Effects of melatonin on 24-h rhythms of neuroendocrine and immune changes
in Freunds adjuvant-induced arthritis
by Ana I. Esquifino & Daniel P. Cardinali
melatonin, ornithine descarboxylase, acethylcholine, noradrenaline
Old rats had significantly lower
values of the amplitude of pineal melatonin content at any time
point studied. Complete Freunds adjuvant administration
reduced the amplitude of melatonin rhythm. On day 18 of arthritis
development, decreased pineal melatonin contents were also seen
in young rats. On day 18, a global depressive effect of arthritis
development on pineal melatonin content was found. However,
prolactin levels increased in old as compared to young rats.
Freunds adjuvant administration brought about changes
in the secretory pattern of prolactin in young and old animals
that are opposite to those described for melatonin. Cell proliferation
as assessed by ornithine decarboxylase activity exhibited significant
24-h variations with maximal activity of the enzyme during daily
hours, acrophases varying from 13:15 to 16:52 h (lymph nodes).
The mesor and amplitude of ornithine decarboxylase activity
were lowest in old rats. Melatonin (100 µg) augmented amplitude
of daily rhythm in submaxillary lymph node ornithine decarboxylase activity significantly. These data
indicate that melatonin and prolactin change differentially
during arthritis development in young and old animals, perhaps
indicating opposite effects in the induction and maintenance
of adjuvant-arthritis. The changes are compatible with the values
of ornithine descarboxylase activity.
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