Abstract
Chromogranin A, CgA, is co-released with catecholamines by exocytosis from the adrenal medulla and sympathetic nerve endings. It has been reported that CgA reflects the sympathoadrenal medullary activity, and the secretion of CgA is specifically enhanced by psychological stress. Salivary CgA is used as a marker of psychological stress, because the secretion of CgA is higher than that of cortisol in the saliva, and saliva samples can be collected noninvasively. However, it is unclear what types of stress increase its secretion. In the present study, to clarify the relationship between the appearance of pain and the secretion of CgA, the changes in the secretion of salivary CgA under pain-related stress were investigated using both acute and chronic inflammatory pain model rats. In the acute pain study, rats were injected with 4% formaldehyde subcutaneously into the plantar region of the right foot. One hour later, saliva and blood samples were obtained. In the chronic pain study, rats were injected with complete Freund's adjuvant into the same site, and samples were obtained one week later. The levels of plasma corticosterone and salivary CgA, and the salivary α-amylase activity were also measured. The levels of corticosterone and α-amylase activity increased in both pain model rats. However, the salivary CgA level was significantly increased in the chronic inflammatory pain model rats, while it did not change in the acute pain model. The secretion of salivary CgA differed from that of other stress markers even under the same stress conditions. Although the salivary CgA level is used as a parameter of stress, it is necessary to investigate the differences in salivary CgA secretion under various stressful environments.
