Bromocriptine Microcapsules Inhibit Ornithine Decarboxylase Activity Induced by Freund's Complete Adjuvant in Lymphoid Tissues of Male Rats

Abstract

Arthritis is produced in male rats within 9-10 days after a single injection of Freund''s complete adjuvant (FCA) at the base of the tail. WHen bromocriptine, a dopaminomimetic that suppresses PRL secretion, was given in form of long-acting microcapsules (CBLA) 3 days before FCA, the hind limb swelling was significantly reduced by 70%. Here, we showed that plasma PRL levels were significantly elevated (by 150% over controls) during the 6-day period after FCA, particularly at night. Further, within 1-4 days after FCA inoculation, marked increases in ornithine decarboxylase (ODC) activity occurred in bone marrow, thymus, spleen, and lymph nodes (by 190%, 160%, 80% and 75% over control values, respectively). In FCA-treated rats, the circadian rhythm of thymic ODC showed that an important enhancement of activity occurred during the dark phase, which correlated with the peak of PRL secretion (between 2200-0400 h). FInally, pretreatment with CBLA significantly inhibited the indution of ODC in response to FCA in thymus, spleen, and lymph nodes (by 65%, 80%, and 45%, respectively) and inhibited it more weakly in the bone marrow. This in vivo study leaves little doubt about the existence of a PRL-dependent immunostimulatory mechanism, probably involved in the pathogenesis of adjuvant arthritis.