HEPATIC MITOCHONDRIAL RESPIRATORY CAPACITY IN HYPERPHAGIC RATS

We have investigated whether changes in hepatic mitochondrial protein mass and respiration occur in hyperphagic rats. Hyperphagia was induced by a palatable diet. Rats fed such a diet showed a significantly greater energy intake (+40%) without a corresponding greater body weight gain when compared to control rats. They also showed a significantly higher resting metabolic rate (+44%) compared to control rats. The latter increase was abolished by propranolol administration and, as such, was considered to be an adaptative response. No difference in liver mitochondrial protein mass was found in hyperphagic rats. On the other hand, state 3 respiration using succinate as substrate increased, with no difference in ADP/O ratios and, hence, in the degree of coupling. This increase is mediated by the sympathetic nervous system, as it was abolished by propranolol. The above results indicate an increase in ATP synthetic capacity and suggest one possible mechanism by which metabolism contributes to the increased expenditure of hyperphagic rats.