Freund's complete adjuvant induces ornithine decarboxylase activity in the central nervous system of male rats and triggers the release of pituitary hormones.

In male rats, inoculation of Freund's complete adjuvant (FCA, 0.5 mg/rat of Mycobacterium butyricum in paraffin oil) induced high levels of ornithine decarboxylase (ODC) in the hypothalamus and pituitary gland (285% and 245% of controls, respectively, within 12 h to 2 days). ODC activity also was altered in the cerebellum and left neocortex, but not in the right neocortex. This activity reflected a dynamic equilibrium which is influenced by ODC synthesis, degradation, activation, etc. The circadian rhythms of pituitary ODC activity and plasma prolactin level, 3-4 days after FCA, showed that enhancement of enzymatic activity during the dark phase correlated with a marked release of prolactin (Prl). During this early period after FCA, changes in plasma levels of other pituitary hormones were not significant or were less important. Pretreatment with bromocriptine microcapsules inhibited both basal and FCA-induced pituitary ODC activity, as well as Prl secretion. Further, significant increases in plasma luteinizing hormone and adrenocorticotropic hormone were noted from days 4 and 8, respectively, and onwards. Finally, a phase of reduced corticosterone secretion occurred during the latency period. This study shows that FCA influences central nervous system pathways and supports the idea that endogenous Prl is involved in some early events which lead to the development of adjuvant arthritis.