A CIRCADIAN VARIATION EXISTS FOR SOLUBLE LEVELS OF INTERCELLULAR-ADHESION MOLECULE-1 AND E-SELECTIN IN HEALTHY-VOLUNTEERS

1. We have previously shown a circadian variation in leucocyte activat ion and endothelial function which may explain why some inflammatory a nd vascular diseases show a circadian variation in disease activity/oc currence. 2. We have investigated the circadian variation of two solub le cell adhesion molecules, intercellular adhesion molecule-1 and E-se lectin, in 10 healthy volunteers. Soluble intercellular adhesion molec ule-1 is released from both activated leucocytes and endothelial cells while soluble E-selectin is released only from activated endothelium. 3. Results show a circadian variation exists for both soluble interce llular adhesion molecule-1 and E-selectin (both P < 0.0001, analysis o f variance) with a peak activity at 12:00 h for both measures and a mi nimum activity at 04:00 h for intercellular adhesion molecule-1 and 00 :00 h for E-selectin. 4. These results demonstrate the existence of a diurnal variation in cell adhesion molecules, providing evidence in su pport of a diurnal pattern in endothelial and leucocyte activation. An alteration in this biological rhythm may help to explain the diurnal variation in disease activity in certain inflammatory and vascular dis ease states. Furthermore, it stresses the importance of sample time po int standardization in clinical studies.