Neutrophil adherence in rats submitted to light-dark alternance and to constant light

A good amount of experimental data suggests the existence of a circadian control of the inflammatory process. It was shown that migration of neutrophils in chemotactic gradient, ingestion of particles, vascular permeability etc. are rhythmical circadian functions. Melatonin, the pineal hormone secreted during the darkness phase, has been shown to be involved in the control of inflammation. The present study aims to assess whether neutrophil adherence to nylon fibers exhibits circadian rhythmicity and also if its amplitude and/or chronostructure are altered in a constant light regimen. Wistar rats were submitted to either an artificial light-darkness 12/12 regimen (LD) or to constant light (LL), for 15 days. Adherence of the neutrophils in whole blood was assessed at 10:00, 16:00, 22:00, and 04:00 hrs. In LD. neutrophil adherence appears to be a rhythmic, biphasic function, with the acrophase at 10:00, a secondary peak at 22:00 and trough values in the late dark hours. Constant light induces a depression of the adherence ability by about 10%, except for the 04:00 hrs point, where the value in LL is higher than in LD. The fact that adherence and phagocytic activity do not oscillate in phase suggests that the physiological relevance of neutrophil adherence goes beyond that of a first stage of the phagocytic process.