Relative immunity to arteriosclerosis in rabbits during the hair-shedding period

Replacement of dietary saturated fat with monounsaturated fat: effect on atherogenesis in cholesterol-fed rabbits clamped at the same plasma cholesterol level

The aim was to compare the effect on atherogenesis of dietary monounsaturated and saturated fatty acids in cholesterol-clamped rabbits. To obtain an average plasma cholesterol concentration of 20 mmol/l in each rabbit during the 13-week cholesterol-feeding period, dietary cholesterol was adjusted weekly. The amount of fat fed daily was 10 g per rabbit in Expts A (n 23), C (n 36), and D (n 58) and 5 g per rabbit in Expt B (n 24). The source of monounsaturated fatty acids was olive oil in all four experiments. The source of saturated fatty acids was butter in Expt A, lard in Expt B, coconut oil in Expt C, and butter or lard in Expt D. Generally, olive oil-fed groups received more cholesterol and tended to have more cholesterol in VLDL and less in LDL compared with groups receiving saturated fat. Analysis of variance of the combined results of all four experiments showed that, in comparison with saturated fat, olive oil lowered aortic cholesterol by 13 (-9-30, 95% confidence interval) % in the aortic arch, and by 10 (-10-26) % in the thoracic aorta, which was not significant. In the comparison with olive oil, no differences in effects on aortic cholesterol content were detected between butter, lard and coconut oil. These findings do not support the view that replacement of dietary saturated fat with olive oil has a major impact on the development of atherosclerosis in addition to that accounted for by changes in plasma cholesterol levels.

Seasonal variations in the biophysical properties of rabbit aorta and its susceptibility to arteriosclerosis

The physiological variations in the mechanical properties of rabbit aortae in relation to the periods of hair shedding were studied. The load-strain curves of the eight proximal thoracic segment in 15 shedding and 15 non-shedding male albino rabbits were analysed. The slope of the curves (tangent of the angle between the linear region of the load-strain curve and the strain axis) was decreased in the shedding animals compared to that of the non-shedding animals and the toe of the load-strain curves was significantly lower towards the x-axis in the shedding animals. The observations indicate a lower stiffness, that is increased elasticity, of the aortae of rabbits during hair shedding. The increased elasticity during hair shedding may explain the previously reported resistance to experimental arteriosclerosis caused by the hemodynamic strain elicited by exposure to systemic hypoxia. A decrease in the aortic content of collagen and of sulfated glycosaminoglycans, and an increase in the content of hyaluronic acid, may be of importance in the alterations of the mechanical properties of rabbit aorta during hair shedding.

Seasonal variations in the susceptibility of the aortic wall to atherosclerosis. Biochemical studies of glycosaminoglycans and collagen of rabbit atherosclerosis

The aortic content of glycosaminoglycans and collagen as well as the uptake of [125 I] albumin were studied in 53 male albino rabbits during hair-shedding and outside the period of hair-shedding to elucidate the previously reported resistance to experimental arteriosclerosis during the shedding period [1]. The concentration of hyaluronic acid was highest during hair shedding, decreasing towards the non-shedding period. The content of dermatan sulphate, chondroitin-4, 6-sulphate and hydroxyproline was lowest during sheeding and highest outside the sheeding period. Accordingly, the incorportation of [35 S] sulphate in chondroitin -4, 6-sulphate and the dermatan plus heparan sulphate fraction was increased outside shedding, consistent with a stimulated synthesis. The concentration of hyaluronic acid was negatively correlated to the uptake of [125I] albumin, and the dermatan sulphate content was positively correlated to the content of hydroxyproline. The higher concentration of hyaluronic acid during the period of shedding may improve the elastic properties as well as the ability of the aortic wall to absorbe the haemodynamic strain involved in the vascular injury of this type of experimental arteriosclerosis [2]. The decrease in the concentration of hyaluronic acid simultaneously with an increase in the aortic content of collagen as well as of chondroitin-4, 6-sulphate and dermatan sulphate may imply a greater stiffness of the aorta resulting in a higher susceptibility to injury. The relationship between hyaluronic acid and [125 I] albumin is consistent with an importance of hyaluronic acid to the susceptibility of the arterial wall to deposition of macromolecules such as the lipids. Our observations represent an example of endogenous conditioned variations in the aortic content of glycosaminoglycans and hydroxyproline accompanied by a variation in the susceptibility to experimental arteriosclerosis.

Glucocorticoid and starvation effect on glycosaminoglycans in vascular connective tissue. Biochemical studies on repair processes in rabbit aorta

Male rabbits were injured by a single mechanical dilatation injury of aorta and then injected with prednisone 2 mg/kg or saline for 14 days or subjected to starvation. The biosynthesis of the sulfated glycosaminoglycans as evaluated by the uptake of 35S-sulfate and the content of the glycosaminoglycans were measured on the intima-media layer of the descending thoracic aorta. The results indicate that prednisone may inhibit the biosynthesis of heparan and/or dermatan sulfate while starvation increases the biosynthesis of all the sulfated glycosaminoglycans. No alterations were observed in the total amount of glycosaminoglycans in aorta following glucocorticoid injection or starvation. The metabolism of aortic glycosaminoglycans during repair is less sensitive to the action of prednisone than in undamaged aorta. This contrasts with the effect of prednisone on the metabolism of aortic collagen.