Seasonal variations of plasma lipids and lipoproteins in the hedgehog, an animal model for lipoprotein (a) metabolism: relation to plasma thyroxine and testosterone levels

We describe a study of the seasonal variations of hedgehog plasma lipids and lipoproteins and their correlation with changes in the activities of the thyroid and testis. In ten male hedgehogs, plasma concentrations of lipids, thyroxine and testosterone were assayed each month for 1 year beginning in September, while plasma lipoproteins from five of these animals were analyzed at the same dates using density gradient ultracentrifugation. All classes of plasma lipids (cholesterol, total glycerol and phospholipids) exhibited statistically significant seasonal variations in their respective concentrations, with simultaneous maxima (cholesterol: 207 +/- 39 mg/100 ml; total glycerol: 50 +/- 9 mg/100 ml; phospholipids: 266 +/- 25 mg/100 ml) during late fall-early winter, i.e., during the period of the year when plasma levels of both thyroxine and testosterone were minimal. Plasma lipids subsequently decreased to minimal levels either in early summer (cholesterol: 129 +/- 18 mg/100 ml; phospholipids: 178 +/- 20 mg/100 ml) or in late winter (total glycerol: 22 +/- 9 mg/100 ml). Very low density lipoproteins (d less than 1.015 g/ml) were found at low levels (less than 15 mg/100 ml) during the cold months, and then became detectable as trace components only. The total concentration of the mixed lipoprotein population (i.e., low density lipoproteins, Lp(a), and high density lipoprotein (HDL)-like particles) in the d 1.015-1.065 g/ml interval decreased by almost 50% from January to February (from 164.3 to 89.2 mg/100 ml), i.e., following a 10-fold increase in the level of plasma testosterone, and immediately before the rapid doubling in plasma thyroxine concentration. The staining intensity of the electrophoretic band with migration characteristics corresponding to those of Lp(a) decreased considerably during winter. At the same period of the year, lower density (1.032-1.055 g/ml) HDL-like particles disappeared. The concentration of lipoproteins with d 1.065-1.162 g/ml, which included Lp(a) particles in addition to typical HDL, equally underwent seasonal variations. These variations consisted of two successive maxima in late fall (426.4 mg/100 ml) and late winter (458.3 mg/100 ml) with two subsequent decreases leading to minima in February (327.8 mg/100 ml) and August (257.1 mg/100 ml). Finally, very high density lipoproteins (d 1.162-1.259 g/ml) were heterogeneous, containing both cholesterol-rich (d 1.162-1.227 g/ml) and phospholipid-rich (d 1.194-1.259 g/ml) subpopulations.(ABSTRACT TRUNCATED AT 400 WORDS)