EFFECT OF COLD EXPOSURE ON SERUM LIPIDS AND LIPOPROTEINS IN THE RAT

The effect of cold exposure for 1–52 days on the concentration and composition of the serum lipids and lipoproteins in male Wistar rats was studied. Serum lipoproteins were separated by preparative ultracentrifugation into three density classes, very low density (d < 1.006), low-density (d, 1.006–1.070), and high-density (d, 1.070–1.218). On the first day of cold exposure, total serum lipids were reduced by 20–25%, this decrease occurring mainly in the triglyceride fraction. Although the low-density and high-density lipoproteins were not affected by cold exposure, the concentration of the very low density lipoproteins fell markedly to 70–75% below normal levels. These alterations in the pattern of serum lipids and lipoproteins persisted throughout the cold-exposure period. Sex or prior feeding of a high-fat, high-carbohydrate, or high-protein diet did not modify these cold-induced changes. The response of the very low density lipoproteins to cold was immediate and rapid, the rate and degree of change being greatest in the first 4 hours of exposure. Conversely, the recovery of the very low density fraction to normal after removal of the rats from the cold was slow and depended upon the period of prior exposure. Animals exposed to 4 °C for 4 days required 3 days at 22 °C for the very low density lipoproteins to return to normal, and the recovery period was twice as long for cold-acclimatized (4 weeks) animals. The role of the triglyceride-rich very low density lipoproteins as a readily available energy source in the animals is discussed in the light of these results.