Growth hormone, insulin-like growth factor-1, and the insulin-like growth factor binding proteins in rats maintaining reduced body protein following lesions of the lateral hypothalamus

Rats with lesions of the lateral hypothalamus (LH) maintain a reduced body protein mass that they effectively defend when challenged by under- or over -nutrition. The two studies reported here evaluate the potential contributi ons of growth hormone (GH), insulinlike growth factor-1 (IGF-1), and the in sulin-like growth factor-binding (IGFBP) to this persistent maintenance of a reduced body protein mass by LH rats. At 18 weeks postlesion, it was foun d that the serum levels of GH, IGF-1, total IGFBP, and IGFBP-3 of LH rats m aintaining reduced body protein were not different from those of age-matche d controls. However, closer to the time of surgery, at which time the lesio n-induced body protein adjustments are known to occur, altered hormone and binding protein levels were observed. Specifically, at 3 weeks after lesion ing, the IGF-binding proteins of LH rats were significantly elevated, where as their GH levels were lower than those of controls. Because the GH, IGF-1 , and IGF-binding proteins of LH rats were comparable to those of controls at 18 weeks after lesioning, none apparently underlie the chronically reduc ed body protein mass that LH rats display. Closer to the time of lesioning, however, altered GH and IGF binding protein levels may contribute to the p ostlesion adjustments by which the body protein mass of LH rats is lowered to its reduced level, (C) 2000 Elsevier Science Inc. All rights reserved.