Testosterone replacement does not normalize carcass composition in chronically decerebrate male rats

Abstract

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 8 days later, and the study ended 15 days later. Testosterone implants produced 10-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 castrated 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 luteinizing 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 did not explain obesity or decreased lean body mass of CD rats, although CD rats exhibited abnormal levels of circulating reproductive hormones and disrupted testosterone negative feedback.