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Opposite Effect of Cold on Energetic Efficiency in Normal and Obese Wistar Rats with Hypothalamic Lesions

Jan Jeszka, Hans J. Grav*, Halvor Holm*, Bo-Egil Hustvedt*, Arne Løvø*,1 and Øydis Ueland*

Institute of Human Nutrition, Agriculture University, Poznan, Poland * Institute for Nutrition Research, University of Oslo, Norway

Reduced thermogenesis in brown adipose tissue (BAT) may contribute to increased energetic efficiency and obesity in rats with ventromedial hypothalamic (VMH) lesions. Thermogenic activity of BAT is a function of the environmental temperature. If a relationship exists, it follows that the increased energetic efficiency of VMH-lesioned rats likewise should be governed by temperature. We have therefore investigated the energy balance of normal and VMH-lesioned rats housed at 30°C and 10°C. Experiments at differing feeding levels allowed calculation of maintenance energy requirements and the net energetic efficiencies of each group. VMH-lesioned rats at thermoneutrality (30°C) accumulated more body fat at all feeding levels than did normal rats. Maintenance energy requirement was reduced, but the net energetic efficiency did not differ significantly from normal. The reduced maintenance energy requirement of lesioned rats persisted at 10°C. Net energetic efficiency decreased in normal rats acclimated to cold but increased in the lesioned group. The difference was significant (P < 0.05). The cold-induced increase in interscapular brown adipose tissue (IBAT) oxidative capacity of VMH-lesioned rats was only half that of normal rats. Differences in BAT thermogenesis may be the basis for the differing temperature effects on net energetic efficiency.

KEY WORDS: • rats • brown adipose tissue • obesity • energetic efficiency • VMH lesion

1 To whom correspondence should be addressed.

Manuscript received 9 January 1990. Revision accepted 23 October 1990.






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