Effects of maternal and long-term postnatal protein malnutrition on brain size and composition in rhesus monkeys.

Rhesus monkeys consumed purified diets that supplied either low or adequate levels of protein (3.8 vs. 13.9% of energy as casein) from birth until approximately 10 yr of age. A subgroup (PN) was born of mothers that also received low or control levels of protein throughout pregnancy. The deprived groups weighed significantly less than corresponding control groups. Weights of the total brain, cerebellum and brain stem were significantly reduced in the PN deprived group. Analysis of variance also indicated that low protein diets produced a significant reduction in cerebral weight. The concentrations of DNA, protein and eight different lipids from seven different sites in the central and peripheral nervous system were not greatly affected by diet. The total content of lecithin and phosphatidylethanolamine was significantly depressed in some parts of the deprived monkey brains. The deficits in brain weight of the PN group (10% for the cerebrum, 13% for the cerebellum and 18% for the brain stem) were very similar to those observed previously in 1-mo-old monkeys born of protein-deprived mothers and fed low protein diets postnatally. On the other hand, monkeys born of adequately nourished mothers and then fed low protein diets from birth up to 12 yr showed no deficit in brain weight despite reduction in body weight to less than half of control values.

Metabolism of native and acetylated low density lipoproteins in squirrel monkeys with emphasis on aortas with varying severities of atherosclerosis.

We studied the clearance of 131I-labeled native low density lipoproteins (LDL) and 125I-acetyl LDL from the blood of hypercholesterolemic and atherosclerotic squirrel monkeys which had been fed a semipurified diet supplemented with cholesterol for 3 years and from control monkeys which had been fed the same diet without cholesterol. In agreement with previous observations in other species, acetyl LDL left the circulation much more rapidly than native LDL. The cholesterol supplemented monkeys removed native 131I-LDL to the liver, the major site of clearance of both LDL forms, more slowly than controls. The overall clearance of 125I-acetyl LDL was similar for the two groups. The aortic intima plus inner media (AIM) cleared both LDL forms much more slowly than other organs, and the ratio of acetyl LDL to native LDL cleared was quite high. The outer media (OM) showed less selectivity for acetyl LDL than the AIM. While LDL clearance by the OM was not affected by diet, the LDL clearance per g of AIM tissue was increased by 2-fold for both native and acetyl LDL in the cholesterol supplemented monkeys. These monkeys also had a 3-fold increase in AIM weight (due to intimal and subintimal thickening), which resulted in a 6-fold increase in the total LDL cleared by the AIM. The clearance of both LDL forms by the AIM correlated with three indices of atherosclerosis: intimal thickness, AIM weight, and AIM cholesterol concentration. The correlations were higher in the case of acetyl LDL clearance which may be due to the high affinity of the acetylated form for macrophages.

Different susceptibilities to the formation of cholesterol gallstones in mice.

In the search for an animal model of genetic determinants of cholesterol cholelithiasis, we found strain, gender and individual differences in mice. Male black (C57BL6J) mice had a 50% incidence of cholesterol gallstones after they consumed lithogenic food similar to that used by Tepperman et al. for 2 weeks, whereas similarly treated male agouti (CBA/J) mice and females of both strains were free of gallstones. The male and female mice of both strains were fertile at 8 weeks of age, and the male black mice were first susceptible to induction of gallstones at 24 weeks of age. Male agouti mice of the same age did not form gallstones until they had consumed the lithogenic food for 8 weeks. The gallbladder biles of both strains were supersaturated with cholesterol during the lithogenic regimen. The male agouti mice had much higher fractional turnover rates of [24-14C]cholic acid than did the male black mice. In spite of their small total cholate pools, the agouti mice had higher rates of new cholate synthesis than did the black mice. The rate of disappearance of [1,2-3H]cholesterol from the blood was higher in the male agouti than in the black mice. The gallbladders of the agouti mice contained less bile and weighed less empty than gallbladders of the black mice. They also did not increase in volume in response to the lithogenic diet as much as gallbladders of the black mice. The difference in gallstone induction times between male and female black mice was as great as the difference between the two strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of [125I]tyramine cellobiose-labeled low density lipoproteins in squirrel monkeys.

Low density lipoproteins labeled with [125I]tyramine cellobiose ([125I]TC-LDL) were removed from the circulation of squirrel monkeys at a similar but slightly slower rate than LDLs labeled with 125I, [125I]hydroxyphenyl propionic acid, or [3H]leucine. After the simultaneous injection of [125I]TC-LDL and [131I]LDL labeled with 131ICl, the 125I was also removed at a slightly slower rate than 131I. Most of the radioactivity was retained in tissues and not excreted during the 24 h after injection of [125I]TC-LDL. This finding supports the claim of Pittman et al. [18] that [125I]TC-LDL can be used to determine the irreversible uptake of LDL by different tissues. The liver cleared more LDL than any other organ, but the adrenals and ovaries were more active per gram. Trichloroacetic acid (TCA) precipitated more than 80% of the radioactivity in the tissues that had low 125I uptake, but only about 50% of the 125I in more active tissues (liver, adrenals, ovaries, and spleen). Only a small percentage of 125I in urine and bile was TCA-precipitable. In the dual label experiment with [125I]TC-LDL and [131I]LDL there was a selective retention of 125I in samples from liver, spleen, adrenals, and, perhaps testes, and an almost complete selectivity for 125I in bile and feces. The aortic intima plus inner media (AIM) cleared much less LDL than other tissues, but the uptake by the entire AIM was proportional to the cholesterol concentration and weight of the total AIM. There was, however, no correlation between either of the latter two measurements and the uptake of LDL per gram of AIM. The concentration of LDL apolipoprotein in the AIM determined by immunoelectrophoresis did not correlate significantly with LDL uptake per gram. Both the amounts of LDL apolipoprotein present and labeled LDL taken up by the AIM depended on the weight of the sample, and perhaps on the weight of intima in the sample.

Dietary protein effects on lipoproteins and on sex and thyroid hormones in blood of rhesus monkeys.

We studied plasma lipoprotein and hormone concentrations in rhesus monkeys that had consumed either a low protein (3.8% of kilocalories) or a control protein (13.9%) purified diet since birth (6-10 yr before the beginning of this experiment) in order to test the hypothesis that chronic protein deficiency could influence plasma lipoproteins through an effect on the hepatic metabolism of gonadal or thyroid hormones. Protein-deficient monkeys had greater plasma concentrations of very low density lipoproteins (VLDL) plus high density lipoproteins (HDL) than controls. They also had lower serum albumin and greater alkaline phosphatase levels than the controls. Plasma thyroxine (T4) and free T4 concentrations were lower and the triiodothyronine (T3) levels tended to be greater in the protein-deficient group than in controls. This effect was apparent at two widely different levels of dietary iodide. Plasma T3 concentrations were elevated in other adult rhesus monkeys that were fed the low protein diet for only 6 wk. Monkeys injected with estradiol benzoate (100 micrograms/kg body weight) for 4 d had a marked reduction of VLDL concentrations. VLDL triglycerides were depressed more and plasma estrone levels were greater in deficient monkeys than in controls at 24 h after the last injection. In the control monkeys the T3 level rose and T4/T3 fell in response to estrogen injections, whereas the deficient monkeys did not respond.

The effects of nutrition on unconjugated plasma bilirubin concentrations in squirrel monkeys.

Bolivian squirrel monkeys (Saimiri sciureus) have fasting unconjugated hyperbilirubinemia (males: 2.0 +/- 0.14; females: 3.0 +/- 0.26 mg per dl) which resembles that of humans with Gilbert's syndrome. Closely related Brazilian squirrel monkeys have fasting levels (males: 0.29 +/- 0.045; females: 0.36 +/- 0.073 mg per dl) similar to normal people. The purpose of this study was to identify the underlying mechanisms and the nutritional factors involved. Both Bolivian and Brazilian squirrel monkeys had higher plasma bilirubin concentrations after an 18 hr fast than 4 hr after feeding. The development of fasting hyperbilirubinemia was progressive for at least 24 hr. Both populations that received a semipurified diet containing 5% fat had lower fasting and postprandial plasma bilirubin concentrations than did animals receiving 0.3% fat but much lower than those receiving 20% fat. The emulsified complete meal, or glucose, sucrose, casein, or lactalbumin alone when given by intragastric tube lowered the plasma bilirubin levels of Bolivian monkeys to less than one-half of fasting values within 1 to 4 hr. Water or butter did not have a significant effect. Glucose or fructose, when given intravenously, lowered the plasma bilirubin levels to less than half of fasting values; the fat emulsion, Intralipid, did not have a statistically significant effect. Subcutaneous epinephrine increased plasma glucose concentrations and reduced plasma bilirubin concentrations. When glucose or glucose plus butter were given by stomach tube to Bolivian squirrel monkeys for 48 hr, a very low plasma bilirubin concentration resulted whereas butter given alone resulted in high values.(ABSTRACT TRUNCATED AT 250 WORDS)

A nonhuman primate model of Gilbert's syndrome.

A Bolivian population of squirrel monkeys, Saimiri sciureus, exhibits several features of Gilbert's syndrome in man, and is proposed as a nonhuman primate model of the condition. The Bolivian population was found to have higher fasting (40.6 +/- 2.7 microM; mean +/- S.E.) and postcibal (9.9 +/- 0.9 microM) plasma unconjugated bilirubin concentrations (p less than 0.001) than a closely related Brazilian population (fasting 5.5 +/- 0.7 microM); postcibal (2.4 +/- 0.7 microM). After intravenous administration of [3H]bilirubin as a tracer dose or at 3.4 mumoles per kg body weight, there was delayed plasma clearance in the Bolivian monkeys. Hepatic UDP-glucuronyl transferase activity for bilirubin (164 +/- 25 nmoles per 30 min per gm liver) and biliary bilirubin diglucuronide to monoglucuronide ratios (2.9 +/- 0.2) were lower in Bolivian monkeys than in Brazilians (421 +/- 36 nmoles per 30 min per gm liver--p less than 0.01 and 4.1 +/- 0.1--p less than 0.02, respectively). Hepatic cytosol glutathione-S-transferase B activity (ligandin) levels were similar for the two populations. After phenobarbital therapy, fasting (11.1 +/- 0.9 microM) and postcibal (5.3 +/- 1 microM) plasma bilirubin concentrations in Bolivian monkeys were significantly reduced (p less than 0.001). Sulfobromophthalein clearance was slightly slower in the Bolivian than in the Brazilian monkeys. SGOT, lactate dehydrogenase, gamma-glutamyl transpeptidase and alkaline phosphatase activities were not increased in Bolivians. Fasting serum conjugated bile salt concentrations in Bolivian monkeys were lower than that in Brazilian monkeys (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Binding properties of high-density lipoprotein subfractions and low-density lipoproteins to rabbit hepatocytes.

Primary cultures of rabbit hepatocytes which were preincubated for 20 h in a medium containing lipoprotein-deficient serum subsequently bound, internalized and degraded 125I-labeled high-density lipoproteins2 (HDL2). The rate of degradation of HDL2 was constant in incubations from 3 to 25 h. As the concentration of HDL2 in the incubation medium was increased, binding reached saturation. At 37 degrees C, half-maximal binding (Km) was achieved at a concentration of 7.3 micrograms of HDL2 protein/ml (4.06 X 10(-8)M) and the maximum amount bound was 476 ng of HDL2 protein/mg of cell protein. At 4 degrees C, HDL2 had a Km of 18.6 micrograms protein/ml (1.03 X 10(-7)M). Unlabeled low-density lipoproteins (LDL) inhibited only at low concentrations of 125I-labeled HDL2. Quantification of 125I-labeled HDL2 binding to a specific receptor (based on incubation of cells at 4 degrees C with and without a 50-fold excess of unlabeled HDL) yielded a dissociation constant of 1.45 X 10(-7)M. Excess HDL2 inhibited the binding of both 125I-labeled HDL2 and 125I-labeled HDL3, but excess HDL3 did not affect the binding of 125I-labeled HDL3. Preincubation of hepatocytes in the presence of HDL resulted in only a 40% reduction in specific HDL2 receptors, whereas preincubation with LDL largely suppressed LDL receptors. HDL2 and LDL from control and hypercholesterolemic rabbits inhibited the degradation of 125I-labeled HDL2, but HDL3 did not. Treatment of HDL2 and LDL with cyclohexanedione eliminated their capacity to inhibit 125I-labeled HDL2 degradation, suggesting that apolipoprotein E plays a critical role in triggering the degradative process. The effect of incubation with HDL on subsequent 125I-labeled LDL binding was time-dependent: a 20 h preincubation with HDL reduced the amount of 125I-labeled LDL binding by 40%; there was a similar effect on LDL bound in 6 h but not on LDL bound in 3 h. The binding of 125I-labeled LDL to isolated liver cellular membranes demonstrated saturation kinetics at 4 degrees C and was inhibited by EDTA or excess LDL. The binding of 125I-labeled HDL2 was much lower than that of 125I-labeled LDL and was less inhibited by unlabeled lipoproteins. The binding of 125I-labeled HDL3 was not inhibited by any unlabeled lipoproteins. EDTA did not affect the binding of either HDL2 or HDL3 to isolated liver membranes. Hepatocytes incubated with [2-14C]acetate in the absence of lipoproteins incorporated more label into cellular cholesterol, nonsaponifiable lipids and total cellular lipid than hepatocytes incubated with [2-14C]acetate in the presence of any lipoprotein fraction. However, the level of 14C-labeled lipids released into the medium was higher in the presence of medium lipoproteins, indicating that the effect of those lipoproteins was on the rate of release of cellular lipids rather than on the rate of synthesis.

Interaction of free cholesterol and apoproteins of low and high density lipoproteins with isolated rabbit hepatocytes.

Primary cultures of rabbit hepatocytes were incubated with rabbit high density (HDL) and low density (LDL) lipoproteins in order to compare the surface transfer of free cholesterol with the uptake of apoproteins. Hepatocytes were maintained for various intervals with either LDL or HDL which contained both 125I-labeled protein and free [4-14C]cholesterol. After a 3-hr incubation with an LDL concentration equivalent to 25% of the normal rabbit serum level, the percentage of media 14C in hepatocytes was 2.3 times greater than the percentage of 125I; cells that had been incubated with HDL showed an eight-fold selectivity for 14C. Although the influx of free cholesterol from HDL was greater than that from LDL, there was no difference between the uptake of LDL protein and of HDL protein. The degradation of lipoproteins labeled with [3H]-leucine or 125I was compared. Hepatocytes incubated with lipoproteins labeled with [4-14C]cholesterol showed a greater influx of cholesterol from HDL2 than from LDL. The efflux of labeled cellular cholesterol was also greater to HDL2 than to LDL, whether the cellular cholesterol was labeled by prior exchange with labeled HDL2 or by endogenous synthesis of cholesterol from [2-3H]mevalonic acid lactone.

Effects of long-term protein deficiency on plasma lipoprotein concentrations and metabolism in rhesus monkeys.

Lipoprotein concentrations and metabolism were studied in 5- and 9-year-old rhesus monkeys (Macaca mulatta). Both age groups had been divided into control (13.8% of the calories as protein) and low-protein (3.7% protein) subgroups at birth. All were tested before and after their dietary lipid was changed from corn oil to butter plus cholesterol. The concentrations of very-low-density and high density2 lipoproteins (VLDL and HDL2) tended to be higher in monkeys of the low-protein group, and butter plus cholesterol accentuated the difference. All monkeys of the low protein group had elevated levels of at least one of these two classes of lipoproteins. The secretion of nascent VLDL (after intravenous Triton WR-1339) was greater in the low protein than in the control group when both were fed butter plus cholesterol, and rates of VLDL secretion showed a strong positive correlation with the fasting levels of VLDL. Thirty minutes after the intravenous administration of heparin, VLDL triglyceride was almost completely removed, and the apolipoprotein was reduced by 40%; VLDL cholesteryl esters were unchanged. There was a simultaneous decrease in the intermediate density lipoproteins (IDL) and an increase in HDL2, but the low density lipoproteins (LDL) and HDL2 did not change. The rate of VLDL protein removal from plasma was greater in the low protein than in the control group, and the rates for individual monkeys correlated with the levels of VLDL and HDL2 prior to heparin administration. Hepatic postheparin lipase measured in vitro with saturating levels of substrate was significantly higher in the plasma of control than in that of low protein monkeys.

Metabolism of free and esterified cholesterol and apolipoproteins of plasma low and high density lipoproteins.

We studied the patterns of equilibration of free and esterified cholesterol between lipoprotein fractions of plasma separated by heparin-Mn2+ and of their disappearance from plasma and appearance in liver and bile. Free or esterified [4-14C]cholesterol in low density lipoproteins (LDL) and [7(n)-3H]cholesterol in high density lipoproteins (HDL2 or HDL3) were incubated together with plasma or injected simultaneously into squirrel monkeys. The isotope was alternated for successive experiments. Free cholesterol was equilibrated completely between lipoprotein classes within 30-45 min, but esterified cholesterol was not completely equilibrated within 2 h. Within 10 min after the injection of lipoproteins that had labeled free cholesterol, the bile contained labeled free cholesterol and within 20 min labeled bile acids. Both biliary cholesterol and bile acids initially were enriched 5-10-fold with the isotope that was originally contained in plasma HDL. Hepatic cholesterol was less enriched than bile cholesterol with the isotope of HDL. There was much less incorporation of radioactivity into biliary cholesterol and bile acids after the injection of [7(n)-3H]cholesteryl esters in HDL2 or HDL3 and [4-14C]cholesterol esters in LDL than after labeled free cholesterol, and there was little preference for cholesterol from one lipoprotein class. Although cholesteryl esters were equilibrated slowly between lipoprotein classes, their overall rate of removal from plasma was identical to that for the apolipoproteins of 125I-labeled LDL and 125I-labeled HDL during the first 2 h after injection. Labeled free cholesterol initially disappeared from the plasma compartment several times more rapidly than the esterified form or the lipoprotein apolipoprotein. Thus, cholesteryl esters probably interact with cells as part of intact lipoproteins, since they are not exchanged with cellular cholesterol like plasma free cholesterol.

Relationships between cholesterol gallstones, biliary function, and plasma lipoproteins in squirrel monkeys.

We used squirrel monkeys (Saimiri sciureus) as models to investigate human sex differences in susceptibility to cholesterol gallstones, biliary function, and plasma lipoproteins. Cholesterol gallstones developed in a large proportion of intact and gonadectomized male and female Brazilian monkeys maintained on a lithogenic diet, but male Bolivian monkeys were completely resistant. Although the gallbladder bile of nearly all monkeys was saturated with cholesterol, the bile of the Bolivian monkeys had a much greater concentration of total lipids (cholesteriol + phospholipid + bile acids) than did bile of the other groups. The male Bolivian monkeys had the highest percentage of gallbladder bile acids as chenodeoxycholic and the lowest as deoxycholic acids. They also had larger total body pools of cholic and chenodeoxycholic acids than any other group. The lithogenic index of all Brazilian squirrel monkeys with gallstones was greater than that of all Brazilian monkeys that were free of stones. The level of HDLs was much lower in the plasma of Bolivian monkeys than in that of any group of Brazilian monkeys, and the differences were restricted to the HDL2 subfraction. Addition of cholesterol (0.9 mg/Kcal) to the regular semipurified diet containing butter resulted in elevations in the LDLs of all groups and a change in the relative compositions of HDL and LDL (a higher percentage of cholesterol and lower percentage of protein). The occurrence of low plasma HDL2 levels in a population of squirrel monkeys resistant to cholesterol gallstones is consistent with the suggested role of that fraction in net transport of cholesterol to the bile.

Low density lipoprotein receptors and catabolism in primary cultures of rabbit hepatocytes.

Rabbit 125I-labelled low density lipoproteins (LDL) were incubated with primary monolayer cultures of rabbit hepatocytes in studies designed to assess the role of liver in LDL catabolism at the cellular level. After hepatocytes were preincubated for 20 h in lipoprotein-free medium, they exhibited time- and concentration-dependent interaction with 125I-labelled DLD at concentrations to 1 mg LDL protein/ml and times to 24 h. After a 3 h (37 degrees C) incubation with 50 microgram LDL protein/ml, hepatocytes bound 400 ng (LDL protein)/mg (cell protein), internalized 280 ng/mg, and degraded 660 ng/mg. Internalization and degradation may be greater than indicated by these values since pulse studies suggested the presence of a deiodinase which attacks cell associated 125I-labelled LDL. The amounts of LDL bound to hepatocytes after 3 h (37 degrees C) were similar to amounts for fibroblasts, but DLD internalization and degradation were considerably less. Rabbit hyperlipidemic 125I-labelled DLD showed the same amount of binding but 1.39 times more internalization and degradation than normolipidemic 125I-labelled LDL. Binding of both control and hyperlipidemic LDL was 3-fold greater at 24 and 42 h than at O or 3 h but addition of a 50-fold molar excess of high density lipoproteins (HDL) prevented increased LDL binding with time. Induction of specific high affinity receptors for binding LDL was shown to occur by preincubation of hepatocytes for increasing periods in lipoprotein-free medium and then measuring 125I-labelled LDL binding at 4 degrees C in the presence and absence of excess unlabelled LDL. Finally, hepatocytes took up 40 times more LDL than sucrose or dextran over a 24-h period, an indication that the uptake of LDL occurs via some mechanism other than simple bulk fluid endocytosis.

Effect of type of dietary fat and cholesterol on cholesterol absorption rate in squirrel monkeys.

To explore the effect of the type of dietary fat and the level of cholesterol on the rate of cholesterol absorption, 13 different male squirrel monkeys were used for 39 different tests. The plasma isotope ratio technique of Zilversmit, which involved the injection of 3H-cholesterol and gastric intubation of 14C-cholesterol, was shown to give reproducible results which compared well with those based on a method involving labeled beta-sitosterol. The percentages of ingested cholesterol that were absorbed showed considerable variation among individuals, but were relatively constant in the same animal. Safflower oil, a highly unsaturated fat, promoted a higher rate of cholesterol absorption than butter, regardless of the level of dietary cholesterol. The rate of cholesterol absorption was a constant percentage of that fed regardless of the absolute level of cholesterol in the habitual diet or the test meal (up to 218 mg or 5+ mg/kcal). Even at low levels of dietary cholesterol the percent absorption is greater in squirrel monkeys than in man.

Triacylglycerol and very low density lipoprotein secretion into plasma of squirrel monkeys.

We determined the effects of varying the types and level of dietary fat and cholesterol on the increase in plasma total triacylglycerol concentrations after injection of Triton WR-1339, an inhibitor of lipoprotein lipase, into monkeys that had been subjected to an overnight fast. The monkeys that had been treated with Triton WR-1339 were then given a test meal by intragastric intubation. Dietary cholesterol, high levels of fat and saturated fat in the habitual diet reduced the rate of release of triacylglycerol to plasma in the fasted monkey. We also determined the changes in protein and lipid concentrations of the different lipoprotein fractions. The injection of Triton WR-1339 resulted in a linear increase with time in the concentration of protein and triacylglycerol in the very low density (chylomicron-free and d less than 1.006) lipoproteins, but there was an increase in the ratio of traicylglycerol to protein in that fraction. Most of the increase (96%) in very low density protein was in the B protein. Regardless of the habitual diet, a test meal accentuated the rate of triacylglycerol appearance in whole plasma and in the very low density lipoproteins of Triton WR-1339-treated monkeys, and the rate of increase of the protein component after feeding was slightly higher. Thus the administration of a meal to the fasted Triton WR-1339-treated squirrel monkey further increased the proportion of triacylglycerol in very low density lipoproteins. Although dietary cholesterol and saturated fat in the habitual diet depressed the rate of increase in very low density triacylglycerol during fasting, the rate of protein synthesis was not significantly affected. After administration of a test meal the rates of increase in triacylglycerol and protein in the very low density lipoproteins were similar for monkeys from the different diet groups. Triton WR-1339 administration caused a slight and progressive increase in the intermediate density (d 1.006-1.019) lipoproteins and a marked and progressive decrease in the low density (d 1.019-1.063) lipoproteins. There was an immediate (by 5 min) drop of 70% or more in high density (d 1.063-1.21) lipoprotein protein, but the lipids except triacylglycerol remained unchanged. There was a decrease in both the A (the major fraction) and C proteins. The rates of very low density B protein secretion were comparable to the rates of low density lipoprotein catabolism that had been previously demonstrated for this species.

Influence of lysophosphatidylcholine on the metabolism of plasma lipoproteins.

Both low density lipoproteins and cellular membranes are known to have a high affinity for lysophosphatidylcholine. In this study lysophosphatidylcholine influenced the retention of lipoproteins by arterial tissue in vitro and the rate of disappearance of low density lipoproteins from the blood in vivo. Pieces of aorta from rabbits or rhesus monkeys were successively incubated for 90 min each in 2 or 3 solutions. After the last incubation the intima plus inner media was dissected from the remainder of the aorta for analysis. The second incubation always contained lipoproteins labeled with [3H]leucine. When lysophosphaticylcholine was included in the first but not in the second incubation fluid, the retention of low, or high density lipoproteins by the intima plus inner media increased. A subsequent incubation of the piece of artery in a fluid with trypsin or lysophosphatidylcholine caused a release of some of the lipoproteins. Lysophosphatidylcholine was bound simultaneously by plasma low density lipoproteins and vascular tissue in vitro and appeared to promote the association of the latter two components. When lysophosphatidylcholine equal to 2--10 times the usual total intravascular content was injected intravenously into control squirrel monkeys or rabbits, it was rapidly cleared from the blood. On the other hand, injected lysophosphatidylcholine persisted in the blood of hyperlipoproteinemic rabbits and was associated with the low density lipoproteins. In control animals, the injection of lysophosphatidylcholine was associated with an increase in the rate of removal of 125I-labelled low density lipoprotein from plasma and of its appearance in liver.

The effects of dietary fat and cholesterol on the metabolism of plasma low density lipoprotein apoproteins in squirrel monkeys.

Low density lipoprotein apoproteins from squirrel monkeys (Saimiri sciureus) had characteristic 2-phase die-away curves in plasma. The kinetic constants were similar with three methods of labeling: in vitro with 125I by the iodine monochloride or the Bolton-Hunter methods or in vivo by the injection of [3H]-leucine into a donor animal. Dietary cholesterol and the type of dietary fat influenced the concentration of plasma cholesterol and low density lipoproteins. The fractional turnover of low density lipoprotein apoprotein was greaterin monkeys fed semipurified diets with safflower oil than in those on butter but was not influenced by dietary cholesterol. The total low density lipoprotein apoprotein turnover (the product of fractional turnover and plasma lipoprotein concentration) was highest in monkeys fed butter plus added cholesterol and lowest in those on safflower oil without cholesterol. Dietary safflower oil resulted in a smaller proportion of the total low density lipoprotein pool in the intravascular compartment than did butter, regardless of whether cholesterol was added.