Altered secretion of growth hormone and luteinizing hormone after 84 h of sustained physical exertion superimposed on caloric and sleep restriction

1 Military Performance Division, 2 Thermal and Mountain Medicine Division, and 3 Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts Submitted 23 December 2004 ; accepted in final form 24 August 2005 The pulsatile release of growth hormone (GH) and luteinizing hormone (LH) from the anterior pituitary gland is integral for signaling secretion of insulin-like growth factor (IGF)-I and testosterone, respectively. This study examined the hypothesis that 84 h of sustained physical exertion with caloric and sleep restriction alters the secretion of GH and LH. Ten male soldiers [22 yr (SD 3), 183 cm (SD 7), 87 kg (SD 8)] had blood drawn overnight from 1800 to 0600 every 20 min for GH, LH, and leptin and every 2 h for IGF-I (total and free), IGF binding proteins-1 and -3, testosterone (total and free), glucose, and free fatty acids during a control week and after 84 h of military operational stress. Time-series cluster and deconvolution analyses assessed the secretion parameters of GH and LH. Significant results ( P 0.05) were as follows: body mass (–3%), fat-free mass (–2.3%), and fat mass (–7.3%) declined after military operational stress. GH and LH secretion burst amplitude ( 50%) and overnight pulsatile secretion ( 50%), IGF binding protein-1 (+67%), and free fatty acids (+33%) increased, whereas leptin (–47%), total (–27%) and free IGF-I (–32%), total (–24%) and free testosterone (–30%), and IGF binding protein-3 (–6%) decreased. GH and LH pulse number were unaffected. Because GH and LH positively regulate IGF-I and testosterone, these data imply that the physiological strain induced a certain degree of peripheral resistance. During periods of energy deficiency, amplitude modulation of GH and LH pulses may precede alterations in pulse numbers. hormone pulsatility; insulin-like growth factor-I; soldiers; leptin; testosterone Address for reprint requests and other correspondence: B. C. Nindl, Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, MA 01760 (e-mail: bradley.nindl{at}us.army.mil )