THE SPECIFIC-LOCUS AND TIME-COURSE OF THE BODY PROTEIN ADJUSTMENTS PRODUCED IN RATS BY LESIONS OF THE LATERAL HYPOTHALAMUS

Lesions of the lateral hypothalamus (LH) result in a body weight reduc tion characterized by declines in both lean and adipose tissues. The b ody fat of LH-lesioned rats can be restored to or above the levels of nonlesioned rats by overfeeding. However, the protein deficit cannot b e so reversed, suggesting that the lesion-induced body protein reducti on is chronic. To ascertain which specific tissues surrender protein f ollowing LH lesions, the present studies measured skeletal muscle and visceral organ weights at 2 weeks and 6 months postlesion. Daily prote in losses during the first 2 weeks postlesion were also assessed to de termine the temporal pattern of whole-body protein adjustments. The re sults at 6 months postlesion suggest that LH lesions lead to reduction s in the maintained mass of all protein-based tissues. The largest abs olute loss was from skeletal muscle, whereas liver sustained the great est proportional loss. Assessment of daily postlesion protein balance indicate that the majority of body protein losses occurred during the initial 6 days postlesion. Skeletal muscle mass was characterized by l arge losses at 2 weeks, and proportionally smaller losses at 6 months. Reductions of visceral organ mass were marginal at 2 weeks, but subst antial by 6 months postlesion. Thus, whereas all protein-based tissues are reduced by LH lesions, the protein content of specific tissues ap pears to be altered differentially. Major reductions in total body pro tein occur in the first 2 weeks of the LH syndrome, with an apparent r edistribution of protein later. This redistribution results in the par tial restoration of skeletal muscle at the expense of existing viscera l organ protein or its subsequent accretion.