Resiniferatoxin (RTX)

  • analogue of capsaicin, the stuff in chili peppers (genus Capsicum) that makes them so friggin' hot
  • present in high concentrations in the sap of the resin spurge (Euphorbia resinifera), a plant that looks very much like a cactus that is native to Morocco and the Canary Islands
  • along with capsaicin, is able to excite and then desensitize type C afferent fibres (pain-transmitting pathways to the brain and spinal cord) by activating a particular type of calcium channel that is expressed selectively in these fibres
    • the initial excitation of these fibres is responsible for the burning sensation experienced with eating chili peppers and getting sprayed with pepper spray
    • by desensitizing the fibres, the transmission of pain is disrupted, producing an analgesic (painkilling) effect
    • RTX is several thousands times more potent in desensitizing the fibres, making it a potential powerful analgesic agent (drugs based on RTX are currently in development) since it can be given in small enough doses that the initial excitation (and pain) is negligible
  • effective means of increasing bladder capacity in individuals afflicted with neurogenic detrusor overactivity (NDO) of spinal origin
    • NDO is a condition featuring involuntary contractions of the detrusor muscle (the muscular coat of the bladder) while the bladder is filling with pee, causing you to feel like you have to pee a lot and piss yourself because you can't hold it
    • the desensitization of type C fibres that innervate the bladder depresses the activity of the muscle so that it doesn't contract as often
Silva C et al. Urodynamic effect of intravesical resiniferatoxin in patients with neurogenic detrusor overactivity of spinal origin: results of a double-blind randomized placebo-controlled trial. Eur Urol. 2005 Oct;48(4):650-5.

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