Incubation of whole blood samples at 37 degrees C caused a time-dependent increase in plasma cholesterol concentrations. In samples from 40 fasting healthy males, plasma cholesterol rose by 13.6 +/- 3% during 24 h (P less than 0.001). Changes in cholesterol concentrations were found in both the HDL fraction and the VLDL/LDL fraction. The increase in lipoprotein cholesterol concentrations correlated positively with the initial levels of HDL cholesterol and apo A-I; and with the original levels of VLDL/LDL cholesterol, apo B and triglycerides. The increase in plasma total cholesterol was not related to the HDL cholesterol and apo A-I concentrations. It was more pronounced in samples with elevated plasma concentrations of total cholesterol, VLDL/LDL cholesterol, apo B and triglycerides. The elevation in plasma total cholesterol resulted from an increase in cholesteryl esters, whereas free cholesterol decreased. After LCAT inhibition no changes in total, free and esterified cholesterol were observed. Therefore, increase in plasma cholesterol seems to represent a LCAT-dependent cholesterol transport out of blood cells.

The degree of apo E sialylation in VLDL from serum of diabetics and controls was determined by densitometric scanning of the pherograms after isoelectric focusing of the VLDL proteins including treatment with neuraminidase. The distribution pattern of sialylation within the groups of patients and controls followed a Gaussian type. A significantly elevated level of sialylated apo E could be demonstrated in IDDM and NIDDM as compared to the controls. No correlation was found between the apo E phenotype and the diabetic state. From the correlation analysis including the parameters degree of sialylation, age, duration of diabetic state, and blood glucose pattern no significant results were obtained except a significant but only week correlation (r less than 0.3) between sialylation, age, and blood glucose in IDDM patients. Possible consequences of the elevated apo E sialylation in diabetes mellitus are discussed.

To get insight into the low density lipoprotein (LDL)-apoB flux in the rat fetus near term and in the early postnatal period, homologous apoE-free 125I-labeled LDL was injected into the umbilical vein of the rat fetus immediately after Caesarean section. Since the serum LDL-apoB spontaneously declined after birth, a time-dependent two-pool model was used to calculate the flux rates in the neonate from the specific activities of LDL-apoB up to 15 h post partum. An approximate value of LDL-apoB flux in the fetus at birth was obtained by extrapolation of the kinetic data to the time of injection of the tracer. The data revealed that the turnover of LDL-apoB in the fetus (18.6 micrograms LDL-apoB/h per g body weight) exceeded that in the adult rat (0.4 microgram/h per g body weight) by at least one order of magnitude. Even 15 h after delivery, the LDL-apoB influx amounted to 2.5 micrograms/h per g body weight. The fractional catabolic rate of LDL-apoB in the fetus at term (0.39, h-1) slightly exceeded that in the adult animal (0.15, h-1) and reached the adult level within the first 3 h after birth and remained constant thereafter. In the rat fetus, LDL-apoB flux greatly exceeds that of VLDL-apoB. The data support the view of a direct synthesis and secretion of LDL, most probably by the fetal membranes.

The effect of the calcium channel blocker verapamil on structure, formation and secretion of very-low-density lipoproteins (VLDL) from rat hepatocytes in suspension was examined. After 30 min incubation at a verapamil dose of 200 ΜM neither free fatty acid (FFA) uptake nor triglyceride (TG) and phospholipid (PL) secretion into the incubation medium were significantly changed. After 90 min incubation the TG secretion was inhibited by about 60%, whereas the PL output was only insignificantly lowered, indicating the secretion of abnormally composed lipoprotein particles. Morphologically, after 30 min incubation the hepatocytes had lost their microvillous border and exhibited a 2–3-fold increase in volume density and average size of the lysosomes. In the Golgi-containing regions an accumulation of smooth-surfaced microvesicles was regularly evident. The configuration of the Golgi complexes was normal. After 90 min incubation the lysosomes showed a further significant elevation in volume and size. The Golgi complexes exhibited only minor changes, but their content in VLDL particles was reduced per Μm2 Golgi complex by about 75%. Commonly, the VLDL were larger and more heterogenous in size. The diameter of those VLDL secreted into the incubation medium ranged from 31 to 84 nm, thus surpassing the control values by 2–3 times. The secretion of large-sized VLDL was regularly associated with the intracytoplasmic appearance of dilated smooth-surfaced vesicles filled with size-modified VLDL. These vesicles were concentrated within Golgicontaining areas from where they were widely dispersed towards the cell periphery. In summary, our results are strongly indicative that size modification and secretion inhibition of the VLDL caused by verapamil primarily takes place in the endoplasmic reticulum.

About 50% of the individuals with a coronary risk show lipid levels within the normal range. Therefore, apolipoprotein profiles could be better risk indicators than TC or TG. Apolipoproteins generally discussed in this context are apo A1, apo B, and apo E. Their diagnostic validity, however, is ambigously evaluated. The individual iso-protein pattern of apo E is important for the differential diagnosis of the type III hyperlipidemia with its strong predisposition for premature atherosclerosis. Moreover, the extent of the apo E sialylation seems to be important because the modification of apo E by sialic acid alters its metabolism. Our date provide evidence that in IDDM and NIDDM the degree of apo E sialylation is increased. Concerning apo A1 and B we tried to find out parameters suitable for the prediction of the coronary risk both in the hyperlipidemic and the normolipidemic state. 64 male survivors of a myocardial infarc"ion and 60 matched controls were included in the study (group I). From group I a supopulation showing non-pathological values for TC and TG was selected (group II with 31 survivors and 44 controls). The diagnostic validity of the parameters apo A1, apo B, TC, HDL-C, apo A1/apo B, TC/apo B, HDL-C/apo B, TG, TG/apo A1, TG/HDL-C, TC-HDL-C/apo B determined by calculation of their sensitivities, specificities, efficiencies, and predictive values. Only the parameters TC/apo B, HDL-C/apo B, and apo B were suitable in the order given for detection of the coronary risk. Using the TC/apo B ratio 71-76% of the controls and 79% of the survivors could be exactly reclassified independent of the group they belonged to.(ABSTRACT TRUNCATED AT 250 WORDS)

In fetal rats at term LDL carries 75% of the total serum cholesterol, whereas in adult ones this value amounts to 20% only. Using a time-dependent two pool model the flux rates for LDL cholesterol can be calculated for the newborn. The data reveal that at birth the LDL cholesterol flux is 15-20 times higher than in the adult. During the first 2 h of postnatal life the FCR drops down from 0.4 at birth to values measured in the adult. Since at least 75% of LDL is of another origin than VLDL, a direct hepatic LDL synthesis is postulated for the newborn. The liver contributes to about 30% of the total LDL uptake which is mainly realized by a receptor-dependent mechanism, even though the fetus and the newborn exhibit markedly elevated LDL serum concentrations.

The binding and uptake of gold-labeled homologous, apolipoprotein E-free low-density lipoproteins (LDL) by isolated fetal rat liver parenchymal cells in suspension were studied ultrastructurally and morphometrically. Binding experiments using 125I-labeled LDL were also performed. After a 2-h preincubation in a lipoprotein-free medium and a subsequent 1-h postincubation in the presence of LDL-gold, fetal liver parenchymal cells exhibit a binding of 248±17 gold conjugates/100 μm plasma membrane and an uptake of 235±17 gold conjugates/100 μm2 cytoplasm. Compared with values obtained from freshly isolated nonpreincubated cells, these data correspond to a 15-fold and an 18-fold increase in total binding and uptake of LDL-gold, respectively. Competition experiments reveal that this increase is mainly a result of a 23-fold stimulation of specific binding and a 44-fold stimulation of receptor-mediated uptake of LDL-gold. The 125I-LDL binding experiments give a Kd value of 6.3×10-8 M and a maximum binding capacity of 17.3 fmol LDL/106 cells. Our data provide evidence, further to our in vivo studies, that fetal rat liver parenchymal cells possess high-affinity binding sites for native homologous apolipoprotein E-free LDL. These sites may correspond to B, E receptors of adult rat liver parenchymal cells.

Platelet-activating factor (PAF) is a naturally occurring phospholipid that exerts diverse biological activities. In the present study the degradation of PAF as well as lipid concentrations were measured both in plasma from 28 patients suffering from peripheral vascular disease and 18 healthy volunteers of comparable age. Beside some changes of the lipoprotein pattern it was also found that the capacity to degrade PAF is significantly elevated in the patient group. In view of this finding the question arises whether there is any link between the degradation of PAF and the development of atherosclerosis.

VLDL triglyceride influx into fetal serum and the composition of fetal serum VLDL was studied in rats at term. By use of the Triton WR 1339 method the rate of VLDL triglyceride influx into fetal circulation was calculated to be 0.1 mmol/h X 1 serum in comparison to 4.2 mmol/h X 1 in adult rats. Fetal VLDL exhibit a composition differing from that of adults. The experimental data indicate that the main fraction of fetal serum VLDL represents intermediates of VLDL metabolism converted already to apolipoprotein C-free, relatively triglyceride-depleted particles.

To elucidate the participation of fetal rat liver cells in the receptor-mediated internalization of low-density lipoproteins (LDL), rat fetuses were injected with either LDL-gold or albumin-gold conjugates. The degree of binding and uptake of LDL-gold and albumin-gold by parenchymal and sinusoidal cells of the fetal rat liver differs markedly. Endothelial cells exhibit low LDL-gold uptake. In contrast, parenchymal cells internalize LDL-gold more actively (45 ± 8 LDL conjugates/100 μm2 cytoplasm within 60 min). Kupffer cells exceed this value by a factor of 20. The uptake of albumin-gold by endothelial and Kupffer cells is high, whereas it is extremely low in parenchymal cells. Estradiol pretreatment causes a significant doubling (p<0.05) of the LDL-gold particle density/100 μm2 cytoplasm both in parenchymal and Kupffer cells, whereas estradiol has no effect on the albumin uptake. The results strongly indicate that LDL uptake by parenchymal and Kupffer cells in the fetal rat liver is mediated by estrogen-inducible receptors, which may correspond to B, E receptors in the adult liver.

The use of serum from rat fetuses instead of serum from adult rats for preparation of LDL by preparative ultracentrifugation leads to an LDL fraction containing apoB-100 and apoB-95 as the only protein moieties without need for any further purification. The yield of LDL is five times greater compared to the use of adult rat serum. Lipid composition and particle size of LDL from fetal and adult rats are quite similar. The method described allows a simple way for preparation of sufficient amounts of apoE-free LDL for use in metabolic studies.

Binding and internalization of rat low density lipoproteins (LDL) by fetal rat liver cells were studied under in vivo and in vitro conditions by ultrastructural and biochemical methods. By using LDL-gold conjugates it could be shown that on day 22 of gestation hepatocytes and Kupffer cells mainly contribute to specific binding and uptake of LDL, but not endothelial cells. Estrogen administration to the pregnant rats stimulated binding and internalization of LDL-gold. The binding characteristics of isolated fetal hepatocytes were determined by 125I-LDL. The data allow the conclusion that fetal hepatocytes and Kupffer cells possess specific B/E receptors.

Measuring both platelet-stimulating activity and liberation of acetate, the capacity of serum and individual lipoproteins to degrade the platelet-activating factor (PAF) was studied. The highest degrading effect relative to the protein content was found in very low density lipoproteins (VLDL) and in low density lipoproteins (LDL). The effect is about 10- and 100-fold higher than that of high density lipoproteins (HDL) and serum, respectively. In lipoprotein deficient serum (LPDS) less than 5% of serum activity is detectable. Considerable individual variations are observed measuring the degradation of PAF under standard conditions in plasma from 37 healthy volunteers. Moreover, this activity is shown to correlate strongly with the plasma concentration of LDL. On the other hand, a significant negative correlation was found between the PAF-degrading capacity and the plasma concentration of HDL. In contrast, the PAF-degradation is unrelated to the concentration of plasma triglycerides. The results point to a possible role of plasma lipoproteins in regulating the degradation of PAF released into the circulation.