Estrogen Amplifies Pain Responses to Uterine Cervical Distension in Rats by Altering Transient Receptor Potential-1 Function

Department of Anesthesiology, Wake Forest University, Winston-Salem, North Carolina, United States
Anesthesia and analgesia (Impact Factor: 3.47). 06/2007; 104(5):1246-50, tables of contents. DOI: 10.1213/01.ane.0000263270.39480.a2
Source: PubMed


Estrogen sensitizes responses to painful stimuli, but its contribution to acute and chronic pain from the uterine cervix is unknown. Previous studies link the excitatory transient receptor potiential-1 channel (TRPV-1) to sensitization in viscera, and show that estrogen increases TRPV-1 expression in afferents from the uterine cervix. Here, we tested whether estrogen enhanced responses to uterine cervical distension in rats, and whether this involved TRPV-1 channels.
Ovariectomized rats, with or without estrogen replacement, were anesthetized and hypogastric nerve and abdominal muscle contraction reflex responses to graded uterine cervical distension were recorded. Single unit hypogastric nerve fiber firing was measured before and after acute treatment with the TRPV-1 antagonist, capsaizepine, or vehicle.
Abdominal muscle contraction reflex responses to uterine cervical distension were enhanced in estrogen-treated rats. Hypogastric afferent responses to cervical distension were reduced by capsaizepine in estrogen-treated animals, but were unaffected in ovariectomized animals without estrogen replacement.
These data suggest that the TRPV-1 channel is unimportant for normal mechanosensation in the cervix in the absence of estrogen, since capsaizepine failed to reduce responses to uterine cervical distension in rats without estrogen replacement. In contrast, TRPV-1 function is important for estrogen-induced sensitization. These data raise the possibility that acute and chronic pain coming from the cervix, such as labor or cancer, may be enhanced by estrogen and might be reduced by antagonists of TRPV-1.

    • "Also, more than 323 75 % of C-fiber neuronal bodies expressing 324 TRPV1 co-express estrogen receptor α, 325 suggesting a regulatory role for estrogen. TRPV1 326 channel expressing fibers in ovarectomized rats 327 are activated only in the case of hormonal substi- 328 tution therapy (Yan et al. 2007). "
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    • "The gender association for females and capsaicin response is a well-known finding in adults.5,11,12,13,14,15 Mechanistically, estrogen hormone is suggested as a link24 as it experimentally enhances the capsaicin sensing cough receptor, transient receptor potential vanilloid 1 (TRPV1).25,26 Capsaicin cough sensitivity is proven to be up-regulated among females after puberty.27 "
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