Mitochondrial swelling during cold exposure of the rat and hamster

Abstract

Swelling of isolated liver mitochondria of hamsters and rats was measured in a Beckman DK ratio-recording spectrophotometer after 0, 1, 2, 5, 10, 15, and 20 days of cold exposure at 5 C. Swelling was determined by absorbance changes over 10-min intervals at 520 mµ at 37 C in 0.3 m sucrose with and without 1.5 x 10^–7 m l-thyroxin added. Thyroid uptake and plasma content of 0.5 µc I¹³¹ was measured in additional animals at 2, 6, 18, 48, and 144 hr of cold exposure. Swelling rates of rat liver mitochondria increased with time, while hamster liver mitochondria showed no change during 20 days of exposure to cold. Added thyroxin increased swelling rates equally of both rat and hamster liver mitochondria, reducing the early refractory period of the swelling curve. Rat thyroid uptakes of I¹³¹ were higher at room temperature than the hamster. Cold exposure resulted in a severe reduction of hamster thyroid uptake of I¹³¹ while reduction of rat thyroid uptake was minor. Differences in mitochondrial response to swelling media between the cold-exposed hamster and rat paralleled the different functional levels of the thyroid during cold exposure.