Immunofunctional vs immunoreactive growth hormone responses after resistance exercise in men and women

Immunoassays for growth hormone (GH) may yield variable concentrations for the same sample due to the molecular heterogeneity of growth hormone and ep itope specificity of their antibodies. Strasburger et al. developed an "imm unofunctional" assay that only detects those GH molecules possessing intact sites 1 and 2, which are necessary for inducing receptor dimerization and subsequent signal transduction. This study compared the immunoreactive (IR) vs immunofunctional (IF) GH concentrations before and after acute resistan ce exercise (i.e. six sets of 10 repetition maximum squats separated by 2 m in rest periods) in 8 men and 6 women. IF concentrations were determined by an ELISA(DSL) and IR GH by a monoclonal IRMA(Nichols). Both men (M) and wo men (W) demonstrated similar increases for IR (M: 1.47 vs 25.0 ng/ml; W: 4. 0 vs 25.4 ng/ml) and IF (M: 0.55 vs 11.66 ng/ml; W: 1.94 vs 10.41 ng/ml) GH following exercise. Post-exercise IF GH was significantly less than IR GH for both M and W. The ratio of IR/IF after exercise was similar to 2 and si milar for both M and W. In summary, dynamic exercise elicited a similar ris e in M and W for immunofunctionally active GH molecules, but the magnitude is lower than when detected with another conventional assay. (C) 2000 Harco urt Publishers Ltd.