Glycerol: major contributor to the short term protein sparing effect of fat emulsions in normal man

Multiomics assessment of dietary protein titration reveals altered hepatic glucose utilization

Dietary protein restriction (PR) has rapid effects on metabolism including improved glucose and lipid homeostasis, via multiple mechanisms. Here, we investigate responses of fecal microbiome, hepatic transcriptome, and hepatic metabolome to six diets with protein from 18% to 0% of energy in mice. PR alters fecal microbial composition, but metabolic effects are not transferable via fecal transplantation. Hepatic transcriptome and metabolome are significantly altered in diets with lower than 10% energy from protein. Changes upon PR correlate with calorie restriction but with a larger magnitude and specific changes in amino acid (AA) metabolism. PR increases steady-state aspartate, serine, and glutamate and decreases glucose and gluconeogenic intermediates. ¹³C6 glucose and glycerol tracing reveal increased fractional enrichment in aspartate, serine, and glutamate. Changes remain intact in hepatic ATF4 knockout mice. Together, this demonstrates an ATF4-independent shift in gluconeogenic substrate utilization toward specific AAs, with compensation from glycerol to promote a protein-sparing response.

Dietary Energy Partition: The Central Role of Glucose

Humans have developed effective survival mechanisms under conditions of nutrient (and energy) scarcity. Nevertheless, today, most humans face a quite different situation: excess of nutrients, especially those high in amino-nitrogen and energy (largely fat). The lack of mechanisms to prevent energy overload and the effective persistence of the mechanisms hoarding key nutrients such as amino acids has resulted in deep disorders of substrate handling. There is too often a massive untreatable accumulation of body fat in the presence of severe metabolic disorders of energy utilization and disposal, which become chronic and go much beyond the most obvious problems: diabetes, circulatory, renal and nervous disorders included loosely within the metabolic syndrome. We lack basic knowledge on diet nutrient dynamics at the tissue-cell metabolism level, and this adds to widely used medical procedures lacking sufficient scientific support, with limited or nil success. In the present longitudinal analysis of the fate of dietary nutrients, we have focused on glucose as an example of a largely unknown entity. Even most studies on hyper-energetic diets or their later consequences tend to ignore the critical role of carbohydrate (and nitrogen disposal) as (probably) the two main factors affecting the substrate partition and metabolism.

Metabolic effects of glycerol supplementation and aerobic physical training on Wistar rats

We evaluated the effects of oral glycerol supplementation on trained rats fed a normal diet. Wistar rats were distributed among 6 groups in a completely randomized 2 × 3 factorial design. The animals were subjected to 6 weeks of aerobic training. In the last 4 weeks, the animals’ diet was supplemented with saline, glucose, or glycerol. Data were subjected to one-way analysis of variance (ANOVA) followed by a Student–Newmann–Keuls test, with values for P < 0.05 considered statistically significant. The change in body mass was lower in the trained groups, and their food and water consumption were higher. Glycerol supplementation resulted in an increase in the levels of triacylglycerol (TAG) and total cholesterol, as well as in the area and diameter of adipocytes. When associated with training, these parameters were similar to those of other trained groups. Levels of low-density lipoprotein + very-low-density lipoprotein cholesterol decreased in the trained animals that received glycerol compared with the non-trained ones. Glycerol consumption caused a reduction in food intake and increased the villous:crypt (V:C) ratio. No changes in glycemia, high density lipoproteins, or density of adipocytes were observed. Supplementation with glycerol together with aerobic physical training promoted beneficial metabolic effects. However, in non-trained rats glycerol increased the diameter and area of adipocytes, as well as the levels of TAG and total cholesterol.

Effect of crude glycerin on feed manufacturing, growth performance, plasma metabolites, and nutrient digestibility of growing-finishing pigs

Three experiments were conducted to determine the effects of dietary addition of crude glycerin on pellet production efficiency and to evaluate its effect on growth performance and digestibility in growing-finishing pigs. Three dietary treatments were created by addition of 0, 2.5, or 5% crude glycerin to barley-soybean meal-based diet, and 4 batches of each dietary treatment (2 each for grower and finisher diets) were prepared. In the manufacturing process, crude glycerin supplementation linearly increased the feeder speed and production rate (P < 0.05), resulting in a 20 to 29% improvement in the feed production rate compared with the control. Production efficiency (kg/kWh) increased linearly (P < 0.05) as the level of crude glycerin in feed increased. A growth experiment was performed with 240 barrows (30 ± 1 kg initial BW) using a 2-phase feeding program over a 12-wk period with 4 pens per treatment and 20 pigs per pen. On the last day of the growth experiment, blood samples were collected to determine circulating glucose, fructosamine, and IGF-1 concentrations. Overall growth performance was not affected (P > 0.05) by dietary treatment, and there was no effect (P > 0.05) of dietary treatment on any plasma metabolite measured. A digestibility experiment involving 9 male pigs housed in metabolic cages was used to determine the coefficients of apparent fecal digestibility and N and mineral balances. Pigs were assigned to 1 of the 3 diets in each feeding period using a 3 × 3 Latin square arrangement of treatments (43 ± 3 and 74 ± 3 kg initial BW in the growing and finishing periods, respectively). In both feeding periods, fecal digestibility of OM and ether extract were affected by dietary treatment, increasing linearly (P < 0.05) with increasing crude glycerin levels. However, neither CP digestibility nor N retention was affected by the glycerin content in either the growing or finishing period. Digestibilities and balance of Ca and P showed opposite tendencies with the variations in crude glycerin content, which either decreased or increased depending on the feeding period. In conclusion, adding crude glycerin to the diet before pelleting improved feed mill production efficiency. The addition of crude glycerin up to 5% in the diet of growing-finishing pigs had no effect on growth performance, blood metabolites, nutrient digestibility, and N balance, but more studies are needed to determine how crude glycerin affects mineral metabolism and balance.

Glucose-lipid ratio is a determinant of nitrogen balance during total parenteral nutrition in critically ill patients: a prospective, randomized, multicenter blind trial with an intention-to-treat analysis

OBJECTIVE

Protein sparing, the major goal of nutritional support, may be affected by the glucose/lipid ratio. This study in critically ill patients compared the efficacy and tolerance of two isocaloric isonitrogenous total parenteral nutritions (TPN) having different glucose/lipid ratios.

DESIGN

Multicentric prospective randomized study.

PATIENTS

47 patients with SAPS I score higher than 8 and requiring exclusive TPN.

INTERVENTIONS

Patients received glucose/lipid ratios of 50/50 or 80/20. For 7 days all patients received 32 glucidolipidic kcal/kg and 0.27 g/kg nitrogen daily. All-in-one bags were prepared using industrial mixtures and a fat emulsion.

MEASUREMENTS AND RESULTS

We determined TPN efficacy by nitrogen balance, urinary 3-methylhistidine/creatinine ratio, transthyretin and tolerance by glycemia, and liver enzymes. After controlling for five variables with significant effects, patients receiving the 50/50 ratio during TPN had significantly higher nitrogen balance than those receiving the 80/20 ratio. The daily difference in mean nitrogen sparing effect in favor of the latter group was 1.367 g (95% CI 0.0686-2.048). Glycemia on day 4 and gamma-glutamyltranspeptidase on day 8 were higher in group receiving the the 80/20 ratio.

CONCLUSIONS

In critically ill patients TPN at a glucose/lipid ratio of 80/20 ratio induces a small nitrogen sparing effect compared to the ratio of 50/50, at the expense of poorer glycemic control. The clinical significance is unclear.

Efficacy of a high-carbohydrate diet in catabolic illness

OBJECTIVE

To determine within the setting of isocaloric, isonitrogenous enteral diets whether a diet that supplies most of its calories from fat or carbohydrate would be most beneficial at limiting muscle protein wasting in catabolic illness.

DESIGN

Prospective, randomized, crossover trial.

SETTING

Academic pediatric burn unit in tertiary medical center.

PATIENTS

Fourteen severely burned (>40% total body surface area) children underwent systemic metabolic and cross-leg muscle protein kinetic studies.

INTERVENTIONS

All were treated clinically in a similar manner, including early excision and grafting, antimicrobial therapy, and isocaloric, isonitrogenous enteral nutritional support. Subjects randomly received either a high-carbohydrate enteral diet (3% fat, 82% carbohydrate, 15% protein), or a high-fat enteral diet (44% fat, 42% carbohydrates, 14% protein) for 1 week and then crossed over to the other diet for a second week.

MEASUREMENTS AND MAIN RESULTS

On day 5 of each diet, muscle protein kinetics were determined from femoral arterial and venous blood samples during a primed-constant d5-phenylalanine infusion. Indirect calorimetry was used to determine systemic resting energy expenditure and respiratory quotient. The seven boys and seven girls were 7.1 +/- 1.1 (mean +/- sem) years old and suffered burns over 65 +/- 4% of their bodies, with 52 +/- 6% being third-degree burns. Muscle protein degradation markedly decreased (p <.01) with administration of the high-carbohydrate diet. Protein synthesis was unaltered. Endogenous insulin concentrations increased during the high-carbohydrate feeding period. No differences in energy expenditure were seen between study diets.

CONCLUSIONS

In severely burned pediatric patients, enteral nutrition supplied predominantly as carbohydrate rather than fat improves the net balance of skeletal muscle protein across the leg. This is attributable to decreased protein breakdown, suggesting a protein-sparing effect of high-carbohydrate feedings.

Nitrogen balance in clinically normal dogs receiving parenteral nutrition solutions

OBJECTIVE

To determine nitrogen balance in clinically normal dogs receiving parenteral nutrition solutions.

ANIMALS

8 clinically normal female Beagles.

PROCEDURE

Dogs were randomly assigned to receive 4 treatments in random order. Treatment A consisted of IV administration of nonlactated Ringer's solution. Treatments B, C, and D consisted of IV administration of isocaloric parenteral solutions containing 0, 1.36, and 2.04 g of amino acids/kg of body weight/d, respectively, for 7 consecutive days. Urine and feces were collected on days 5, 6, and 7 of each treatment period, and Kjeldahl analysis was used to determine nitrogen balance.

RESULTS

Mean nitrogen balance was negative with treatments A and B but was not significantly different from 0 with treatments C and D. Dogs had the lowest nitrogen balance values and lost the most weight while receiving treatment A. Dogs were able to conserve protein and had higher nitrogen balance values when receiving treatment B, compared with treatment A. Dogs lost the least amount of weight while receiving treatment D. Regression analysis indicated that an IV amino acid intake of 2.32 g/kg/d (95% confidence interval, 2.00 to 2.81 g/kg/d), as supplied by the commercial product used in this study, would result in zero nitrogen balance in clinically normal dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that IV amino acid requirement of clinically normal dogs is approximately 2.3 g/kg/d.

Synthesis and intravenous infusion into the rat of glyceryl bisacetoacetate, 1-acetoacetamido-2, 3-propane diol, and partially reduced glucosyl pentaacetoacetate

The efficacy of parenteral nutrition could be improved by finding a more effective energy source. Esters of short-chain fatty acids have exhibited some promise as alternatives to glucose. The present study reports on two new esters and one amide, each containing acetoacetate as the organic acid. The three compounds: glyceryl bisacetoacetate, N-2',3'-dihydroxypropyl-3-oxo-butanamide (1-acetoacetamido-2,3-propane diol), and partially reduced glucosyl pentaacetoacetate, were synthesized and then continuously infused into rats for 7 d. The infusion rate provided 50% of the rats' estimated metabolic energy requirements, and rats were fed with a reduced-energy oral diet that provided the remaining 50% of energy plus adequate protein. Rat groups for each compound were: (1) experimental-compound-infused and ad libitum-fed, (2) isoenergetic glucose-infused and pairfed, and (3) saline infused and pair-fed. Body-weight changes, N losses and N retention were measured daily. All rats died from partially reduced glucosyl pentaacetoacetate infusion at 100% and 50% of the intended rate. Rats infused with 1-acetoacetamido-2,3-propane diol failed to gain weight and to increase the plasma ketone-body concentration. Glyceryl bisacetoacetate produced hyperketonaemia, and weight gain and N variables that were similar to those for glucose-infused rats. It was concluded that only glyceryl bisacetoacetate would make a satisfactory parenteral nutrient.

Reduction of free fatty acids may ameliorate risk factors associated with abdominal obesity

Experimental data as well as logical considerations suggest that the increased cardiovascular risk associated with abdominal obesity is mediated primarily by increased levels and flux of free fatty acids. Practical strategies for decreasing free fatty acid levels and/or flux may include: a very-low-fat, low-glycemic-index diet; promotion of insulin sensitivity (via exercise training, chromium, soluble fiber or drugs); anti-lipolytic agents; and stimulation of hepatic lipid oxidation with hydroxycitrate, carnitine and possibly fish omega-3s. Fortunately, many of these measures should also promote a leaner physique. Thus, even when abdominal obesity cannot be corrected, it may prove feasible to mitigate its dangers.

Hemodynamic, respiratory, and metabolic effects of medium-chain triglyceride-enriched lipid emulsions following valvular heart surgery

STUDY

A lipid emulsion containing 10 percent medium-chain triglycerides (MCT) and 10 percent long-chain triglycerides (LCT) was infused at a rate of 1 ml/kg/h (3.3 mg/kg/min) for 2 h, in 12 patients (2 males, 10 females; mean age, 54 +/- 3 (SEM) years; range, 34 to 67 years) 24 h after open-heart surgery (mitral valve replacement).

METHODS

Hemodynamic factors (pulmonary and radial artery indwelling catheters), oxygen and carbon dioxide partial pressures, oxygen saturation, oxygen delivery and consumption, and intrapulmonary shunt fraction were obtained before, during, and after lipid infusion (for 2 h), at 30-s intervals, along with some metabolic indexes (triglycerides, free fatty acids, glucose, insulin, lactate, acetoacetate).

RESULTS

No statistically significant changes in heart rate, cardiac index, systemic and pulmonary pressures and resistances, central venous and pulmonary capillary pressures, or arterial oxygen partial pressure were observed during infusion. Arterial carbon dioxide partial pressure values were constantly reduced throughout and after the end of lipid infusion, as compared with baseline values, while oxygen consumption was increased significantly without any change in oxygen delivery. No adverse effects on intrapulmonary shunt fraction were observed. Statistically significant increases of triglycerides, free fatty acids, acetoacetate and insulin (peak values at end of the lipid infusion) were found in comparison with baseline values. Plasma glucose increased significantly during lipid infusion and remained higher than baseline values until the end of the study. Lactate levels were unchanged except for a slight decrease at the end of the study, without any derangement of acid-base equilibrium. Neither arrhythmias nor adverse clinical reactions were observed as a consequence of lipid infusion.

CONCLUSIONS

Fat emulsions containing both MCT and LCT, when given at 3.3 mg/kg/min for 120 min following valvular heart surgery, do not exert negative cardiopulmonary effects, and could represent a source of rapidly metabolized substrates.

Nutritional support in the critical care setting (Part 1)

Over the past two decades nutritional support has rapidly become an integral part of the medical care of critically ill patients. As scientific evidence accumulates supporting the important role of underlying nutritional status in determining the eventual outcome of many illnesses, aggressive nutritional intervention has become commonplace in our medical and surgical ICUs. However, nutritional support, particularly parenteral alimentation, is expensive and associated with important morbidity and even mortality. Furthermore, definite evidence of its clinical efficacy under certain specific conditions is often lacking and in need of properly done prospective studies. This review summarizes the basic principles of nutrition as applied to the critically ill patient in the clinical setting. Special emphasis is on practical considerations regarding cost, efficacy (or lack thereof), and potential advantages, disadvantages, and risk of complications of each proposed approach.

Comparison of medium and long chain triglyceride metabolism in intensive care patients on parenteral nutrition

The metabolic effects of an intravenous lipid emulsion containing medium chain triglycerides (MCTs) were studied in eleven critically ill, ventilated patients receiving parenteral nutrition. The effects were compared in a cross-over study with those of a conventional emulsion containing only long chain triglycerides (LCTs). The lipid was well tolerated, but there were differences in the metabolic effects with a significantly greater increase in the plasma concentrations of glycerol and ketones during MCT/LCT infusion compared to LCT. The plasma concentration of non esterified fatty acids was also higher. This fell rapidly post infusion. Since non esterified fatty acids and ketones are readily available energy sources for tissues lipid emulsions containing MCT may prove valuable for catabolic, critically ill patients.

Regulation of leucine catabolism by caloric sources. Role of glucose and lipid in nitrogen sparing during nitrogen deprivation

Previously we showed that hypocaloric amounts of glucose reduce leucine catabolism while an isocaloric amount of fat does not (1985. J. Clin. Invest. 76:737.). This study was designed to investigate whether the same difference exists when the entire caloric need is provided either as glucose or lipid. Rats were maintained for 3 d on total parenteral nutrition (350 cal/kg per d), after which the infusion of amino acids was discontinued and rats received the same amount of calories entirely as glucose or lipid for three more days. A third group of rats was infused with saline for 3 d. In comparison to glucose, lipid infusion resulted in higher urinary nitrogen excretion (55 +/- 3 vs. 37 +/- 2 mg N/24 h, P less than 0.05), muscle concentrations of tyrosine (95 +/- 8 vs. 42 +/- 8 microM, P less than 0.01), and leucine (168 +/- 19 vs. 84 +/- 16 microM, P less than 0.01), activity of BCKA dehydrogenase in muscle (2.2 +/- 0.2 vs. 1.4 +/- 0.04 nmol/mg protein per 30 min, P less than 0.05), and whole body rate of leucine oxidation (3.3 +/- 0.5 vs. 1.4 +/- 0.2 mumol/100 g per h, P less than 0.05). However, all these parameters were significantly lower in lipid-infused than starved rats. There was no significant difference between leucine incorporation into liver and muscle proteins of lipid and glucose-infused rats. On the other hand, starved rats showed a lower leucine incorporation into liver proteins. The data show that under conditions of adequate caloric intake lipid has an inhibitory effect on leucine catabolism but not as great as that of glucose. The mechanism of this difference may be related to a lesser inhibition of muscle protein degradation by lipid than glucose, thereby increasing the leucine pool, which in turn stimulates leucine oxidation.

Protein-sparing effect of substrate infusion in surgical patients is governed by the clinical state, and not by the individual substrate infused

We have determined iostopically the effect of either glucose or lipid infusion on rates of glucose turnover, glucose oxidation, and net protein catabolism (NPC) in three groups of surgical patients. Kinetic measurements were performed using the primed constant infusion of 3H-glucose, and either 14C-glucose or 14C-urea. The three groups included patients with: (1) sepsis and/or trauma (ST); (2) upper gastrointestinal cancer (UGI); (3) lower gastrointestinal cancer (LGI). In each patient group the effect of either glucose infusion (approximately 4 mg/kg.min) or lipid infusion (20% Intralipid lipid emulsion infused to provide calories approximately isocaloric to the glucose infusion) was assessed. The infusion of calories as either glucose or lipid was equally effective as a means of suppressing NPC in each individual patient group, and the degree of response was governed by the clinical disease state. In the LGI and ST patients the infusion of either glucose or fat resulted in a significant suppression of NPC (p less than 0.005) of approximately 15%. However, the ongoing rate of NPC that occurred despite substrate infusion was more than twice as great in the ST patients as in the LGI patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of protein sparing effect of total parenteral nutrition in the surgical infant

To determine the best formula to prevent protein depletion, 31 surgical infants on intravenous (IV) diet were studied. The study was divided into two phases. Phase I diet included 5% glucose and 1.5% or 2% amino acid infusion; phase II diet consisted of 5% glucose and 1.5% or 2% aminoacid plus 10% Intralipid. In each phase, oxygen consumption, carbon dioxide production, and energy expenditure were determined. The utilization of carbohydrate, fat, and protein was calculated from urinary nitrogen excretion and nonprotein respiratory quotient. The mean caloric intake during phase I and phase II was 62 and 94 kcal/kg/d, respectively. A positive nitrogen balance was obtained in infants receiving fat-free total parenteral nutrition (TPN) with a mean protein intake of 2.6 g/kg/d and a mean energy intake exceeding the energy expenditure by 24%. Infusion of more calories as Intralipid (phase II) caused a significant reduction in protein oxidation, thus protein contribution to the energy expenditure and an increase in protein retention. We conclude that supplementation of low-calorie TPN diets with Intralipid increases protein sparing and is preferable to the administration of very high glucose loads.

The effect of total parenteral nutrition on hepatic drug oxidation

Hepatic dysfunction is a frequent complication of total parenteral nutrition (TPN), indicated by derangement of standard liver function tests. However, such changes are variable and nonspecific, and represent hepatic injury rather than changes in hepatic function. Antipyrine (Phenazone) clearance is a sensitive indicator of hepatic microsomal enzyme activity and provides a more specific indication of hepatic function. This was used to investigate the effect of different TPN regimens. Patients receiving a postoperative 2000 kcal TPN regimen providing all nonprotein calories as dextrose (n = 16) showed a 34% reduction of mean antipyrine clearance after 7 days of TPN compared to controls (n = 13, p less than 0.05). This effect was seen also in patients receiving a 1600 kcal dextrose-based regimen (n = 8). In patients receiving a 2000 kcal TPN regimen in which 500 kcal were provided as lipid (n = 10), mean antipyrine clearance was not significantly different from that of the control group. This study indicates the sensitivity of hepatic microsomal oxidative function, an important route of drug metabolism, to different TPN regimens.

A key to the literature of total parenteral nutrition: update 1987

This comprehensive bibliography is intended to enhance the education of the practitioner, student, and academician in the area of parenteral nutrition. This bibliography is not all-inclusive but serves as an update from the original published in 1983. Of particular note in this work is the addition of topics that reflect a growing interest in medical specialties with regard to patient nutritional status and support.

Double-blind study of glycerol vs glucose in parenteral nutrition of postsurgical insulin-treated diabetic patients

Twenty-five insulin-treated diabetic patients were randomly assigned postoperatively to 5 days of intravenous infusions of ProcalAmine (3% amino acids, 3% glycerol, and electrolytes) or FreAmineIII + dextrose and electrolytes. The solutions were given isocalorically and isonitrogenously. Insulin was adjusted to keep glycemia at the level of 150-200 mg/dl. The ProcalAmine group by the 5th day had plasma glucose of 158 +/- 25 mg/dl and required 1.20 +/- 0.10 U/hr insulin. The FreAmine + dextrose group had plasma glucose of 169 +/- 53 mg/dl and required 2.28 +/- 0.13 U/hr. At all time points postsurgically, the ProcalAmine group required less insulin.

Energy sources for intravenous nutrition

Controversy exists concerning the appropriate use of carbohydrate solutions and fat emulsions as energy sources in intravenous nutritional regimens. Current evidence suggests that glucose is the carbohydrate energy source of choice and that when infused with appropriate quantities of protein it provides cheap and effective nutritional support in the majority of patients and clinical circumstances. During glucose infusion, blood glucose and acid-base balance should be closely monitored and, when indicated, exogenous insulin should be added to the regimen to combat hyperglycaemia and improve protein anabolism. Fat emulsions, although expensive, may justifiably be used in patients with moderate or severe stress to provide up to 50% of non-protein energy, especially in circumstances where attempts to satisfy energy requirements exclusively with glucose would impose an additional metabolic stress.

A new intravenous emulsion containing medium-chain triglyceride: studies of its metabolic effects in the perioperative period compared with a conventional long-chain triglyceride emulsion

The effects of carbohydrate, lipid, and nitrogen metabolism of recently available lipid emulsions containing either 50% medium-chain triglyceride (MCT) and 50% long-chain triglyceride (LCT) or 100% LCT were compared in elective surgical patients. Postoperative urinary urea excretion was similar during isocaloric MCT/LCT and LCT infusions (1.9 mg/kg/min) and was decreased compared with a standard infusion of 5% glucose (1 mg/kg/min). Plasma glucose and insulin concentrations were similar during both lipid and low dose glucose infusions. However, plasma triglyceride and nonesterified fatty acid concentrations were decreased during the MCT/LCT infusion compared with the LCT infusion, suggesting that the MCT/LCT emulsion was cleared from the circulation faster than pure LCT. Ketone body concentrations were similar during all three infusions. MCT/LCT emulsion can be safely infused perioperatively and has similar nitrogen conserving properties to LCT in these circumstances.

Effects of intravenous infusion of a ten percent soybean emulsion on hormones, amino acids and other substrates in blood

Acute responses in hormone and substrate concentrations to intravenous administration of a fat emulsion were studied in metabolically normal subjects. Eight subjects were infused with either a fat emulsion or an aqueous solution of glycerol for 3 h. Serum triglycerides (TG), free fatty acids (FFA), glucose, glycerol, 3-hydroxybutyrate (3-OH butyrate), insulin, thyroid hormones, plasma glucagon, norepinephrine, and amino acids were measured. The infusion of a fat emulsion induced a 30% increase in glucose and a 22% decrease in alanine together with significant elevations of TG (> 10 mM) and FFA (> 1 mM). A small increase in insulin (4 microU/ml) and a reduction in glucagon (40 pg/ml) were observed. Eight-fold increases in glycerol occurred with both the fat emulsion and glycerol infusions. The administration of a fat emulsion resulted in a 4-fold increase in 3-OH butyrate, whereas glycerol infusion reduced its level by 50%. Glycerol infusion produced no measurable effects on the substrates other than glycerol or 3-OH butyrate. No significant changes were observed in thyroid hormones or norepinephrine after either solution was given. The data suggest that acute elevation of FFA by means of intravenous fat emulsions leads to preferential oxidation of FFA and stimulates hepatic ketogenesis with resulting glucose conservation as well as inhibition of alanine production without many alterations in hormonal concentrations.

Energy and protein requirements of general surgical patients requiring intravenous nutrition

General surgical patients require intravenous nutrition either because their gastrointestinal tract is blocked, too short or inflamed or because it cannot cope. Such patients can be grouped into four nutritional/metabolic categories: normal and unstressed; normal and stressed; depleted and unstressed; depleted and stressed. The energy requirements of patients in each of these groups vary according to their energy expenditure. Normally nourished and stressed patients have the highest energy expenditure and therefore require the highest energy input (45-55 kcal.kg-1day-1). Other groups of patients rarely require more than 40 kcal.kg-1day-1. Energy can be given mainly as dextrose although calories needed above 40 kcal kg-1day-1 should be given as fat (unless lipogenesis is desirable). In very stressed patients high rates of glucose infusion can themselves constitute a metabolic stress and fat may play a bigger role as a calorie source. For long term feeding, 1 litre of 10 per cent fat emulsion should be given weekly to avoid essential fatty acid deficiency. The level of nitrogen intake required to maintain a positive nitrogen balance is a lot higher in surgical patients than the suggested recommended dietary allowances for normal subjects. It is dependent not only on the nutritional and clinical state of the patient but also on the levels of energy and nitrogen intake given. When energy intake is below energy needs, normally nourished patients cannot retain nitrogen, although depleted patients can. When energy intake exceeds energy needs, both normally nourished and depleted patients retain nitrogen at levels of nitrogen intake ranging from 250 mg kg-1day-1 (depleted and unstressed) to over 400 mg kg-1day-1 (stressed). Depleted patients can maintain a positive nitrogen balance at lower levels of calorie and nitrogen intake than normally nourished patients and in this respect are analogous to a growing child. In all surgical patients, energy and nitrogen intakes can be manipulated to provide for a controlled maintenance or restoration of either wet lean tissue and/or fat. There is little place for protein sparing therapy or the use of insulin and anabolic steroids to promote nitrogen retention in surgical patients requiring intravenous feeding.

Nutritional care of the critically ill patient

Nutritional care is a supportive measure. Just as ventilatory support does not "cure" underlying pulmonary disease, nutritional support may not in itself resolve the disease that causes inadequate intake of nutrients. In the setting of multimodality care in the ICU, the provision of calories and protein to maintain the body cell mass is the initial goal. Such an approach will minimize feeding complications yet prevent nutritional debility. An acceptably low rate of complications is possible but can only be achieved by strict attention to detail. When the acute phase of the disease resolves, more vigorous nutritional support is possible and will restore body composition to normal.

Oral glycerol for the treatment of traumatic intracranial hypertension

Hyperosmolar agents are a primary therapeutic modality employed in the treatment of traumatic intracranial hypertension. Profound hyperosmolarity accompanied by systemic dehydration is a potentially serious problem when these drugs are used repeatedly for control of intracranial pressure. Because glycerol, a water-soluble alcohol, is metabolized in the liver, its dehydrating capacity may be reduced in comparison to other agents. A series of 15 patients were treated with oral glycerol (0.5 to 1.0 gm/kg) with only minor changes in serum electrolytes, glucose, and urea nitrogen. Serum osmolarity rose from a baseline of 305 mOsm/liter to 355 mOsm/liter after 10 days of therapy. Glycerol was found to be effective and safe when employed in this protocol and proved to be a valuable adjunct to the standard methods available for control of intracranial hypertension.

Studies with a safflower oil emulsion in total parenteral nutrition

The prevention of essential fatty acid deficiency and the provision of adequate amounts of energy are two major concerns in total parenteral nutrition. Since earlier preparations of fat emulsion used to supplement the usual regimen of hypertonic glucose and amino acids have widely varying clinical acceptability, a new product, a safflower oil emulsion available in two concentrations (Liposyn), was evaluated. In four clinical trials the emulsion was used as a supplement to total parenteral nutrition. In five surgical patients 500 ml of the 10% emulsion infused every third day prevented or corrected essential fatty acid deficiency; however, in some cases in infusion every other day may be necessary. In 40 patients in severe catabolic states the emulsion provided 30% to 50% of the energy required daily: 10 patients received the 10% emulsion for 14 to 42 days, 9 patients received each emulsion in turn for 7 days, and 21 patient received the 20% emulsion for 14 to 28 days. All the patients survived and tolerated the lipid well; no adverse clinical effects were attributable to the lipid infusions. Transient mild, apparently clinically insignificant abnormalities in the results of one or more liver function tests and eosinophilia were observed in some patients. Thus, the safflower oil emulsion, at both concentrations, was safe and effective as a source of 30% to 50% of the energy required daily by seriously ill patients.

Influence of total parenteral nutrition on tissue lipoprotein lipase activity during chronic and acute illness

This study examines the influence of total parenteral nutrition (TPN) compared with 5% dextrose (D5) infusion on skeletal muscle and adipose tissue lipoprotein lipase (LPL) activity in nutritionally depleted, injured and infected patients. The plasma concentrations of glucose, free fatty acid (FFA), triglyceride and insulin were also measured. During TPN, nutritionally depleted subjects showed an increase in adipose tissue LPL activity, "fat cell size," and plasma insulin concentration. Skeletal muscle LPL activity and plasma FFA concentration decreased. In comparison, trauma patients showed a less marked rise in adipose tissue LPL activity and skeletal muscle LPL activity increased. Infected patients had a much smaller rise in adipose tissue LPL activity than either of the other groups, and muscle activity rose. The depleted and injured patients showed a linear relationship between adipose tissue LPL activity and plasma insulin concentration and an inverse hyperbolic relationship between adipose tissue LPL activity and plasma FFA concentration.

Evidence for a role of free fatty acids in the regulation of somatostatin secretion in normal and alloxan diabetic dogs

To investigate the effect of acute elevation of plasma free fatty acids (FFA) on the secretion of splanchnic somatostatin-like immunoreactivity (SLI), the peripheral venous, pancreatic, and gastric venous effluent levels of SLI were measured in normal and chronic alloxan diabetic dogs before and after the infusion of a fat emulsion supplemented with heparin. In normal conscious dogs heparin injected during the infusion of a fat emulsion elevated FFA levels from a mean (+/-SE) base-line level of 0.7+/-0.1 meq/liter to a peak value of 1.5+/-0.1 meq/liter (P < 0.001) and plasma SLI rose from a mean (+/-SE) base-line value of 145+/-7 pg/ml to a peak of 253+/-44 pg/ml (P < 0.05). Neither the infusion of glycerol, of fat emulsion without heparin, of heparin alone nor of saline itself had an effect on either the plasma level of FFA or SLI. In another group of anesthetized dogs with surgically implanted catheters the administration of fat emulsion plus heparin was accompanied by more than a two-fold rise in the concentration of SLI in the venous effluent of the pancreas and of the gastric fundus and antrum in association with an elevation of FFA levels. In a group of conscious diabetic dogs fat emulsion plus heparin raised FFA from a mean base-line level of 1.2+/-0.2 to 1.6+/-0.3 meq/liter (P < 0.05) and SLI rose from a mean base-line level of 185+/-9 pg/ml to a peak value of 310+/-44 pg/ml (P < 0.01). Although SLI levels were significantly greater than in normal dogs at several time points after the rise in FFA, the magnitude of the increment in diabetic dogs did not differ from normal. These results demonstrate that a rise in FFA levels is a potent stimulus for SLI secretion from the pancreas and stomach and raise the possibility that FFA is an important physiological regulator of SLI secretion.

Evaluation and management of nutritional status before surgery

Preoperative evaluation of all patients should include evaluation of nutritional status. Factors of greatest clinical usefulness are nutritional history correlated with the clinical situation, and measures of body height and weight, serum albumin concentration, and muscle mass. Depressed immune function suggested by a lack of skin test reactivity to standard antigens may correlate with the risk of postoperative complications and death, but further studies are required to determine the specific relation of nutrient deficiencies and immune function. Micronutrient deficiencies must be identified and corrected rapidly. Nutritional support in patients with nutritional deficiencies should be started preoperatively either by enteral or intravenous techniques and continued postoperatively.

Protein-sparing therapy during pneumococcal infection in rhesus monkeys

A model was developed in the rhesus monkey to determine if the marked wasting of body proteins associated with sepsis could be prevented by an intravenous supply of various nutritional substrates. All monkeys were given a basic infusion of 0.5 gm of amino acid nitrogen/kg body weight via an indwelling catheter in the jugular vein. Three groups were given diets with no added calories, 85 calories/kg from dextrose or 85 calories from lipid. In each group, six monkeys were inoculated with 3 x 10(8) Streptococcus pneumoniae and four with heatkilled organisms. In the monkeys infused with the amino acids alone, pneumococcal sepsis resulted in a fourfold increase in loss of body proteins compared with calorie-restricted controls. Addition of 85 calories/kg/day of either dextrose or lipid reduced body wasting associated with infectious disease. The calories from lipid were utilized bythe septic host as a source of energy, with a slightly reduced efficiency when compared with the isocaloric infusion of dextrose. The nitrogen sparing of the fat emulsion could not be accounted for by its glycerol content. Therefore, the septic monkey seemed to utilize fatty acids as an energy substrate. It appears that the carbohydrate calories tend to favor the synthesis of peripheral proteins (associated mainly with skeletal muscle), while lipid calories favor synthesis of visceral proteins such as plasma albumin and acute-phase proteins.

Substrate interaction in intravenous feeding: comparative effects of carbohydrate and fat on amino acid utilization in fasting man

Data are presented on the metabolic and endocrine effects of intravenous infusions in normal fasting man observed under highly controlled conditions over a period of six to eight days duration. There are comparative data on a variety of intravenous feeding programs. The data on total starvation are based on studies from the literature, some of which were carried out in this laboratory. The data on low dose glucose, high dose glucose, glycerol, fat emulsion, and amino acids, each given separately, demonstrate changes seen with simple infusion of a single substrate in fasting. These data are now compared with the utilization of amino acid infusions when accompanied by low dose glucose, high dose glucose, glycerol, and fat emulsion. In all, nine experimental intravenous feeding programs are presented, based on data from 35 subjects observed over a total of 370 subject-days. The findings show a strong interaction between glucose or lipid and protein metabolism. In fasting, glucose had protein sparing effect, most evident when given at high dose. Glycerol, in an amount equal to that contained in 2000 ml of ten per cent fat emulsion, had a mild protein sparing effect. Fat emulsion was no more effective. When amino acids were given alone, normal fasting human subjects were always in negative nitrogen balance with the daily nitrogen loss half that seen in starvation alone. Although amino acids given alone have a protein sparing effect, this is accomplished only at the expense of a high nitrogen excretion including an amount equivalent to the entire infusion plus an additional loss from the body's native proteins. The provision of energy yielding non-protein substrates with the amino acids markedly improved nitrogen economy in the following order: glycerol, low dose glucose, fat emulsion and high dose glucose. When caloric provision with glucose approached the isocaloric level for normal diet, the utilization of amino acids was maximized. When given with amino acids, fat emulsion was more effective than the available glycerol alone. THE ACCOMPANYING ENDOCRINE AND BIOCHEMICAL CHANGES SUGGEST THAT THE MILIEU FOR IDEAL UTILIZATION OF INFUSED AMINO ACIDS IS VARIABLE: ketones at low range (carbohydrate) or moderately elevated (fat emulsion); insulin elevated (carbohydrate) or unchanged (fat emulsion). The utilization of the infused amino acids was markedly improved in both endocrine settings, suggesting that it is the provision of energy as substrate as well as the endocrine setting that determines amino acid utilization. There were other changes in plasma intermediates, particularly fatty acids, glucose and urea, all consistent with the concept that when amino acids are given without other substrates, the amino acids must be maximally utilized for gluconeogenesis. When other substrates are provided (particularly glucose at high dose) then this mandate no longer exists and protein synthesis from the amino acids is favored. Several of the plasma amino acid concentrations responded to glucose when added to amino acid infusion. Amino acids alone produced increases in concentration of all the amino acids found in the infusion with the exception of alanine, arginine, and threonine. Many of these increases were abated by the addition of glucose to the amino acid infusion, suggesting an increased utilization rate. Glycerol and fat emulsion, while modulating increases in the plasma amino acid concentration, did so to a lesser extent than did glucose. This lowering of amino acid concentration was unaccompanied by an increase in urinary excretion. The assumption is therefore made that the provision of the added glucose favors the incorporation of amino acid into protein. There is no evidence from these data to suggest that a rising concentration of ketones in the blood favors amino acid utilization or protein synthesis.