Urinary excretion of LH and testosterone from male rats during exposure toincreased gravity: Post-spaceflight and centrifugation

A dissociation between plasma luteinizing hormone (LH) and testosterone (T) appears to exist during exposure to altered gravity. The pulsatile nature of LH release and the diurnal variability of T secretion may mask or bias t he effects of altered gravity on the pituitary-gonadal axis when analyzing plasma concentrations. Therefore, we examined the relationship between the excretion of urinary LH and T in male Sprague-Dawley rats during exposure t o increased gravity upon return to Earth following a 14-day spaceflight (n = 6) and by 12 days of centrifugation at 2g (n = 8), Excreted LH and T were elevated on the first 3 days postflight, Excreted T was elevated between D ays 1 and 8 of centrifugation; however, excreted LH was reduced on Days 2 a nd 3 compared with control animals. Excreted LH and T were significantly co rrelated (R = 0.731 and 0.706, respectively) in postspaceflight and centrif uged animals. Correlation curves had similar slopes (0.0213 and 0.023, resp ectively), but different y-intercepts (-1.43 and 3.32, respectively), The s ustained increase in excreted T during centrifugation suggests that the pit uitary-gonadal axis in postspaceflight animals may adapt quicker to increas ed gravity, The upward shift in the correlation curve exhibited by the cent rifuged animals suggests that the sensitivity of LH-induced T release is in creased in these animals. The previous dissociation between plasma LH and T during altered gravity was not observed in the present study in which excr eted LH and T were measured.