Medial elastin in the thoracic and abdominal aorta of sheep and lambs

Aortas were removed from six mature lambs and four sheep and pressure fixed at 100 and 120 mmHg pressure (1 mmHg = 133.322 Pa), respectively, in 10% buffered formalin. The numbers of elastin layers were counted from cross sections at different distances down the aorta, from the distal arch to the iliac bifurcation, and showed a linear decrease in the thoracic aorta. In the abdominal aorta there was no difference in values from the diaphragm to the aortoiliac bifurcation in the lamb, but a slight decrease in the sheep. If y = mx + b, where y is the number of medial lamellar units (MLU), b the intercept, x the distance from the last brachiocephalic branch in centimetres, and m the slope, we obtained the following equations (with standard deviations): lamb thoracic aorta; y = -6.29 (+/- 0.71)x + 106 (+/- 12); sheep thoracic aorta; y = -3.46 (+/- 0.40)x + 140 (+/- 21.4); lamb abdominal aorta; y = 0.51 (+/- 1.48)x + 37 (+/- 7.7); sheep abdominal aorta; y = -0.85 (+/- 0.28)x + 66 (+/- 5.9). Tension per lamellar unit was calculated and plotted versus distance yielding a linear increase in the entire lamb aorta but an abrupt increase between thoracic and abdominal aortas in the sheep. This causes the pulse wave to move uniformly with increasing speed along the length of the lamb aorta but would cause an abrupt change in the wave at or about the diaphragm in the sheep. Distortions in the pulse wave could produce local stress concentrations in the abdominal aorta which might render it more susceptible to atherosclerosis than the thoracic aorta.

Experimental atherosclerosis in hypercholesterolemic mini-pigs. Regression of cholesterol ester accumulation in aorta and coronary arteries after treatment with clofibrate, beta-pyridylcarbinol or a normo-lipidemic diet

Studies have been performed on groups of mini-pigs 21-23 months of age, which after 18 months of hypercholesterolemia (approximately 10 mmol) had developed raised atherosclerotic lesions with high levels of cholesterol esters, especially in the abdominal aorta and the coronary arteries. If the hypercholesterolemia was continued for 18 months, no significant change in the cholesterol ester content in the aorta occurred; in the coronary arteries there was a significant decrease in these older pigs. If the hypercholesterolemic pigs also were treated with beta-pyridylcarbinol the findings were very similar to the first. When hypercholesterolemic pigs were treated with clofibrate, or when the hypercholesterolemic diet was replaced with the basal food for 18 months, the plasma cholesterol level was normalized (approximately 2 mmol) within 1-2 months. The cholesterol ester content in the thoracic aorta was reduced in both groups but not that in the abdominal aorta. Clofibrate decreased the cholesterol ester level in the coronary arteries when compared to the hypercholesterolemic group; the drug also reduced the free cholesterol level when compared to the basal group. We suggest that an increased plasma cholesterol level initiated the development of the atherosclerotic lesions; their later development was only partly dependent on the plasma cholesterol level.

Use of 3H-cholesteryl linoleyl ether for the quantitation of plasma cholesteryl ester influx into the aortic wall in hypercholesterolemic rabbits

In this study use was made of 3H-cholesteryl linoleyl ether CLE), a nondegradable analogue of cholesteryl ester (CE) to measure plasma lipoprotein CE influx into rabbit aorta. Autologous serum labeled with 3H-CLE was injected into seven hypercholesterolemic rabbits, and more than 90% of the label was recovered in the plasma compartment 10 minutes after injection. Between 4 hours and 3 days the label was cleared from the circulation with a t1/2 of about 24 hours. Between 4 and 24 hours the lipoproteins isolated at d less than 1.006, d less than 1.019, and d less than 1.063 approached similar specific activity, assuming that 3H-CLE had mixed with the lipoprotein CE pool. The rabbits were killed 7 to 14 days after injection when plasma radioactivity decreased to less than 0.03% of injected dose/ml. Total recovery of the CLE ranged from 70% to 95% and 48% to 72% were found in the liver. The minimum influx of plasma CE into the aortic intima was determined by dividing the label found in the artery by the mean specific activity of the labeled compound in the plasma. The minimum influx into regions with atheromatous involvement ranged from 0.8 to 3.4 micrograms CE/cm2/hr. The rate of influx was highly correlated with the amount of CE mass in the intima and media indicating that the bulk of aortic CE is derived from plasma lipoprotein CE. The method described might be useful in distinguishing between possible effects of "antiatherogenic" drugs on plasma CE influx into the aortic wall from an effect on intracellular CE hydrolysis and subsequent efflux of free cholesterol from the artery.

Additive statistical effects of cadmium and lead on heart-related disease in a North Carolina autopsy series

The association of heart-related mortality with tissue cadmium and lead in a study of autopsies performed on persons who resided in a soft-water, leached-soil area of North Carolina was examined. Liver cadmium concentrations and aortic lead level were indices of these elements. Both cadmium and lead levels had statistically significant correlations with cause of death (heart-related disease vs. non-heart-related disease, excluding cancer). Although cause of death was significantly associated with age, the association with cadmium and lead persisted after statistical adjustment for the effect of age. The combined effects of cadmium and lead provided sufficient information in an additive model to predict cause of death correctly for 80% of the cases, with age contributing insignificantly. These findings indicate the intimate relation of these two trace metals with increased risk of heart-related mortality, even in light of known conventional causes of such deaths.

The expression of results of lipid determinations in arterial tissues: mass per unit weight vs mass per unit area

The interrelations among four methods of expressing the results of lipid determinations in the intima of the abdominal aorta were examined using rank order and product moment correlation methods. The rank order correlations among the four methods were all uniformly high (0.90 or better), indicating that the method of expressing results of lipid analyses is not important when ranking by amount of lipid is the object. The product moment correlations showed a pattern of strong association when the methods paired are expressions of either "content" (mg lipid per 1/2 abdominal aorta vs mg lipid per unit area of aorta, r = 0.980) or "concentration" (mg lipid per dry weight of tissue vs mg lipid per dry defatted weight of tissue, r = 0.980). Correlations of paired methods that express "content" and "concentration" were lower and share only about 50% of common variability. This result can be interpreted as evidence that it is worthwhile to consider reporting chemical findings in reference to units of intimal (or artery) area as well as to unit of weight. If both methods are used some of the problems in interpreting chemical findings in the arterial wall may be clarified.

Isolation and preliminary characterization of proteoglycans dissociatively extracted from human aorta

Aortic proteoglycans (PG) were isolated from human aorta intima-media preparations with 4 M guanidine hydrochloride in the presence of protease inhibitors. The extracted PG mixture comprised 67% of the total aortic PG and was composed of 65% chondroitin sulfate, 22% dermatan sulfate, 8% heparan sulfate, and 4% hyaluronate. Attempts at isolation and purification of PG monomers using isopycnic CsCl gradient centrifugation under associative and dissociative conditions resulted in appreciable loss of PG through associations with co-extracted aortic proteins. The addition of a gel chromatographic step on Sepharose CL-4B under dissociative conditions resulted in separation of PG from the majority of co-extracted proteins. In addition, the procedure resulted in a separation of the PG into a population (PG-I) eluting near the column V0 and one (PG-II) included with a Kav of 0.38. Hyaluronic acid co-eluted with PG-I. The major glycosaminoglycan in PG-I was chondroitin sulfate, (85 to 95%). No dermatan sulfate was detected in PG-I, but this glycosaminoglycan was the predominant glycosaminoglycan in PG-II (50 to 70%). Heparan sulfate was present in small amounts in both PG-I and PG-II. Data presented support the proposal of at least three species of PG monomers in the aortic wall. Chromatographic studies under dissociative and associative conditions indicated that PG comprising PG-I but not PG-II were capable of associations with hyaluronic acid.

Evans blue dye. Accumulation in swine aortic intimal cell collections and atherosclerotic lesions

A two-part study concerned the accumulation of intravenously injected Evans blue dye in the abdominal aorta of swine. In normolipidemic swine weighing up to 90 kg each, Evans blue accumulated predominantly in areas of the aorta that were the site of intimal smooth muscle cell collections. The second part of the study dealt with Evans blue accumulation in swine with advanced atherosclerosis. The extent of blue staining in these animals was not significantly different than in normolipidemic, nonatherosclerotic swine of the same size. The dye showed a predilection for raised atherosclerotic lesions, but only one quarter of the surface of these lesions was stained. Histologic studies of the uppermost portion of blue and nonblue lesion areas showed that the dye preferentially accumulated in regions with lower concentrations of foam cells. Injected isotopic cholesterol tended to accumulate in the blue rather than the nonblue areas.

Possible relationship of cholesterol accumulation and collagen synthesis in rabbit aortic tissues

Male adult New Zealand rabbits were fed a 2% cholesterol diet for 60 days followed by 10, 20, or 30 days of normal low cholesterol diet. Collagen synthesis was estimated by measuring aortic prolyl hydroxylase activity. Tissue cholesterol accumulation rates were estimated by dividing total tissue cholesterol by the number of experimental days. It was found there was a high degree of correlation between aortic collagen synthetic activity and the rate of aortic cholesterol accumulation. These data were interpreted as suggesting that increased collagen synthesis may be associated with the accumulation and/or retention of increased aortic cholesterol.

Copper salts for growth stimulation and alleviation of aortic rupture losses in turkeys

Approximately 4000 Large White, day-old turkey poults were used in a series of eight experiments to study the effects of dietary copper supplementation. The hens were grown to 15 or 16 weeks and toms to 24 weeks of age. Either copper as the oxide or sulfate (hydrate) at 120 ppm stimulated growth up to 10% with a concurrent reduction in feed requirement. Levels of 60 ppm were not adequate, whereas 240 ppm were not toxic. There was a greater response to copper in the presence of 4-nitrophenylarsonic acid (4-nitro) or with low protein diets. In two of the eight studies copper enhanced aortic elastin content. Incidence of aortic rupture was greater in the presence of 4-nitro and was reduced by one-half through copper supplementation. Liver copper was not altered by 60 or 120 ppm Cu; 240 ppm caused a significant increase.

The plasminogen activator of the arterial wall

The plasminogen activator in 645 specimens of various human arteries--thoracic, abdominal aorta, carotic, pulmonary, renal, basilar, coronary - was studied using Todd's histochemical method. 92 cadavers were used, 1--18 hours post mortem from subjects aged from 272 days to 83 years. 45 specimens of pulmonary, renal and splenic arteries were obtained during surgery. The greatest fibrinolytic activity was within the adventitia. Intima occasionally showed very little fibrinolytic activity, or none at all. No statistically significant differences in plasminogen activator activity were found between the various arteries examined. A statistically significant increase in fibrinolysis in adventitia of atherosclerotic arteries was established. No correlation was found between the fibrinolytic activity of the arteries and their alkaline phosphatase content. Some properties of the plasminogen activator of the arterial vessel wall were evaluated. Influence of storage, inactivation with epsilonaminocaproic acid and extracted with potassium thiocyanate was studied.

Abnormal ion and water composition of veins and normotensive arteries in coarctation hypertension in rats

We examined the water, sodium, and potassium composition of the thoracic aorta, abdominal aorta (plus iliac arteries), and veins (vena cava and portal vein) from rats with aortic coarctation. The aortas of 10 rats (group A) were coarcted above the renal arteries to produce hypertension. Control groups consisted of 10 rats sham-coarcted above and 10 rats coarcted below the renal arteries. In group A rats heart weights and carotid artery pressures were elevated over controls (P less than 0.01), whereas there were no significant differences in femoral arterial pressures. In group A rats both the hypertensive thoracic aorta and the normotensive abdominal aorta contained about 20% more water per unit of wet weight, and about 35% and 60% more sodium and potassium, respectively, per unit of dry weight than did the corresponding portions of aorta from control rats (P less than 0.01). In group A rats water (P less than 0.01), sodium (P less than 0.02), and potassium (P less than 0.05) contents of veins also were increased. There were no significant correlations between level of carotid arterial pressure and magnitude of changes in arterial and venous composition, nor were there significant differences between the magnitude of changes in the normotensive and hypertensive portions of the aorta. These results indicate that in rats abnormalities in vascular wall salt and water content are not necessarily a direct effect of the elevated pressure in hypertension.

Renin secretion at the individual nephron level

Blood was collected from the descending aorta, from a renal efferent arteriole and from the renal vein of a rat. The renin concentrations of the blood samples were measured. The renal vein renin concentration was 673 +/- 81 (SE) ng ml-1h-1 which was significantly higher than the concentration in the aorta of 456 +/- 50 (SE) ng ml-1h-1. The concentration of renin in the renal efferent arteriole was significantly lower than that in the aorta. These observations imply that net renin secretion is a combination of two processes; removal between artery and efferent arteriole and entry between efferent arteriole and renal vein. It appears that renin is released into the interstitium and enters the circulation at the capillary level rather than being released into the afferent or efferent arterioles. This mode of secretion supports the suggestion that the renin angiotensin system may primarily work intra-renally rather than through the systemic circulation.

Oxygen tensions in healing anastomosis of rabbit aorta

Tissue oxygen tensions in healing anastomoses of rabbit abdominal aortas were measured with ultramicro-oxygen cathodes with 1 to 3 mum tips. Two days after constructing the anastomosis, the over-all profile of intramural oxygen tension was different markedly from that of normal aortic wall, showing a progressive fall of Po2 from adventitia to media and no increasing gradient from media to intima. One week after operation to intimal Po2 increased and the oxygen gradient due to diffusion from the lumen was re-established. By the end of the second week adventitial and medial oxygen tensions reached their minimum. Six weeks after operation the oxygen tensions in the anastomosis resembled those of an intact aortic wall, suggesting that the availability of oxygen to the injured area had been re-established fully.

Lipid profile in the evolution of experimental atherosclerotic plaques from thrombus

Nonocclusive white mural thrombosis was induced in the abdominal aortae of normolipidemic rabbits by insertion of a polyethylene catheter into the abdominal aortae. The thrombus subsequently organized into intimal thickenings which resembled fibrofatty type atherosclerosis seen in man, showing large numbers of foam cells containing stainable lipid, fatty necrotic centers, cholesterol clefts, calcification, and fibrous caps. The lipid composition of the thrombus and lesions was followed at serial time intervals from 4 hours to 60 weeks. Lipid analysis showed significant concentrations of lipid in the early lesions and with time these lipid concentrations increased and later decreased. These studies demonstrate that the fibrofatty lesions derived from a white thrombus have significant amounts of the same lipids that characterize the atherosclerotic lesions of man, however, there is a lower proportion of cholesterol to the other constituents and a higher proportion of phospholipids. The free cholesterol and cholesteryl ester of the 4-day lesions were much greater than that of platelets alone indicating that significant amounts of plasma are trapped in a thrombus when it forms.

Chemical composition of the rabbit aorta during development

Changes in both the relative and the absolute amounts of collagen and elastin in segments of the aortic wall of New Zealand white rabbits (1-130 weeks old) were determined by chemical analysis. As in other mammals, elastin was the major component of the wall of the thoracic aorta although the proportion of collagen increased along the abdominal aorta and into the more distant arteries. Data on the absolute amounts of collagen and elastin per aorta showed that collagen and elastin deposition was most rapid during the early postnatal weeks. Although this deposition slowed in later weeks, it continued in both segments of the aorta throughout the period of this study. The proportion of the wall mass attributable to collagen and to elastin increased very rapidly during the first postnatal weeks and then, after 20 weeks, declined. The results of the present study indicate that there is a significant increase in some unidentified nonscleroprotein component within the aortic wall of older rabbits.

Action of growth hormone and thyroxine on aortas of hypophysectomized dogs

Young dogs were surgically hypophysectomized and maintained for eleven weeks postoperatively with age-matched normal controls. For three weeks prior to sacrifice, four hypophysectomized dogs were given daily injections of bovine growth hormone (GH, 0.2 mg./kg.) and another four were given daily injections of thyroxine (T4, 5 μg./ kg.). Aortas were removed, cleaned of adventitia and divided into three segments: arch, thoracic and abdominal. Each portion was analyzed for collagen, elastin, deoxyribonucleic acid (DNA), calcium, total mucopolysaccharides (MPS), hyaluronic acid (HA), heparan sulfate (HS), dermatan sulfate (DS) and chondroitin sulfate (GS). The arch and thoracic aortas of normal animals were found to contain more DNA, CS and elastin but less collagen than the abdominal aorta. Removal of the hypophysis resulted in an overall increase in elastin and DNA content and caused a decrease in all sulfated MPS. Administration of either CH or T4 to hypophysectomized dogs had a profound effect on the majority of constituents in all segments of aorta. GH returned the content of elastin, DS and CS toward normal in at least two of the three aortic segments. T4 returned the content of DNA, DS and CS toward normal in all segments. Moreover, T4 treatment caused significant reductions in collagen and HA contents of thoracic and abdominal segments. These results indicate that: (1) the composition of normal aorta varies with the segment studied; (2) the composition of the aorta is markedly affected by hypophysectomy, CH and T4 treatment; and (3) individual aortic segments show differential sensitivity to a given hormone.