Cholesterol-fed heterozygous Watanabe heritable hyperlipidemic rabbits: a new model for atherosclerosis

Homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits are used widely to study atherosclerosis, but the WHHL heterozygous rabbit has received little attention. To study their potential as a model for atherosclerosis, heterozygous WHHL and New Zealand white (NZW) rabbits were fed diets containing 0%, 0.5% and 1.0% cholesterol. Plasma lipids were analyzed at 0, 4, 8, 12, 16 and 24 weeks, and animals were killed at 12 and 24 weeks. Plasma cholesterol levels were significantly higher in cholesterol-fed WHHL heterozygotes at 8 weeks compared with NZW rabbits, but no differences were apparent at other times. Atherosclerotic plaques in the aortas of cholesterol-fed WHHL heterozygous rabbits differed from those in NZW rabbits, in that the WHHL had complicated lesions with necrosis, cholesterol clefts, fibrous caps and calcification, similar to that found in humans and homozygous WHHL rabbits. In contrast, NZW rabbits had predominantly foam cell lesions. Heterozygous WHHL rabbits also had less extensive extravascular foam cell deposits. Our results suggest that the cholesterol-fed heterozygous WHHL rabbit may provide a promising model for studying the pathogenesis of atherosclerosis.     

Circulating IgA-Lp complexes in Watanabe heritable hyperlipidemic and cholesterol fed NZW rabbits

Auto-immune immunoglobulin-lipoprotein complexes (Ig-Lp), as well as other modified lipoproteins, are activators of the transformation of macrophages into foam cells which may be the first step in atherogenesis. In humans circulating Ig-Lp have been demonstrated in autoimmune hyper- or dyslipidemia (AIH, DIH) and found to be associated with conditions related to atherosclerosis. Thus Ig-Lps may be significant and potentially primary atherogenic factors. In order to test this hypothesis we compared the distribution of Ig-Lps in 14 WHHL homozygote rabbits and in 15 normal fed and 8 cholesterol-fed NZW rabbits, all males aged 4-6 months. The Ig-Lps were detected by ELISA using 2 different capture anti-Lp and 4 indicator antibodies specific for either total Igs or the IgA, IgM or IgG classes. Some Ig-Lp of all classes were found in normal fed NZW. As compared with these normal levels, IgA-Lp are increased 2.5-fold in both the WHHL and the cholesterol-fed NZW rabbits (P = 0.0002). During cholesterol feeding the increase of IgA-Lp and total cholesterol and their decrease after returning to a normal diet were parallel in NZW rabbits, but their variation was mainly independent. IgM-Lp was also increased, but to a much lesser extent, in WHHL and in cholesterol-fed NZW. IgG-Lp was not increased in WHHL and only moderately increased in some of the cholesterol-fed NZW. The WHHL and the cholesterol-fed NZW rabbits did not differ by the IgA-Lp content of the serum, but the level of IgM-Lp was higher in the former.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparative study on serum lipids and atherosclerotic plaque formation in diet-induced and familial hypercholesterolemia in rabbits, and the effect of partial ileal bypass

Aim of the present study was to compare an alimentary and a hereditary rabbit model for hypercholesterolemia. Serum lipids, serum lipoproteins and distribution and prevention of atherosclerotic plaque formation were studied in (1%) cholesterol-fed NZW rabbits and both heterozygous and homozygous WHHL rabbits. Cholesterol-fed NZW rabbits showed a hypercholesterolemia without hypertriglyceridemia, caused by accumulation of a spectrum of cholesterol ester-rich beta-migrating lipoproteins with a relatively low density. The WHHL rabbits displayed both a hypercholesterolemia with an elevation of LDL, and a hypertriglyceridemia. The hypertriglyceridemia in the WHHL homozygotes was due to accumulation of VLDL remnants and in the heterozygotes to a slight rise in normal pre-beta VLDL. Despite the pronounced quantitative and qualitative differences in lipoproteins, the location and extent of atherosclerotic plaques which had developed after 13 weeks cholesterol-rich diet in NZW rabbits and in 10 months old homozygous WHHL rabbits, was quite similar. Partial ileal bypass surgery lowered serum cholesterol in all three groups and also prevented atherogenesis.     

Insulin resistance in the St. Thomas' mixed hyperlipidaemic (SMHL) rabbit, a model for familial combined hyperlipidaemia

The St. Thomas mixed hyperlipidaemic (SMHL) rabbit exhibits an inherited hyperlipidaemia similar to that seen in familial combined hyperlipidaemia (FCHL). In this study, we investigated whether the SMHL rabbit is insulin resistant, a condition often associated with FCHL. Six young and six mature combined hyperlipidaemic SMHL rabbits, age/sex matched New Zealand White (NZW) control rabbits and six young hypercholesterolaemic Watanabe heritable hyperlipidaemic (WHHL) control rabbits were fed a 0.08% (w/w) cholesterol-enriched diet for at least 1 month prior to the start of the experiment. We performed an oral glucose tolerance test after an overnight fast by dosing the rabbits with a solution of 1 g of glucose per kg body weight. Blood was withdrawn just before and 15, 30, 45, 60 and 120 min after administration of the oral glucose dose. Plasma glucose levels were similar in SMHL, WHHL and NZW rabbits throughout the oral glucose tolerance test. Fasting glucose levels were slightly increased in WHHL rabbits but not in young and adult SMHL rabbits as compared to NZW rabbits. The area under the curve (AUC) for the insulin response was significantly increased for both young (P<0.05) and mature (P<0.05) SMHL rabbits, and in WHHL rabbits, compared with NZW rabbits. The AUC for the ratio of glucose:insulin response to the glucose dose was decreased in young and mature SMHL rabbits (P<0.05 and P<0.01, respectively) and in young WHHL rabbits (P<0.05), compared with NZW rabbits. Only WHHL rabbits showed an increased AUC for the non-esterified fatty acid response compared to NZW rabbits. Log-transformed plasma triglycerides values were significantly correlated with the log-transformed AUC for the insulin response in young SMHL rabbits (r=0.81; P<0.05) and with the AUC for the insulin response in mature SMHL rabbits (r=0.84; P<0.05). WHHL rabbits showed no significant correlation. In conclusion, SMHL rabbits are insulin resistant, the severity of which appears to increase with age. Therefore, the SMHL rabbit offers a valuable animal model in which to study the relation between hypertriglyceridaemia and insulin resistance.     

Characterisation of the lipoprotein structure in the St. Thomas' Mixed Hyperlipidaemic (SMHL) rabbit

Familial combined hyperlipidaemia (FCHL) is a complex genetic disorder of unknown aetiology. Study of this human condition over many decades has been hampered by likely genetic heterogeneity. In order to find better phenotypic markers, we have characterised the structures of VLDL, IDL and LDL in the St. Thomas' Mixed Hyperlipidaemic (SMHL) rabbit--an animal model of FCHL in which the hyperlipidaemia is caused primarily by an increased production rate of apolipoprotein B (apoB)--containing lipoproteins-and compared them with those in the Watanabe Heritable Hyperlipidaemic (WHHL) rabbit, in which hyperlipidaemia is caused mainly by a defect in lipoprotein clearance, and those in the normolipidaemic New Zealand White (NZW) animal. All three rabbit strains were fed a cholesterol-enriched (0.08%, w/w) diet for at least 3 months prior to blood sampling. Both SMHL and WHHL rabbits showed combined hyperlipidaemia as evidenced by significantly increased levels of plasma cholesterol and triglycerides. Raised plasma lipids in the SMHL rabbit were attributable mainly to an overabundance of lipoprotein particles with the same lipid composition as those in NZW rabbits. VLDL and IDL in the SMHL rabbit showed a significantly increased sphingomyelin to phosphatidyl choline ratio. In the WHHL rabbit there was a high concentration of particles that were significantly enriched in cholesteryl esters and depleted in triglycerides. Phospholipids in all lipoprotein fractions from WHHL rabbits contained significantly more sphingomyelin and less phosphatidyl choline resulting in a significantly increased sphingomyelin to phosphatidyl choline ratio. We found that the VLDL of SMHL rabbits could be distinguished from that of NZW rabbits on the basis of the cholesterol:apoB and the sphingomyelin:phosphatidylcholine ratios, and from that of WHHL rabbits by the sphingomyelin:triglyceride ratio. Extrapolating these findings to the human condition, an assessment of particle core composition, together with the proportion of sphingomyelin in phospholipids especially in VLDL might help in the differentiation of the combined hyperlipidaemia of FCHL into disorders of lipoprotein overproduction versus decreased clearance.     

Retinyl palmitate labeled intestinally derived lipoproteins accumulate in the circulation of WHHL rabbits

The behavior of native retinyl palmitate labeled intestinally derived lipoproteins and their remnants was studied in 8 NZW and 8 WHHL (5 homo- and 3 heterozygote) normal-fed rabbits and in 3 cholesterol-fed NZW, after 1 month of cholesterol feeding, and 3 and 5 months after resuming normal feeding. Palmitate labeled lipoproteins were produced by the intestine after administration of 50,000 IU of Vitamin A, together with olive oil via gastric intubation. Blood was drawn before and 3,6,9,12,24, and in some instances, 48 h later. Retinol (R) and retinyl palmitate (RP) were measured in whole serum and in the chylomicron, d less than 1006, d greater than 1006 less than 1019, d greater than 1019 less than 1063, d greater than 1063 less than 1210 g/ml lipoprotein fractions and in the infranatant. The R content of the serum was almost all concentrated in the infranatant, it did not change during the vitamin A test and was similar in WHHL, and normal- or cholesterol-fed NZW rabbits. In the normal-fed NZW the RP content of the serum increased within 6 h after giving the vitamin A fat meal (peak value less than 200 microgram/100 ml) and then decreased. In the WHHL homozygotes, the RP increased to a much greater degree (peak value 600-1820 micrograms) and for a much longer time, as it was still increased in the 5 cases studied after 24 h, and in 3 cases studied after 48 h. Similar RP curves were obtained in NZW rabbits, after 1 month of cholesterol feeding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endothelium-dependent relaxation, cholesterol content and high energy metabolite balance in Watanabe hyperlipemic rabbit aorta

Functional and metabolic parameters of thoracic aorta from Watanabe heritable hyperlipemic (WHHL) rabbits (aged 11-14 months) were investigated in vitro. The aortic preparations, normally responsive to noradrenaline, showed a diminished response to the endothelium-dependent agent, acetylcholine, in comparison with control preparations from age-matched New Zealand rabbits (maximal relaxation: 33 +/- 4% in WHHL vs. 52 +/- 2% in controls: P less than 0.005). ATP relaxant effect (only partially endothelium-dependent) was unimpaired in WHHL aorta, and it was much higher than in controls (maximal response: 63 +/- 6% vs. 37 +/- 3%, respectively; P less than 0.005). The response to NaNO2, an endothelium-independent relaxant, was unchanged in WHHL aortas. Acetylcholine-induced response was found to be inversely related to the degree of total cholesterol infiltration in aorta (r = -0.62, P less than 0.05). No correlation was observed between either total serum cholesterol or triglycerides and ACh-induced response. Furthermore, the concentration of adenine nucleotides and nucleosides in the aortic tissue of WHHL rabbits was lower than in controls, indicating a loss of energy balance. The results indicate a functional damage induced by genetic hyperlipidemia on endothelium-dependent relaxation and an impairment of energy-rich phosphate metabolism of the aortic wall. The relationship between functional and metabolic parameters is not yet clarified.     

Sympathetic neurotransmission in the Watanabe heritable hyperlipidaemic rabbit mesentery artery.

STUDY OBJECTIVE--The aim was to examine sympathetic neurotransmission in the mesenteric artery of atherosclerotic (Watanabe heritable hyperlipidaemic, WHHL) rabbits. DESIGN--Contractile responses to perivascular nerve stimulation (8-64 Hz) and exogenous application of the cotransmitters noradrenaline (0.1-100 microM) and adenosine triphosphate (1 microM) were measured. Catecholamine containing nerves were localised using fluorescence histochemistry. EXPERIMENTAL MATERIAL--Female WHHL rabbits at 4, 6, and 12 months of age were used, with New Zealand white (NZW) rabbits as controls. MEASUREMENTS AND MAIN RESULTS--The contractile responses to nerve stimulation were significantly smaller in 12 month old WHHL compared to NZW rabbits, although there was no difference at 4 and 6 months of age. Contractile responses of WHHL vessels to noradrenaline (0.1-100 microM) were greater than NZW controls at 4 months, but no differences were seen at 6 and 12 months. Contractile responses to alpha, beta-methylene ATP (0.1 microM) were greater in WHHL rabbits at 6 months but were unchanged at 4 and 12 months. There was no difference in the contractile responses to potassium chloride (120 mM) between 4, 6, and 12 month old WHHL and NZW rabbits. There was no variation in either strain of rabbit in the density of catecholamine containing nerves between 4 and 12 months of age. CONCLUSIONS--The reduction of sympathetic neurotransmission in WHHL rabbits at 12 months of age may largely be due to a reduction in the release of the cotransmitters noradrenaline and ATP. The reduced contractile response to nerve stimulation in 12 month old WHHL rabbits is discussed in terms of "protection" of the mesenteric artery from potential vasospasm and atherogenesis.     

Nifedipine suppressed atherosclerosis in cholesterol-fed rabbits but not in Watanabe heritable hyperlipidemic rabbits

We studied the effects of nifedipine, a calcium antagonist, on atherosclerosis in cholesterol-fed rabbits and Watanabe heritable hyperlipidemic rabbits (WHHL rabbits). Japanese White rabbits were fed 120g of 2% cholesterol rabbit chow daily, and WHHL rabbits were fed standard rabbit chow. In each experiment, the rabbits were divided into two groups. Twenty milligrams of nifedipine was given orally twice a day to the nifedipine group, and the control group was given a placebo in the same way. The rabbits were sacrificed at the end of the 12th week in the case of cholesterol-fed rabbits, and the 20th week in the case of WHHL rabbits. Among the cholesterol-fed rabbits, the percentage of aortic intimal surface area covered by atherosclerotic lesions (AS%) was 25.9 +/- 7.6% (mean +/- S.D.) in the nifedipine group (n = 7), and 55.6 +/- 22.8% in the placebo group (n = 8) (p less than 0.01). The cholesterol content of thoracic and abdominal aorta in the nifedipine group was lower than those in the placebo group (p less than 0.05). Among the WHHL rabbits, the AS% was 33.4 +/- 14.1% in the nifedipine group (n = 5), and 27.0 +/- 11.7% in the placebo group (n =6) (n.s.). The aortic cholesterol and calcium contents also showed no significant differences between the two groups. We concluded that nifedipine suppressed atherosclerosis in cholesterol-fed rabbits but not in WHHL rabbits. The different responses suggest that the effect of nifedipine could be mediated by low density lipoprotein receptors or that the early exposure to hyperlipidemic serum from birth might affect cell functions of WHHL rabbits.     

Sustained thrombocytopenia in mice: serial studies of megakaryocytes and platelets

We studied thrombopoiesis in mice after the experimental induction of sustained, immune thrombocytopenia with platelet antiserum (PAS). Utilizing light and electron microscopy and a digital image analyzer to determine platelet sectional areas, we examined platelets and megakaryocytes (MK) after 120 h of sustained, severe thrombocytopenia (120CT) and during recovery from thrombocytopenia at 48 h (48R), 72 h (72R), and 120 h (120R) after cessation of administration of PAS. Mean platelet volume (MPV), determined by electrical impedance, also was measured at each time point. Platelets at 120CT (platelet count less than 50,000/microliter), 48R (platelet count 100-200,000/microliter), and 72R (platelet count approximately 1 x 10(6)/microliter) were significantly larger in sectional area than control platelets and contained increased profiles of endoplasmic reticulum and Golgi cisternae, a lower concentration of surface-connected canalicular system, and occasional membrane complexes. The largest median platelet sectional area was detected at 48R and was the largest median value observed in response to either chronic or acute thrombocytopenia. At 120R, most platelets were normal in size and cytoplasmic appearance, although some large cells remained present in the circulation. MPV paralleled the morphometric changes in platelet sectional area. MK were increased in number at 120CT, 48R, 72R, and 120R. In addition, at least half of the MK examined at 48R contained small areas of cytoplasm, devoid of organelles, that were interspersed between larger areas of organelle-filled, undemarcated cytoplasm. The modal bone marrow megakaryocyte ploidy class, determined using two-color fluorescence-activated flow cytometry, shifted from 16N to 32N in response to sustained thrombocytopenia. In contrast, during recovery and development of rebound thrombocytosis, the relative frequency of 8N megakaryocytes was significantly increased. Because there was no consistent correlation between megakaryocyte cytoplasmic characteristics and platelet morphology, these data support the hypothesis that platelet formation is not determined by compartmentalization of MK cytoplasm into platelet areas as MK mature in the bone marrow, but involves a rearrangement of MK cytoplasm immediately prior to platelet release.     

The effect of alpha-interferon on bone marrow megakaryocytes and platelet production rate in essential thrombocythemia

In 10 patients with previously untreated essential thrombocythemia (ET), by using 111In-labeled platelets and megakaryocyte morphometry, the relation between platelet production rate and bone marrow megakaryocytes was evaluated before and during alpha-2b-interferon (IFN) therapy. A highly significant decrease in platelet count occurred during IFN therapy; the platelet counts, at baseline and after 2 and 6 months of IFN therapy, were 1,102 +/- 345 x 10(9)/L, 524 +/- 169 x 10(9)/L (P less than .0001), and 476 +/- 139 x 10(9)/L (P less than .0001), respectively. The decrement in platelet count was mainly a result of diminished platelet production rate, which at baseline and after 2 and 6 months of IFN therapy was 89 +/- 30 x 10(10) platelets/d, 53 +/- 18 x 10(10) platelets/d (P = .0033), and 45 +/- 20 x 10(10) platelets/d (P less than .0001), respectively. Also, a slight shortening of platelet mean life-span (MLS) was observed in response to IFN treatment; platelet MLS was 7.96 +/- 0.69 days at baseline and 6.68 +/- 1.30 days (P = .012) after 6 months of IFN therapy. IFN induced a significant decrease in bone marrow megakaryocyte volume; both megakaryocyte nuclear and cytoplasmatic volumes were affected. The mean megakaryocyte volume was 372 +/- 126 x 10(2) pL/microL at baseline and 278 +/- 147 x 10(2) pL/microL (P = .049) after 6 months of IFN therapy. However, the number of megakaryocytes did not show any significant change in response to IFN. It is concluded that alpha-IFN reduces platelet production rate and the peripheral platelet count in ET mainly through an anti-proliferative action on the megakaryocytes and to a considerably lesser degree by a shortening of platelet MLS.     

Low density lipoprotein receptor-independent hepatic uptake of a synthetic, cholesterol-scavenging lipoprotein: implications for the treatment of receptor-deficient atherosclerosis.

The metabolism of infused 111In-labeled phospholipid liposomes was examined in Watanabe heritable hyperlipidemic (WHHL) rabbits, which lack low density lipoprotein (LDL) receptors, and in normal control rabbits. The half-times (t1/2) for clearance of 111In and excess phospholipid from plasma were 20.8 +/- 0.9 hr and 20.3 +/- 4.6 hr in WHHL and 20.0 +/- 0.8 hr and 19.6 +/- 2.2 hr in the normal rabbits (means +/- SEM; n = 4). By 6 hr postinfusion, the plasma concentration of unesterified cholesterol increased by 2.2 +/- 0.23 mmol/liter in WHHL and 2.1 +/- 0.04 mmol/liter in normal rabbits, presumably reflecting mobilization of tissue stores. Disappearance of excess plasma cholesterol was greater than 90% complete in both groups of rabbits by 70 hr postinfusion. By quantitative gamma camera imaging, hepatic trapping of 111In-labeled liposomes over time was indistinguishable between the two groups. At autopsy, the liver was the major organ of clearance, acquiring 22.0% +/- 1.7% (WHHL) and 16.8% +/- 1.0% (normal of total 111In. Aortic uptake of 111In was less than 0.02%. Thus, mobilization of cholesterol and hepatic uptake of phospholipid liposomes do not require LDL receptors. Because phospholipid infusions produce rapid substantial regression of atherosclerosis in genetically normal animals, our results suggest that phospholipid liposomes or triglyceride phospholipid emulsions (e.g., Intralipid) might reduce atherosclerosis in WHHL rabbits and in humans with familial hypercholesterolemia.     

Macrothrombocytes in the peripheral circulation of patients with cardiogenic hypertrophic osteoarthropathy

The objectives of this study were: first, to determine the platelet morphology in the peripheral circulation of patients with cyanotic congenital heart diseases and thus its possible link to the development of hypertrophic osteoarthropathy. Second: to test the mathematical model which proposes that in normal individuals megakaryocytes are fragmented in the lungs. We prospectively studied 14 patients with cyanotic heart disease and clubbing of the 20 digits, and compared them with 14 randomly assigned controls. We measured the platelet count, mean platelet volume (MPV) and platelet volume distribution curve (PVDC). Patients had a significantly lower platelet count (x +/- SD, 171,528 +/- 81,810 vs 319,929 +/- 69,460, p less than 0.001) and larger MPV (11.028 +/- 3.09 vs 8.414 +/- 0.79, p less than 0.005). The PVDC of the controls were uniform, in all cases showing a log-normal configuration. The patient's curves were different; they lost the log-normal shape and demonstrated a heterogeneous platelet population. These findings agree with the mathematical model which proposes that in normal individuals platelets are generated in the lungs, and also suggest a role for the macrothrombocytes in the pathogenesis of cardiogenic hypertrophic osteoarthropathy.     

Enhanced aortic atherosclerosis in transgenic Watanabe heritable hyperlipidemic rabbits expressing lipoprotein lipase

OBJECTIVE: This study was designed to address the effects of increased lipoprotein lipase (LPL) activity on atherosclerosis in the setting of LDL receptor deficiency. METHODS: We generated transgenic (Tg) Watanabe heritable hyperlipidemic (WHHL) rabbits overexpressing human LPL and compared their plasma lipids and aortic atherosclerosis with non-Tg WHHL rabbits. RESULTS: Increased expression of LPL significantly ameliorated hypertriglyceridemia and hypercholesterolemia in Tg WHHL rabbits [64% reduction in total cholesterol (TC) and 91% reduction in triglycerides (TG) vs. non-Tg]. In spite of this beneficial effect of LPL, Tg WHHL rabbits had two-fold greater aortic atherosclerosis than non-Tg WHHL rabbits. Analysis of plasma lipoprotein profiles revealed that increased LPL activity in Tg WHHL rabbits resulted in the dramatic reduction of large TG-rich lipoproteins (VLDL, d<1.006 g/ml and IDL, d=1.006-1.02) but concomitant increases in LDL fractions, especially those of small and dense LDL particles (d=1.04-1.06, 2.6-fold over non-Tg). Using apoB-containing lipoproteins, we found that small-sized LDL from Tg WHHL rabbits contained more oxidizable substrate and exhibited higher affinity to biglycan than large TG-rich LDL of non-Tg WHHL rabbits. CONCLUSIONS: We conclude that in the absence of LDL receptor function, increased LPL activity accelerates the catabolism of large TG-rich VLDL (possibly via the LRP pathway) and subsequently improves hyperlipidemia. However, LPL may also enhance the generation and accumulation of small dense LDLs, which are more atherogenic.     

Cigarette smoking increases the mean platelet volume in elderly patients with risk factors for atherosclerosis.

To study the effects of cigarette smoking and atherosclerosis on platelet size, we measured the mean platelet volume (MPV) and other platelet parameters in 142 elderly smokers and nonsmokers with or without atherosclerotic risk factors. The MPV and the platelet count were highest and their inverse correlation was strongest in the atherosclerotic smokers (r = 0.54, P < 0.05) when compared with the nonsmoking and non-atherosclerotic groups. A 10% decrease of MPV was found in 8 smoking subjects in the atherosclerotic group, who successfully discontinued smoking (P < 0.05). These results suggest that smoking may increase platelet consumption in atherosclerotic vessels and that subsequently megakaryocytes are activated to produce larger platelets, which are more active. Thus, an increase in MPV due to smoking may also contribute to the acceleration of atherosclerosis and should be considered as a risk factor for atherosclerotic disease.     

Evidence for an inverse relation between plasma triglyceride and aortic cholesterol in the coconut oil/cholesterol-fed rabbit

Rabbits fed a commercial chow diet containing 0.5% cholesterol and 14% coconut oil developed more severe hyperlipidemia and atherosclerosis than rabbits fed the same diet containing olive oil in place of coconut oil. Average plasma cholesterol was twice as high in the coconut oil/cholesterol-fed rabbits than in olive oil/cholesterol-fed rabbits. Final plasma triglycerides, although highly variable, were approx. 20-fold higher than basal plasma triglyceride in coconut oil/cholesterol-fed rabbits; plasma triglyceride in olive oil/cholesterol-fed rabbits remained unchanged throughout the study period. In coconut oil/cholesterol-fed rabbits, a direct relationship between plasma triglyceride and aortic cholesterol was not found. Plasma cholesterol and aortic cholesterol were also not correlated at a statistically significant level (r = 0.26, P greater than 0.25). However, when both plasma cholesterol and triglyceride were simultaneously introduced as predictors of aortic cholesterol, the correlation between these plasma lipids and aortic cholesterol became highly significant (r = 0.64, P less than 0.02). Aortic cholesterol increased in proportion to plasma cholesterol concentrations but appeared to be inversely related to plasma triglyceride levels.     

Mean platelet volume in patients with subclinical hypothyroidism

Subclinical hypothyroidism (SCH) is frequently encountered in the general population. Since it is generally asymptomatic, these patients are mostly identified through routine screening or evaluation of non-specific symptoms. It has been suggested as a risk factor for cardiovascular disease. On the other hand, mean platelet volume (MPV), which is a determinant of platelet function, is an independent risk factor for cardiovascular disease. The aim of this study was to evaluate MPV values in subclinical hypothyroidic patients when they were subclinical hypothyroidic and became euthyroidic after 12 weeks of levothyroxine replacement therapy. Sixty patients with subclinical hypothyroidism and 78 euthyroid healthy subjects matched for age, gender and body mass index were enrolled in the study. None of the study subject had diabetes, hypertension or dyslipidemia. All the study subjects were evaluated by biochemical and platelet parameters. Subclinical hypothyroidic patients were then reevaluated with the same parameters when they became euthyroid after 12 weeks of levothyroxine treatment. Platelet counts and metabolic parameters, except serum triglyceride and high density lipoprotein cholesterol (HDLC) levels, were similar between the two groups. Serum triglyceride and MPV values were significantly higher (pTG=0.007 and pMPV<0.001) while HDLC levels were lower (pHDLC=0.008) in the subclinical hypothyroidic group. MPV was found to be correlated with only antithyroid peroxidase (anti-TPO) antibody levels (P<0.001). MPV values were decreased after subclinical hypothyroidic patients became eythyroid. However, post-treatment MPV values were still higher (p=0.035) in the patient group than in control group. These results suggest that subjects with SCH are susceptible to increased platelet activation and increased MPV values which contribute to increased risk of cardiovascular complications.     

Adenosine-induced coronary flow reserve in Watanabe heritable hyperlipidemic rabbits

The Watanabe heritable hyperlipidemic (WHHL) rabbit develops coronary atherosclerosis and hypercholesterolemia because of a genetic deficiency of low-density lipoprotein receptors and is therefore a good animal model for studying the relationships of coronary atherosclerosis, hypercholesterolemia and coronary flow reserve. The aim of the present study was to assess myocardial perfusion at baseline and during adenosine infusion (0.2 mg x kg(-1) x min(-1)) in 8 WHHL rabbits (13.8+/-0.5 months) with 13N-ammonia, small-animal positron emission tomography (PET) and colored microspheres. Results were compared with those from 6 age-matched Japanese white rabbits. Plaque distribution was also examined in the extramural coronary arteries. All 8 WHHL rabbits had coronary plaques, with 6 showing multiple plaques. Mean global myocardial blood flow (ml x min(-1) x g(-1)) did not differ significantly between control and WHHL groups both at baseline (3.67+/-0.72 vs 4.26+/-1.12 ml x min(-1) x g(-1), p=NS) and with adenosine (7.92+/-2.00 vs 9.27+/-2.91 ml x min(-1) x g(-1), p=NS), nor did coronary flow reserve (2.16+/-0.37 vs 2.18+/-0.41, p=NS). None showed evidence of regional perfusion abnormalities by visual and semiquantitative analyses of PET images. It was concluded that WHHL rabbits preserve adenosine-induced coronary flow reserve despite coronary atherosclerosis and hypercholesterolemia, suggesting that a compensatory mechanism develops in this animal model.     

家兔新基因Gnas的鉴定及其在高脂血症中的功能

目的探讨家兔新基因Gnas在高脂血症中的功能。方法用高脂饲料复制家兔高胆固醇血症模型,分别用胆固醇、25羟胆固醇、低密度脂蛋白刺激HepG2细胞,采用荧光半定量逆转录聚合酶链反应技术检测GenBank中登录号为AY248719的家兔新基因表达情况。结果高胆固醇兔动物模型复制成功,该组血浆和肝脏的总胆固醇及肝脏甘油三酯水平增加均超过10倍,血浆甘油三酯也显著增高。高脂组Gnas基因表达水平明显高于对照组。胆固醇、25羟胆固醇刺激HepG2细胞后Gnas表达无明显改变,400 mg/L低密度脂蛋白刺激HepG2细胞后Gnas表达增强2.15倍。结论对家兔新基因Gnas的研究有助于进一步揭示高脂血症的分子机理。