Seasonal variation in Na +-K +-ATPase in tissues of field acclimatized woodrats, Neotoma lepida

Abstract

1. 1. Woodrats, Neotoma lepida, were captured in the field over a 12 month period. 2. 2. The masses of the liver, kidney and intrascapular brown adipose tissue (IBAT) were lowest during the latter part of the summer as was the specific activity of Na +-K +-ATPase in the liver and kidney. 3. 3. With cooling temperatures in the fall, liver mass and the Na + -K +-ATPase activity of both liver and kidney increased significantly. 4. 4. During the coldest months, December and January, the mass of IBAT increased above the low summer values and remained elevated through the following spring. 5. 5. N. lepida acclimated to 5° and 21°C in the laboratory had 2–4 times more IBAT than did field acclimatized animals at any time of the year. 6. 6. Only with 35°C acclimated animals was IBAT reduced to the minimal levels seen in the field acclimatized animals at the end of summer.