Impaired thermoregulation in cold-exposed rats with hypothalamic obesity

Experimental obesity: a homeostatic failure due to defective nutrient stimulation of the sympathetic nervous system

The basic hypothesis of this review is that studies on models of experimental obesity can provide insight into the control systems regulating body nutrient stores in humans. In this homeostatic or feedback approach to analysis of the nutrient control system, we have examined the afferent feedback signals, the central controller, and the efferent control elements regulating the controlled system of nutrient intake, storage, and oxidation. The mechanisms involved in the beginning and ending of single meals must clearly be related to the long-term changes in fat stores, although this relationship is far from clear. Changes in total nutrient storage in adipose tissue can arise as a consequence of changes in the quantity of nutrients ingested in one form or another or a decrease in the utilization of the ingested nutrients. A change in energy intake can be effected by increased size of individual meals, increased number of meals in a 24-hour period, or a combination of these events. Similarly, a decrease in utilization of these nutrients can develop through changes in resting metabolic energy expenditure which are associated with one of more of the biological cycles such as protein metabolism, triglyceride for glycogen synthesis and breakdown, or maintenance of ionic gradients for Na+ + K+ across cell walls. In addition, differences in energy expenditure related to the thermogenesis of eating or to the level of physical activity may account for differences in nutrient utilization.

Long-term effects of lateral hypothalamic lesions on brown adipose tissue in rats

A classic feature of animals with lateral hypothalamic (LH) lesions is their regulation of body weight at sub-normal levels. The present studies were done to determine whether this is associated with enhanced thermogenic activity of their brown adipose tissue (BAT). Three groups of young chow-fed male Holtzman rats were formed: (1) animals receiving bilateral radiofrequency heat lesions of the dorsal LH and then permitted free access to chow (LH rats); (2) non-lesioned animals that were pair-fed (PF) to the lesioned rats during a 2 week post-operative recovery period (Phase 1); (3) non-lesioned, ad lib fed (NORM) controls. After Phase 1, each group was divided and permitted free access to chow alone or an additional selection of palatable, novel food items (a "cafeteria" diet) for 2-3 weeks (Phase 2) to stimulate diet-induced thermogenesis in BAT. Finally, half of each sub-group was exposed to 4 degrees C for 15 hr to stimulate nonshivering thermogenesis in BAT. During Phase 1 LHs and PFs ate 50% less than NORMs. This resulted in a weight deficit of 16% for LHs and 12% for PFs. After the additional period of feeding palatable foods (Phase 2) LHs collectively weighed 14% less than NORMs whereas previously PFs had a weight deficit of only 4%. They gained less weight than NORMs or PFs despite a similar energy intake. LHs had small deposits of gonadal white adipose tissue [both total amount and expressed per metabolic body mass (kg 0.75)]. The weight of interscapular BAT was less in the LHs but its concentration of protein (mg/g) was higher.(ABSTRACT TRUNCATED AT 250 WORDS)