Peripheral application of cyclo-somatostatin, a somatostatin antagonist, increases the mechanosensitivity of rat knee joint afferents.

Recently it has been shown that neuropeptides may be involved in the regulation of the mechanosensitivity of fine afferent nerve fibres. Somatostatin seems to provide a tonic inhibition of the sensitivity of sensory endings in normal tissue. In the present study cyclo-somatostatin, a somatostatin antagonist, was used to test this hypothesis. In a normal joint, 50% (8/16) of the examined primary afferents significantly increased their responses to noxious joint movements after the cyclo-somatostatin application. In an acutely inflamed joint, however, only 9% (1/11) of the nerve fibres significantly increased the response to noxious movements. These data further support the hypothesis that the mechanosensitivity of articular afferents in a normal joint is also regulated by a balance of pro-inflammatory peptides and anti-inflammatory peptides such as somatostatin. In an inflamed joint, pro-inflammatory peptides predominate and together with other mediators, they may be involved in the sensitization of the peripheral nerve fibres.