Effects of simulated digests of Biota orientalis and a dietary nutraceutical on interleukin-1- induced inflammatory responses in cartilage explants

OBJECTIVE

To test the hypothesis that simulated digests of Biota orientalis (BO) and a dietary nutraceutical (DN; composed of mussel, shark cartilage, abalone, and BO seed lipid extract) inhibit prostaglandin E2 (PGE2), nitric oxide (NO), and glycosaminoglycan (GAG) production in interleukin (IL)-1-stimulated cartilage explants.

SAMPLE POPULATION

Cartilage tissue from 12 pigs.

PROCEDURES

Articular cartilage explants were conditioned with a simulated digest of BO (BOsim) or DN (DNsim) at concentrations of 0, 0.06, or 0.18 mg/mL or indomethacin (INDOsim; 0 or 0.02 mg/mL) for 72 hours. Control explants received digest vehicle only. Explants were or were not stimulated with recombinant human-IL-1beta (10 or 0 ng/mL) during the final 48 hours of culture. Concentrations of PGE2, GAG, and NO in media samples (mPGE2,mGAG, and mNO concentrations, respectively) were analyzed, and explant tissue was stained fluorochromatically to determine chondrocyte viability. Treatment effects during the final 48-hour culture period were analyzed.

RESULTS

IL-1 increased mPGE2, mGAG, and mNO concentrations in control explants without adversely affecting cell viability. Treatment with INDOsim blocked PGE2 production and increased mNO concentration in IL-1-stimulated and unstimulated explants and increased mGAG concentration in unstimulated explants. Treatment with DNsim (0.06 and 0.18 mg/mL) reduced mPGE2 concentration in IL-1-stimulated and unstimulated explants, reduced mNO concentration in IL-1-stimulated explants, and increased mNO concentration in unstimulated explants. Treatment with 0.18 mg of DNsim/mL increased cell viability in the presence of IL-1. In IL-1-stimulated explants, BOsim (0.06 and 0.18 mg/mL) reduced mPGE2 concentration, but 0.18 mg of BOsim/mL increased cell viability.

CONCLUSIONS AND CLINICAL RELEVANCE

Effects of IL-1 on cartilage explants in vitro were modulated by DNsim and BOsim.

Oral acetate supplementation after prolonged moderate intensity exercise enhances early muscle glycogen resynthesis in horses

Oral acetate supplementation enhances glycogen synthesis in some mammals. However, while acetate is a significant energy source for skeletal muscle at rest in horses, its effects on glycogen resynthesis are unknown. We hypothesized that administration of an oral sodium acetate-acetic acid solution with a typical grain and hay meal after glycogen-depleting exercise would result in a rapid appearance of acetate in blood with rapid uptake by skeletal muscle. It was further hypothesized that acetate taken up by muscle would be converted to acetyl CoA (and acetylcarnitine), which would be metabolized to CO2 and water via the tricarboxylic acid cycle, generating ATP within the mitochondria and thereby allowing glucose taken up by muscle to be preferentially incorporated into glycogen. Gluteus medius biopsies and jugular venous blood were sampled from nine exercise-conditioned horses on two separate occasions, at rest and for 24 h following a competition exercise test (CET) designed to simulate the speed and endurance test of a 3 day event. After the CETs, horses were allowed water ad libitum and either 8 l of a hypertonic sodium acetate-acetic acid solution via nasogastric gavage followed by a typical hay-grain meal (acetate treatment) or a hay-grain meal alone (control treatment). The CET significantly decreased muscle glycogen concentration by 21 and 17% in the acetate and control treatments, respectively. Acetate supplementation resulted in a rapid and sustained increase in plasma [acetate]. Skeletal muscle [acetyl CoA] and [acetylcarnitine] were increased at 4 h of recovery in the acetate treatment, suggesting substantial tissue extraction of the supplemented acetate. Acetate supplementation also resulted in an enhanced rate of muscle glycogen resynthesis during the initial 4 h of the recovery period compared with the control treatment; however, by 24 h of recovery there was no difference in glycogen replenishment between trials. It is concluded that oral acetate could be an alternative energy source in the horse.

Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

We hypothesized that postexercise rehydration using a hypotonic electrolyte solution will increase the rate of recovery of whole body hydration, and that this is associated with increased muscle glycogen and electrolyte recovery in horses. Gluteus medius biopsies and jugular venous blood were sampled from six exercise-conditioned Standardbreds on two separate occasions, at rest and for 24 h following a competitive exercise test (CET) designed to simulate the speed and endurance test of a 3-day event. After the CETs, horses were given water ad libitum, and either a hypotonic commercial electrolyte solution (electrolyte) via nasogastric tube, followed by a typical hay/grain meal, or a hay/grain meal alone (control). The CET resulted in decreased total body water and muscle glycogen concentration of 8.4 ± 0.3 liters and 22.6%, respectively, in the control treatment, and 8.2 ± 0.4 liters and 21.9% in the electrolyte treatment. Electrolyte resulted in an enhanced rate of muscle glycogen resynthesis and faster restoration of hydration (as evidenced by faster recovery of plasma protein concentration, maintenance of plasma osmolality, and greater muscle intracellular fluid volume) during the recovery period compared with control. There were no differences in muscle Na, K, Cl, or Mg contents between the two treatments. It is concluded that oral administration of a hypotonic electrolyte solution after prolonged moderate-intensity exercise enhanced the rate of muscle glycogen resynthesis during the recovery period compared with control. It is speculated that postexercise dehydration may be one key contributor to the slow muscle glycogen replenishment in horses.

Do multiple ionic interactions contribute to skeletal muscle fatigue?

During intense exercise or electrical stimulation of skeletal muscle the concentrations of several ions change simultaneously in interstitial, transverse tubular and intracellular compartments. Consequently the functional effects of multiple ionic changes need to be considered together. A diminished transsarcolemmal K(+) gradient per se can reduce maximal force in non-fatigued muscle suggesting that K(+) causes fatigue. However, this effect requires extremely large, although physiological, K(+) shifts. In contrast, moderate elevations of extracellular [K(+)] ([K(+)](o)) potentiate submaximal contractions, enhance local blood flow and influence afferent feedback to assist exercise performance. Changed transsarcolemmal Na(+), Ca(2+), Cl(-) and H(+) gradients are insufficient by themselves to cause much fatigue but each ion can interact with K(+) effects. Lowered Na(+), Ca(2+) and Cl(-) gradients further impair force by modulating the peak tetanic force-[K(+)](o) and peak tetanic force-resting membrane potential relationships. In contrast, raised [Ca(2+)](o), acidosis and reduced Cl(-) conductance during late fatigue provide resistance against K(+)-induced force depression. The detrimental effects of K(+) are exacerbated by metabolic changes such as lowered [ATP](i), depleted carbohydrate, and possibly reactive oxygen species. We hypothesize that during high-intensity exercise a rundown of the transsarcolemmal K(+) gradient is the dominant cellular process around which interactions with other ions and metabolites occur, thereby contributing to fatigue.

The effect of oral sodium acetate administration on plasma acetate concentration and acid-base state in horses

Aim

Sodium acetate (NaAcetate) has received some attention as an alkalinizing agent and possible alternative energy source for the horse, however the effects of oral administration remain largely unknown. The present study used the physicochemical approach to characterize the changes in acid-base status occurring after oral NaAcetate/acetic acid (NAA) administration in horses.

Methods

Jugular venous blood was sampled from 9 exercise-conditioned horses on 2 separate occasions, at rest and for 24 h following a competition exercise test (CET) designed to simulate the speed and endurance test of 3-day event. Immediately after the CETs horses were allowed water ad libitum and either: 1) 8 L of a hypertonic NaAcetate/acetic acid solution via nasogastric tube followed by a typical hay/grain meal (NAA trial); or 2) a hay/grain meal alone (Control trial).

Results

Oral NAA resulted in a profound plasma alkalosis marked by decreased plasma [H⁺] and increased plasma [TCO₂] and [HCO₃^-] compared to Control. The primary contributor to the plasma alkalosis was an increased [SID], as a result of increased plasma [Na⁺] and decreased plasma [Cl^-]. An increased [A_tot], due to increased [PP] and a sustained increase in plasma [acetate], contributed a minor acidifying effect.

Conclusion

It is concluded that oral NaAcetate could be used as both an alkalinizing agent and an alternative energy source in the horse.

Anti-inflammatory and chondroprotective effects of nutraceuticals from Sasha's Blend in a cartilage explant model of inflammation

New Zealand green lipped mussel (NZGLM), abalone (AB), and shark cartilage (SC) are extensively used for treatment of and/or as preventatives for arthritis, despite a relative paucity of scientific evidence for efficacy. This research integrated a simulated digestion protocol with ultrafiltration and cartilage explants to generate new information on the anti-inflammatory and chondroprotective properties of NZGLM, SC, and AB. Each nutraceutical was artificially digested using simulated gastric and intestinal fluids, and the crude digest was ultrafiltered (50 kDa). Each filtrate was applied individually to cartilage explants before the explants were stimulated with IL-1 to induce an acute inflammatory response. Media were collected daily for 48 h and analyzed for prostaglandin E(2) (PGE(2)), glycosaminoglycan (GAG), and nitric oxide (NO), and cartilage tissue was differentially stained to determine the relative proportion of live and dead cells. SC and NZGLM significantly inhibited IL-1-induced PGE(2) synthesis and IL-1-induced GAG release, and AB was an effective inhibitor of IL-1-induced NO production. The three test nutraceuticals affect at least three major pathways involved in the catabolic cycle of arthritis and may prove important treatments and/or preventatives for the pain and degradation associated with this condition. The methodology and results describe a useful model for evaluating dietary nutraceuticals in vitro.

Effects of dietary strong acid anion challenge on regulation of acid-base balance in sheep1

The acid-base status of the extracellular fluid is directly affected by the concentrations of strong basic cations and strong acid anions that are absorbed into the bloodstream from the diet. The objective of this study was to develop and characterize a model for dietary acid challenge in sheep by decreasing the dietary cation-anion difference (DCAD) using NutriChlor (HCl-treated canola meal), an anionic feed supplement. Ten fully fleeced sheep (Rideau-Arcott, 54.3 +/- 6.7 kg of BW) were fed either a control supplement [200 g/d of canola meal, DCAD = 184 mEq/kg of DM, calculated as (Na+ + K+) - (Cl- + S2-)] or an anionic supplement (AS; 200 g/d of NutriChlor, DCAD = -206 mEq/kg of DM) offered twice daily at 0700 and 1100 in a randomized complete block design. The sheep were individually housed and limit-fed a basal diet of dehydrated alfalfa pellets (22% CP and 1.2 Mcal of NE(g)/kg, DM basis) at 1.1 kg of DM/d offered twice daily at 1000 and 1300. Two days before the beginning of the experiment, the sheep were fitted with vinyl catheters (0.86-mm i.d., 1.32-mm o.d.) in the left jugular vein to facilitate blood sampling. Blood and urine samples were obtained daily from 1100 to 1130 on d 1 through 9 and at 0700, 1000, 1300, 1600, and 1900 on d 10. Blood was analyzed for hematocrit, plasma pH, gases, strong ions, and total protein. Urine samples were analyzed for pH. The AS induced a nonrespiratory acid-base disturbance associated with lower (P < 0.05) plasma pH (7.47 vs. 7.39), lower (P < 0.05) urine pH (8.13 vs. 6.09), and lower (P < 0.05) strong ion difference (42.5 vs. 39.5). The AS reduced (P < 0.05) the concentration of plasma glucose, base excess, and bicarbonate and increased (P < 0.05) the concentration of K+ and Cl-. Lowering DCAD increased (P < 0.05) Ca2+ concentrations in plasma by 13%. In conclusion, this dietary model successfully induced a significant acid-base disturbance in sheep. Although the acidifying effects of negative DCAD in the diet may have short-term prophylactic effects of elevating the concentration of Ca2+ in plasma, negative DCAD may have detrimental effects on acid-base balance.

Effects of prepartum administration of a monensin controlled release capsule on rumen pH, feed intake, and milk production of transition dairy cows

Effects of prepartum administration of a monensin controlled release capsule (CRC) on rumen pH, dry matter intake, and milk production during the transition period and early lactation were determined in 16 multiparous Holstein cows. Cows were divided into blocks of 2 depending on calving date. Cows were fed either a close-up dry cow or a lactating cow total mixed ration ad libitum. Rumen pH was monitored continuously using indwelling probes. Monensin did not affect average daily rumen pH, time below pH 6, time below pH 5.6, area below pH 6, and area below pH 5.6 throughout the experiment. Average daily pH, time below pH 6, and time below pH 5.6 before calving were 6.62, 65.6 min/d, and 17.6 min/d, respectively, and did not differ among the weeks before calving. Average daily pH, time below pH 6, and time below pH 5.6 were 6.19, 443.3 min/d, and 115.5 min/d, respectively, during the first week after calving, and were 6.36, 204.3 min/d, and 52.4 min/d, respectively, during the sixth week after calving. In the weeks after calving, average daily pH showed a quadratic increase, time below pH 6 showed a quadratic decrease, and time below pH 5.6 showed a linear decrease. Monensin did not affect dry matter intake and daily yields of milk, milk fat, and milk protein. Results suggest that prepartum administration of a monensin CRC did not increase rumen pH in multiparous cows fed the experimental diets during the transition period and early lactation.

Hydration of exercised standardbred racehorses assessed noninvasively using multi-frequency bioelectrical impedance analysis

REASONS FOR PERFORMING STUDY

In human and animal clinical practice, multi-frequency bioelectrical impedance analysis (MF-BIA) is increasingly used as a diagnostic tool to assess hydration of intra-and extracellular fluid compartments. Accurate determination of changes in hydration status within individuals over time has remained problematic due to the requirement for complete impedance-frequency relationships at the time points of interest.

OBJECTIVES

To use MF-BIA in 13 Standardbred racehorses and 7 'endurance' research horses to determine if MF-BIA could be used to track changes in total body water (TBW), intracellular fluid volume (ICFV) and extracellular fluid volume (ECFV) resulting from exercise.

METHODS

Jugular venous blood was sampled at rest and for 2-13 h following exercise. TBW, ECFV and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). TBW, ECFV, ICFV and PV were correlated to impedance measures and predictive equations used to determine hydration status from MF-BIA measures.

RESULTS

TBW loss continued throughout the recovery period, and was primarily borne by the ECF compartment at 90 min of recovery.

CONCLUSIONS

MF-BIA predictions of compartmental hydration status were significantly correlated to measured/calculated decreases in these compartments.

POTENTIAL RELEVANCE

Practical applications for MF-BIA in horses include monitoring of hydration status during transport and competition, assessment of body compostion, clinical health assessment and critical care management.

Physicochemical analysis of acid–base status during recovery from high-intensity exercise in Standardbred racehorses

The present study used the physicochemical approach to characterize the changes in acid–base status that occur in Standardbred racehorses during recovery from high-intensity exercise. Jugular venous blood was sampled from nine Standardbreds in racing condition, at rest and for 2 h following a high-intensity training workout. Plasma [H+] increased from 39.1±1.0 neq l−1 at rest to 44.8±2.7 neq l−1 at 1 min of recovery. A decreased strong ion difference ([SID]) was the primary contributor to the increased [H+] immediately at the end of exercise, while increased plasma weak ion concentration ([Atot]) was a minor contributor to the acidosis. A decreased partial pressure of carbon dioxide (PCO2) at 1 min of recovery had a slight alkalinizing effect. The decreased [SID] at 1 min of recovery was a result of a 15.1±3.1 meq l−1 increase in [lactate−], as [Na+] and [K+] were also increased by 6.5±0.7 and 1.14±0.06 meq l−1, respectively, at 1 min of recovery. It is concluded that high-intensity exercise and recovery is associated with significant changes in acid–base balance, and that full recovery of many parameters that determine acid–base status requires 60–120 min.

Cyclical plasma electrolyte and acid–base responses to meal feeding in horses over a 24-h period

The present study used the physicochemical approach to characterize the changes in plasma electrolyte and acid–base states that occur in horses in response to feeding. Jugular venous blood was sampled every 0.5–2 h over a 24-h period from two groups (n = 4 and n = 5) of Standardbreds fed a mixed hay and grain ration at 8 am and 7 pm. One group of horses was studied in October, and one in December. The time course and magnitude of feeding responses differed between groups, and between the morning and evening meals. Feeding-induced changes in plasma electrolyte and acid–base variables occurred rapidly, within the first 1–3 h of meal consumption. The plasma acidosis associated with eating the meal was marked by increased plasma [H+] and decreased TCO2. The primary contributors to the increases in plasma [H+] were the decrease in the plasma concentration of strong ions ([SID]) and the pCO2. The increase in plasma total weak acid (protein) concentration ([Atot]) post-feeding had only a minor effect on the acid–base state. The feeding-induced acidosis abated 3–6 h after the meal, showing cyclical recovery of physicochemical variables that contributed to the acid–base disturbance. It is concluded that several key plasma electrolyte and acid–base parameters undergo significant, cyclical fluctuations in response to feeding in horses.

Time course and magnitude of changes in total body water, extracellular fluid volume, intracellular fluid volume and plasma volume during submaximal exercise and recovery in horses

The purpose of the present study was to determine the time course and magnitude of changes in extracellular and intracellular fluid volumes in relation to changes in total body water during prolonged submaximal exercise and recovery in horses. Seven horses were physically conditioned over a 2-month period and trained to trot on a treadmill. Total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). Changes in TBW were assessed from measures of body mass, and changes in PV and ECFV were calculated from changes in plasma protein concentration. Horses exercised by trotting on a treadmill for 75–120 min incurred a 4.2% decrease in TBW. During exercise, the entire decrease in TBW (mean±standard error: 12.8±2.0 l at end of exercise) could be attributed to the decrease in ECFV (12.0±2.4 l at end of exercise), such that there was no change in intracellular fluid volume (ICFV; 0.9±2.4 l at end of exercise). PV decreased from 22.0±0.5 l at rest to 19.8±0.3 l at end of exercise and remained depressed (18–19 l) during the first 2 h of recovery. Recovery of fluid volumes after exercise was slow, and characterized by a further transient loss of ECFV (first 30 min of recovery) and a sustained increase in ICFV (between 0.5 and 3.5 h of recovery). Recovery of fluid volumes was complete by 13 h post exercise. It is concluded that prolonged submaximal exercise in horses favours net loss of fluid from the extracellular fluid compartment.

Time course and magnitude of fluid and electrolyte shifts during recovery from high-intensity exercise in Standardbred racehorses

The present study characterized the fluid and electrolyte shifts that occur in Standardbred racehorses during recovery from high-intensity exercise. Jugular venous blood was sampled from 13 Standardbreds in racing condition, at rest and for 2 h following a high-intensity training workout. Total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). Changes in TBW were assessed from measures of body mass, and changes in PV and ECFV were calculated from changes in plasma protein concentration. Exercise resulted in a 26.9% decrease in PV. At 10 min of recovery TBW and ECFV were decreased by 2.2% and 16.5% respectively, while intracellular fluid volume was increased by 7.1%. There was a continued loss of fluid due to sweating throughout the recovery period such that TBW was decreased by 3.9% at 90 min of recovery. This decrease in TBW was nearly equally partitioned between the extracellular and intracellular fluid compartments. Plasma Na+ and Cl− contents were decreased at 1 min of recovery, but not different from rest by 40 min of recovery. Plasma K+ content at 1 min post exercise was not different from the pre-exercise value; however, by 5 min of recovery K+ content was significantly decreased and it remained decreased throughout the recovery period. It is concluded that there are very rapid and large fluid and electrolyte shifts between body compartments during and after high-intensity exercise, and that full recovery of these shifts requires 90–120 min.

Effects of mild heat stress and grain challenge on acid-base balance and rumen tissue histology in lambs1

The effect of heat stress (HS) and grain challenge (GC) on acid-base balance and rumen tissue histology in lambs was investigated using 24 yearling wether lambs (58 +/- 4.5 kg of BW) in a 2 x 2 factorial experiment with repeated measures for day (10, 14, and 17) of sampling. The factors were temperature [thermoneutral zone (TN) vs. HS] and diet (control vs. GC). Lambs were blocked by BW and assigned to 1 of 4 treatments in temperature-controlled rooms: 1) TN (temperature = 18 to 20 degrees C; relative humidity = 30%; 2) TN + GC; 3) HS (temperature = 35 degrees C for 9 h/d, 20 degrees C for 15 h/d; relative humidity = 40%); and 4) HS + GC. Venous blood samples were collected at 1800 on the first day of GC (d 10), in the middle of GC (d 14), and at the end of the trial (d 17) by jugular venipuncture and analyzed for pH, gases, hematocrit, plasma ions, and total protein. After all measurements in live animals were taken on d 17, lambs were slaughtered, and tissue samples were obtained from the ventral sac of the rumen for histological assessment. Except for the concentration of plasma glucose (P = 0.04) and total protein (P < 0.01), there were no (P > 0.05) diet x temperature interactions. With HS, the concentration of Na+ and Cl- in the control group decreased at d 14 and then increased by d 17, and respiration rates in the control group decreased linearly (P < 0.05). Compared with the control group, respiration rates and the concentration of Cl- in the GC lambs increased linearly over time, whereas the concentration of Na+ decreased linearly (P < 0.05) across time. Under HS, the partial pressure of carbon dioxide, total carbon dioxide, the partial pressure of oxygen and oxygen saturation, and the concentration of Mg2+, glucose, and HCO3- showed quadratic (P < 0.05) responses with time. In both treatments, DMI, base excess of extracellular fluid, base excess of blood, and standard bicarbonate increased linearly (P < 0.05), and hematocrit, plasma protein, Ca2+, anion gap, and plasma strong ion difference decreased linearly (P < 0.05) across day. Compared with the control group, the GC group had decreased papillae count in the ruminal ventral sac (1.3 vs. 1.5; P < 0.05). These results suggest that under HS the acidifying effects of GC on acid-base balance in lambs were counteracted in the short-term through respiratory adaptation.

An improved method for constructing and selectively silanizing double-barreled, neutral liquid-carrier, ion-selective microelectrodes

We describe an improved, efficient and reliable method for the vapour-phase silanization of multi-barreled, ion-selective microelectrodes of which the silanized barrel(s) are to be filled with neutral liquid ion-exchanger (LIX). The technique employs a metal manifold to exclusively and simultaneously deliver dimethyldichlorosilane to only the ion-selective barrels of several multi-barreled microelectrodes. Compared to previously published methods the technique requires fewer procedural steps, less handling of individual microelectrodes, improved reproducibility of silanization of the selected microelectrode barrels and employs standard borosilicate tubing rather than the less-conventional theta-type glass. The electrodes remain stable for up to 3 weeks after the silanization procedure. The efficacy of a double-barreled electrode containing a proton ionophore in the ion-selective barrel is demonstrated in situ in the leaf apoplasm of pea (Pisum) and sunflower (Helianthus). Individual leaves were penetrated to depth of approximately 150 microm through the abaxial surface. Microelectrode readings remained stable after multiple impalements without the need for a stabilizing PVC matrix.

Hematological and acid-base changes in men during prolonged exercise with and without sodium-lactate infusion

An emerging technique used for the study of metabolic regulation is the elevation of lactate concentration with a sodium-lactate infusion, the lactate clamp (LC). However, hematological and acid-base properties affected by the infusion of hypertonic solutions containing the osmotically active strong ions sodium (Na+) and lactate (Lac−) are a concern for clinical and research applications of LC. In the present study, we characterized the hematological and plasma acid-base changes during rest and prolonged, light- to moderate-intensity (55% V̇o2 peak) exercise with and without LC. During the control (Con) trial, subjects were administered an isotonic, isovolumetric saline infusion. During LC, plasma lactate concentration ([Lac−]) was elevated to 4 meq/l during rest and to 4–7 meq/l during exercise. During LC at rest, there were rapid and transient changes in plasma, erythrocyte, and blood volumes. LC resulted in decreased plasma [H+] (from 39.6 to 29.6 neq/l) at the end of exercise while plasma [HCO3−] increased from 26 to 32.9 meq/l. Increased plasma strong ion difference [SID], due to increased [Na+], was the primary contributor to decreased [H+] and increased [HCO3−]. A decrease in plasma total weak acid concentration also contributed to these changes, whereas Pco2 contributed little. The infusion of hypertonic LC caused only minor volume, acid-base, and CO2 storage responses. We conclude that an LC infusion is appropriate for studies of metabolic regulation.