SEASONAL-VARIATION IN BROWN ADIPOSE-TISSUE MASS AND LIPID DROPLET SIZE OF SOREX MINUTUS, THE PYGMY SHREW - THE RELATIONSHIP BETWEEN MORPHOLOGY AND METABOLIC-RATE

l. Metabolic rate, brown adipose tissue (BAT) mass and BAT lipid dropl et size, were measured in winter-, summer- and spring-acclimatized Pyg my shrews, Sorex minutus. 2. BAT mass changed significantly with seaso n both in relative and absolute terms. Winter-acclimatized shrews had the smallest (135 +/- 10 mg) and spring-acclimatized shrews had the he aviest BAI depots (310 +/- 28 mg). Relative BAT mass varied between 2- 7% depending on season. Median BAT lipid droplet size (mu m(2)) was sm allest in winter-acclimatized (106 mu m(2)) and largest in spring-accl imatized shrews (326 mu m(2)) 3. Resting metabolic rate and thermoregu latory thermogenesis were significantly positively related to BAT mass . There was a significant inverse relationship between mass independen t metabolic rate and lipid droplet size in all seasonally acclimatized shrews. 4. Winter-acclimatization of BAT in S. minutus is characteris ed by a decrease in BAT mass signifying a marked utilisation of lipid stores and by a reduction in BAT lipid droplet size, signifying an inc rease in thermogenic activity. (C) 1997 Published by Elsevier Science Ltd.