Effect of gonadectomy on AgRP-induced weight gain in rats

Department of Physiology, Southern Illinois University Carbondale, School of Medicine, Carbondale, Illinois Submitted 4 April 2008 ; accepted in final form 11 October 2008 Agouti-related peptide (AgRP), the endogenous antagonist to the melanocortin 3 and 4 receptors, elicits robust hyperphagia and weight gain in rodents when administered directly into the central nervous system. The relative influence of AgRP to cause weight gain in rodents partially depends on the activity level of the melanocortin agonist-producing proopiomelanocortin neurons. Both proopiomelanocortin and AgRP neurons within the arcuate nucleus receive energy storage information from circulating peripheral signals such as leptin and insulin. Another modulator of AgRP activity includes the cell surface molecule syndecan-3. Because leptin and insulin affect food intake in a sexually dimorphic way in rodents and syndecan-3-deficient mice regulate adiposity levels through distinct physiological mechanisms, we hypothesized that AgRP-induced weight gain would also be sexually dimorphic in rats. In the present study, the behavioral and physiological effects of centrally-administered AgRP in male and female were investigated. In male rats, AgRP (1 nmol) induced 5 days ( P < 0.0001) of significantly elevated feeding compared with vehicle-treated controls, while females displayed 3 days of hyperphagia ( P < 0.05). However, 1 wk after the injection, both male and female rats gained the same percent body weight (6%). Interestingly, female rats exhibited a greater reduction in energy expenditure ( VO 2 ) following AgRP compared with male rats ( P < 0.05). Removal of the gonads did not alter cumulative food intake in male or female rats but did attenuate the dramatic reduction in V O 2 exhibited by females. Both intact and gonadectomized rats demonstrated significantly increased respiratory quotient supporting the anabolic action of AgRP ( P < 0.01). These findings are novel in that they reveal sex-specific underlying physiology used to achieve weight gain following central AgRP in rats. AgRP; melanocortin; energy expenditure; sex; food intake Address for reprint requests and other correspondence: A. D. Strader, Assistant Professor, Dept. of Physiology, Southern Illinois Univ. Carbondale, School of Medicine, 1135 Lincoln Dr., Life Science III Rm. 2066, Carbondale, IL 62901 (e-mail: astrader{at}siumed.edu ) Related articles in AJP - Regu: Corrigendum AJP - Regu 2009 296: R1290. [Full Text]