The Emirates Mars Mission

The Emirates Mars Mission (EMM) was launched to Mars in the summer of 2020, and is the first interplanetary spacecraft mission undertaken by the United Arab Emirates (UAE). The mission has multiple programmatic and scientific objectives, including the return of scientifically useful information about Mars. Three science instruments on the mission's Hope Probe will make global remote sensing measurements of the Martian atmosphere from a large low-inclination orbit that will advance our understanding of atmospheric variability on daily and seasonal timescales, as well as vertical atmospheric transport and escape. The mission was conceived and developed rapidly starting in 2014, and had aggressive schedule and cost constraints that drove the design and implementation of a new spacecraft bus. A team of Emirati and American engineers worked across two continents to complete a fully functional and tested spacecraft and bring it to the launchpad in the middle of a global pandemic. EMM is being operated from the UAE and the United States (U.S.), and will make its data freely available.

Erythropoiesis in the Rps19 disrupted mouse: Analysis of erythropoietin response and biochemical markers for Diamond-Blackfan anemia

The human ribosomal protein S19 gene (RPS19) is mutated in approximately 20% of patients with Diamond-Blackfan anemia (DBA), a congenital disease with a specific defect in erythropoiesis. The clinical expression of DBA is highly variable, and subclinical phenotypes may be revealed by elevated erythrocyte deaminase (eADA) activity only. In mice, complete loss of Rps19 results in early embryonic lethality whereas Rps19+/- mice are viable and without major abnormalities including the hematopoietic system. We have performed a detailed analysis of the Rps19+/- mice. We estimated the Rps19 levels in hematopoietic tissues and we analyzed erythrocyte deaminase activity and globin isoforms which are used as markers for DBA. The effect of a disrupted Rps19 allele on a different genetic background was investigated as well as the response to erythropoietin (EPO). From our results, we argue that the loss of one Rps19 allele in mice is fully compensated for at the transcriptional level with preservation of erythropoiesis.

Follow-up of plasma semicarbazide-sensitive amine oxidase activity and retinopathy in Type 2 diabetes mellitus

Plasma activity of the enzyme semicarbazide-sensitive amine oxidase (SSAO) is high in diabetes. Production of angiotoxic substances (an aldehyde, hydrogen peroxide, and ammonia) in vessel walls is catalysed by SSAO, suggesting a role for SSAO in the development of complications of diabetes. The objective of the present study was to follow up plasma SSAO activity (measured radiometrically), HbA(1c) (using ion exchange chromatography), and retinopathy (by fundus photography) after 2.8 years, in 34 patients with Type 2 diabetes. We also measured urinary levels of an SSAO substrate, methylamine, by fluorometric high-performance liquid chromatography (HPLC). As at baseline, plasma SSAO activity was now higher in subjects with retinopathy (mean 19.5) than in subjects without retinopathy (mean 16.0), 95% confidence interval (CI) for difference 0.6-6.3 nmol benzylamine ml(-1) plasma h(-1). SSAO activity had not changed significantly since baseline, mean difference -1.65 and 95% CI for difference -3.76 to 0.46 nmol benzylamine ml(-1) plasma h(-1). Mean HbA(1c) level remained higher for patients with retinopathy (now 7.9%) compared to those without retinopathy (6.1%), 95% CI for difference 0.6-3.0%. Comparing baseline and the present study, retinopathy was nonproliferative; level had worsened for five and improved for two patients. Urinary methylamine/creatinine ratio was lower in the group of patients with retinopathy (mean 0.99) than in those without retinopathy (mean 1.78), 95% CI for difference 0.1-1.5 microg mg(-1). The results of the present study are compatible with a role for SSAO in the development of diabetic retinopathy.

Electrospray tandem mass spectrometry in the rapid identification of alpha-chain haemoglobin variants

The potential use of electrospray tandem mass spectrometry in the rapid characterisation of haemoglobin variants found in the Swedish population has been assessed. Analysis times of the order of 5 -10 min were routinely achieved, and identification of variants using mass spectrometry as the sole analytical technique was possible. However, additional information, readily available from isoelectric focusing experiments, made identification simpler and more secure. In the present communication we report on the identification of the alpha-chain variants, Hb Russ, Hb Le Lamentin and Hb Q-Iran. The identifications were confirmed by the use of nucleotide sequencing techniques.

Bioavailability of cyclosporine in rats after intragastric administration: a comparative study of the L2-phase and two other lipid-based vehicles

The purpose of this study was to evaluate formulations based on surface active dietary lipids only as oral vehicles for cyclosporine. The absolute bioavailability of cyclosporine from two new lipid vehicles was determined in rats after intragastric administration and compared to that of Sandimmun oral solution, which contains non-ionic surface active substances in addition to dietary lipids. In the new vehicles, cyclosporine was dissolved in two different mixtures of glycerides from long-chained fatty acids. One mixture forms an L2-phase, an oil with very low interfacial tension towards water, and was administered both as the oily L2-phase and as a predispersed emulsion formulation. The other mixture forms a liquid crystalline phase and was administered only as an aqueous dispersion. The mean bioavailability of cyclosporine from Sandimmun was 8% while it was 34% from the L2-phase, 38% from the predispersed L2-phase and 27% from the dispersed liquid crystalline phase. The coefficients of variation in area under the blood concentration curve after administration of the two formulations based on the L2-phase were quite low (31% for the L2-phase and 24% for the predispersed L2-phase) and comparable to that after intravenous administration (24%), while the dispersed liquid crystalline phase gave a higher variability (91%), comparable to that of Sandimmun oral solution (101%). The low variabilities found with the two L2-phase vehicles suggest that this formulation is "self-emulsifying' in the gastrointestinal tract. Since the L2-phase is based on dietary lipids only, it is expected to be well tolerated and could prove to be a good vehicle for long-term clinical use of oral cyclosporine.

Two different mutations in codon 97 of the beta-globin gene cause Hb Malmö in Sweden

An abnormal hemoglobin with increased oxygen affinity, Hb Malmö [alpha 2 beta 297(FG4)His-->Gln], was found to cause erythrocytosis in two apparently unrelated Swedish families. Direct nucleotide sequencing of amplified DNA demonstrated a CAC-->CAA substitution in one family and a CAC-->CAG substitution in the other. Both mutations resulted in a His-->Gln substitution in codon 97. This finding prompted us to examine the possible point mutations underlying the different hemoglobin variants reported in the literature.

Initiation codon mutation (ATG --> ATA) of the beta-globin gene causing beta-thalassemia in a Swedish family

An initiation codon mutation ATG-->ATA of the beta-globin gene was found in seven members of three generations of a family living in northern Sweden. This mutation, which has not previously been described, changes the initiation codon for methionine into a codon for isoleucine and will then result in a beta zero-thalassemic phenotype. The affected family members all present hematological findings typical for beta-thalassemic trait, with slight anemia, marked microcytosis, and increased levels of Hb A2.

Hb Trollhättan [beta 20(B2)Val-->Glu]--a new haemoglobin variant with increased oxygen affinity causing erythrocytosis

Erythrocytosis is sometimes caused by the presence of haemoglobin (Hb) variants with increased oxygen affinity. Here we describe a beta-globin variant found by isoelectric focusing (IEF) of Hb from a 23-year-old Swedish male with moderate erythrocytosis. Amplification of DNA corresponding to the beta-globin gene and subsequent nucleotide sequencing revealed heterozygosity for a GTG-->GAG mutation at codon 20, thus suggesting a Val-->Glu substitution, which was confirmed at the protein level. This mutation occurs at the same position as Hb Olympia [beta 20(B2)Val-->Met], another variant associated with erythrocytosis due to increased oxygen affinity. The novel variant, Hb Trollhättan [beta 20(B2)Val-->Glu], which was also associated with increased oxygen affinity, was shown to be present in three generations of the patient's family.

Haemoglobin Köln as de novo mutations in Sweden: diagnosis by PCR and specific enzymatic cleavage

Three independent cases of chronic haemolytic anaemia in Sweden have recently been demonstrated to be due to the unstable haemoglobin variant Hb Köln. The patients, all of whom have partially compensated chronic haemolytic anaemia, presented with aggravated haemolysis during acute infections in childhood. In one case, acute B19 parvovirus infection induced an aplastic crisis. The substitutions all seem to have occurred as de novo mutations. Diagnosis was based on haemoglobin instability testing and isoelectric focusing of haemoglobin dimers. The final identification procedure for the substitutions included extraction of DNA from whole blood, polymerase chain reaction (PCR) amplification of parts of the beta-globin gene and nucleotide sequencing of the resulting material, or studies of restriction length polymorphisms (RFLPs) using the restriction endonucleases Mae II or Nla III. The use of PCR-RFLP is recommended as a valuable tool for diagnosing Hb Köln.

Rare beta chain hemoglobin variants found in Swedish patients during HBA1c analysis

Here we report the occurrence of five different beta chain hemoglobin variants not previously described in Sweden. The variants were found during quantification of HbA1c using ion exchange high performance liquid chromatography (HPLC) or isoelectrofocusing. Samples were examined either at protein level by separation of globin chains on C8 reversed phase HPLC, digestion with trypsin or lysylendopeptidase and separation of peptides by C18 reversed phase HPLC, or at DNA level by direct nucleotide sequencing of double-stranded DNA fragments amplified from exon 1 + 2 of the beta-globin gene. The variants were: Hb Raleigh [beta 1 (NA1)Val-->Ac-Ala], Hb J-Baltimore [beta 16(A13)Gly-->Asp], Hb Tacoma [beta 30(B12)Arg-->Ser], Hb K-Ibadan [beta 46(CD5)Gly-->Glu], and Hb Fukuyama [beta 77(EF1)His-->Tyr]. Hb Tacoma, Hb K-Ibadan, and Hb Fukuyama were slightly unstable in the isopropanol test, but no signs of hemolysis were found in the patients who all had normal hematological findings.

Hb Karlskoga or alpha 2 beta (2)21(B3) Asp-->His: a new slow-moving variant found in Sweden

An abnormal variant comprising approximately 39% of total hemoglobin was found in a 48-year-old Swedish woman. The variant was eluted from ion exchange high performance liquid chromatography (HPLC) used for routine quantification of Hb A1c at a position similar to Hb S. Amplification of beta-globin exons and nucleotide sequencing revealed heterozygosity for a GAT-->CAT mutation in codon 21, corresponding to the amino acid substitution Asp-->His at position 21. This mutation was confirmed by amino acid composition and peptide sequence determinations. Substitutions in this position are not likely to affect the function of the hemoglobin molecule and the hemoglobin variant, for which the name Hb Karlskoga is proposed, was not associated with any overt hematological abnormalities.

Unstable haemoglobin causing haemolytic anaemia: de novo mutation in Sweden identified by PCR

A 38-year-old Swedish woman was investigated because of mild anaemia resistant to iron therapy. Mild haemolytic disease was found by routine blood tests. Neither HPLC (HbA1c quantification) nor Hb-electrofocusing revealed any major abnormal fraction, although in vitro testing of haemoglobin instability indicated the presence of unstable haemoglobin. PCR was used to amplify coding regions of the beta globin gene. Direct nucleotide sequencing of this material revealed heterozygosity for a substitution corresponding to the haemoglobin variant alpha 2 beta 2 135(H13)Ala-->Pro. This clearly unstable variant, named Hb Altdorf, has earlier been described only in a family of Italian descent. Examination of beta globin genes from six family members of the proposita by PCR followed by specific cleavage with the restriction enzyme Ban I, revealed the mutation in her two children but not in her parents or siblings. This case demonstrates that haemoglobin variants can not be ruled out as a cause of haematological disease even if the parents lack symptoms and standard tests, such as HPLC and electrophoresis/electrofocusing, do not reveal major abnormalities.

Plasma apolipoprotein A-I levels and bile lipid secretion during thoracic duct drainage in the rat

A large part of the circulating apolipoprotein A-I (apoA-I) is produced by the intestine. Yet the plasma levels of apoA-I are retained or even increased in rats with thoracic duct drainage (Johansson, B. and Nilsson, A, (1981) FEBS Lett. 130, 305-308 and Franzén, J. et al. (1987) Biochim. Biophys. Acta 918, 11-15). In this study we examined the effects of biliary drainage and of combined biliary and lymphatic drainage on the plasma apoA-I levels, and also the effects of lymphatic drainage on the output of biliary lipids in the rat. 63 h of biliary drainage caused a 40% decrease of the serum apoA-I concentration. In contrast the concentration in rats with combined thoracic duct and biliary drainage was 153% of that in control rats. The biliary secretion of bile acids, phosphatidylcholine and cholesterol declined to a lower level in rats with combined thoracic duct and biliary drainage, but increased at the later time intervals to the same levels as in rats with bile fistulas only. Intravenous chyle infusion 3-36 h after commencing the biliary drainage did not prevent the decrease in biliary lipid output. The study thus provided no evidence that the reduced hepatic inflow of apoB-containing lipoproteins during biliary drainage is of importance for the reduced biliary lipid output. The loss of all the chyle lipoproteins leads, however, to an even more pronounced decrease in the biliary lipid secretion. The drainage of all the chyle constituents also leads to an increased apoA-I synthesis that more than compensates for the apoA-I loss in chyle, whereas biliary drainage only lowers the plasma apoA-I levels.

Metabolism of chylomicron arachidonic and linoleic acid in the rat

Chyle and chylomicrons, obtained after feeding thoracic duct cannulated rats [3H]arachidonic (20:4) and [14C]linoleic acid (18:2) in cream, were injected i.v. into recipient animals. 7.5-15 min after injection, the 14C/3H ratio of the triacylglycerols remaining in plasma was about half of that in the injected chylomicrons, indicating that the chylomicron remnants formed retained relatively more [3H]20:4 than [14C]18:2. The 14C/3H ratio of plasma diacylglycerols was about 6-fold lower than that of plasma free fatty acids. The proportion of [3H]20:4 found in plasma cholesteryl esters was several-fold higher than that of [14C]18:2. Inhibition of hepatic lipase by a specific antiserum did not significantly influence the clearance of triacylglycerols, but increased the amount of 3H in plasma diacylglycerols. It also prevented the rapid clearance of phosphatidylethanolamine from plasma. The liver uptake of [3H]20:4 exceeded that of [14C]18:2. Antiserum against hepatic lipase diminished the difference. In contrast, the 14C/3H ratio of adipose tissue was higher than that of the injected chyle lipoproteins.

Absorption and lymphatic transport of exogenous and endogenous arachidonic and linoleic acid in the rat

[3H]Arachidonic (20:4) and [14C]linoleic acid (18:2) were fed to thoracic duct-cannulated rats in test meals of either tracers alone, cream, Intralipid, pure arachidonic acid, or pure linoleic acid. Less [3H]20:4 than [14C]18:2 was recovered in chyle during the first 5 h. After cream feeding, the proportion of radioactivity found in phospholipids was high and increased during the first 3 h. After the meal (3-5 h) 61 +/- 6% of the 3H and 57 +/- 10% of the 14C was in phosphatidylcholine, and 11 +/- 3% of the 3H and 3.0 +/- 4% of the 14C was in phosphatidylethanolamine. Changing the fat vehicle to Intralipid or pure 18:2 decreased the proportion of label in the phospholipids and increased the 3H and 14C radioactivity in the triacylglycerol fraction, the distribution of 14C being influenced more than that of 3H. After feeding the tracers in 200 microliters of pure 20:4, greater than 90% of both isotopes was in triacylglycerol. During fasting, triacylglycerol transported 56% (0.7 mumol/h), phosphatidylcholine transported 34% (0.4 mumol/h), and phosphatidylethanolamine transported 10% (0.1 mumol/h) of the 20:4 mass. After cream or Intralipid feeding, the output of 20:4-containing phosphatidylcholine and phosphatidylethanolamine increased 2.1- to 2.8-fold, whereas the transport of 20:4 with triacylglycerol remained constant. Phospholipids thus became the predominant transport form for 20:4. After feeding 200 microliters of 20:4, the intestine produced, however, 20:4-rich triacylglycerols that transported 89% of the chyle 20:4.

Hydrolysis of chylomicron arachidonate and linoleate ester bonds by lipoprotein lipase and hepatic lipase

Chylomicrons labeled with [3H]arachidonic and [14C]linoleic acid were incubated with bovine milk lipoprotein lipase or rat postheparin plasma, containing both lipoprotein lipase and hepatic lipase. During incubation with bovine lipoprotein lipase, [3H]arachidonic acid was released from chylomicron triacylglycerols at a slower rate than [14C]linoleic acid. Only small amounts of [14C]linoleic acid were found as 1,2(2,3)-diacylglycerols, whereas a transient accumulation as [14C]monoacylglycerols was observed. In contrast, significantly more [3H]arachidonic acid was found as 1,2(2,3)-diacylglycerols than as monoacylglycerols at all time intervals investigated. The initial pattern of triacylglycerol hydrolysis by postheparin plasma was similar to that of bovine lipoprotein lipase. However, in contrast to the results obtained with bovine lipoprotein lipase, little [3H]1,2(2,3)-diacylglycerol accumulated. The addition of antiserum to hepatic lipase increased the amount of 3H found in 1,2(2,3)-diacylglycerols and inhibited the formation of free [3H]arachidonic acid. The antiserum also caused a significant inhibition of the hydrolysis of [3H]-but not of [14C]triacylglycerol. With regard to chylomicron phospholipids, the rate of hydrolysis of [14C]linoleoyl phosphatidylcholine with milk lipoprotein lipase was twofold higher than that of the [3H]arachidonyl phosphatidylcholine. However, the hepatic lipase of postheparin plasma had similar activity towards the two phosphatidylcholine species. Postheparin plasma rapidly hydrolyzed chylomicron 3H-labeled and 14C-labeled phosphatidylethanolamine to the same degree, and lipoprotein lipase similarly hydrolyzed 3H-labeled and 14C-labeled phosphatidylethanolamine at approximately equal rates. Antiserum to hepatic lipase inhibited the postheparin plasma hydrolysis of phosphatidylethanolamine and 3H-labeled phosphatidylcholine by about 60%, but the 14C-labeled phosphatidylcholine by only 27%.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting the impaired hepatic uptake of chylomicron remnants in the cholestatic rat

We have previously shown that bile duct ligation inhibits the hepatic uptake of chylomicron remnants in rats. In the present study we have investigated different possible causes of this inhibition. Intravenous infusion of bile or sodium taurocholate reduced the hepatic chylomicron remnant uptake. Perfused livers from bile duct-ligated rats metabolized chylomicron remnants at a reduced rate. Rat hepatocyte monolayer cultures metabolized remnants formed in cholestatic rats and those formed in hepatectomized animals equally well, but serum from cholestatic rats inhibited remnant uptake more strongly than control serum. Bile duct ligation did not influence the clearance from plasma of human low-density lipoprotein, and the inhibition of hepatic remnant uptake was not affected by treatment of cholestatic rats with ethinylestradiol. The clearance of 125I-labeled asialofetuin was only slightly impaired by cholestasis, indicating that no strong inhibition of all endocytic processes of the hepatocytes occurred. The reduced hepatic uptake of chylomicron remnants in the cholestatic rat is thus not due to formation of abnormal remnant particles. An increased plasma bile acid concentration rapidly reduced the hepatic remnant uptake without causing any significant hyperlipidemia. However, the pathological lipoproteins accumulating in the cholestatic rat aggravated the hepatic uptake defect even further.

Efficient hepatic uptake of chylomicron remnant cholesterol in rats with a portacaval anastomosis

Portacaval-shunted and sham-operated male rats, fed ad libitum and of similar weight, were studied 2-3 weeks after surgery. At this time serum cholesterol levels did not differ significantly between the two groups, whereas serum triacylglycerols and phospholipids were lower in the shunted group. These animals also showed an increased serum bile acid level and an increased serum estradiol to testosterone ratio. The metabolism of native chyle labeled with [3H]cholesterol and [14C]linoleic acid or of preformed chylomicron remnants with the same labeling was studied in the groups of rats. Ten minutes after intravenous injection of chylomicron remnants 10.6 +/- 0.5% (means +/- SEM, n = 8) of the injected [3H]cholesterol and 7.6 +/- 0.4% of the [14C]linoleic acid were found per 1 g liver in the portacaval-shunted rats; the corresponding figures in the sham-operated group (n = 8) were 6.4 +/- 0.4 and 4.9 +/- 0.3, respectively (p less than 0.001 for both 3H and 14C). Thus, despite a greater than 40% reduction of liver weight induced by the shunting procedure, the total liver uptake of chylomicron remnants was not significantly decreased. The uptake of chylomicron lipids per unit liver weight was normal in the atrophic livers of portacaval-shunted rats also when very large loads of chyle were administered.

Rat alpha 1-microglobulin. Purification from urine and synthesis by hepatocyte monolayers

Rat alpha 1-microglobulin was isolated from the urine of rats treated with sodium chromate, and was purified by the use of gel chromatography, affinity chromatography on concanavalin-A-Sepharose and ion-exchange chromatography. The protein was heterogeneous in charge, had a tendency to form dimers, and was associated with a brown-coloured chromophore. The size of the protein (25 kDa) was similar to guinea pig alpha 1-microglobulin but smaller than the human protein, when measured with sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Immunological cross-reaction with human and guinea pig alpha 1-microglobulin was demonstrated. The concentration of alpha 1-microglobulin in rat serum was 16.4 mg/l (SD = 8.5 mg/l, n = 13) and rat serum alpha 1-microglobulin was eluted from a gel chromatography column at two different positions corresponding to monomeric alpha 1-microglobulin and IgA. The latter alpha 1-microglobulin activity could be absorbed by anti-IgA serum. Rat alpha 1-microglobulin and albumin were continuously released into the medium of rat hepatocyte monolayers, and alpha 1-microglobulin was isolated from the medium by the use of immunoprecipitation with anti-(alpha 1-microglobulin). Tritiated leucine, added to the medium, was incorporated into the protein, suggesting a de novo synthesis of alpha 1-microglobulin by the hepatocytes. The size of hepatic alpha 1-microglobulin was similar to that of purified urinary rat alpha 1-microglobulin, when determined with sodium dodecyl sulfate/polyacrylamide gel electrophoresis.

A role for hepatic lipase in chylomicron and high density lipoprotein phospholipid metabolism

The rate of removal of phosphatidylethanolamine and phosphatidylcholine from the plasma of rats treated with antiserum to hepatic lipase was measured. The hepatic lipase antiserum was injected intravenously into animals prior to injection of 32P-labeled chylomicrons or 32P-labeled high density lipoproteins. In experiments in which 32P-labeled chylomicrons were injected, antiserum treatment inhibited removal of [32P]phosphatidylethanolamine from chylomicrons, and the unlabeled serum phosphatidylethanolamine levels increased 2-2.5-fold in 30 min. In contrast, hepatic lipase antiserum had no significant effect on the clearance of chylomicron [32P]phosphatidylcholine or on unlabeled phosphatidylcholine concentrations in serum after injection of chylomicrons. In experiments in which 32P-labeled high density lipoproteins were injected, the inhibitory effect of the antiserum on the rapid removal of [32P]phosphatidylethanolamine from the circulation was even more marked than its effect on the removal from chylomicrons. The removal of high density lipoprotein phosphatidylcholine on the other hand was unaffected by the antiserum, although a moderate increase in serum phosphatidylcholine concentration was seen. In antiserum-treated rats injected with 32P-labeled chylomicrons or high density lipoproteins, hepatic [32P]phosphatidylethanolamine radioactivity was decreased. Significantly more [32P]phosphatidylethanolamine was recovered from blood plus liver in the antiserum-treated rats, indicating that the antiserum inhibited the overall degradation of injected [32P]phosphatidylethanolamine. The data suggest that phosphatidylethanolamine is a preferred substrate for hepatic lipase in the metabolism of chylomicron and high density lipoprotein phospholipid.

Metabolism of chylomicron phosphatidylethanolamine in the rat

10 min after intravenous injection of 32P-labelled chylomicrons 69% of the [32P]phosphatidylethanolamine, but only 34% of the [32P]phosphatidylcholine, was cleared from plasma. Over this time period the plasma phosphatidylethanolamine concentration that was increased after the chylomicron injection returned to normal, indicating that the rapid clearance of [32P]phosphatidylethanolamine was primarily due to metabolism and not due to exchange with tissue phospholipids. Also after chylomicron [32P]phospholipids had been transferred to high-density lipoproteins in vitro a greater fraction of [32P]phosphatidylethanolamine than of [32P]phosphatidylcholine was eliminated both in the intact rat and in the perfused rat liver. In the latter system the uptake of [32P]phosphatidylethanolamine was reduced by preperfusion with heparin to remove heparin-releasable hepatic lipase. Experiments with hepatocytes and non-parenchymal liver cells, which both contain only minor amounts of surface-bound hepatic lipase, did not demonstrate any rapid uptake of [32P]phosphatidylethanolamine by exchange with cellular phospholipids. This study shows that there is a mechanism for rapid clearance of chylomicron phosphatidylethanolamine, which maintains a low plasma phosphatidylethanolamine level (30-40 micrograms/ml) despite a significant transport of phosphatidylethanolamine with the intestinal lipoproteins. A major part of the rapid phosphatidylethanolamine metabolism occurs in the liver, where the activity of the hepatic lipase is likely to be of crucial importance.