Urinary Excretion of LH and Testosterone from Male Rats During Exposure to Increased Gravity: Post‐Spaceflight and Centrifugation

Abstract

Abstract. 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.

Male gonadal function, prolactin secretion and lactotroph population in an experimental model of cirrhosis

“…Circulating testosterone and estradiol levels were determined by radioimmunoassay using solid phase DPC-Medlab kits (Los Angeles, CA, USA) previously adapted for determination in rats (13,14). The sensitivity of the testosterone assay was 10.0 ng/mL, and intra-assay and inter-assay coefficients <8%.…”