Comparative Biochemistry and Physiology Part A 134 (2003) 573–578 1095-6433/03/$ - see front matter  2002 Elsevier Science Inc. All rights reserved. doi:10.1016/S1095-6433(02)00363-X Hibernation reduces pancreatic amylase levels in ground squirrels Andreas Balslev-Clausen, Julia M. McCarthy, Hannah V. Carey* Department of Comparative Biosciences, University of Wisconsin, School of Veterinary Medicine, 2015 Linden Drive, Madison, WI 53706, USA Received 11 October 2002; received in revised form 19 November 2002; accepted 19 November 2002 Abstract Pancreatic enzyme levels in mammals are influenced by food intake and dietary composition. In this study, we examined the activity and expression of pancreatic amylase in a hibernating mammal, a natural model for long-term fasting. Pancreatic tissues were obtained from summer-active 13-lined ground squirrels and hibernating squirrels that had not eaten for at least 6 weeks. Amylase specific activity was reduced by ;50% in the torpid hibernators compared with summer squirrels, and immunoblot analysis revealed that amylase protein expression was reduced by ;40% in the hibernators. Similar reductions in amylase specific activity were observed in interbout euthermic hibernators. These results support a strong influence of food intake on pancreatic enzyme expression in hibernating mammals. The maintenance of basal levels of this key digestive enzyme at ;50% of summer values despite the extended winter fast likely facilitates the rapid resumption of digestive function after terminal arousal in the spring.  2002 Elsevier Science Inc. All rights reserved. Keywords: Pancreas; Amylase; Ground squirrel; Hibernation; Digestive enzymes; Fasting; Digestion; Torpor 1. Introduction Mammalian hibernation comprises a suite of physiological and morphological changes that facilitate survival during seasonal periods of low ambient temperatures and relative food scarcity. Significant energy conservation during the hiber- nation season is achieved through prolonged bouts of torpor, when body temperature falls to a few degrees above ambient temperatures (typically 0– 10 8C) and metabolic rates are reduced to less than 4% of active levels. Seasonal hibernators like the 13-lined ground squirrel (Spermophilus tride- cemlineatus) consume little or no food during the ;5–6 month hibernation season and instead rely *Corresponding author. Tel.: q1-608-263-0418; fax: q1- 608-263-3926. E-mail address: careyh@svm.vetmed.wisc.edu (H.V. Carey). exclusively on fat stores for fuel (Lyman et al., 1982). This change in nutritional status has the potential to alter the structural and functional characteristics of organ systems. The gastrointes- tinal tract is particularly affected by the winter fast; by the end of the hibernation season, the masses of the stomach and small and large intes- tines are significantly reduced in ground squirrels and marmots (Carey, 1990; Hume et al., 2002). Interestingly, although the mass of the small intes- tine decreases by ;50% during hibernation, intes- tinal brush border enzyme activity and transport function per mg of mucosal protein is maintained at normal or only slightly decreased levels (Carey, 1990, 1992; Carey and Martin, 1996; Carey and Sills, 1992, 1996). In addition to the intestinal mucosa, the exocrine pancreas is also critical for digestion. The secre- tions from exocrine pancreatic tissue are required