Effects of prolonged exercise on agouti-related protein: a pilot study
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RESEARCH LETTER
Effects of prolonged exercise on agouti-related protein: a pilot study Robert R. Kraemer • V. Daniel Castracane • Michelle Francois • Abbass Ghanbari-Niaki • Bovorn Sirikul • Rolda´n A. Valverde
Received: 1 February 2012 / Accepted: 22 March 2012 / Published online: 3 April 2012 Ó Springer Science+Business Media, LLC 2012
Abstract Agouti-related protein (AgRP), is a signaling peptide that affects feeding behavior, energy homeostasis, and has also been shown to stimulate the hypothalamic– pituitary–adrenal axis. The purpose of this study was to determine the effects of 90 min of treadmill exercise on circulating AgRP concentrations and the relationship of AgRP responses to cortisol. Seven young males completed a preliminary trial followed by counterbalanced experimental and control trials 4–5 weeks apart. The experimental trial began 2.5 h after consumption of a standard nutrient beverage and consisted of treadmill exercise at 60 % of previously determined VO2max for 90 min. Blood samples were collected before (-30 and 0 min), during (18, 36, 54, 72, and 90 min), and following exercise (20, 40, and 60 min). Blood samples were collected in a resting, control trial at the same time points as the experimental trial. Plasma lactate was significantly higher in the exercise than the control trial. Although AgRP increased from 18 min of exercise to peak at 90 min, these increases were not significantly different than values in the control trial. Cortisol responses during the
R. R. Kraemer (&) M. Francois B. Sirikul Department of Kinesiology and Health Studies, Southeastern Louisiana University, SLU10845, Hammond, LA 70402, USA e-mail: [email protected] V. D. Castracane Department of Obstetrics and Gynecology, Texas Tech University Health Sciences Center, Odessa, TX 79763, USA A. Ghanbari-Niaki Exercise Biochemistry Division, Faculty of Physical Education and Sport Sciences, Mazandran University, Babolsar, Iran R. A. Valverde Department of Biological Sciences, Southeastern Louisiana University, SLU10736, Hammond, LA 70402, USA
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exercise trial were significantly higher than the control trial. AgRP concentrations during early exercise were positively correlated with cortisol levels later in recovery. The obtained data suggest that AgRP concentrations during prolonged steady-state exercise are associated with subsequent cortisol increases, but further study is required to determine whether there is a causal effect. Keywords Orexigenic peptide HPA-axis Steady-state exercise Cortisol
Introduction Agouti-related protein (AgRP), an a-melanocyte stimulating hormone antagonist, is a signaling peptide that affects feeding behavior, energy homeostasis, and adiposity [9]. AgRP acts as an inverse agonist of melanocortin receptor 4 (MCR4) and mutations of MCR4 appear to be associated with early onset obesity [15]. AgRP has also been shown to stimulate the hypothalamic–pituitary–adrenal (HPA) axis and augment the HPA axis response to interleukin-1 [10, 19]. In humans, AgRP is mainly expressed in the hypot
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