CIRCADIAN-RHYTHM IN EXPERIMENTAL GRANULOMATOUS INFLAMMATION IS MODULATED BY MELATONIN

Biological rhythms are detected in a variety of physiological and path ological conditions in man and animals, such as rheumatoid arthritis a nd asthma. Here we describe a circadian rhythm in experimental infecti ous and non-infectious granuloma, After 30 days of BCG (Bacillus Calme tte-Guerin) or nystatin inoculation in the left hind foot of C57B1/6 m ice, there is an oscillation with a period of approximately 24 hr in t he variation of paw thickness, indicating a circadian rhythm. The acro phase occurred during the light phase, between 9:00 and 13:00 hr, whil e the nadir occurred in the dark phase, between 21:00 and 01:00 hr. Th e vascular permeability around the granulomatous lesions was higher at 12:00 hr than at 24:00 hr. This is in agreement with the observation that the thickness of a paw with granulomatous lesion is larger during the light phase,This rhythmic variation was eliminated by either pine alectomy or superior cervical ganglionectomy, which greatly reduce mel atonin levels in the blood. Nocturnal replacement of melatonin in pine alectomized mice led to the re-establishment of the circadian rhythm. Thus, the rhythm of the granulomatous lesion is due to the rhythmic me latonin release by the pineal gland. This approach opens new questions regarding the modulation of chronic inflammation in inflammatory dise ases that present rhythmic symptoms throughout the day.