Background: The interaction between oxidative status markers and
biological rhythms is considered particularly important in the pathogenesis of
many diseases and more effective therapies. We aimed to determine if the salivary
secretion of myeloperoxidase exhibits diurnal variations, and if the potential
daily variability differs seasonally. Methods: The study was performed
in Poznan, Poland (52,25°N, 16,58°E) in 10 healthy male
volunteers (age median 23.5 years). Whole mixed unstimulated saliva was collected
in summer (August) and winter (December) during 36 h at 2-h intervals starting at
6 a.m. on Saturday and ending at 6 p.m. on Sunday, in the domestic setting. The
samples were analysed for myeloperoxidase (MPO) and cortisol by immunoassays. The
presence of the circadian rhythm of cortisol secretion in saliva confirmed the
rhythmicity of the volunteers. Results: For salivary MPO, significantly
higher concentrations compared to midnight and noon were observed for 4 a.m. in
both summer and winter. Using the cosinor analysis, the variations in salivary
MPO levels showed a moderate fit for the 12-h period rhythm (acrophases: in
summer 05:37/17:37, in winter 06:16/18:16), without significant differences in
the rhythm parameters in summer and winter. However, higher self-reported Global
Seasonal Score (which may predispose to seasonal affective disorder) was
associated with significantly stronger relative amplitude (R
