Cold-induced thermogenesis in rats nutritionally deprived early in life.

Preweaning nutritional deprivation with or without postweaning partial energy restriction produces animals of small size with defective nonshivering thermogenesis. This is also associated with their inability to tolerate cold exposure to 5 degrees C. Adequate nutritional rehabilitation for a reasonable length of time of 10 days abolishes the defect in cold induced thermogenesis (CIT) although the deficits in body weight or body size are not corrected. This may indicate that the defect may be possibly due to the non availability of enough substrates rather than to a change in the functioning of thermogenic organs such as brown adipose tissue. Sucrose feeding which enhances caloric intake and hence sympathetic activity can reverse the defect in CIT only in older rats suggesting the possibility of delayed maturation of thermoregulatory functions in young rats which are energy deprived. The results of this study possibly indicate that there may be a temporary reduction of the sympathetic nervous system activity during the period of energy restriction which compromises cold tolerance and which is reactivated rapidly following nutritional rehabilitation.