Effect of long-term immunization of rabbits of different ages with homologous heart antigen on blood lipid and lipoprotein content

The data are provided on the content of lipid and lipoproteins in the blood of young and old rabbits during long-term immunization with homologous heart antigen (once a week for 2.5 months). Two weeks after the beginning of the experiment the blood of immunized animals showed cardiac antibodies whose content rose, especially in young animals, in the course of the experiment. The content of immune complexes circulating in the blood also increased, with this increase being more pronounced in old rabbits. During immunization, the blood levels of lipoproteins total cholesterol, and triacylglycerins in old animals increased earlier and more intensely.     

Evaluation of rat and rabbit sera lipoproteins in experimentally induced hyperlipidemia by analytical ultracentrifugation

Animals of various species are widely used as models with which to study atherosclerosis and the lipoprotein metabolism. The objective of this study was to investigate the lipoprotein profiles in Wistar rats and New Zealand white rabbits with experimentally induced hyperlipidemia by means of ultracentrifugation. The Schlieren curves were utilized to compare suckling and adult rat sera to determine whether aging causes alterations in lipoprotein profiles. A striking feature of the data is the high concentration of low-density lipoproteins (LDL), (>5.2 mmol/l cholesterol) in the 2-week old rat serum pool which was greatly decreased in the 3-weeks rat serum pool (<1.3 mmol/l cholesterol). Additional experiments were performed to permit a direct comparison of the amounts of lipoprotein present in rat sera in experimental hyperlipidemia post-Triton WR 1339 administration. Rapid changes in concentrations in very low-density lipoproteins (VLDL), LDL and high-density lipoproteins (HDL) were observed after Triton injection. The administration of Triton WR 1339 to fasted rats resulted in an elevation of serum cholesterol levels. Triton physically alters VLDL, rendering them refractive to the action of lipolytic enzymes in the blood and tissues, preventing or delaying their removal from the blood. Whereas the VLDL concentration was increased markedly, those of LDL and HDL were decreased at 20 h after Triton treatment. Rabbits were fed a diet containing 2% cholesterol for 60 days to develop hyperlipidemia and atheromatous aortic plaques. A combination of preparative and analytical ultracentrifugation was used to investigate of LDL aliquots, to prepare radioactive-labeled lipoproteins and to study induced hyperlipidemia in rabbits. Analytical ultracentrifugation was applied to investigate the LDL flotation peaks before and after cholesterol feeding of rabbits. Modified forms of LDL were detected in the plasma of rabbits with experimentally induced atherosclerosis. ApoB-containing particles, migrating as LDL, intermediate density lipoproteins and VLDL were the most abundant lipoproteins. Gamma camera in vivo scintigraphy on rabbits with radiolabeled lipoproteins revealed visible signals corresponding to atherosclerotic plaques of the aorta and carotid arteries.     

The spike reactions of the motor cortex neurons of old rabbits to specific stimuli

Spike reactions of motor cortex neurons to tactile and electrocutaneous stimulation of a forelimb were studied in aged (6-7-year old) rabbits. As compared with young adult animals, the neuronal reactions to afferent stimuli were rarely recorded in the motor cortex of aged rabbits (66.7 and 50%, respectively). The activation manifested in increasing firing rate over its spontaneous level was less intensive than in young animals. The neuronal reactions of aged animals were characterized by the slower activation with longer latencies and slower development of spike responses. The parameters of slow activation could be partly corrected by the iontophoretic application of acetylcholine to the soma region. Neuronal inhibition recorded in the motor cortex of aged rabbits was not markedly changed compared to inhibition reactions in young animals. It is suggested that impairment of the functional state of dendrites in aging is responsible for the changes observed.     

Characterization of arachidonic acid metabolism in Watanabe heritable hyperlipidemic (WHHL) and New Zealand white (NZW) rabbit aortas

WHHL rabbits develop progressive atherosclerosis. There are no visible signs of the disease at 1 month, however, by 12 months, the formation of aortic plaques is extensive. This study characterized arachidonic acid (AA) metabolism in 1 and 12 month old WHHL and NZW rabbit aortas. Vessels incubated with 14C-AA and A23187 metabolized AA to a number of oxygenated products as identified by high pressure liquid chromatography. The major AA metabolites produced by WHHL and NZW aortas were 6-keto PGF1 alpha, PGE2, 12- and 15-hydroxyeicosatetraenoic acids (HETEs). The structures of the HETEs were confirmed by gas chromatography-mass spectrometry. Indomethacin blocked the synthesis of prostaglandins (PGs) but not HETEs whereas ETYA, NDGA or removal of the endothelium attenuated the production of both PGs and HETEs. Measurement of 6-keto PGF1 alpha, 12- and 15-HETE by specific radioimmunoassays indicated that as the rabbits aged and as atherosclerosis progressed, aortas lost the ability to synthesize 6-keto PGF1 alpha and 15-HETE. Prior to the development of atherosclerosis, 1 month old WHHL aortas produced 70% less 15-HETE than did NZW aortas. Atherosclerotic aortas from 12 month old WHHLs synthesized 60% less 6-keto PGF1 alpha during stimulation with AA or A23187 than did 12 month old NZW aortas. We conclude that the development and expression of atherosclerosis in WHHL rabbits impairs the ability of aortas to metabolize AA to both PGs and HETEs.     

Impaired triacylglycerol catabolism in hypertriglyceridemia of the diabetic, cholesterol-fed rabbit: a possible mechanism for protection from atherosclerosis

The etiology of the hypertriglyceridemia in alloxan-diabetic rabbits was studied by two independent methods. Production and removal rates of VLDL triacylglycerol were measured in diabetic rabbits by injection of [3H]palmitate-labelled VLDL. Similarly, triacylglycerol total removal rates were determined in non-diabetic rabbits which were infused with Intralipid to mimic the plasma triacylglycerol concentrations of diabetic rabbits. Compared to nondiabetic rabbits, triacylglycerol removal rats were decreased in diabetic rabbits, particularly at higher levels of plasma triacylglycerol. During cholesterol and triacylglycerol supplementation of the diet, post-heparin plasma lipoprotein lipase activity of diabetic rabbits with severe hypertriglyceridemia averaged 36% of that of nondiabetics, suggesting an impaired triacylglycerol removal capacity. Furthermore, plasma triacylglycerol was inversely related to post-heparin plasma lipoprotein lipase activity among diabetic rabbits. VLDL triacylglycerol production increased with increasing plasma triacylglycerol concentration among diabetic cholesterol-fed rabbits with moderately severe hypertriglyceridemia, but reached an apparent plateau among rabbits with plasma triacylglycerol concentrations from approx. 2000-9000 mg/dl. Thus, severe hypertriglyceridemia in this model of insulin deficiency can be attributed only partially to VLDL hypersecretion, whereas a removal defect, resulting in saturation of the triacylglycerol removal mechanism, appears to be largely responsible. The impaired removal of plasma triacylglycerol is also related to the presence of cholesterol predominantly in lipoproteins of increased size. The data support the hypothesis that protection against atherosclerosis in cholesterol-fed diabetic rabbits results from exclusion of very large cholesterol-containing lipoproteins from the arterial wall.     

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 hyperlipidemia on lipoprotein metabolism in squirrel monkeys and rabbits.

We studied the metabolism of different classes of lipoprotein in squirrel monkeys and rabbits. Lipoproteins were labeled in vivo in donor animals with (3H)leucine and (3H)cholesterol. The rate of disappearance from plasma of recipient squirrel monkeys of the protein moiety of the very low density lipoproteins was rapid, that of high density lipoproteins slow, and the rate for low density lipoproteins was intermediate. The fractional turnover of the apoprotein of low density lipoproteins was slightly reduced in hyperlipidemic monkeys, but the absolute rates of synthesis and catabolism were increased. Hyperdipidemia in rabbits resulted in a dramatic reduction in the fractional catabolic rate of low density lipoprotein apoprotein. Hyperlipidemia in the donors of biosynthetic low density lipoproteins also influenced the rates of catabolism in rabbits. We showed the cycloheximide that although there was recycling of (3H)leucine into other proteins, the reutilization of leucine from low density lipoproteins for nascent low density lipoproteins was not significant. In most tissues the ratio of cholesterol:protein radioactivity was much greater than that for plasma 24 h after administration of labeled low density lipoproteins, but the ratios for aortic intima plus inner media and for plasma low density lipoproteins were similar. The presence of atherosclerosis resulted in a large increase in the apparent uptake of low density lipoproteins by the aortas of rabbits and monkeys.     

兔先天性青光眼网络膜血管改变

目的　研究青光眼对视网膜脉络膜血液循环的影响。方法　选24月龄、体重3.5～4kg的先天性青光眼大耳白兔5只(7只眼),选10只同龄大耳白兔作为对照组。另选10只2月龄、体重2kg大耳白兔前房内灌注生理盐水制成急性高眼压模型。对三组兔进行眼底照像、闪光视诱发电位(FVEP)检查,观察视网膜脉络膜血管形态和FVEP的变化。对人工急性高眼压组还进行了闪光视网膜电流图(FERG)检查。结果　先天性青光眼组与同龄对照组相比视网膜脉络膜末梢血管网明显减少;人工急性高眼压组眼压升高后首先使视网膜脉络膜末梢血管网灌流不足,随着眼压的继续升高脉络膜大血管变细,末梢血管网灌流不足加重,眼压极度升高时脉络膜大血管血流中断。同龄正常对照组的FVEP的主波P100潜伏期是(83±9)ms,先天性青光眼组则为(112±14)ms,差异有非常显著意义(P＜0.01);人工急性高眼压组高眼压前为(69±5)ms,眼压60～80mm　Hg时延长为(81±7)ms,眼压在100～130mmHg时FVEP波形低平,近似直线;眼压恢复正常后2hFVEP的P100潜伏期为(82±8)ms。人工急性高眼压前后FERG变化显著。结论　青光眼可以影响视网膜脉络膜血液循环;可使FVEP、FERG发生变化。     

Defective plasma clearance of chylomicron-like lipid emulsions in Watanabe heritable hyperlipidemic rabbits

Human patients with familial hypercholesterolemia (FH) and Watanabe heritable hyperlipidemic rabbits (WHHL), while lacking normal receptors recognizing low-density lipoproteins (LDL), are said to have normal clearance of chylomicrons. In the present study, emulsions with a similar lipid composition to chylomicrons were injected intravenously in homozygous WHHL rabbits and normal control rabbits fed diet with low or high cholesterol. Radioactive labels tracing emulsion triolein and cholesteryl oleate were both removed rapidly from the bloodstream, with the removal rate of triolein always faster than that of cholesteryl oleate. This pattern was similar to the clearance of normal chylomicrons in rabbits or rats, and was consistent with the formation of remnant lipoproteins after hydrolysis of emulsion triolein by lipoprotein lipase, followed by hepatic uptake of the remnants. The removal of cholesteryl oleate was significantly slower in WHHL rabbits than in normal controls, suggesting that the absence of LDL receptor function led to impaired remnant clearance. Measured in post-heparin plasma, the activity of lipoprotein lipase was decreased in WHHL rabbits, but this was not associated with clear evidence of defective lipolysis of emulsion triolein. Apolipoprotein E did not appear to be deficient in WHHL rabbits. Plasma devoid of lipoproteins less than 1.006 g/ml from WHHL and normal control rabbits transferred similar amounts of apolipoprotein E to chylomicron-like emulsions after incubation. Impaired clearance of chylomicron remnants possibly contributes to the hypertriglyceridemia of WHHL rabbits and to accelerated atherogenesis when the function of LDL receptors is defective.     

The morphofunctional characteristics of the neurons in the sensorimotor cortex of old rabbits during the trace assimilation of rhythm]

Extracellular neuronal activity was recorded from 460 neurons from alert young (5-7 months), middle-aged (54-65 months) and old (66-85 months) rabbits. Trace rhythmic activity of sensorimotor cortical neurons was examined after long-lasting (10-20 min) rhythmic (0.5-2 Hz) electrocutaneous stimulation of the contralateral forelimb. Spectral analysis of spike activity showed age-related differences in capability of producing a rhythm of previous stimulation in spontaneous neuronal activity. In young animals propriate rhythmic fluctuations of firing rate appeared after the first or second sessions of stimulations (on the first experimental day), in middle-aged ones--after 2-4 sessions (on the second or third days); cortical neurons in old rabbits did not exhibit trace rhythmic activity. Significant morphological changes in glial and neuronal cells were observed in sensorimotor cortex of old rabbits. It is proposed that morphological deteriorations may be the reason of the impairement of trace processes during aging.     

Rabbit liver secretes oxidated lipoproteins in experimental atherosclerosis]

It is shown in rabbits, that alimentary hypercholesterolemia proceeds with increasing lipid peroxidation in liver homogenate, blood serum and apo-B-containing lipoproteins. It is established in the model of liver perfusion in rabbits, that liver cells produce apo-B-containing level of lipid peroxidation. The lipid peroxidation increases in perfusate and in the fraction of lipoproteins (d less than 1,065 g/cm3) from this perfusate. Lipid peroxidation can interfere in the changing of physicochemical characteristics of lipoproteins at the stage of synthesis and secretion of lipoproteins by liver cells.     

Measurement of apolipoprotein B radioactivity in whole blood plasma by precipitation with isopropanol

A method to measure apolipoprotein B radioactivity in whole blood plasma is described that is suitable for routine use in kinetic experiments in vivo. Radiolabeled apolipoprotein B is precipitated from plasma diluted 15- to 30-fold in the presence of carrier low density lipoproteins by 50% isopropanol. The amount of radioiodine in apoB is estimated from the difference between total radioiodine concentration in whole plasma and the fraction soluble in 50% isopropanol. Addition of up to 100 microliters of plasma to radioiodinated lipoproteins did not alter the percent of radioiodine precipitated in 1500 microliters of 50% isopropanol. The percent of radioiodine precipitated by isopropanol 3 min after intravenous injection of homologous radioiodinated very low density lipoproteins, intermediate density lipoproteins, and low density lipoproteins into rabbits was almost identical to that in the injected lipoproteins (y = 1.009 X +/- 0.462; r = 0.997).     

Human monocyte colony-stimulating factor enhances the clearance of lipoproteins containing apolipoprotein B-100 via both low density lipoprotein receptor-dependent and -independent pathways in rabbits

To investigate the effects of recombinant human monocyte colony-stimulating factor (M-CSF) on plasma cholesterol metabolism, we injected M-CSF intravenously into New Zealand White rabbits (n = 13) at a dose of 100 micrograms/day for 7 days. After the treatment, the plasma cholesterol levels fell by 33.2% from 61.4 +/- 25.9 to 41.0 +/- 10.2 mg/dl (mean +/- S.D.). We also injected a large dose of M-CSF (500 micrograms/day) for 6 days into Watanabe Heritable Hyperlipidemic rabbits, which are deficient in low density lipoprotein (LDL) receptors. Again, there was a significant reduction in plasma cholesterol levels by 36.2% from 730.5 +/- 176.4 to 466.0 +/- 104.9 mg/dl (n = 4). In the kinetic studies in New Zealand White rabbits with very low density lipoprotein, LDL, and methylated LDL, the removal rates of those lipoproteins were increased 1.9-, 1.7-, and 2.0-fold, respectively, after the treatment. Immunoblot analysis of LDL receptors in the treated rabbits showed no significant changes in LDL receptor proteins in livers but a great increase in spleens and bone marrows compared with the controls. Messenger RNA was also estimated by Northern blotting in both groups, and the results were compatible with those from the immunoblot. The data suggest that M-CSF stimulates the clearance of lipoproteins containing apolipoprotein B-100 via both LDL receptor-dependent and -independent pathways in target cells of M-CSF and reduces plasma cholesterol.     

Postnatal development of the scratch reflex in rabbits]

The development of the scratch reflex was studied in newborn (up to 2 months old) rabbits in norm and after elimination or activation of some parts of their nervous system (reticular formation, cerebellum, caudate nucleus, cerebral cortex, superior cervical sympathetic ganglia). The experiments with the section of the brain stem at the border between the medulla and the midbrain showed that in very young (5-10 days old) rabbits in norm the scratch reflex is controlled by the spinal cord with no influences of structures situated above the section's level. Later on the spinal mechanism of the scratch reflex becomes subject to supraspinal influences, among which in 2-3 weeks old animals facilitatory effects are predominant produced, in particular, by the reticular formation and the cerebellum, whereas in older age prevail inhibitory influences of the cerebral cortex, cerebellum, caudate nucleus and the sympathetic nervous system.     

Age-related features of the state of plasma lipoproteins in rats with hereditary retinal degeneration

The content of lipids and lipoproteins was determined in the blood plasma of Campbell rats with inherited retina degeneration and Wistar rats used as control. It was shown that in the 30-day old Campbell rats the content of cholesterol in high density lipoproteins sufficiently exceeded that of control. When the distribution of lipoproteins particles in the density gradient was studied after ultracentrifugation, some "anomalous" particles were revealed in the 30-45 day old rats with inherited retina degeneration, which with respect to the flotation rate occupy intermediate position between the low and high density lipoproteins. The obtained data show that the development of inherited retina degeneration in rats involves a disturbance, of the lipoprotein spectrum of blood plasma.     

Conditioned reflex activity in the aging process in white rats

In Wistar rats, irrespectively of their age, conditioned reflexes to present stimuli are preserved and elaborated. Neither the mechanism of time intervals estimation is disturbed in aged and old rats (24-32 months). Long intervals between experiments (3-5 months) do not influence their state. Distinct changes are revealed of spatial-temporal differentiations in T-maze: significant worsening of their state is observed in 8-10 months age; in this age it is neither possible to elaborate them again. In simplified experimental conditions in the T-maze the old rats preserve the spatial orientation.     

Regional differences in PACAP transport across the blood-brain barrier in mice: a possible influence of strain,amyloid beta protein,and age

The blood–brain barrier (BBB) controls the exchange of peptides and regulatory proteins between the central nervous system (CNS) and the blood. Transport across the BBB of such regulatory substances is altered in animal models of Alzheimer’s disease. These alterations could lead to cognitive impairments or diminish their therapeutic potential. Here, we measured the transport rate of radioactively labeled pituitary adenylate cyclase-activating polypeptide (PACAP) from blood into whole brain and into 11 brain regions in three groups of mice: young (2 months old) ICR, young (2 months old) SAMP8, and aged (12 months old) SAMP8 mice. The SAMP8 is a strain which develops impaired learning and memory with aging that correlates with an age-related increase in brain levels of amyloid β protein (AβP). PACAP is a powerful neurotrophin that may have a therapeutic role in neurodegenerative diseases. We found that I-PACAP crossed the BBB fastest at the hypothalamus and the hippocampus in all three groups. Slower transport rates into the whole brain, the olfactory bulb, the hypothalamus, and the hippocampus for aged SAMP8 mice was likely related to differences both from strain and expression of AβP with aging.     

Secretion of cholesteryl-ester-rich lipoproteins by the perfused livers of rabbits fed a wheat-starch-casein diet

Rabbits fed a cholesterol-free semi-synthetic wheat-starch-casein diet had a high plasma cholesterol concentration; most of the cholesterol was associated with low-density lipoproteins (LDL). Chemical analyses of plasma lipoproteins revealed that very-low-density lipoproteins (VLDL), intermediate lipoproteins and LDL from casein-fed rabbits contained more cholesteryl ester than that of lipoproteins isolated from chow-fed animals. The fatty acid composition of cholesteryl esters of plasma lipoproteins showed that there were higher contents of oleic acid than linoleic acids in lipoproteins from casein-fed rabbits. Lipoproteins isolated from liver perfusates of casein-fed rabbits had higher cholesteryl oleate content than lipoproteins from chow-fed rabbit liver perfusates. There was a marked increase in secretion of apolipoproteins from perfused livers of casein-fed rabbits. We conclude that the high levels of plasma cholesterol in casein-fed rabbits are of hepatic origin and that one of the hypercholesterolemic actions of dietary casein in rabbits is the induction of hepatic synthesis and secretion of cholesteryl-ester-rich lipoproteins.     

Regulation of hepatic receptor-dependent degradation of LDL by mevinolin in rabbits with hypercholesterolemia induced by a wheat starch-casein diet

Rabbits fed a wheat starch-casein diet develop a marked hypercholesterolemia and have a slower rate of removal of rabbit 125I-labeled low density lipoproteins (LDL) from plasma. Treating rabbits with mevinolin, a highly potent competitive inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, at a daily dose of 20 mg per animal prevents the increase in plasma and LDL cholesterol. The mevinolin effect is mediated through an increased rate of removal of rabbit 125I-labeled LDL from plasma. To study the role of mevinolin on the regulation of the hepatic LDL receptor in rabbits, the binding of 125I-labeled LDL and 125I-labeled beta-VLDL (beta-migrating very-low-density lipoproteins) to liver membranes prepared from rabbits fed the wheat starch-casein diet with or without mevinolin was investigated. Liver membranes from wheat starch-casein-fed rabbits have no demonstrable EDTA-sensitive binding activity of 125I-labeled LDL and low (37 ng/mg protein) binding activity of 125I-labeled beta-VLDL. Treatment of the wheat starch-casein fed rabbits with mevinolin results in high levels of specific EDTA-sensitive binding of 125I-labeled LDL (28.7 ng/mg protein) and 125I-labeled beta-VLDL (120 ng/mg protein). To assess the functional role of the hepatic LDL receptor in response to mevinolin, the catabolism of 125I-labeled LDL by perfused rabbit livers was studied. Perfused livers from mevinolin-treated rabbits show a 3.3-fold increase in the rate of receptor-dependent catabolism of 125I-labeled LDL (4.6% X h-1) when compared with that of livers from rabbits not treated with mevinolin (1.4% X h-1). Thus, these studies demonstrate that mevinolin prevents the increase of plasma LDL cholesterol level in rabbits fed a wheat starch-casein diet by regulating the levels of hepatic LDL-binding sites and the rate of receptor-dependent catabolism of LDL by the liver.     

Effect of zinc on the lipid peroxidation and the antioxidant defense systems of the alloxan-induced diabetic rabbits

The effects of oral zinc supplementation on lipid peroxidation and the antioxidant defense system of alloxan (80-90 mg/kg)-induced diabetic rabbits were examined. Forty-five New Zealand male rabbits, 1 year old, weighing approximately 2.5 kg, were allocated randomly and equally as control, diabetic, and zinc-supplemented diabetic groups. After diabetes was induced, zinc-supplemented diabetic rabbits had 150 mg/L of zinc as zinc sulfate (ZnSO(4)) in their drinking tap water for 3 months. The feed and water consumption was higher in diabetic groups than (P<0.01) healthy rabbits. The body weight was lower in diabetic rabbits compared to control. The blood glucose levels were higher in diabetic groups than controls. The elevated plasma malondialdehyde (MDA) levels were determined in the diabetic group (P<0.01). The glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD), glutathione (GSH), and ceruloplasmin levels in the diabetic group were decreased by the effect of diabetes but there was no difference between zinc-supplemented diabetic and control rabbits. Serum zinc concentrations were lower in diabetic rabbits but iron (Fe) and copper (Cu) levels in sera were not different among the groups. As a result, it was concluded that daily zinc supplementation could reduce the harmful effects of oxidative stress in diabetics.