Salivary 3-methoxy-4-hydroxyphenylglycol increases after awakening in healthy young adults.

Levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) may reflect central noradrenergic activity. In this study, we investigated salivary MHPG changes after awakening, and explored their relationships with cortisol and peripheral autonomic activity. The participants were 25 college students. Saliva samples were collected on awakening and 30 min after awakening to determine MHPG and cortisol. Ambulatory electrocardiograms were obtained to assess heart rate, cardiac sympathetic index (CSI), and cardiac vagal index (CVI) before and after awakening. MHPG levels increased significantly during the first 30 min after awakening. Similarly, cortisol, heart rate, and CSI increased during the 30 min after awakening, but changes in MHPG did not correlate with changes in cortisol, heart rate, CSI, and CVI during that period. This study demonstrated that salivary MHPG levels increase after awakening, in common with cortisol, heart rate, and cardiac sympathetic activity.

Short sleeping time and psychobiological responses to acute stress.

The aim of this study was to examine the association between self-reported sleeping time and psychobiological stress responses [3-Methoxy-4-hydroxyphenylglycol (MHPG) and Secretory immunoglobulin A (IgA), perceived stress responses]. Thirty seven healthy men and women were recruited, and participants were divided according to the habitual number of hours of sleep as follows: adequate sleepers (AS) (6-8h sleep per night regularly) (N=22) and short sleepers (SS) (less than 5h sleep per night regularly) (N=15). Salivary MHPG, s-IgA and perceived stress were measured at baseline, immediately after task and recovery period. An increase in free-MHPG during the task period was observed in AS although free-MHPG increased only after the task period in SS. The level of s-IgA in both groups significantly increased during the task period, and quickly returned to a basal level during the recovery period. The results show that less than 5h of sleep was associated with different responsiveness to the Stroop color word conflict task compared to sufficient sleep, especially in the NA system.