Corticosteroid potentiation of surfactant dose response in preterm rabbits

Fetal rabbits were treated with corticosteroids by maternal administration for 48 h before delivery at 27 days gestational age. Both corticosteroid-treated and control animals then received exogenous natural rabbit surfactant at birth at doses of 0-75 mg lipid/kg. After 10 min of ventilation at tidal volumes of 12-15 ml/kg, static pressure-volume measurements were made. At all surfactant doses there was a significantly higher maximal lung volume, higher dynamic compliance, and lower pressure requirement in the corticosteroid-treated than in the control rabbits (P less than 0.01). Control animals showed incremental improvements in dynamic compliances and maximal lung volumes up to a dose of 50 mg/kg, whereas corticosteroid treated animals improved to a maximum at the low dose of 15 mg/kg (P less than 0.01). However, surface tension as assessed by lung stability index improved with increasing surfactant dose but was not significantly different between corticosteroid-treated and control animals at a given dose. The results imply that maternal corticosteroid treatment potentiates surfactant replacement by a change in lung structure that is independent of surface tension effects.     

Corticosteroids and surfactant increase lung volumes and decrease rupture pressures of preterm rabbit lungs

We measured the effects of corticosteroids and surfactant individually and in combination on lung pressure-volume relationships, rupture pressures, and rupture volumes. Pregnant does were injected with betamethasone (0.1 mg/kg per day im) or vehicle on days 24 and 25 of gestation, and fetal rabbits were delivered on days 26 and 27. Natural surfactant (50 mg/kg body wt) was instilled intratracheally into half of the lungs after tracheotomy. After nine cycles of inflation with air to 40 cmH2O and deflation, air pressure-volume curves were measured. Then the lungs were filled with air to rupture, and rupture volume and pressure were recorded. Both corticosteroids and surfactant caused an increase in maximal lung volumes (P less than 0.01) and a decrease of lung rupture pressures (P less than 0.01) compared with controls. The effects of corticosteroids plus surfactant on lung volumes were the sum of each effect individually, but rupture pressures were the same as those for corticosteroids or surfactant alone. Surfactant, in addition, caused an increase in lung stability at deflation, an effect that was not evident in the corticosteroid-treated groups. Measurements of saturated phosphatidylcholine in alveolar washes and lung tissue indicated comparable values in the corticosteroid and control groups. We conclude that changes in static properties and rupture pressures presumably reflect changes in lung structure caused by corticosteroids that are independent of a corticosteroid effect on surfactant pool sizes.     

Respiratory distress and surfactant inhibition following vagotomy in rabbits

We used the model of bilateral cervical vagotomy of adult rabbits to cause respiratory failure characterized by pulmonary edema, decreased lung compliance, and atelectasis. We documented an 18-fold increase in radiolabeled albumin leak from the vascular space into alveolar washes of vagotomy vs. sham-operated rabbits (P less than 0.01). Despite a twofold increase in percent of prelabeled saturated phosphatidylcholine secreted (P less than 0.01), the alveolar wash saturated phosphatidylcholine pool sizes were not different. The minimum surface tensions were 19.6 +/- 2.5 vs. 9.4 +/- 2.2 dyn/cm for alveolar washes from vagotomy and control rabbits, respectively (P less than 0.01). The soluble proteins from alveolar washes inhibited the surface tension lowering properties of natural surfactant, whereas those from the control rabbits did not (P less than 0.01). When vagotomy rabbits in respiratory failure were treated with 50 mg natural surfactant lipid per kilogram arterial blood gas values and compliances improved relative to control rabbits. Vagotomy results in alveolar pulmonary edema, and surfactant dysfunction despite normal surfactant pool sizes and respiratory failure. A surfactant treatment can improve the respiratory failure.     

Lung mechanics in papain-treated rabbits

To further investigate the effects of airway cartilage softening on static and dynamic lung mechanics, 11 rabbits were treated with 100 mg/kg iv papain, whereas 9 control animals received no pretreatment. Lung mechanics were studied 24 h after papain injection. There was no significant difference in lung volumes, lung pressure-volume curves, or chest wall compliance. Papain-treated rabbits showed increased lung resistance: 91 +/- 63 vs. 39 +/- 22 cmH2O X l-1 X s (mean +/- SD; P less than 0.05), decreased maximal expiratory flows at all lung volumes, and preserved density dependence of maximal expiratory flows. We conclude that increased airway wall compliance is probably the mechanism that limited maximal expiratory flow in this animal model. In addition the increased lung resistance suggests that airway cartilage plays a role in the regulation of airway caliber during quiet tidal breathing.     

Intrapulmonary catabolism of surfactant-saturated phosphatidylcholine in rabbits

Intrapulmonary surfactant catabolism was investigated by use of a phospholipase A1- and A2-resistant analogue of dipalmitoylphosphatidylcholine (DPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPC ether). [14C]DPC ether, made into liposomes with [3H]DPC and associated with 32P-labeled rabbit surfactant, was given intratracheally to 1-kg rabbits, which were killed at preset times to 48 h. Recoveries of radiolabel as saturated phosphatidylcholine (Sat PC) isolated from alveolar wash (AW), postlavage lung homogenate (LH), and alveolar macrophages were measured. All groups had similar AW and LH Sat PC pool sizes, indicating no perturbation of endogenous Sat PC pools. Despite a nearly fivefold accumulation of [14C]DPC ether in the lung by 48 h (P less than 0.01), the three probes had similar alveolar clearance curves. Furthermore, the Sat PC reutilization efficiency (41.6%) and turnover time (5.9 h) calculated for DPC ether were not different from values for the DPC and rabbit surfactant. Of the DPC ether (0.7%) and DPC (9%) labels recovered as PC in organs outside the lung, greater than 85% was unsaturated, indicating de novo synthesis using precursors from degraded PC. DPC ether was a useful probe of intrapulmonary DPC catabolism, and after alveolar uptake there was no direct reentry of intact DPC from the catabolic compartment(s) into the secretory pathway.     

Aerosolized surfactant treatment of preterm lambs

To evaluate the potential for aerosolized surfactant treatments of surfactant deficiency, twin lamb fetuses were delivered at 130-132 days gestational age and received nebulized natural surfactant (Neb NS), nebulized Survanta (Neb Surv), tracheally instilled natural surfactant (Inst NS), or nebulized saline (Neb Saline). Neb NS and Neb Surv groups had significant increases in ventilatory efficiency index and dynamic compliance values (P less than 0.05). Both groups also had pressure-volume curves that were comparable to the Inst NS group. The Neb Saline control group had deterioration of the ventilation efficiency index and dynamic compliance values over time as well as pressure-volume curves that demonstrated smaller lung volumes compared with all three surfactant-treated groups (P less than 0.01). Delivery of aerosolized surfactant to the lung was only approximately 2 mg lipid/kg for the nebulized groups, a dose one-twentieth of that previously noted to be effective in instillation protocols. Distribution histograms of the aerosolized surfactant-treated groups differed from the instilled animals as there was more deposition in the right upper lobes and tracheae in the nebulized groups compared with the instilled group (P less than 0.05). Pulmonary blood flow was not altered by aerosolized surfactant treatment. Administration of aerosolized surfactant to preterm lambs improved lung function at a very low surfactant dose.     

Stimulation of surfactant phospholipid biosynthesis in the lungs of rats treated with silica.

The effects of intratracheally instilled silica (10 mg/rat) on the biosynthesis of surfactant phospholipids was investigated in the lungs of rats. The sizes of the intracellular and extracellular pools of surfactant phospholipids were measured 7, 14 and 28 days after silica exposure. The ability of lung slices to incorporate [14C]choline and [3H]palmitate into surfactant phosphatidylcholine (PC) and disaturated phosphatidylcholine (DSPC) was also investigated. Both intra- and extra-cellular pools of surfactant phospholipids were increased by silica treatment. The intracellular pool increased linearly over the 28-day time period, ultimately reaching a size 62-fold greater than controls. The extracellular pool also increased, but showed a pattern different from that of the intracellular pool. The extracellular pool increased non-linearly up to 14 days, and then declined. At its maximum, the extracellular pool was increased 16-fold over the control. The ability of lung slices to incorporate phospholipid precursors into surfactant-associated PC and DSPC was elevated at all time periods. The rate of incorporation of [14C]choline into surfactant PC and DSPC was maximal at 14 days and was nearly 3-fold greater than the rate in controls. The rate of incorporation of [3H]palmitate was also maximal at 14 days, approx. 5-fold above controls for PC and 3-fold for DSPC. At this same time point, the microsomal activity of cholinephosphate cytidylyltransferase was increased 4.5-fold above controls, but cytosolic activity was not significantly affected by silica treatment. These data indicate that biosynthesis of surfactant PC is elevated after treatment of lungs with silica and that this increased biosynthesis probably underlies the expansion of the intra- and extra-cellular pools of surfactant phospholipids.     

Diaphragmatic fatigue in normoxia and hyperoxia

The effect of choline deficiency on the lung lipids of actively growing male Sprague-Dawley rats was investigated using a washed soy protein diet deficient in choline and methionine (lipotrophic). The livers from deficient animals had a significantly increased total lipid content and decreased phosphatidylcholine (PC) content and PC-to-phosphatidylethanolamine ratio (P less than 0.01). Although lung free choline levels were decreased 40% compared with controls (P less than 0.05), the PC content of the whole lung homogenate was unchanged. However, disaturated phosphatidylcholine from animals receiving the lipotrophic diet was significantly increased in the lavage and proportionally decreased in the lavaged lung tissue compared with controls (P less than 0.01). This study indicates that, despite decreased lung choline levels as a result of ingesting a lipotrophic diet, and unlike the liver, lung PC content is maintained at normal values. Although the lung total PC levels are maintained, there is a change in the partition of this lipid pool between the tissue and the alveolar space.     

Surfactant treatments alter endogenous surfactant metabolism in rabbit lungs

The effect of exogenous surfactant on endogenous surfactant metabolism was evaluated using a single-lobe treatment strategy to compare effects of treated with untreated lung within the same rabbit. Natural rabbit surfactant, Survanta, or 0.45% NaCl was injected into the left main stem bronchus by use of a Swan-Ganz catheter. Radio-labeled palmitic acid was then given by intravascular injection at two times after surfactant treatment, and the ratios of label incorporation and secretion in the left lower lobe to label incorporation and secretion in the right lung were compared. The treatment procedure resulted in a reasonably uniform surfactant distribution and did not disrupt lobar pulmonary blood flow. Natural rabbit surfactant increased incorporation of palmitate into saturated phosphatidylcholine (Sat PC) approximately 2-fold (P less than 0.01), and secretion of labeled Sat PC increased approximately 2.5-fold in the surfactant-treated left lower lobe relative to the right lung (P less than 0.01). Although Survanta did not alter incorporation, it did increase secretion but not to the same extent as rabbit surfactant (P less than 0.01). Alteration of endogenous surfactant Sat PC metabolism in vivo by surfactant treatments was different from that which would have been predicted by previous in vitro studies.     

Endogenous opioids modulate fetal rabbit lung maturation

To test the hypothesis that endogenous opioids modulate fetal lung development, separate groups of pregnant rabbits received daily injections of saline, morphine (1 mg/kg body wt), or the opioid antagonist naloxone (0.4 and 5.0 mg) for 10 days during their last trimester of pregnancy. The corresponding groups of fetuses were then delivered prematurely on day 28 of gestation (term approximately 31 days) and evaluated with respect to differences in body weight, lung weight, and the ratios of wet to dry lung weight and lung dry weight to body weight, the static inflation and deflation air and saline pressure-volume (P-V) characteristics of the lungs, and lung morphology. Mean values for body weight, lung weight, and the ratios of lung wet to dry weight and lung dry weight to body weight were not significantly different among the saline control (C), morphine (M)-, and naloxone (NLX)-treated fetuses. On the other hand, the fetal air P-V curves varied significantly (P less than 0.001), wherein the M-treated group depicted increased lung distensibility and alveolar stability on lung deflation, whereas the opposite was obtained in the NLX-treated fetuses. Moreover, morphometric analyses demonstrated that the mean alveolar air space-to-tissue ratio in lungs from M-treated fetuses were significantly greater than that observed either in C or in NLX-treated fetuses (P less than 0.05); however, the air space-to-tissue ratio did not significantly vary between the C and NLX-treated animals. These observations provide new evidence that endogenous opioids enhance fetal lung maturation.     

Compartmentation of phosphorylated precursors of phospholipid biosynthesis in cultured neuroblastoma cells

The continuous turnover of membrane phospholipids requires a steady supply of biosynthetic precursors. We evaluated the effects of decreasing extracellular Na+ concentration on phospholipid metabolism in cultured neuroblastoma (N1E 115) cells. Incubating cultures with 145 to 0 mM NaCl caused a concentration-dependent inhibition of [32P]phosphate uptake into the water-soluble intracellular pool and incorporation into phospholipid. Phospholipid classes were differentially affected; [32P]phosphate incorporated into phosphati-dylethanolamine (PE) and phosphatidylcholine (PC) was consistently less than into phosphatidylinositol (PI) and phosphatidylserine (PS). This could not be attributed to decreased phospholipid synthesis since under identical conditions, there was no effect on arachidonic acid or ethanolamine incorporation, and choline utilization for PC synthesis was increased. The effect of Na+ was highly specific since reducing phosphate uptake to a similar extent by incubating cultures in a phosphate-deficient medium containing Na+ did not alter the relative distribution of [32P]phosphate in phospholipid. Of several cations tested only Li+ could partially (50%) replace Na+. Incubation in the presence of ouabain or amiloride had no effect on [32P]phosphate incorporation into phospholipid. The differential effects of low Na+ on [32P]phosphate incorporation into PI relative to PC and PE suggests preferential compartmentation of [32P]phosphate into ATP in pools used for phosphatidic acid synthesis and relatively less in ATP pools used for synthesis of phosphocholine and phosphoethanolamine, precursors of PC and PE, respectively. This suggestion of heterogeneous and distinct pools of ATP for phospholipid biosynthesis, and of potential modulation by Na+ ion, has important implications for understanding intracellular regulation of metabolism.     

Statin therapy restores sympathovagal balance in experimental heart failure.

Inhibitors of hydroxymethylglutaryl-CoA reductase or statins have been shown to alleviate endothelial dysfunction. Their effects on constitutive nitric oxide synthase in the central nervous system may hypothetically affect the autonomic balance in sympathoexcitatory states, such as chronic heart failure (CHF). To address this issue, simvastatin (SIM) (0.3, 1.5, or 3 mg. kg-1. day-1 po) was given to rabbits with pacing-induced CHF over a 3-wk period. Normal and CHF vehicle-treated rabbits served as controls. Autonomic balance was assessed by measuring heart rate variability, including power spectral analysis (PSA). In addition, changes in resting heart rate were assessed before and after vagal and sympathetic autonomic blockade by atropine and metoprolol, respectively. The SD for all intervals was 8.9 +/- 0.7 ms in normal, 4.9 +/- 0.6 ms in CHF (P < 0.01), 3.8 +/- 0.6 ms in CHF with 0.3 mg. kg-1. day-1 SIM (P < 0.001), 5.7 +/- 0.9 in CHF with 1.5 mg. kg-1. day-1 SIM (P < 0.05), and 7.2 +/- 0.5 in CHF with 3.0 mg. kg-1. day-1 SIM. Similarly, total power was 40.5 +/- 6.3 ms2 in normal, 10.1 +/- 3.0 ms2 in CHF (P < 0.01), 6.0 +/- 1.6 ms2 in CHF with 0.3 mg. kg-1. day-1 SIM (P < 0.01), 13.2 +/- 3.9 ms2 in CHF with 1.5 mg. kg-1. day-1 SIM (P < 0.05), and 22.0 +/- 3.0 ms2 in CHF with 3.0 mg. kg-1. day-1 SIM. Both PSA data for low (0.625-0.1875 Hz) and high frequencies (0.1875-0.5625 Hz) showed recovery in CHF animals on medium and high SIM doses without changes in the low-to-high-frequency ratio. SIM beneficially affects autonomic tone in CHF as seen by the reversal of depressed HRV and total power of PSA. These data have important implications for the treatment of patients with autonomic imbalance.     

Lipid metabolism in T47D human breast cancer cells: 31P and 13C-NMR studies of choline and ethanolamine uptake.

31P and 13C-NMR were used to determine the kinetics of choline and ethanolamine incorporation in T47D clone 11 human breast cancer cells grown as small (150 microns) spheroids. Spheroids were perfused inside the spectrometer with 1,2-13C-labeled choline or 1,2-13C-labeled ethanolamine (0.028 mM) and the buildup of labeled phosphoryl-choline (PC) or phosphorylethanolamine (PE) was monitored. Alternatively the PC and GPC pools were prelabeled with 13C and the reduction of label was monitored. 31P spectra were recorded from which the overall energetic status as well as total pool sizes could be determined. The ATP content was 8 +/- 1 fmol/cell, and the total PC and PE pool sizes were 16 and 14 fmol/cell, respectively. PC either increased by 50% over 24 h or remained constant, while PE remained constant in medium without added ethanolamine but increased 2-fold within 30 h in medium containing ethanolamine, indicating a dependence on precursor concentration in the medium. The 31P and 13C data yielded similar kinetic results: the rate of the enzymes phosphocholine kinase and phosphoethanolamine kinase were both on the order of 1.0 fmol/cell per h, and the rate constants for CTP:phosphocholine cytidyltransferase and CTP:phosphoethanolamine kinase were 0.06 h-1 for both enzymes. The kinetics of choline incorporation did not alter in the presence of 0.028 mM ethanolamine indicating that they have non-competing pathways.     

Corticosteroid and thyrotropin-releasing hormone effects on preterm sheep lung function

Four groups of twin sheep fetuses were catheterized at 121 days of gestational age and intravenously infused with saline, 0.75 mg.kg-1.h-1 cortisol for 60 h, five intermittent bolus injections of 5 micrograms/kg thyrotropin-releasing hormone (TRH) at 12-h intervals, or both hormones before delivery at 128 days. At birth, the lambs were randomized to receive surfactant or no treatment. Surfactant treatment improved lung function of all the groups. Corticosteroids alone and in combination with TRH improved compliance and gas exchange as well as pressure-volume curves. Corticosteroids alone dramatically decreased the recovery of intravenously administered radiolabeled albumin in the lung tissue and air space and improved the pulmonary response to surfactant treatment. There were no additional effects of TRH when given with corticosteroids on lung function or albumin leak. There were no changes in alveolar surfactant-saturated phosphatidylcholine pool sizes after any hormone treatment. The single significant effect of combined corticosteroid and TRH treatment was a fivefold increase in surfactant protein A in alveolar lavage fluid relative to all other groups.     

Altered surfactant function and metabolism in rabbits with acute lung injury

Lung injury was induced in rabbits with N-nitroso-N-methylurethane (NNNMU), and saturated phosphatidylcholine (Sat PC) pool sizes and phospholipid compositions were measured in alveolar wash subfractions isolated by differential centrifugation (large and small surfactant aggregates). Surfactant metabolism also was studied using intravascular and intratracheal radiolabels. Protein permeability, gas exchange, and compliance were significantly abnormal as lung injury progressed. At peak injury, there was a decrease in the large aggregate Sat PC pool size in alveolar wash accompanied by increased uptake of Sat PC from the air space and increased specific activity of both intravascular and intratracheal radiolabels in lamellar bodies. This was followed by a marked rise in the small aggregate pool size in the alveolar wash and increased secretion of Sat PC into the air spaces. Phospholipid compositions, total phospholipid-to-protein ratios, and in vivo functional studies using a preterm ventilated rabbit model were abnormal for both large and small aggregate surfactant fractions from the lung-injured rabbits. These studies characterize quantitative, qualitative, and functional changes of alveolar wash surfactant subfractions in NNNMU-injured lungs.     

Partial ileal bypass reduces the production rate of low density lipoproteins in Watanabe heritable hyperlipidemic rabbits

Partial ileal bypass surgery in homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits resulted in a decrease of low density lipoproteins (LDL)-cholesterol from 14.2 +/- 2.4 to 7.0 +/- 1.2 mmol/l. To investigate the effect of partial ileal bypass on receptor-mediated and receptor-independent LDL catabolism, turnover studies were performed of radiolabeled native LDL and chemically modified LDL (methyl-LDL) in WHHL rabbits after partial ileal bypass, in WHHL control rabbits, and in New Zealand White ("normal") rabbits. The plasma LDL pool in WHHL control rabbits was increased 10-fold. The receptor-mediated LDL clearance was essentially zero in WHHL rabbits, both in controls and after ileal bypass surgery; the fractional catabolic rates for total LDL were equal in both WHHL groups and were also similar to that for methyl-LDL in the normal rabbits. Seventy percent of the total LDL clearance in the normal rabbits occurred via the LDL receptor pathway. In the animals with a partial ileal bypass, the plasma LDL-protein pool was appreciably lower than in WHHL controls (41.6 +/- 5.7 vs 73.4 +/- 9.9 mg/kg, P less than 0.02). The absolute catabolic rate was almost 50% lower in the PIB group (21.4 +/- 2.0 vs 40.0 +/- 7.5 mg X kg-1 X day-1, P less than 0.02). These results indicate that the decrease of LDL after partial ileal bypass surgery in WHHL rabbits is the result of a reduced production rate of LDL.     

R?le of histamine on plasma fibrinogen levels in rats with surgical injury (laparotomy)

The probable r?le of endogenous histamine in the increase of plasma fibrinogen in rats submitted to tissue injury (laparotomy) was studied. In laparotomized rats with 10 mg kg-1 day-1 of diphenhydramine (a H1-histamine receptor blocker) plasma fibrinogen decreased significantly as compared to the group of rats laparotomized only (P less than 0.02), reaching values similar to those observed in rats laparotomized with removal of the adrenal medulla or laparotomized with severing of splanchnic nerves. There is a significant difference between these latter groups and the normal noninjured group (P less than 0.01). Plasma fibrinogen did not modify (as compared with the uninjured group) in rats injected only with histamine (1 mg kg-1 day-1) or with diphenhydramine. Taking into account the results obtained and the mechanism of action of diphenhydramine, it would seen that endogenous histamine takes part in the increase of plasma fibrinogen in laparotomized rats, perhaps indirectly through stimulation of the adrenal medulla secretion.     

Postnatal transformations of alveolar surfactant in the rabbit: changes in pool size,pool morphology and isoforms of the 32–38 kDa apolipoprotein

To clarify perinatal transformations of surfactant we performed lung lavage in term fetuses and in 0–24-h-old newborn rabbits. Lavage fluid was separated into three pools, namely lavage pellet, lavage supernatant and cells. We found that at birth the pellet contains 94.1 ± 1.4% (S.E.) saturated phosphatidylcholine, while the supernatant and cells contain traces of it. At birth the pellet contains secreted lamellar bodies while the supernatant lacks any recognizable structure. After birth, the alveolar saturated phosphatidylcholine level increases 5.1-times in 24 h, the proportions between pools reaching adult values in 90 min (pellet = 75.9 + 4.8%, supernatant = 22.7 ± 4.9%), and small vesicles appear in the supernatant, probably originating from the turnover of alveolar surfactant during breathing. The saturated phosphatidylcholine associated with cells remains unchanged. At birth, the 32–38 kDa surfactant apolipoprotein appears to be less extensively sialylated than in adult life.     

Turnover of 125I-VLDL and 131I-LDL apolipoprotein B in rabbits fed diets containing casein or soy protein

Rabbits fed low-fat, cholesterol-free, semi-purified diets containing casein developed a marked hypercholesterolemia compared to rabbits fed a similar diet containing soy protein (plasma cholesterol 281 +/- 31 vs. 86 +/- 9 mg/dl; P less than 0.05). Turnover studies (three per dietary group) were carried out in which homologous 125I-labeled VLDL and 131I-labeled LDL were injected simultaneously into casein- (n = 8) or soy protein- (n = 9) fed rabbits. ApoB-specific activities were determined in VLDL, IDL and LDL isolated from the pooled plasma of two or three rabbits per dietary group. The production rate of VLDL apoB (1.20 +/- 0.3 vs. 1.09 +/- 0.1 mg/h per kg) was similar for the two dietary groups. The fractional catabolic rate of VLDL apoB was lower for the casein group (0.15 +/- 0.03 vs. 0.23 +/- 0.01.h-1; 0.05 less than P less than 0.10). Although the pool size of VLDL apoB was higher in the casein group (8 +/- 2 vs. 5 +/- 0.3 mg/kg), this value did not reach statistical significance. For LDL apoB, the increased pool size in casein-fed rabbits (30 +/- 5 vs. 5 +/- 1 mg/kg; P less than 0.01) was associated with a decreased fractional catabolic rate (0.03 +/- 0.005 vs. 0.08 +/- 0.008.h-1; P less than 0.01) and a 2-fold increase in the production rate of LDL apoB (1 +/- 0.3 vs. 0.4 +/- 0.06 mg/kg per h; 0.05 less than P less than 0.10) compared to rabbits fed soy protein. Analysis of precursor-product relationships between the various lipoprotein fractions showed that casein-fed rabbits synthesized a higher proportion of LDL apoB (95% +/- 2 vs. 67% +/- 2; P less than 0.001) independent of VLDL catabolism. These results support the concept that the hypercholesterolemia in casein-fed rabbits is associated with impaired LDL removal consistent with a down-regulation of LDL receptors. These changes do not occur when the casein is replaced by soy protein.     

Arachidonic acid turnover in peritoneal macrophages is altered in endotoxin-tolerant rats

Peritoneal macrophages from endotoxin-tolerant rats have been found to exhibit depressed metabolism of arachidonic acid (AA) to prostaglandins and thromboxane in response to endotoxin. The effect of endotoxin tolerance on AA turnover in peritoneal macrophages was investigated by measuring [14C]AA incorporation and release from membrane phospholipids. Endotoxin tolerance did not affect the amount of [14C]AA incorporated into macrophages (30 min-24 h). However, the temporal incorporation of [14C]AA into individual phospholipid pools (15 min-24 h) was altered. In endotoxin-tolerant macrophages, [14C]AA incorporation into phosphatidylcholine (PC) (2, 4, 24 h) and phosphatidylethanolamine (PE) (8 h) was increased, while the incorporation into phosphatidylserine (PS) (2-24 h) was reduced (P less than 0.005) compared to control macrophages. There was no change in [14C]AA incorporation into phosphatidylinositol (PI). Following 2 or 24 h of incorporation of [14C]AA, macrophages were incubated (3 h) with endotoxin (50 micrograms/ml) or A23187 (1 microM), and [14C]AA release was measured. Endotoxin-tolerant macrophages released decreased (P less than 0.05) amounts of [14C]AA in response to both endotoxin and the calcium ionophore A23187 compared to controls. Control macrophages in response to endotoxin released [14C]AA from PC, PI and PE. In contrast, tolerant cells released [14C]AA only from PC (P less than 0.05). A23187 released [14C]AA from all four pools in the control cells, but only from PC and PE in the tolerant cells. These data demonstrate that endotoxin tolerance alters the uptake and release of AA from specific macrophage phospholipid pools. These results suggest that changes in AA turnover and/or storage are associated with endotoxin tolerance.