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 reduction characterized by declines in both lean and adipose tissues. The body fat of LH-lesioned rats can be restored to or above the levels of nonlesioned rats by overfeeding. However, the protein deficit cannot be so reversed, suggesting that the lesion-induced body protein reduction is chronic. To ascertain which specific tissues surrender protein following LH lesions, the present studies measured skeletal muscle and visceral organ weights at 2 weeks and 6 months postlesion. Daily protein losses during the first 2 weeks postlesion were also assessed to determine the temporal pattern of whole-body protein adjustments. The results at 6 months postlesion suggest that LH lesions lead to reductions in the maintained mass of all protein-based tissues. The largest absolute loss was from skeletal muscle, whereas liver sustained the greatest 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 large losses at 2 weeks, and proportionally smaller losses at 6 months. Reductions of visceral organ mass were marginal at 2 weeks, but substantial by 6 months postlesion. Thus, whereas all protein-based tissues are reduced by LH lesions, the protein content of specific tissues appears to be altered differentially. Major reductions in total body protein occur in the first 2 weeks of the LH syndrome, with an apparent redistribution of protein later. This redistribution results in the partial restoration of skeletal muscle at the expense of existing visceral organ protein or its subsequent accretion.