Diet-induced and physiologically occurring hypercholesterolemias in the spontaneous hypothyroid European badger (Meles meles L.): a density gradient study of lipoprotein profile

A year-long study of changes induced by castration in the plasma lipid and lipoprotein spectrum in the European badger

In man, an influence of male sex hormones on plasma lipid transport is well established; however, recent data on this subject in the literature are both relatively lacking and occasionally conflicting. The male European badger exhibits seasonal variations of large amplitude in its gonadic function. We have therefore attempted to establish the influence of male sex steroids on plasma lipids and lipoproteins in this species. For this purpose, we have examined the plasma lipid and lipoprotein spectrum in a group of castrated male badgers every month for a year, non-operated animals being used as controls. Our analyses included measurement of plasma lipid levels, density gradient ultracentrifugation of lipoproteins, electrophoresis of lipoproteins and apolipoproteins, and evaluation of plasma testosterone and thyroxine levels. The differences observed between the 2 groups of animals were maximal during the months when plasma testosterone was elevated in intact badgers (January to July). For this period, castration resulted in higher plasma concentrations of cholesterol, phospholipids and triglycerides, while the latter alone remained significantly more elevated in operated animals until the end of our experiments. With regard to lipoproteins, the main effect of castration consisted of a large augmentation in the concentration of lipoproteins with d approximately equal to 1.027-1.065 g/ml which were responsible for the transport of most of the increased amounts of triglycerides present in the plasma of castrated badgers. The proportion of apoprotein B in the protein moiety of these lipoprotein components was enhanced after castration. Other changes in the lipoprotein spectrum included (1) a moderate increase in the concentration of lipoproteins with d less than 1.015 g/ml and 1.019-1.027 g/ml, and (2) a modification of the respective proportions of high density lipoproteins with d 1.065-1.100 g/ml and d 1.100-1.162 g/ml. Finally, no considerable differences between the 2 groups of animals were noted in the respective percentages of the various chemical constituents in each lipoprotein subfraction assayed, except for those with d 1.023-1.027 g/ml, which, in castrated badgers, did not exhibit the enrichment in triglycerides usually noted during late winter and spring in intact animals.

A year-long study of changes induced by thyroidectomy in the plasma lipid and lipoprotein spectrum in the European badger

Hypothyroidism is associated with hypercholesterolemia and increased risk for atherosclerotic disease. The European badger exhibits large seasonal changes in thyroid activity and the annual minimum of plasma thyroxine level in this species occurs at the same period of the year (i.e. late fall) as a pronounced hypercholesterolemia. We examined the plasma lipid and lipoprotein spectrum in a group of thyroidectomized male badgers every month for a year. Non-operated animals were used as controls. Our analyses included measurement of plasma lipid levels, density gradient ultracentrifugation of lipoproteins, electrophoresis of lipoproteins and apolipoproteins, and histological studies. Maximal differences between the two groups of animals were observed during spring, occurring concomitantly with the annual maximum of plasma thyroxine concentration in control badgers. Comparison with the latter animals revealed a permanent hypercholesterolemia and hyperphospholipidemia in thyroidectomized badgers, while their lipoprotein spectrum was characterized by the continual presence of elevated concentrations of cholesterol-rich lipoproteins of d congruent to 1.015 - 1.027 g/ml. The ratio of triglyceride/cholesteryl ester content in such lipoproteins remained constant throughout the year, resembling that noted in intact animals during late fall. Other features distinguishing the lipoprotein spectrum in thyroidectomized badgers were: (1) higher levels of lipoproteins with d 1.027 - 1.065 g/ml and d 1.065 - 1.100 g/ml, and (2) a cholesteryl ester enrichment of both these lipoprotein subclasses. The two groups of animals shared a heterogeneity of low density lipoprotein subfractions isolated on density gradients, together with the presence of apolipoproteins with molecular weights respectively typical of human apolipoproteins A-I and B throughout the low density range. Arterial walls and heart tissues from intact and thyroidectomized animals were free of atherosclerotic lesions at the end of the experimental period.

Distribution and partial characterization of the plasma lipoproteins in the hedgehog (Erinaceus europaeus L.), a hibernator with potential use in the study of the hormonal regulation of lipoprotein metabolism

The hedgehog is a hibernator in which yearly cycles of several endocrine activities and seasonal variations of plasma lipids have already been demonstrated. We have consequently undertaken a study of plasma lipids and lipoproteins in this animal, bled during late April and May. Plasma cholesterol levels (178 +/- 30 mg/100 ml) were comparable with those in normal humans, while triacylglycerol was lower (46 +/- 17 mg/100 ml) and phospholipids higher (252 +/- 35 mg/100 ml). The main characteristics of the plasma lipoprotein spectrum, as determined by sequential and density gradient preparative ultracentrifugation, analytical ultracentrifugation and gel filtration chromatography, were (1) a low concentration of very-low-density components (d less than 1.006 g/ml, about 20 mg/100 ml); (2) a continuity between the low (1.006-1.063 g/ml) and high (1.063-1.21 g/ml) density components, the former (about 150 mg/100 ml) exhibiting a considerable heterogeneity upon polyacrylamide gel electrophoresis while the latter were largely predominating (570 mg/100 ml); (3) the presence, at a density of 1.087 g/ml, of a band migrating electrophoretically like human low-density lipoproteins, a finding consistent with the results of apolipoprotein electrophoresis, which showed the presence of a high-molecular-weight counterpart to apolipoprotein B, in both the low- and high-density ranges defined above; (4) the presence, throughout the entire density spectrum, of an apolipoprotein with molecular weight and mobility in polyacrylamide/urea gels similar to human apolipoprotein A-I, and (5) the presence of very-high-density lipoproteins (d 1.178-1.259 g/ml) responsible for the transport of approximately 15% of plasma cholesterol and 20% of phospholipids.