Dependence of cytokine levels on the sex of experimental animals: a pilot study on the effect of oestrogen in the temporomandibular joint synovial tissues

The aim of this study was to evaluate the effects of 17β-oestradiol (E2) on cartilage thickness and cytokine levels in the temporomandibular joint (TMJ). Thirty rats (15 female, 15 male) were orchidectomized (ORX), ovariectomized (OVX), or sham-operated. After 21 days, animals were assigned to six groups: (1) sham-ORX; (2) ORX; (3) ORX+E2; (4) sham-OVX; (5) OVX; and (6) OVX+E2. Treatments were administered daily for 21 days. The thickness of cartilage layers (fibrous, proliferative, maturation, and hypertrophic) and cytokine levels (interleukins IL-1α, IL-1β, IL-6, and tumour necrosis factor alpha (TNF-α)) were measured by histomorphometry and ELISA, respectively. Kruskal–Wallis/Dunn's tests were used (alpha = 5%). Sham-ORX showed thicker layers than ORX+E2, but not thicker than ORX. All layers, except the hypertrophic layer, were thicker in sham-OVX than OVX or OVX+E2. Although IL-1β levels were higher in castrated animals, E2 did not affect the level of this cytokine. IL-1α levels were higher in both ORX (P = 0.0010) and ORX+E2 (P = 0.0053) than in sham-ORX. However, E2 decreased IL-1α levels in OVX (P = 0.0129). When compared to sham-ORX/OVX, IL-6 levels were not affected by E2 in males but were reduced in OVX (P = 0.0079) and increased in OVX+E2 (P = 0.0434). Levels of TNF-α were reduced by E2 in both ORX+E2 and OVX+E2. E2 treatment caused gender- and layer-dependent changes in the cartilage. Castration increased all cytokine levels, except for IL-6, without respect to gender.