/P ratio), on multiple factors (bone mass, strength, size, geometry, material properties, turnover) influencing bone strength during the bone accrual period. Rats, age 28days were supplemented for 4weeks with high Ca (1.2%), adequate Ca (0.5%) or low Ca level (0.2%). Bone metabolism and structural parameters were measured. No changes in body weight or food intake were observed among the groups. As anticipated, compared to the adequate Ca intake, low-Ca intake had a detrimental impact on bone growth (33.63 vs. 33.68mm), bone strength (-19.7% for failure load), bone architecture (-58% for BV/TV) and peak bone mass accrual (-29% for BMD) due to the hormonal disruption implied in Ca metabolism. In contrast, novel, surprising results were observed in that higher than adequate Ca intake resulted in improved peak bone strength (106 vs. 184N/mm for the stiffness and 61 vs. 89N for the failure load) and bone material properties (467 vs. 514mPa for tissue hardness) but these effects were not accompanied by changes in bone mass, size, microarchitecture or bone turnover. Hormonal factors, IGF-I and bone modeling were also evaluated. Compared to the adequate level of Ca, IGF-I level was significantly lower in the low-Ca intake group and significantly higher in the high-Ca intake group. No detrimental effects of high Ca were observed on bone modeling (assessed by histomorphometry and bone markers), at least in this short-term intervention. In conclusion, the decrease in failure load in the low calcium group can be explained by the change in bone geometry and bone mass parameters. Thus, improvements in mechanical properties can be explained by the improved quality of intrinsic bone tissue as shown by nanoindentation. These results suggest that supplemental Ca may be beneficial for the attainment of peak bone strength and that multiple factors linked to bone mass and strength should be taken into account when setting dietary levels of adequate mineral intake to support optimal peak bone mass acquisition.

Free and protein-bound glutamine have identical splanchnic extraction in healthy human volunteers.

The objectives of the present study were to determine the splanchnic extraction of glutamine after ingestion of glutamine-rich protein ((15)N-labeled oat proteins) and to compare it with that of free glutamine and to determine de novo glutamine synthesis before and after glutamine consumption. Eight healthy adults were infused intravenously in the postabsorptive state with L-[1-(13)C]glutamine (3 micromol x kg(-1) x h(-1)) and L-[1-(13)C]lysine (1.5 micromol x kg(-1) x h(-1)) for 8 h. Four hours after the beginning of the infusion, subjects consumed (every 20 min) a liquid formula providing either 2.5 g of protein from (15)N-labeled oat proteins or a mixture of free amino acids that mimicked the oat-amino acid profile and contained L-[2,5-(15)N(2)]glutamine and L-[2-(15)N]lysine. Splanchnic extraction of glutamine reached 62.5 +/- 5.0% and 66.7 +/- 3.9% after administration of (15)N-labeled oat proteins and the mixture of free amino acids, respectively. Lysine splanchnic extraction was also not different (40.9 +/- 11.9% and 34.9 +/- 10.6% for (15)N-labeled oat proteins and free amino acids, respectively). The main conclusion of the present study is that glutamine is equally bioavailable when given enterally as a free amino acid and when protein bound. Therefore, and taking into consideration the drawbacks of free glutamine supplementation of ready-to-use formulas for enteral nutrition, protein sources naturally rich in this amino acid are the best option for providing stable glutamine.

Effect of glutamine supplementation of the diet on tissue protein synthesis rate of glucocorticoid-treated rats.

Although glutamine status in the critically ill patient can be improved by nutritional means, the most effective way of effecting such supplementation has received little attention. We evaluated two different ways of supplementing clinical nutrition products with glutamine, either with free glutamine or by providing a glutamine-rich protein source, in acute glucocorticoid-treated (intraperitoneal dexamethasone, 120 mg/kg) rats. During the recovery period, the animals received isonitrogenous and isoenergetic diets containing either casein, mixed whey proteins with or without glutamine, or carob protein plus essential amino acids. Plasma and tissue amino acids and glutathione as well as tissue protein synthesis were measured. Dexamethasone treatment lowered weight gain, muscle glutamine, and muscle and jejunal protein synthetic rate. Muscle protein synthesis was increased (from 15.9% to 24.2%/d) only when glutamine was included in the diet as a free amino acid. This increase paralleled a rise in plasma glutamine. We speculate that glutamine provided in dietary protein is extensively metabolized by the splanchnic tissues and does not influence peripheral glutamine status to the same extent as glutamine provided in a free amino acid form. However, both forms of glutamine supplementation were equally effective in increasing protein synthesis in the jejunum (by 25%). This is likely the main benefit of glutamine supplementation of enteral nutrition formulas.

Neither glutamine nor arginine supplementation of diets increase glutamine body stores in healthy growing rats.

The aim of the work was to resolve whether glutamine and arginine supplemented diets affect plasma and tissue (muscle, liver and intestinal mucosa) glutamine concentrations, as well as glutaminase and glutamine synthetase specific activities. The trial was performed in growing rats fed 10% protein diets for 3 weeks. Protein sources were: whey proteins (W); whey proteins+free glutamine (WG); whey proteins+arginine (WA); and casein+wheat protein hydrolysate+acid whey (39:39:22), as source containing protein-bound glutamine (CGW). Rats fed the control diet (6.4% glutamine) (W) showed comparable glutamine body stores to those of rats fed the WG diet. In fact, glutamine sup- plementation down-regulated the hepatic glutamine synthetic capacity of growing rats (W/WG: 6.8+/-0.3 vs 6.0+/-0.2 nmol/min/mg protein). Arginine supplementation of the diet (up to 9% of the protein content) resulted in a decrease in plasma and tissue glutamine concentrations (W/WA: plasma, 1218+/-51 vs 1031+/-48 micromol/L; liver 7.5+/-0.4 vs 6.5+/-0.2 micromol/g; muscle: 5.7+/-0.2 vs 4.0+/-0.2 micromol/g). These data suggest that glutamine supplementation of the diet does not increase plasma and tissue glutamine concentrations in healthy growing rats, while the addition of arginine to the diet decreases glutamine body stores.

Protein hydrolysate vs free amino acid-based diets on the nutritional recovery of the starved rat.

BACKGROUND AND AIMS: To test the hypothesis that a peptide-based enteral product was equivalent to a low-fat, free amino acid-based formula in the nutritional and functional recovery of the starved rat. METHODS: Sixteen male Wistar rats were starved for 3 days. Then, rats were randomised to a whey protein hydrolysate-based diet or a free amino acid-based diet and refed for 3 days. The experiment was designed to provide the same energy intake in both groups. The parameters studied included body weight gain, nitrogen retention, plasma free amino acid concentrations, muscle glutamine concentrations and glutathione levels in gut mucosa and liver. RESULTS: Weight gain was statistically higher on the peptide-based diet than on the elemental diet after the refeeding period. This difference in weight gain was associated with a statistically higher nitrogen retention. Plasma and muscle free glutamine concentrations were higher in rats fed the whey protein hydrolysate-based diet than those in rats refed the free amino acid-based diet, even though the glutamine intake was higher in the latter group. Glutathione concentrations in liver and gut mucosa were similar in the groups. CONCLUSION: We conclude that enteral diets containing peptides were more effective than a diet containing free amino acids in the nutritional recovery of the starved rat.

Food deprivation and refeeding influence growth, nutrient retention and functional recovery of rats.

The objective of this work was to determine the effects of starvation and refeeding on growth, nutritional recovery and intestinal repair in starved rats. Male Wistar rats, weighing 200 g, were starved for 3 d, then refed a soy-based diet for another 3 d. Normally fed rats were given the same diet and used as controls. The variables assessed were as follows: body weight gain and nitrogen retention during recovery after starvation; muscle glutamine concentration; tissue protein content; gut mucosa and liver glutathione levels; intestinal permeability to ovalbumin, lactulose and mannitol; and intestinal tissue apoptosis. Starvation was associated with lower muscle glutamine levels and intestinal mucosa impairment, including a lower content of mucosal protein, a higher level of oxidized glutathione, enhanced permeability to macromolecules and greater numbers of apoptotic cells. Refeeding for 3 d resulted in rapid repair of gut atrophy and normalization of not only intestinal permeability but also of the majority of metabolic markers assessed in other tissues. In conclusion, with the use of severely starved rats, we have established a reversible experimental animal model of malnutrition that might prove useful in comparing the effectiveness of different enteral diets.

Fecal bile acid excretion and taurine status in cats fed canned and dry diets.

Cats conjugate their bile acids with taurine but are unable to synthesize sufficient quantities of this amino acid to meet their needs. To maintain the same blood taurine level, canned foods must contain more taurine than dry foods. In the present study we examined the effect of soluble fiber on fecal bile acid excretion and taurine status and compared the quantity and profile of fecal bile acids in cats fed canned and dry diets. In a cross-over design, 10 adult cats were fed a typical canned diet containing 0.25% kappa carrageenan with or without the addition of 0.5% guar gum (2.5% on a dry matter basis) for 6 wk. All cats were then transferred to a dry diet. The addition of guar gum to the canned diet had no significant effect on taurine status, but the dry diet, which contained less taurine than the canned diet, resulted in an increase in plasma taurine. With the dry diet, total bile acid excretion was reduced by approximately 65%. The profile of bile acids in feces was also radically different with a marked decrease in secondary bile acids. This work suggests that when canned rather than dry diets are fed, the conversion of primary to secondary bile acids is greater and is indicative of an alteration in the activity of the gut flora that may lead to an increase in taurine degradation.

The effect of Maillard reaction products on zinc metabolism in the rat.

The effect of giving Maillard reaction products (MRP) on zinc metabolism was investigated in the rat. In Expt 1, MRP were prepared by incubating casein with either glucose or lactose under controlled reaction conditions, and were quantified as either 'early' or 'advanced' after estimation of lysine loss and lysine destruction respectively. In Expt 2, the effect of the purified early MRP fructose--lysine (FL) on Zn metabolism was studied. The experimental diets containing 20 mg Zn/kg were given to weanling rats for 21 d. Zn balance was assessed over 9-14 d (Expt 1), or 1-14 d (Expt 2). Femur, liver, kidney and serum Zn concentrations were determined at 21 d. The major effect of the MRP in the casein-sugar mixtures was on urinary Zn excretion. The casein-glucose MRP induced up to a 6-fold increase in the quantity of Zn excreted in the urine. The magnitude of the hyperzincuria increased with the extent of the Maillard reaction. Similar dietary levels of casein-lactose MRP increased urinary Zn loss 2-fold. Free FL had no effect on urinary Zn. Faecal Zn, Zn retention, liver, femur and serum Zn were generally not influenced by giving MRP from casein-sugar mixtures or by giving free FL, although kidney Zn was decreased in rats fed on FL. It was concluded that although urinary Zn excretion can be increased by the presence of MRP in the diet, this is only a minor excretory pathway and would have little influence on overall Zn nutrition in individuals fed on a diet adequate in Zn.