THURSDAY, April 16 (HealthDay News) -- Hormone levels in female rats can affect the perception of pain in the temporomandibular joint (TMJ), providing a possible explanation for the higher incidence of TMJ pain in females, according to a study published online April 9 in Endocrinology.
Phillip R. Kramer, Ph.D., and Larry L. Bellinger, Ph.D., from Baylor College of Dentistry at Texas A&M Health Science Center in Dallas cycled ovariectomized rats with physiological levels of 17β-estradiol (E2) or progesterone (P4). They then injected the rats bilaterally in the TMJ with complete Freund's adjuvant at different stages of the cycle to induce inflammation.
The researchers found that when E2 levels were varied TMJ nociception increased, but less so when the adjuvant injection was given during diestrus-2 (low E2) and even less when given during proestrus (high E2). When P4 levels were varied, TMJ nociception increased when the adjuvant injection was given during proestrus (major P4 surge), estrus (low P4), and metestrus (low P4), but not during diestrus-2 (end of minor P4 surge). Changes in hormone levels did not affect the levels of several TMJ cytokines or the trigeminal ganglia calcitonin gene-related peptide, according to the study.
"The results suggest that the cyclic estrous cycle concentrations of E2 and P4 can influence complete Freund's adjuvant-induced TMJ nociception in the rat," Kramer and Bellinger conclude.
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