Decreased metabolic rates contingent upon lateral hypothalamic lesion-induced body weight losses in male rats.

Abstract

Animals that had reduced body weights [BW] following small lateral hypothalamic (LH) lesions had lower fasting heat production (FHP, equivalent to basal metabolic rate). The decreased FHP were not a secondary consequence of reduced BW, since animals whose BW were chronically reduced by restricting their water intake did not show a reduction in FHP. Animals with LH lesions were adipsic and aphagic only for a brief period and had none of the permanent deficits associated with the LH syndrome. They drank water when it was presented alone, they were not prandial drinkers and they ate following systemic hypoglycemia. The FHP of the animals with LH lesions were elevated immediately postsurgery, but dropped below normal after about 1 wk. These decreased FHP were not the result of any change in animals'' activity levels. The thyroids of the animals with LH lesions were smaller, and their blood levels of thyroxine were lower than those of the sham animals. Goiters resulting from ingestion of a diet containing .015% propylthiouracil were significantly smaller in animals with LH lesions than in sham animals. Complete thyroidectomy of normal animals resulted in BW curves identical to those of the animals with the largest LH lesions and the lowest FHP.