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

Background: Alterations in mass loading have been shown to stimulate the pi tuitary-gonadal and pituitary-adrenal axes resulting in changes in testoste rone (T) and corticosterone (B) production which may account for the previo usly reported Variations in muscle mass under these conditions. Hypothesis: Centrifugation and hindlimb suspension will induce opposing effects on tes tosterone and corticosterone excretion. Methods: Effects of mass loading (c entrifugation at -2Gx) and unloading (hind-limb suspension, HLS) on excrete d 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 co ntrols and 10 suspended) rats were studied during the centrifugation and su spension portions of the study, respectively. Following the completion of e ach 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 8 levels were elevated fo r the first 4 d of centrifugation. Suspension reduced absolute and relative testicular mass. Excreted T levels were reduced from days 3-12 of suspensi on, while excreted B levels were only elevated on the first day of suspensi on. Conclusions: Centrifugation stimulated an increase in T excretion despi te a lack of a change in absolute testicular mass. Conversely, suspension r esulted 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 consistent with previously reported increases in lean bod y mass following centrifugation, while the HLS-induced reduction in T excre tion correlates with previously reported decreases in lean body mass follow ing suspension.