The role of lactate in the exercise-induced human growth hormone response: evidence from McArdle disease.
OBJECTIVE
Increased blood lactate concentration has been suggested as a primary stimulus for the exercise-induced growth hormone response (EIGR). Patients with McArdle disease are unable to produce lactate in response to exercise and thus offer a unique model to assess the role of lactate in the EIGR. Accordingly, McArdle's patients were exercised to test the hypothesis that lactate is a major stimulus of the EIGR.


METHODS
11 patients with McArdle disease (3 male, 8 female; age: 35.5 (SD 13.9) years, height: 166 (8) cm, body mass: 75.2 (13.1) kg) were recruited for the study. The patients walked initially at 0.42 m/s, increasing by 0.14 m/s per 3 min stage. Exercise was terminated when participants completed 3 minutes at 1.80 m/s or when a Borg CR10 pain scale rating of "4" was reached. Stages were separated by 60 s for capillary blood sampling for analysis of hGH and blood lactate concentration.


RESULTS
McArdle's patients' blood lactate levels remained at resting levels (0.3-1.2 mmol/l) as exercise intensity increased. Nine out of 11 participants failed to demonstrate an EIGR obtaining hGH values below the clinical definition of a response (>3 microg/l).


CONCLUSIONS
The absence of an EIGR in nine out of 11 participants suggests that lactate could play a major role in the EIGR in humans.
Godfrey
R J
RJ
Centre for Sports Medicine and Human Performance, School of Sport and Education, Brunel University, Uxbridge, UB8 3PH, United Kingdom. richard.godfrey@brunel.ac.uk
Whyte
G P
GP
Buckley
J
J
Quinlivan
R
R
D000293:Adolescent; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006012:Glycogen Storage Disease Type V / Q000097:blood*; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D016138:Walking; D055815:Young Adult
D019382:Human Growth Hormone; D019344:Lactic Acid