抄録
Effects of cold adaptation and high-fat diet on the metabolic responses as well as cold resistance to acute cold exposure were investigated in rats with emphasis on elucidating the mechanism underlying the favorable effect of high-fat diet in a cold environment previously reported.
An increment in body weight was greater in rats on a high-fat diet and smaller in cold-adapted rats than in control rats. However, food intake was significantly greater in cold-adapted rats. Daily urine volume and urinary nitrogen excretion increased in cold-adapted rats, but did not change in rats on a high-fat diet. The high-fat diet caused higher bloodfree fatty acid (FFA) and ketone body concentrations, and lower urinary excretion of ketone bodies. Urinary vanilmandelic acid excretion was significantly elevated in cold-adapted rats, while it was lower in rats fed a high-fat diet as compared with that in control rats. This result suggests an increased sympathetic activity in cold-adapted rats and a rather suppressed activity in rats on a high-fat diet.
The fall in the colonic temperature due to cold exposure for the period of time up to four hours was significantly less in cold-adapted rats, but did not differ in animals fed a high-fat diet from that in control rats. This result signifies that there is no significant difference in cold resistance between control rats and rats on a high-fat diet. Blood FFA level as well as blood ketone body level was significantly raised in all experimental groups in response to cold exposure. It was observed, however, that an increment in blood FFA concentration was less in cold-adapted rats. The degree of increase in blood FFA became greater with length of exposure to the cold. Blood glucose concentration was significantly elevated in cold-adapted rats after an eighty minutes exposure to the cold, but did not vary in control rats and rats on a high-fat diet. Four hours after the cold exposure the blood glucose level was significantly decreased in all groups as compared with that at 25°C.
There was a significant correlation between the blood FFA and ketone body concentrations on the whole data before and after cold exposure in all groups. Regression coefficient between blood compositions was significantly greater in rats fed a high-fat diet than in control and coldadapted rats. It was also shown that there was an inverse correlation between the blood glucose and FFA levels after cold exposure. Furthermore, lessened falling of colonic temperature due to cold exposure was significantly associated with less variations in the blood FFA and glucose levels concomitantly determined in control and cold-adapted rats and this tendency was strongly documented in cold-adapted rats.
The present results indicate that the prolonged cold exposure increases the cold resistance to acute cold exposure, while the high-fat diet feeding may not be necessarily favorable to the cold resistance, although a high-fat diet causes certain metabolic changes, suggesting a favorable effect to some extent.
