Postprandial intestinal and whole body nitrogen kinetics and distribution in piglets fed a single meal

Our aim was to characterize the postprandial total and dietary N fluxes in the portal drained viscera (PDV) and whole body after administration of a single meal in young pigs. Seven 4-wk-old piglets, implanted with a portal flow probe and portal, arterial and venous catheters, received a primed constant [(18)O]urea intravenous infusion and were studied for 8 h after a bolus mixed meal ingestion (46 mmol N/kg body wt) intrinsically labeled with (15)N to trace dietary N fluxes. The real cecal digestibility of the formula was 94.3% (SD 1.8). PDV output of dietary N was found principally in the pool of circulating protein (51% of the measured dietary N PDV output), in the free alpha-amino N pool (44%), and to a lesser extent in ammonia (5%). Dietary N release in alpha-amino N and ammonia mainly occurred during the first 3 h. Total and exogenous postprandial urea productions were 5.8 and 2.0 mmol N/kg body wt, respectively. At the end of the postprandial period, losses of dietary N amounted to 10.3% of the dose: 5.7% through ileal losses and 4.6% by deamination and transfer to urea. Net postprandial retention of dietary N was 90.4% (SD 1.3), of which 20% was found in splanchnic zone (small intestine 10%, liver 5%, and plasma protein 3%) and 42% in peripheral zone (muscle 31%, skin 6%). In conclusion, our results show a high efficiency of dietary N utilization for muscular uptake and anabolic utilization. However, the results obtained point out the necessity to further explore the form of dietary N released into the portal blood.     

Cysteine fluxes across the portal-drained viscera of enterally fed minipigs: effect of an acute intestinal inflammation

Cysteine is considered as a conditionally indispensable amino acid. Its dietary supply should thus be increased when endogenous synthesis cannot meet metabolic need, such as during inflammatory diseases. However, studies in animal models suggest a high first-pass extraction of dietary cysteine by the intestine, limiting the interest for an oral supplementation. We investigated here unidirectional fluxes of cysteine across the portal-drained viscera (PDV) of multi-catheterized minipigs, using simultaneous intragastric l-[¹⁵N] cysteine and intravenous l-[3,3D2] cysteine continuous infusions. We showed that in minipigs fed with an elemental enteral solution, cysteine first-pass extraction by the intestine is about 60% of the dietary supply, and that the PDV does not capture arterial cysteine. Beside dietary cysteine, the PDV release non-dietary cysteine (20% of the total cysteine release), which originates either from tissue metabolism or from reabsorption of endogenous secretion, such as glutathione (GSH) biliary excretion. Experimental ileitis induced by local administration of trinitrobenzene sulfonic acid, increased liver and ileal GSH fractional synthesis rate during the acute phase of inflammation, and increased whole body flux of cysteine. However, cysteine uptake and release by the PDV were not affected by ileitis, suggesting an adaptation of the intestinal sulfur amino acid metabolism in order to cover the additional requirement of cysteine linked to the increased GSH synthesis. We conclude that the small intestine sequesters large amounts of dietary cysteine during absorption, limiting its release into the bloodstream, and that the other tissues of the PDV (colon, stomach, pancreas, spleen) preferentially use circulating methionine or cysteine-containing peptides to cover their cysteine requirement.     

Contribution of erythrocytes and plasma in threonine and lysine transfer across the portal drained viscera and the liver in pigs. Effect of threonine and lysine dietary supply

Contributions of erythrocytes and plasma to threonine and lysine transport across the PDV and the liver were determined in growing pigs successively fed a threonine deficient diet and a control well-balanced diet (experiment 1) or a lysine deficient or a well-balanced diet (experiment 2). The animals were surgically prepared for insertion of chronic catheters in the mesenteric vein (MV), the portal vein (PV), a hepatic vein (HV) and the carotid artery (CA). Plasma and whole blood AA concentrations in PV, HV and CA and PV and HV blood flows were determined during 6 hours of para-aminohippuric acid constant infusion. During this period the pigs were continuously fed (1 meal per hour). The contribution of plasma to lysine and threonine transport was higher in pigs fed the well balanced diets. More than 50% of threonine and lysine appearing in the PV and in the HV are transported by the plasma. Our results suggest that erythrocytes are probably little involved in lysine and threonine transfer across the liver and digestive tract of pig continuously fed.     

异育银鲫幼鱼对饲料中赖氨酸的利用及需要量研究

以添加晶体氨基酸的半精制饲料饲喂异育银鲫幼鱼,通过69d的生长实验来确定其赖氨酸需要量。饲料以白鱼粉为主要蛋白源,饲料中的总赖氨酸含量分别为1.82%、2.32%、2.82%、3.32%3、.82%、4.32%和4.82%7个水平。实验在室内循环水养殖系统中进行,每种饲料随机3个重复。实验结果表明,异育银鲫能够利用饲料中的晶体赖氨酸、蛋氨酸。在投喂后3h,其血浆中的游离赖氨酸、蛋氨酸含量最高。当饲料中赖氨酸含量为3.32%时,异育银鲫的终末尾均重、特定生长率和鱼空壳占体重的百分比最高,肝体指数最低。当饲料中赖氨酸含量为3.82%时,异育银鲫的干物质表观消化率显著高于其他组(PPP>0.05)。血红蛋白含量以赖氨酸含量为2.82%的饲料组最高,4.82%组最低;随着饲料中赖氨酸含量的升高,异育银鲫红细胞数下降,血清脲氮含量升高,且血清脲氮含量具有组间显著性差异(P<0.05)。根据折线法,由异育银鲫的特定生长率同饲料中赖氨酸水平的相关性得出其赖氨酸需要量为3.27%,占饲料蛋白的8.52%。       

Dietary starch sources affect net portal appearance of amino acids and glucose in growing pigs

Four male pigs (Duroc × Landrace × Yorkshire; average initial (mean ± SEM) BW = 22.5 ± 1.1 kg), fitted with permanent catheters in the portal vein, ileal vein and carotid artery, were used in a 4 × 4 Latin square experimental design to measure the effect of dietary starch sources on the net portal appearance of glucose and amino acids. Dietary starch sources were resistant starch (RS), maize, sticky rice and brown rice. Diets were provided at 0730, 1530 and 2330 h during a 6-day adjustment period and 1-day collection period. On day 7 of each period, blood samples were collected from the portal vein and carotid artery at 0730 h (prior to feeding) and hourly up to 8 h after meal. Blood samples were used to determine glucose, amino acid, packed cell volume and partial pressure of oxygen (pO2). When calculated per 100 g feed intake, cumulative portal glucose appearance was lower (P < 0.05) for resistant starch than for maize, sticky rice or brown rice up to 8 h after the meal. Cumulative portal glucose appearance was higher (P < 0.05) for sticky rice and brown rice than for other diets until 4 h after the meal, but maize had higher cumulative glucose appearance after 4 h. Net cumulative portal concentrations of most amino acids for resistant starch were also reduced (P < 0.05) than for the other starch sources. Cumulative portal appearance of amino acid represented 48.39%, 63.76%, 61.80% and 59.18% of dietary intake for resistant starch, maize, sticky rice and brown rice, respectively. Collectively, our results indicate that dietary starch sources substantially affect the appearance of amino acids and glucose in the portal circulation.     

Metabolic and hormonal effects of test meals with various protein contents in pigs

The postprandial release of immunoreactive insulin, glucagon, gastrin, somatostatin, pancreatic polypeptide (PP), and gastric inhibitory polypeptide (GIP) was studied in parallel with the absorption of sugars and amino acids in conscious pigs. Six pigs fitted with permanent catheters in the portal vein and arterial blood system as well as within an electromagnetic flow probe around the portal vein received successively at 3-day intervals, three meals of 800 g each containing 0, 14, or 28% protein (semisynthetic diets based on fish protein). Blood samples were collected and portal blood flow was recorded during a postprandial period of 8 h. For the same level of feed intake, an increase in the dietary protein concentration led to a higher alpha-amino nitrogen absorption and to a lower appearance of reducing sugars in the portal vein; in addition, the carbohydrate absorption efficiency (amounts absorbed as a percentage of amounts ingested) was reduced, showing the competition between the absorption of amino acids and glucose. The largest absorption occurred during the first 4 h after the meal, but neither the digestion of proteins nor that of carbohydrates were finished 8 h after the meal since portoarterial differences could still be observed. All test meals induced a rise of portal and peripheral concentrations of insulin, gastrin, somatostatin, and PP, and of the systemic level of GIP. Glucagon increased after the 28% protein meal only. The rise of plasma insulin paralleled that of blood glucose, and bore a significant positive relationship to the systemic GIP level in the early postprandial period. In terms of absolute amounts, portoarterial concentration gradients increased postprandially. Insulin release was significantly the highest after intake of the 14% protein diet. The gastrin response was significantly correlated to the amount of protein. Similarly the release of glucagon and somatostatin tended to increase with increasing dietary amount, but differences failed to reach significance (P less than 0.05), except for glucagon 2 h after the meal. There were very close relationships between the hourly amounts of alpha-amino nitrogen absorbed and gastrin and glucagon production, as between insulin and PP secretions. From the present results, the induction of physiological increments of plasma peptide concentration in 60-kg pigs would require infusion rates of about 50-250 micrograms/h for insulin, 1-4 micrograms/h for gastrin 17, 5-10 micrograms/h for glucagon and somatostatin, and 5-50 micrograms/h for PP.     

Somatotropin-induced protein anabolism in hindquarters and portal-drained viscera of growing pigs

To differentiate the effect of somatotropin (ST) treatment on protein metabolism in the hindquarter (HQ) and portal-drained viscera (PDV), growing swine (n = 20) treated with ST (0 or 150 microg x kg(-1) x day(-1)) for 7 days were infused intravenously with NaH(13)CO(3) and [(2)H(5)]phenylalanine and enterally with [1-(13)C]phenylalanine while in the fed state. Arterial, portal venous, and vena cava whole blood samples, breath samples, and blood flow measurements were obtained for determination of tissue and whole body phenylalanine kinetics under steady-state conditions. In the fed state, ST treatment decreased whole body phenylalanine flux, oxidation, and protein degradation without altering protein synthesis, resulting in an improvement in whole body net protein balance. Blood flow to the HQ (+80%), but not to the PDV, was increased with ST treatment. In the HQ and PDV, ST increased phenylalanine uptake (+44 and +23%, respectively) and protein synthesis (+43 and +41%, respectively), with no effect on protein degradation. In ST-treated and control pigs, phenylalanine was oxidized in the PDV (34-43% of enteral and arterial sources) but not the HQ. In both treatment groups, dietary (40%) rather than arterial (10%) extraction of phenylalanine predominated in gut amino acid metabolism, whereas localized blood flow influenced HQ amino acid metabolism. The results indicate that ST increases protein anabolism in young, growing swine by increasing protein synthesis in the HQ and PDV, with no effect on protein degradation. Differing results between the whole body and the HQ and PDV suggest that the effect of ST treatment on protein metabolism is tissue specific.     

Amino acid metabolism in the portal-drained viscera of young pigs: effects of dietary supplementation with chitosan and pea hull

Recent studies indicate extensive catabolism of amino acids (AA) by the portal-drained viscera (PDV) of pigs and humans. Because of ethical concerns over invasive surgical procedures on infants or adults, in vivo investigations are often performed with the pig which is both an agriculturally important livestock species and a widely used animal model for nutritional and physiological studies in humans. Here, we described a new technique for implanting chronic catheters into the portal vein, ileal mesenteric vein, and carotid artery to study AA metabolism in the PDV of young pigs. This method allowed for the reduction of surgery time by 1 h and measurements of the entry of dietary AA into the portal circulation. Using such an approach, we found that dietary supplementation with 100 mg/kg chitosan (a prebiotic and a polysaccharide not digested by animal cells) reduced oxygen consumption, as well as the net absorption of dietary AA into the portal vein, thereby enhancing their bioavailability for extraintestinal tissues. In contrast, opposite results were obtained with dietary supplementation of 12% pea-hull (containing 95% of fermentable nonstarch polysaccharide). Thus, this improved technique is useful to quantify in vivo absorption and metabolism of dietary AA in young pigs.     

Anabolic signaling and protein deposition are enhanced by intermittent compared with continuous feeding in skeletal muscle of neonates

Orogastric tube feeding is indicated for neonates with impaired ability to ingest and can be administered by intermittent bolus or continuous schedule. Our aim was to determine whether feeding modalities affect muscle protein deposition and to identify mechanisms involved. Neonatal pigs were overnight fasted (FAS) or fed the same amount of food continuously (CON) or intermittently (INT; 7 × 4 h meals) for 29 h. For 8 h, between hours 20 and 28, pigs were infused with [(2)H(5)]phenylalanine and [(2)H(2)]tyrosine, and amino acid (AA) net balances were measured across the hindquarters. Insulin, branched-chain AA, phenylalanine, and tyrosine arterial concentrations and whole body phenylalanine and tyrosine fluxes were greater for INT after the meal than for CON or FAS. The activation of signaling proteins leading to initiation of mRNA translation, including eukaryotic initiation factor (eIF)4E·eIF4G complex formation in muscle, was enhanced by INT compared with CON feeding or FAS. Signaling proteins of protein degradation were not affected by feeding modalities except for microtubule-associated protein light chain 3-II, which was highest in the FAS. Across the hindquarters, AA net removal increased for INT but not for CON or FAS, with protein deposition greater for INT. This was because protein synthesis increased following feeding for INT but remained unchanged for CON and FAS, whereas there was no change in protein degradation across any dietary treatment. These results suggest that muscle protein accretion in neonates is enhanced with intermittent bolus to a greater extent than continuous feeding, mainly by increased protein synthesis.     

许氏平鲉幼鱼的赖氨酸需求量

通过8周的生长实验确定了许氏平(Sebastes schlegeli)幼鱼的赖氨酸需求量。饲料必需氨基酸组成(除赖氨酸外)参照鱼体肌肉蛋白的氨基酸模式,配制赖氨酸含量为1.542、.04、2.54、3.04、3.54和4.04%的等氮等能的六种半精制饲料。研究结果表明,随着饲料中赖氨酸含量的增加,增重率逐渐提高,当饲料中赖氨酸含量为3.54%时,达到最大值(P0.05)。基础饲料组的蛋白质贮积率最低,且显著低于3.54%组(P0.05),和其他组之间差异不显著(P0.05)。随着饲料中赖氨酸含量的增加,饲料系数逐渐降低,当饲料中赖氨酸含量为3.54%时达最小值,随着饲料中赖氨酸含量继续增加饲料系数呈上升趋势(P0.05)。饲料中赖氨酸水平对鱼体的干物质、蛋白质、脂肪、灰分和能量含量均无显著影响(P0.05)。饲料中赖氨酸水平对血清谷丙转氨酶(ALT)、谷草转氨酶(AST)活性有显著性影响(P0.05),而对血清甘油三酯及胆固醇含量没有显著性影响(P0.05)。通过回归分析,得出许氏平幼鱼最大生长的饲料赖氨酸需求量2.99%,占饲料蛋白的6.16%。       

Glucagon-like peptide-2 (GLP-2) increases net amino acid utilization by the portal-drained viscera of ruminating calves

Glucagon-like peptide-2 (GLP-2) increases small intestinal mass and blood flow in ruminant calves, but its impact on nutrient metabolism across the portal-drained viscera (PDV) and liver is unknown. Eight Holstein calves with catheters in the carotid artery, mesenteric vein, portal vein and hepatic vein were paired by age and randomly assigned to control (0.5% bovine serum albumin in saline; n = 4) or GLP-2 (100 μg/kg BW per day bovine GLP-2 in bovine serum albumin; n = 4). Treatments were administered subcutaneously every 12 h for 10 days. Blood flow was measured on days 0 and 10 and included 3 periods: baseline (saline infusion), treatment (infusion of bovine serum albumin or 3.76 μg/kg BW per h GLP-2) and recovery (saline infusion). Arterial concentrations and net PDV, hepatic and total splanchnic fluxes of glucose, lactate, glutamate, glutamine, β-hydroxybutyrate and urea-N were measured on days 0 and 10. Arterial concentrations and net fluxes of all amino acids and glucose metabolism using continuous intravenous infusion of [U¹³-C]glucose were measured on day 10 only. A 1-h infusion of GLP-2 increased blood flow in the portal and hepatic veins when administered to calves not previously exposed to exogenous GLP-2, but after a 10-day administration of GLP-2 the blood flow response to the 1-h GLP-2 infusion was substantially attenuated. The 1-h GLP-2 infusion also did not appreciably alter nutrient fluxes on either day 0 or 10. In contrast, long-term GLP-2 administration reduced arterial concentrations and net PDV flux of many essential and non-essential amino acids. Despite the significant alterations in amino acid metabolism, glucose irreversible loss and utilization by PDV and non-PDV tissues were not affected by GLP-2. Fluxes of amino acids across the PDV were generally reduced by GLP-2, potentially by increased small intestinal epithelial growth and thus energy and amino acid requirements of this tissue. Increased PDV extraction of glutamine and alterations in PDV metabolism of arginine, ornithine and citrulline support the concept that GLP-2 influences intestine-specific amino acid metabolism. Alterations in amino acid metabolism but unchanged glucose metabolism suggests that the growth effects induced by GLP-2 in ruminants increase reliance on amino acids preferentially over glucose. Thus, GLP-2 increases PDV utilization of amino acids, but not glucose, concurrent with stimulated growth of the small intestinal epithelium in post-absorptive ruminant calves.     

Effects of supplemental methionine and lysine on the nutritional value of housefly larvae meal (Musca domestica) fed to rats

The performance and blood composition of rats fed housefly larvae meal supplemented with, or without, methionine and lysine, or fed at high concentration were investigated. Rats fed supplemental methionine alone achieved highest body weight gain (P < 0.05). Dietary supplementation of both methionine and lysine or high dietary concentration of larvae meal depressed (P < 0.05) rat feed intake. The blood composition of rats was superior (P < 0.05) on methionine-supplemented larvae meal. Additional amino acids from larvae elicited higher (P < 0.05) serum proteins, cholesterol and triglyceride; however, other blood biochemical profiles were lower (P < 0.05) than in the unsupplemented group. In conclusion, housefly larvae meal seemed deficient in methionine and it benefited the rat tremendously to supplement with this amino acid: however, additional lysine and high dietary inclusion of larvae meal as sole protein source appeared nutritionally inconsequential.     

Differences in portal flow rates of amino acids and liver composition between rats fed casein or lactalbumin

The portal appearance rates and net rates of amino acids' absorption were studied in rats fed semi-synthetic diets containing either casein or lactalbumin (CAS and LA, respectively) as the only protein sources. Rats were pre-adapted to the experimental diets for 5 days prior to the absorption studies. Rats fed the LA diet had higher (p < 0.05) portal vein concentrations of free essential amino acids than those fed the CAS diet at 0, 60, 105 and 150 min after feeding. Portal and arterial concentrations of arginine, leucine, tryptophan, lysine and methionine were higher (p < 0.05) in rats fed LA at most time points tested, while concentrations of tyrosine were higher (p < 0.05) in CAS fed rats. When portal flow rates were compared, values for arginine, threonine, alanine, leucine, tryptophan and lysine were higher (p < 0.05) in LA at most time points tested, while proline, tyrosine and valine were higher (p < 0.05) for CAS fed rats after 60 and 105 min feeding. Portal blood flow varied (p < 0.05) with time in rats fed protein-free or LA diets, and was higher (p < 0.05) than that of CAS at 105 min. Intestinal net rates of absorption of tyrosine, valine, leucine and lysine were higher (p < 0.05) for LA fed rats as compared to those fed CAS at most time points tested, while alanine and proline net rates were higher (p < 0.05) for CAS fed rats at 60, 105 and 150 min. Amounts of protein in stomach contents of rats fed the CAS diet were significantly higher (p < 0.05) than those in LA fed rats at 60, 105 and 150 min after feeding. The relative liver weight of the rats fed the CAS diet was lower (p < 0.05) than that of animals fed the LA diet. Lower (p < 0.05) liver glycogen and lipid contents were determined in rats fed CAS diet respect to LA or protein-free fed rats. Results indicate that dietary and plasma amino acids profile are only partially related, and that under normal feeding conditions amino acids from CAS and LA are absorbed at different rates, which is likely to affect liver composition and metabolism.     

Prandial lactate infusion inhibits spontaneous feeding in rats

To investigate the acute effects of lactate on spontaneous feeding, we infused lactate in the hepatic portal vein (0.5, 1.0, and 1.5 mmol lactate/meal) or in the vena cava (1.0 and 1.5 mmol lactate/meal) of ad libitum-fed rats during their first spontaneous nocturnal meal. Infusions (5 min, 0.1 ml/min) were remotely controlled, and a computerized feeding system recorded meal patterns. In separate crossover tests, meal size decreased independent of the infusion route after 1.0 and 1.5 mmol but not after 0.5 mmol lactate. The subsequent intermeal interval (IMI) tended to decrease only after vena cava infusion of 1.0 mmol lactate. The size of the second nocturnal meal increased after the 1.0 mmol lactate infusion. Hepatic portal infusion of 1.5 mmol lactate increased the satiety ratio [subsequent IMI (min)/meal size (g)] by 175%, which was higher than the insignificant 43% increase after vena cava infusion. Hepatic portal infusion of 1.5 mmol lactate also increased systemic plasma lactate but not glucose concentration at 1 min after the end of infusion. The results are consistent with the idea that meal-induced increases in circulating lactate play a role in the control of meal size (satiation). Moreover, the results suggest that lactate also contributes to postprandial satiety and that the liver is involved in this effect. The exact mechanisms of lactate's inhibitory effects on feeding and the site(s) where lactate acts to terminate meals remain to be identified.     

Transition from parenteral to enteral nutrition induces immediate diet-dependent gut histological and immunological responses in preterm neonates

Necrotizing enterocolitis (NEC) in preterm infants develops very rapidly from a mild intolerance to enteral feeding into intestinal mucosal hemorrhage, inflammation, and necrosis. We hypothesized that immediate feeding-induced gut responses precede later clinical NEC symptoms in preterm pigs. Fifty-six preterm pigs were fed total parenteral nutrition (TPN) for 48 h followed by enteral feeding for 0, 8, 17, or 34 h with either colostrum (Colos, n = 20) or formula (Form, n = 31). Macroscopic NEC lesions were detected in Form pigs throughout the enteral feeding period (20/31, 65%), whereas most Colos pigs remained protected (1/20, 5%). Just 8 h of formula feeding induced histopathological lesions, as evidenced by capillary stasis and necrosis, epithelial degeneration, edema, and mucosal hemorrhage. These immediate formula-induced changes were paralleled by decreased digestive enzyme activities (lactase and dipeptidylpeptidase IV), increased nutrient fermentation, and altered expression of innate immune defense genes such as interleukins (IL-1α, IL-6, IL-18), nitric oxide synthetase, tight junction proteins (claudins), Toll-like receptors (TLR-4), and TNF-α. In contrast, the first hours of colostrum feeding induced no histopathological lesions, increased maltase activity, and induced changes in gene expressions related to tissue development. Total bacterial density was high after 2 days of parenteral feeding and was not significantly affected by diet (colostrum, formula) or length of enteral feeding (8-34 h), except that a few bacterial groups (Clostridium, Enterococcus, Streptococcus species) increased with time. We conclude that a switch from parenteral to enteral nutrition rapidly induces diet-dependent histopathological, functional, and proinflammatory insults to the immature intestine. Great care is required when introducing enteral feeds to TPN-fed preterm infants, particularly when using formula, because early feeding-induced insults may predispose to NEC lesions that are difficult to revert by later dietary or medical interventions.     

Escherichia coli regulatory mutation affecting lysine transport and lysine decarboxylase

A spontaneous thiosine-resistant mutant of Escherichia coli was shown to have the following characteristics: lowered initial rate of lysine uptake and lowered plateau level of accumulation of exogenous lysine by both the lysine-specific and the general basic amino acid transport systems; altered repressibility of these two lysine transport systems; a derepressed level of lysine decarboxylase; normal growth rate; parental levels of lysyl-transfer ribonucleic acid synthetase and the inducible and constitutive arginine and ornithine decarboxylases. Both the mutant (lysP) and its parent (lysP+) feed a lysine auxotroph when they are plated in proximity on solid medium. However, the feeding response was observable after 1 day less of incubation when the mutant was the feeding strain. Despite the derepressed level of lysine decarboxylase in exponential cultures of the mutant extracts of these cultures had no detectable cadaverine pool. Conjugation experiments established the following gene order: gyrA (formerly nalA) lysP metG his. All thiosine-resistant recombinants assayed showed reduced lysine transport. In many of these recombinants the derepression of lysine decarboxylase was not expressed.     

Dilazep-induced vasodilation is mediated through adenosine receptors

Administration of dilazep, an inhibitor of adenosine uptake, significantly reduced systemic arterial blood pressure and increased superior mesenteric arterial conductance without affecting the plasma adenosine levels of femoral arterial or portal venous blood. Administration of a bolus dose of 8-phenyltheophylline (8-PT), an antagonist of adenosine receptors, blocked adenosine-mediated autoregulation of the superior mesenteric artery. After the blockade of adenosine receptors by 8-PT, dilazep did not produce vasodilation. These data suggest that dilazep has a vasodilating effect in vivo that is mediated by adenosine.     

Time course of the total and radioactive carbon dioxide production by piglets receiving dietary [14C]phenylalanine

The influence of experimental protocol (i.e., timing of feeding and of the collection of expired carbon dioxide) upon the sensitivity of using the oxidation of a labelled amino acid as an indicator of the adequacy of the dietary amino acid balance was investigated using 2.5-kg piglets confined in ventilated chambers. In the first experiment it was shown that consumption of two meals, each of 20 g and separated by 2 h, after an overnight fast resulted in a rapid rise in carbon dioxide concentration in the air withdrawn from the chamber. The concentration peaked 12 min after the second meal and remained elevated for 50 min. In the second experiment the piglets received two meals containing three levels of either lysine (8, 10, and 12 g/kg) or tryptophan (1.3, 1.8, and 2.0 g/kg) plus 10 microCi L-[alanine-1-14C]phenylalanine (1 Ci = 37 GBq) in each meal. Radioactivity released as 14CO2 peaked in the second hour following the last meal, but there was such great variation in the mean for the three diets that they were not statistically different. However, in the third hour following the second meal both the means and their variances had decreased with the differences between the diets being statistically significant for this time period. An experiment with varying levels of tryptophan showed a similar effect of meal consumption on 14CO2 release. The third experiment confirmed the effect of time of collection upon the statistical significance of the dietary amino acid balance measured by the release of radioactivity from [14C]phenylalanine.     

A simple kinetic model for myeloma cell culture with consideration of lysine limitation

A simple kinetic model is developed to describe the dynamic behavior of myeloma cell growth and cell metabolism. Glucose, glutamine as well as lysine are considered as growth limiting substrates. The cell growth was restricted as soon as the extracellular lysine is exhausted and then intracellular lysine becomes a growth limiting substrate. In addition, a metabolic regulator model together with the Monod model is used to deal with the growth lag phase after inoculation or feeding. By using these models, concentrations of substrates and metabolites, as well as densities of viable and dead cells are quantitatively described. One batch cultivation and two fed-batch cultivations with pulse feeding of nutrients are used to validate the model.