ABSTRACT
OBJECTIVES: Previously, we found in cultures of primary neurons and in animals that sensitized primary neurons can be desensitized by treatment with e.g. beta-adrenergic receptor agonists. We now tested whether also in human sensitization such as UVB-radiation induced sunburn-like hyperalgesia can be reduced by intradermal injection of the beta-adrenergic receptor agonist terbutaline. METHODS: In our prospective randomized study, 17 participants received an individual UVB dose to cause a defined local sunburn-like erythema at four locations, two on each forearm. Twenty-four hours later, the sensitized four areas were injected intradermally with terbutaline pH 4.3, terbutaline pH 7.0, saline pH 4.3 or saline pH 7.0, respectively. Pain thresholds were examined before and after induction of UVB-sensitization, and 15, 30 and 60 min after injection of the respective solution. Mechanical pain thresholds of the skin and of deeper tissues were determined by pinprick and pressure algometer measurements, respectively. RESULTS: UVB-irradiation decreased mechanical pain thresholds for pinprick and pressure algometer measurements demonstrating a successful sunburn-like sensitization. Intradermal injection of terbutaline pH 7.0 into the sensitized skin reduced the sensitization for all measured timepoints as determined by pinprick measurements. Pinprick measurements of sensitization were not reduced by injection of terbutaline pH 4.3, saline solution pH 7.0 or saline solution pH 4.3. Also, sensitization of deeper tissue nociceptors were not altered by any of the injections as measured with the pressure algometer. CONCLUSIONS: Similar to our cellular observations, also in humans beta-adrenergic agonists such as terbutaline can reduce the sensitization of primary neurons in the skin. SIGNIFICANCE: We previously showed in model systems that beta-adrenergic stimulation can not only sensitize but also desensitize nociceptors. Our study shows that also in humans beta-adrenergic agonists desensitize if injected into UVB-sensitized skin. This indicates an analgesic activity of adrenergic agonists in addition to their vasoconstrictory function.