Lactation during hibernation in wild black bears: effects on plasma amino acids and nitrogen metabolites.

Abstract This study examined the seasonal and reproductive influences on individual plasma amino acid concentrations and nitrogen metabolites in a black bear population (Ontario, Canada). During hibernation, 11 of 23 plasma amino acids were significantly higher (13%–108%) in lactating than in nonlactating females, without an alteration in plasma total protein or total essential or nonessential amino acid levels. The greatest changes were observed in glutamine, arginine, and glycine levels. Plasma urea, urea/creatinine, and ammonia levels were significantly lower in hibernating compared with active female bears, but lactation had no effect on these parameters. Taken together these results show that lactation during hibernation is an additional metabolic challenge that results in increased mobilization of individual plasma amino acids and no accumulation of nitrogen end products, underlining the remarkable efficiency of amino acid and urea recycling in denning female black bears.