Influence of estrogen cycle on temporomandibular joint synovial membrane in rat with deviated mandible

Temporomandibular disorders (TMD) are knownto be more prevalent and severe in women than inmen, especially in those who are in their reproductiveage. In those patients reproductive hormonesmay play a vital role in the host adaptive capacity ofthe temporomandibular joint (TMJ). In order toclarify the relationship between TMD prevalenceand estrogen cycle, a mandible deviated animalmodel was carried out, and the expression ofinducible nitric oxide synthase (iNOS), an essentialenzyme in the pathogenesis of inflammatoryarthritis, was investigated in the rat’s synovial tissue.An appliance was attached to the rat’sincisors to produce a lateral deviation of themandible during the metestrus phase, and theanimals were sacrificed in the proestrus andestrus phase, when the estrogen was at the highestand lowest level, respectively. Immunostainingwas then performed for 2 consecutive estrouscycles to demonstrate iNOS expression in thesynovial membrane of the TMJ. The immunoreactivityfor iNOS was more intense in the synovialmembrane on the contralateral side in theproestrus phase (estrogen peak phase). Theseobservations suggest that iNOS expression in thesynovial membrane with mandibular deviationmay be exacerbated in the presence of estrogen.