Background and Goal of Study: Several evidences have showed that patients with Fibromyalgia Syndrome (FMS) accompanied with decreased growth hormone (GH) or/and thyroid stimulation hormone (TSH). However, the mechanisms of decreasing hormone in patients with FMS and which comes first; decreased hormones or onset of FMS are unclear. The goal of this study is to clarify the relationship between experimental pain in normal volunteers and GH/TSH secretion after the stimulation.
Materials and Methods: After getting approval of ethical committee of Osaka University, we got the written informed consents from the 21 volunteers. The 6 times 1min continuous experimental heat stimulation with 1 min rest applied to each participants using Pathway (Medoc Co Ltd; Israel). The applied temperature was decided the pre-trial to the amount of stimuli which the participants couldn’t endure any more or over 80 of visual analogue scale. Blood samples are collected 5 times; before stimulation, just after, 15min after, 30 min after, and 50 min after the series of stimulation. Serum GH and TSH were determined by enzyme-linked immunosorbent assay (ELISA) using commercially available kits. Assay specific for human GH was purchased from R & D system and for TSH was purchased from Cayman Chemical Company. The interassay coefficient of variation of GH and TSH assays were 6.9% and 4.6%, respectively. The analytical sensitivities of GH and TSH assays were 0.64 pg/ml and 0.2mIU/L, respectively. The paired t-test was used for statistical analysis of the data by using JMP12.0 and 5% level of significance was considered.    
Results and Discussion: The paired t-test revealed that serum GH level decreased in just after, 15min after, 30min after, and 60min after the stimulation compared to pre-stimulation(p<0.01, 0.005, 0.005, 0.5, respectively)and in 15min after the stimulation compared to just after stimulation ‘p<0.05). TSH level decreased in just after, 15min after, 30min after, and 60min after the stimulation compared to pre-stimulation(p<0.05, 0.005, 0.001, 0.005, respectively)and in 30min after the stimulation compared to just after stimulation ‘p<0.05). These results indicated that intermittent 6min stimulation could affect the pituitary function and changes in the brain prolonged at least 60min. The observed changes of GH/TSH decreasing in the patients with FMS might not be the cause but the results of suffering from severe pain for a long time. 
Conclusion(s): Even though the participants were healthy subjects, experimental heat pain could significantly affect the serum GH/TSH level and these changes could prolong at least until 60 min after the stimulation.
Acknowledgements: This work was funded by ImPACT Program of Council for Science,
Technology and Innovation (Cabinet Office, Government of Japan).

Pituitary hormone secretion changes after experimental pain stimulation. Are GH/TSH changes in patients with Fibromyalgia syndrome in a situation of chicken or egg?