Abstract
Groups of lean and obese female lean, and obese LA/Ntul//cp (corpulent) rats were subjected to measures of thermic responses to feeding, noradrenaline administration, and responses to 14 hours of cold exposure to access their capacity for thermoregulation beginning at 6 to 8 weeks of age. Body weights and adipose tissue mass were greater in the obese than the lean phenotype (p=<0.05). RMR and the dose related thermic responses to norepinephrine (NE) in lean were greater than in obese. Cold exposure at 4°C resulted in decreases in rectal but not core temperature in obese rats, and the thermic responses to 45 minutes of 4°C cold exposure on VO2 were typical but were significantly greater in lean than obese animals at all points measured. Circulating thyroid hormone concentrations were similar in lean and obese rats and T3 but not T4 increased dramatically in both phenotypes following the cold exposure, consistent with phenotype- and IBAT-linked changes in T4-5’ deiodinase and thyroidal activity in this strain. These thermoregulatory changes are consistent with previous studies and may contribute to phenotype mediated aspects of energy metabolism, storage, and adipose tissue deposition and to a phenotype specific selective epigenetic propensity for the expression of obesity during the early postweaning period
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