Metabolic intermediates, enzymes and lysosomal activity in aortas of spontaneously hypertensive rats

Adaptation to arterial wall hypoxia demonstrated in vivo with oxygen microcathodes

Iliofemoral arteries of 9 rabbits were balloon de-endothelialized resulting in subintimal thickening. Contrary to expectation, enzyme and lactate determinations did not indicate arterial wall hypoxia when compared with arteries of 10 control rabbits. The explanation came from in vivo measurement of oxygen tension profiles across the de-endothelialized and control femoral arteries and from the subsequent histological findings. They showed that the impaired oxygen supply of the de-endothelialized arteries with subintimal thickening was counteracted by a centripetal oxygenation of the arterial wall obviously induced by proliferation of newly formed nutrient vessels in the adventitia. Such adaptation is an important mechanism against hypoxia induced by arterial injury and may be an essential protective factor in atherogenesis.

Immunocytochemical demonstration of lysosomal matrix vesicles in the arterial wall of the rat

Following necrobiosis of the smooth muscle cells (SMC) of the vessel wall, lysosomes are still able to live for a time in the extracellular space. Here they are known as lysosomal matrix vesicles (MV). Their lysosomal origin can be confirmed by the immunocytochemical demonstration of beta-N-acetylglucosaminidase (beta-NAG) in extracellular MV. A positive reaction to the enzyme-cytochemical test for acid phosphatase establishes that these lysosomal MV are enzymatically active. The role of the lysosomal MV in the pathogenesis of vascular diseases is seen in an uncontrolled, locally limited destruction and alteration of the intercellular substance.

The effect of combined deendothelialization and hypercholesterolemia on some arterial lysosomal and glycolytic enzymes and lactate in rabbits

In eight New Zealand white male rabbits the abdominal aorta and one iliofemoral artery was balloon deendothelialized (group A). After 2 weeks they were kept for 6 weeks on a high cholesterol diet together with eight unoperated rabbits (group B). Eight more rabbits were kept on a commercial diet only (group C). The degree of atherosclerosis was much higher in the deendothelialized Group A vessels than in the uninjured group B vessels. The activity of lactate dehydrogenase and of the rate-limiting glycolytic pyruvate kinase was significantly increased and the activity of lipoamide dehydrogenase decreased in the group A aortas. In the iliofemoral arteries a similar but statistically insignificant tendency was detected. There was no significant difference, however, in aortic lactate between the three groups. Thus, local hypoxia did not significantly contribute to the high degree of atherosclerosis in the group A animals in spite of the enzyme activity differences. Previous experience of the authors, using arterial microcathode pO2 measurements, indicates that following deendothelialization an adaptive proliferation of nutrient vessels and increased arterial oxygenation takes place. The average activity of the lysosomal N-acetyl-beta-glucosaminidase was five times and that of beta-glucuronidase, seven times higher in the Group A than Group B aortas; in the iliofemoral arteries the differences were even larger. The huge elevation of these hydrolases, which are involved in glycosaminoglycan catabolism, provides indirect indication that accumulation of glycosaminoglycans and possibly their ability to form complexes with apoB-containing lipoproteins played a major role in the much increased degree of atherosclerotic lesions in the Group A rabbits.

Ethanol induced cardiomyopathy--role of periodic fasting

The periodic fasting in presence of continuous ethanol feeding produces pronounced morphological changes in the myocardium and its organelles of the rats. This effect of ethanol could be directly related to the sensitive state of myocardium to the former, specially when ethanol becomes an important source of energy. This is proved further by intraperitoneal injection of 40% ethanol, when profound mitochondrial morphological changes, even leading to formation of lysosome like structures, are evident in the myocardium. The study has stressed the pronounced direct effect of ethanol and its metabolites in the development of morphological changes of the myocardium.

Tunica media changes in the spontaneously hypertensive rat (SHR)

The histological, ultrastructural, morphometrical and histochemical aspects of the arterial media were studied in young and aged SHR, and compared to normotensive Wistar Kyoto rats. The diffuse thickening was the most characteristic feature of the hypertensive media. It seems due to three processes: Early generalized hypertrophy of smooth muscle cells (smc); connective matrix neogenesis and smc proliferation, more evident in peripheral vasculature. The present paper discusses the following hypertensive tunica media changes in relation to the atherosclerotic process: the decrease in lipolytic esterase and cholinesterase activities; the activation of some lysosomal enzymes; the increase in collagen, glycosaminoglycan and elastin content; the increased media thickness; the modified smc behavior (migration, secretion, proliferation). These alterations might positively influence arterial susceptibility to atherosclerosis through reduced smc lipolytic activity; slowed transmural diffusion; perturbed efflux and aggravated media hypoxia.

Postlathyric fibroelastosis of the rat aorta related to topical factors of experimental atherosclerosis

Postlathyric aortic fibroelastosis was produced in rats with the aid of low-percentage fetal lathyrism. Subsequently the rats were kept on an atherogenic regimen for one year, and at the end of that period the aortas were studied to detect the relation of postlathyric alterations to the experimental atherosclerotic lesions. In the ascending aorta and the arch the fibroelastosis neither enhanced nor suppressed the development of mixed atherosclerotic plaques. In contrast, fibroelastosis of the thoracic and abdominal aorta usually causing a slight tunnel-shaped stenosis of the affected segment significantly reduced the development of intimal lipoidosis. The present experiment permitted to identify a new postlathyric lesion, namely sac-shaped microaneurysms situated at the sites of origin of lumbar arteries. Despite the fact that otherwise virtually the only lesion developing in the abdominal aorta was intimal lipoidosis, the aneurysms were filled up with mixed atheromatous masses. The above postlathyric vascular lesion appeared to significantly support the local development of atherosclerosis. The results presented have been discussed in view of the some recent facts stressing the indisputable importance of haemodynamic factors for the localization and development of atherosclerosis.

Aromatic L-amino acid decarboxylase, dopamine beta-hydroxylase, monoamine oxidase, malondialdehyde, and acid phosphatase in rat brain capillaries and kidney glomeruli in experimental hypertension

Some metabolic consequences of experimental hypertension on rat brain capillaries and kidney glomeruli have been studied in rats made hypertensive by a combination of deoxycorticosterone acetate injection and elevated salt intake (DOCA-salt hypertension) and isoproterenol injection. Enzyme activities were studied in vitro to ascertain directly or indirectly any changes in the metabolism of catecholamines and prostaglandins, and lysosomal integrity under conditions of experimental hypertension. Experimental hypertension was accompanied by an elevation in the activities of aromatic L-aminoacid decarboxylase, dopamine beta-hydroxylase, and malondialdehyde concentration, both in the brain capillaries and kidney glomeruli of rats. On the other hand, monoamine oxidase activity increased in brain capillaries but decreased in kidney glomeruli. Acid phosphatase activity increased marginally in kidney glomeruli but decreased significantly in brain capillaries. The catecholamine-synthesizing potential appears to have been augmented in both the tissue capillaries with a compensatory increase in the degrading enzyme activity in the brain capillaries of hypertensive rats. The absence of such an increase and an actual decrease in the monoamine oxidase activity in the kidney glomeruli may be responsible for the sustained maintenance of the hypertensive state. Increased malondialdehyde concentration may be due to the stimulation of the prostaglandin metabolism by the augmented catecholamine metabolism.

Aortic enzymes and lactate in high altitude-raised and cholesterol-fed rabbits

Fourteen male rabbits born at elevation 4000 ft (first experimental series) were transferred at age of 2 months to elevation 12470 ft and raised there for 18 weeks. Half of the animals remained on a commercial rabbit chow (group H) while the other half was on the same diet supplemented with cholesterol (group C). Eight male rabbits raised at sea level served as controls (group S). Intima-media homogenates from the thoracic aortas were assayed for lactate dehydrogenase (LDH), malate dehydrogenase (MDH), lipoamide dehydrogenase, pyruvate kinase (PK), phosphofructokinase (PFK) and the lysosomal hydrolases beta-glucuronidase and N-acetyl-beta-glucosaminidase (NAGA). Aortic lactate and glucose were also measured. Thirty-two male rabbits (second experimental series) were subdivided into 4 groups. Rabbits were fed a cholesterol-supplemented diet not only at high altitude (8 rabbits matching group C) but also 8 animals raised at sea level. The degree of atherosclerosis in the aortas of these 4 groups was assessed by measuring the aortic cholesterol contents. Plasma cholesterol was also determined. In the aortas of the rabbits of group H the activity of PK was significantly elevated, and the activity of the lysosomal hydrolases significantly decreased compared with aortas of group S rabbits. There was no difference in the other enzyme activities or in the aortic glucose and lactate content of these groups. Cholesterol feeding of the animals of group C resulted in a significantly increased activity of the lysosomal hydrolases as well as of LDH and PK. The lipid analyses (second experimental series) revealed a trend to a lower concentration of aortic cholesterol in the high altitude than in the sea level animals, both fed a cholesterol diet, in spite of the higher plasma cholesterol concentrations in the high altitude animals. The low aortic lysosomal hydrolase activities in the high altitude rabbits are in accord with their comparatively lower susceptibility to experimental atherosclerosis. This metabolic feature may be due to a lower degree of exposure of these aortas to injurious factors, such as infections or lower blood pressure. The elevated activity of PK without increased lactate content in group H animals seems to parallel the well-known general adaptation of the organism to high altitude hypoxia, and does not indicate a metabolic switch toward anaerobic glycolysis.

Ultrastructural study of lysosomes in the myocardium of spontaneously hypertensive rats under chronic salt ingestion

The presence of lysosomes and lysosomal-like bodies in the myocardium of spontaneously hypertensive rats (SHRs) under the influence of 1% NaCl was studied. In SHRs, 2 weeks and older, there was an observable increase of lysosomes and lysosomal-like bodies in the myocardium when compared to the myocardium of age-matched controls. It is postulated that degradation is initiated by primary lysosomes and that mitochondria seem to be a prime target. The degradation process is also believed to be a relevant factor in cardiac hypertrophy of SHRs and that a high NaCl intake coupled with a sustained high blood pressure enhanced this process.

Trophic effect of the sympathetic nervous system on vascular smooth muscle

While the vasomotor effect of the sympathetic nervous system (SNS) on the arterial wall is well recognized, its trophic function is not. It is the aim of these studies to demonstrate this all-important function as it relates to the vascular muscle. Although the exact mechanism by which sympathetic nerve impulses influence the metabolism of the vessel wall is unknown, effects of sympathectomy can be demonstrated. Several lines of evidence indicate that chronic absence of sympathetic innervation in rabbits increases collagen synthesis and decreases activity of tricarboxylic acid cycle enzymes in the vascular wall. When chemically sympathectomized rabbits were fed a 1% cholesterol dietary supplement for 80 days, the aortas of these rabbits contained significantly more cholesterol and total lipids than those from fully innervated controls in spite of insignificant differences in plasma lipids. In a subsequent series of experiments we analyzed the efficacy of the SNS in two strains of pigeons. White Carneau (WC) pigeons are known by the susceptibility to atherosclerosis of the aorta while Show Racer (SR) pigeons are not. Our results demonstrate that the abdominal aorta of WC pigeons has less sympathetic innervation and it declines faster with age than that of SR pigeons. The results of the described studies documenting the direct trophic influence of the SNS on the arterial wall are reinforced by the similarity to the vessel wall changes induced by partial sympathectomy and natural ageing.