Proline hydroxylase activity and collagen content of pigeon aortas with naturally-occurring and cholesterol-aggravated atherosclerosis

Influx, efflux, and accumulation of LDL in normal arterial areas and atherosclerotic lesions of white Carneau pigeons with naturally occurring and cholesterol-aggravated aortic atherosclerosis

This study investigated the hypothesis that increased influx of low-density lipoprotein (LDL) accounts for the natural development of atherosclerosis in a characteristic (susceptible) site in the distal thoracic aorta of White Carneau (WC) pigeons and the exacerbation of atherosclerosis by cholesterol feeding. The influence of dietary cholesterol-induced changes in LDL composition on LDL influx into the artery was also investigated. As a measure of the influx of LDL into the artery, we determined the arterial accumulation of radiolabeled LDL after 1 hour. Nine 50-month-old WC pigeons with naturally occurring atherosclerosis and seven 14-month-old WC pigeons with atherosclerosis accelerated by 10 months of cholesterol feeding were studied. In the absence of atherosclerotic lesions, we found no evidence for increased accumulation of LDL at the susceptible site. In fact, more LDL accumulated in less susceptible normal arterial areas near the heart (approximately 90 nl/h per square centimeter) than in the susceptible distal thoracic aorta (approximately 35 nl/h per square centimeter). In the absence of atherosclerotic lesions, LDL accumulation (nanoliters per hour per square centimeter) was not influenced by hypercholesterolemia, although mass transport of LDL cholesterol into the artery was increased. Naturally occurring atherosclerotic lesions accumulated five times as much LDL as the adjacent normal arterial area (P < .001), whereas cholesterol-aggravated atherosclerotic lesions in different arterial sites accumulated four to 26 times as much LDL as the adjacent normal artery (P < .05). Cholesterol-aggravated atherosclerotic lesions at the most susceptible site accumulated five times as much LDL as naturally occurring atherosclerotic lesions in the corresponding arterial site (823 +/- 241 vs 175 +/- 45 nl/h per square centimeter, mean +/- SEM; P < .005). Arterial accumulation of LDL was influenced very little by changes in LDL composition induced by cholesterol feeding. In another study with young WC pigeons free of atherosclerosis and other WC pigeons with cholesterol-aggravated atherosclerosis, we injected differently labeled LDL 0.5 and 1 hour before sacrifice to investigate whether efflux of LDL from the artery was significant during a 1-hour period of LDL uptake. Although efflux of LDL from all arterial sites occurred during 1 hour, differential efflux could not account for regional differences in 1-hour arterial LDL accumulation. This study suggests that the characteristic susceptibility of the distal thoracic aorta of WC pigeons to atherosclerosis and the exacerbation of atherosclerosis by cholesterol feeding cannot be explained by differences in influx or efflux of LDL.(ABSTRACT TRUNCATED AT 400 WORDS)

Elastin and collagen content in the aorta of rabbits experimentally immunized with soluble elastin

Experimental immunization of rabbits with soluble porcine elastin was performed. A statistically significant decrease in the level of insoluble elastin in the aorta of the immunized animals was observed. Estimations of soluble collagen fractions showed the rise of both salt-soluble and acid-soluble collagen in the aorta of rabbits immunized with soluble porcine elastin.

Biosynthesis of aortic collagen and glycosaminoglycan following immunological injury

The effect of immunological injury upon the early in vivo changes in aortic connective tissue metabolism was studied. It was found that a single antigen (bovine serum albumin), when administered in multiple doses, activated collagen synthesis and increased the rate of lgycosaminoglycan synthesis in the arterial wall. The degree of stimulation of both connective tissue components was higher in animals receiving a higher dose of antigen.

Enhanced synthesis and accumulation of collagen in cholesterol-aggravated pigeon atherosclerosis

Atherosclerotic segments of pigeon aorta synthesized collagen at four times the rate found in normal aorta (Athero = 2071 +/- 1339 ng/g/h; Control = 497 +/- 192 ng/g/h; P less than 0.025). Similar results were obtained when synthesis was expressed per mg DNA. Elevation in collagen synthesis was relatively specific, collagen accounting for 4% of total protein synthesis in lesion-free aorta and 11.5% in atherosclerotic aorta. Substantial increases in total collagen were observed in atherosclerotic aortas (Athero = 9.9 +/- 3.1 mg/aorta; Control = 6.0 +/- 1.3 mg/aorta; P less than 0.05). Ultrastructural studies revealed the accumulation of large amounts of dense fibrillar collagen in the sub-endothelial region of the plaque. Plaque cells contained multiple vacuoles, an extensive rought endoplasmic reticulum and many mitochondria, suggesting active protein synthesis. It is concluded that increased collagen biosynthesis and deposition is an important metabolic derangement in lipid-rich atherosclerotic lesions whihc promotes their gradual conversion to fibrous plaques.

Early changes in the arterial wall of chickens fed a cholesterol diet

A total of 160 1-2 day old chickens were fed a 2% cholesterol diet for a period of 8 to 42 days and compared with an equal number of controls. Aortas were analyzed for various indexes of reactivity of connective tissue, cholesterol content and scanning electron microscopy (SEM) characteristics of the endothelial lining. Cholesterol feeding for a period up to 6 weeks resulted in doubling the level of serum cholesterol. It was, however, without effect on the activity of prolyl hydroxylase, lysyl oxidase, collagenase and collagen content in the aortic wall. As early as 3 weeks of feeding significant changes occurred in total and esterified cholesterol content. At the same time endothelial cells were characteristically contracted with several long cytoplasmic elongations and protrusions. A significant decrease of activity of the above enzymes was found in aortic tissue with increased age of the chicken. Collagen content in aortas increased with age of chickens. It is concluded that cholesterol as an atherogenic agent induces marked changes in endothelial cells and lipids of chicken aorta at earlier periods, prior to the activation of connective tissue.