GH responses to two consecutive bouts of neuromuscular electrical stimulation in healthy adults.
BACKGROUND
It is well established that repeated GHRH administration or repeated voluntary exercise bouts are associated with a complete blunting of GH responsiveness when the administration of the second stimulus follows the first one after a 2-h interval.


OBJECTIVE
To evaluate GH responses to neuromuscular electrical stimulation (NMES) in healthy adults.


METHODS
Six volunteers (mean age+/-s.d. 31.7+/-5.5 years) were studied before and after two consecutive bouts of NMES exercise (a series of 20 contractions at the maximum of individual tolerance, frequency: 75 Hz, pulse duration: 400 mus, on-off ratio: 6.25-20 s) administered at a 2-h interval.


RESULTS
Baseline GH levels (mean: 0.3+/-0.2 ng/ml) significantly increased after the first NMES (peak: 4.2+/-3.7 ng/ml), with a complete normalization after 120 min (0.3+/-0.3 ng/ml). The administration of the second bout of NMES of comparable characteristics also resulted in a significant GH increase (peak: 5.2+/-3.2 ng/ml), which was comparable with that observed after the previous one. GH net incremental area under the curve after the first and second bouts of NMES were not significantly different (155.1+/-148.5 and 176.9+/-123.3 ng/ml per h, P=0.785).


CONCLUSIONS
Unlike repeated pharmacological stimuli and voluntary exercise bouts, subsequent sessions of NMES administered at a 2-h interval appear to circumvent feedback mechanisms and to re-induce the GH responses, thus indicating a possible different underlying mechanism elicited by different GH-releasing stimuli.
Sartorio
A
A
Istituto Auxologico Italiano, IRCCS, Divisione Malattie Metaboliche 3 and Laboratorio Sperimentale di Ricerche Auxo-Endocrinologiche, 28921 Verbania, Italy. sartorio@auxologico.it
Jubeau
M
M
Agosti
F
F
De Col
A
A
Marazzi
N
N
Lafortuna
C L
CL
Maffiuletti
N A
NA
D000328:Adult; D004558:Electric Stimulation; D015444:Exercise / Q000502:physiology*; D025461:Feedback, Physiological / Q000502:physiology; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism; D019382:Human Growth Hormone / Q000097:blood*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology
D019382:Human Growth Hormone; D019344:Lactic Acid; D013007:Growth Hormone-Releasing Hormone; D006854:Hydrocortisone