ABSTRACT
<p><b>AIM</b>To determine the exact roles of prolactin (PRL) in the pathogenesis of rheumatoid arthritis (RA) and supply experimental basis for clinical treatment of RA, and to investigate the expression of matrix metalloproteinase-9 (MMP-9) in the synovium of adjuvant arthritis rats.</p><p><b>METHODS</b>Forty rats were divided into four groups (n = 10): (1) Normal control group (group A); (2) Adjuvant arthritis control group (group B); (3) Hyperprolactinemic adjuvant arthritis group (group C); (4) Hypoprolactinemic adjuvant arthritis group (group D). The content of PRL in the serum was detected by radio-immunoassay method. The activity of MMP-9 was analyzed by gelatin zymography. The alteration of MMP-9 immunoreactivity were investigated by means of immunohistochemistry in the synovium of all groups. The expressions of MMP-9 were investigated by Western blot in the synovium of all groups.</p><p><b>RESULTS</b>Compared with group A, the activity and expression of MMP-9 of group B in the synovium were highly increased. The activity and expression of MMP-9 in the synovium were the most distinctive in group C. Compared with group B, the activity and expression of MMP-9 in the synovium were decreased in group D, but still higher than group A.</p><p><b>CONCLUSION</b>The present results indicated that PRL might involved in the pathogenesis of RA by regulating the secretion of MMP-9 in the synovium.</p>