Influence of centrifugation and hindlimb suspension on testosterone and corticosterone excretion in rats

Background: Alterations in mass loading have been shown to stimulate the pituitary-gonadal and pituitary-adrenal axes resulting in changes in testosterone (T) and corticosterone (B) production which may account for the previously reported variations in muscle mass under these conditions. Hypothesis: Centrifugation and hindlimb suspension will induce opposing effects on testosterone and corticosterone excretion. Methods: Effects of mass loading (centrifugation at -2Gx) and unloading (hind-limb suspension, HLS) on excreted T and B levels, and testicular mass were examined in Sprague-Dawley rats. For 12 d, 16 (8 controls and 8 centrifuged) rats and 20 (10 unsuspended controls and 10 suspended) rats were studied during the centrifugation and suspension portions of the study, respectively. Following the completion of each study, testicular mass was measured. Results: Absolute testicular mass was not different following 12 d of centrifugation. Excreted T was elevated between days 1 and 6 of centrifugation. Excreted B levels were elevated for the first 4 d of centrifugation. Suspension reduced absolute and relative testicular mass. Excreted T levels were reduced from days 3-12 of suspension, while excreted B levels were only elevated on the first day of suspension. Conclusions: Centrifugation stimulated an increase in T excretion despite a lack of a change in absolute testicular mass. Conversely, suspension resulted in a reduction in T excretion which may have been associated with a decrease in absolute testicular mass. The centrifugation-induced increase in T excretion is consistant with previously reported increases in lean body mass following centrifugation. while the HLS-induced reduction in T excretion correlates with previously reported decreases in lean body mass following suspension.