DIURNAL RHYTHMS IN ORNITHINE DECARBOXYLASE ACTIVITY AND NOREPINEPHRINE AND ACETYLCHOLINE SYNTHESIS IN SUBMAXILLARY LYMPH-NODES AND SPLEEN OF YOUNG AND AGED RATS DURING FREUNDS ADJUVANT-INDUCED ARTHRITIS

Aging has been associated with attenuation of amplitude and changes in period of many circadian rhythms. The present study was carried out t o examine, in young (50 days old) and old (18 months old) rats, whethe r 24-h rhythms of cell proliferation (as assessed by measuring ornithi ne decarboxylase activity) and of presynaptic adrenergic and cholinerg ic markers change in lymph nodes and spleen during Freund's adjuvant-i nduced arthritis. Groups of young and old Sprague-Dawley rats were stu died the day before, and on days 6, 12 and 18 after Freund's adjuvant injection. On day 16 after adjuvant injection, inflammation of hind pa ws, mainly in the ankle joints, was less marked in old than in young r ats. Lymph node and splenic ornithine decarboxylase activity exhibited significant 24-h variations with maximal activity during daily hours. Before treatment, enzyme activity values were significantly lower in old rats in both tissues examined. During the immune reaction, lymph n ode and splenic ornithine decarboxylase augmented 8-10-fold, with prog ressively smaller amplitude of daily variations as arthritis developed . In every case, mesor and amplitude of ornithine decarboxylase activi ty were lowest in old rats. Submaxillary lymph node and splenic tyrosi ne hydroxylase activity attained maximal values at night. At every tim e interval after mycobacterium adjuvant injection, amplitude and mesor of tyrosine hydroxylase activity rhythm were lowest in old rats. A ma ximum in submaxillary lymph node H-3-acetylcholine synthesis occurred at the afternoon. On day 6 and 12 after Freund's adjuvant injection, l ymph node H-3-acetylcholine synthesis was significantly smaller in old rats. Day-night differences in submaxillary lymph node or splenic orn ithine decarboxylase and tyrosine hydroxylase activities, or in submax illary lymph node H-3-acetylcholine synthesis, of rats treated with th e adjuvant's vehicle, did not differ significantly from those seen in untreated controls. The results are compatible with an age-dependent d ecline of immune-mediated inflammatory responses. The activity of the central circadian oscillator, driven to the organs in part via the aut onomic nervous system, seems also to deteriorate during aging. (C) 199 8 Elsevier Science B.V.