Table 2.

Changes in plasma cortisol, GH secretion, and plasma TSH during bed rest and exercise studies at different times of 24-h cycle

Rest Exercise P Level
Cortisol
 Baseline level, μg/dl
  Afternoon11.4 ± 1.4 7.6 ± 0.7 NS
  Night 3.3 ± 0.8 3.2 ± 0.7NS
  Early morning 7.1 ± 1.810.0 ± 2.7 NS
 3-h Area above (+) or below (−) baseline, μg ⋅ min ⋅ dl−1
  Afternoon −585 ± 185 +365 ± 242<0.03
  Night +356 ± 115 +502 ± 273NS
  Early morning +512 ± 251+449 ± 304 NS
GH Secretion
 During baseline period, μg
  Afternoon10 ± 4 9 ± 4 NS
  Night69 ± 44 118 ± 65 NS
  Early morning 7 ± 1 11 ± 6 NS
 During next 3 h, μg
  Afternoon 42 ± 10233 ± 48 <0.005
  Night 45 ± 29228 ± 48 <0.06
  Early morning32 ± 8 189 ± 60 <0.05
TSH
 Baseline level, μU/ml
  Afternoon3.1 ± 0.5 2.8 ± 0.4 NS
  Night* 4.1 ± 0.7 3.8 ± 0.7NS
  Early morning 4.0 ± 0.43.2 ± 0.2 NS
 3-h Area above (+) or below (−) baseline, % of basal ⋅ min
  Afternoon−1,203 ± 303 +5,115 ± 1,462 <0.01
  Night +2,971 ± 882 +15,801 ± 2,289<0.0001
  Early morning −3,575 ± 724+2,504 ± 1,655 <0.003
  • * Measured by a different assay than afternoon or early morning levels. Data are means ± SE. GH, growth hormone; TSH, thyrotropin-stimulating hormone.