Urinary excretion of LH and testosterone from male rats during exposure to increased 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 the 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 to 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 Days 1 and 8 of centrifugation; however, excreted LH was reduced on Days 2 and 3 compared with control animals. Excreted LH and T were significantly correlated (R = 0.731 and 0.706, respectively) in postspaceflight and centrifuged animals. Correlation curves had similar slopes (0.0213 and 0.023, respectively), but different y-intercepts (-1.43 and 3.32, respectively). The sustained increase in excreted T during centrifugation suggests that the pituitary-gonadal axis in postspaceflight animals may adapt quicker to increased gravity. The upward shift in the correlation curve exhibited by the centrifuged animals suggests that the sensitivity of LH-induced T release is increased in these animals. The previous dissociation between plasma LH and T during altered gravity was not observed in the present study in which excreted LH and T were measured.
Ortiz
R M
RM
Life Science Division, NASA Ames Research Center, MS 239-11, Moffett Field, California 94035, USA. rortiz@mail.arc.nasa.gov
Wade
C E
CE
Morey-Holton
E
E
D000222:Adaptation, Physiological; D000818:Animals; D002498:Centrifugation; D006112:Gravitation; D007986:Luteinizing Hormone / Q000652:urine*; D008297:Male; D010902:Pituitary Gland / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013026:Space Flight; D013737:Testis / Q000502:physiology; D013739:Testosterone / Q000652:urine*; D013997:Time Factors
D013739:Testosterone; D007986:Luteinizing Hormone