Submitted on January 13, 2009
Revised on April 13, 2009
Accepted on April 13, 2009
Testosterone replacement does not normalize carcass composition in chronically decerebrate male rats
Ruth B.S. Harris1, Emily W Kelso1, William P. Flatt2, Harvey J Grill3, and Timothy J Bartness4*
1 University of Georgia
2 University of Georgia, Athens
3 University of Penn
4 Georgia State University
* To whom correspondence should be addressed. E-mail: bartness{at}gsu.edu.
Chronically decerebrate (CD) rats, in which the forebrain and its descending projections are completely neurally isolated from hindbrain and rostral projections, gain substantial amounts of body fat, lose lean tissue and have low circulating testosterone concentrations. We tested whether testosterone replacement would normalize body composition of male CD rats. Five groups of rats were used: CD placebo, CD testosterone, Control placebo, Castrate placebo and Castrate testosterone. Testosterone replacement was initiated at the first stage of CD surgery in both CDs and castrate controls. The second stage of CD surgery occurred eight days later and the study ended 15 days later. Testosterone implants produced ten-fold normal circulating concentrations. Food intake was fixed for all rats by tube-feeding. CD rats had substantially more body fat and less lean tissue than neurally-intact rats. Testosterone replacement did not affect adiposity of CD rats, but did increase carcass water content. Energy expenditure of CD rats was significantly lower than that of Control placebo and castrate rats. Testosterone lowered respiratory equivalency ratio and ameliorated a fall in energy expenditure late in the intermeal interval in CD rats. Castration increased and testosterone decreased leuteinizing hormone (LH) and follicle stimulating hormone (FSH) in neurally-intact controls. LH was undetectable and FSH was equivalent to neurally-intact controls in CD rats and neither was affected by testosterone. Collectively, low testosterone does not explain obesity or decreased lean body mass of CD rats although CD rats exhibit abnormal levels of circulating reproductive hormones and disrupted testosterone negative feedback.
