Abstract
Growth hormone (GH) exists as a family of molecular weight (MW) variants with different biological activities and whose response patterns to exercise are poorly understood. Whereas the pulsatile release of GH is known to be sexually dimorphic, no data are available that directly compare GH MW variant exercise responses in men and women. Such information may be important in understanding sex-related differences in exercise and metabolic adaptations. PURPOSE: To compare GH MW variant responses to acute resistance exercise in men and women. METHODS: 10 men and 10 women performed an acute exercise test (AET; 6 sets of 10 RM squats), and had blood drawn pre, mid, and post (0, +15, and +30 min post) of the AET. Serum samples were fractionated using high pressure liquid chromatography into 3 MW pools (A: >60 kDa; B: 30-60 kDa; C: <30 kDa) which correspond to GH oligomers, GH dimers and GH monomers, respectively. GH concentrations were determined using a commercially-available immunoassay. Data were analyzed with repeated measures ANOVA. RESULTS: Across all time points and sex, Fraction C (GH monomer) was the highest MW variant collected (C: 14.3±1.8 > A: 9.6±1.7 > B: 5.2±0.7 ng; p<0.05). Interactions with fraction, time, and sex (p<0.01) indicated that women experienced GH increases in all 3 MW variants examined from pre to mid exercise (A: pre: 7.7±7.1 vs mid: 14.9±12.4; B: pre: 4.1±3.1 vs. mid: 6.8±5.3; C: pre: 8.9±7.2 vs. mid: 19.7±15.8), while men did not increase until post-exercise (A: pre: 2.1±2.5 vs. +15 post: 11.0±8.5; B: pre: 0.9±1.1 vs. post: 5.7±3.7; C: pre: 2.7±2.3 vs. post: 17.1±8.9). In recovery, men maintained elevations of the B (pre: 0.9±1.1 vs. +30 post: 5.5±3.9) and C fractions (pre: 2.7±2.3 vs. +30 post: 14.9±10.7) for at least 30 min (p<0.05), while all fractions in women returned to baseline within 15 min (p>0.05). CONCLUSIONS: Women experienced earlier increases in all GH variants during exercise whereas men demonstrated more sustained increases in GH monomers and dimers in the post-exercise milieu. Temporal GH molecular variant responses to exercise differ in men and women.
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