Prostaglandin E1-induced sensitization of A delta moderate pressure mechanoreceptors

Prostaglandins of the E series (PGEs) have been detected in high quantities in inflamed tissues; when injected in the circulation that supplies the skin they cause inflammation and pain. Evidence of PGE sensitization of C-nociceptors (polymodals) already exists. The present work establishes that PGE1 has a wider sensitizing effect: when injected subdermally it affects mechanoreceptive elements as well. Of moderate-threshold, slow-adapting A delta mechanoreceptors isolated in the skin of the rat leg and responding to punctate stimulation, 79% were sensitized by PGE1 injections nearby (8--12 mm) as judged by their increased responses to innocuous stimulation (0.5--5 g delivered by a stylus with 0.5 mm tip diameter). Of such units, 10.5% were not sensitized and another 10.5% were inhibited or lost. Controls showed at most a small and transient increase immediately following the injection whereas the PGE1 effect lasted from between 30 min to 3 h or longer. These results are discussed in connection with mechanoreceptor sensitization by other pain-producing and irritant substances. At the receptor level, 'nociception' under abnormal conditions (e.g. inflammation) may not be solely mediated by unambiguously 'nociceptive' units; in such conditions a wider sensitization of receptive elements may be a contributing factor in hyperalgesic or hyperaesthetic phenomena.