Inhibitory effect of somatostatin on the mechanosensitivity of articular afferents in normal and inflamed knee joints of the rat

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Abstract
N, movements of the joint and i.a. injections of KCl (10−4 mol, 0.1 ml) close to the joint. Somatostatin (10−4 mol, 0.2 ml) caused no direct response of the units. In normal joints, somatostatin did not change the discharges evoked by non-noxious movements but decreased the responses to noxious movements significantly to about 63% of the responses before the application. In acutely inflamed joints, somatostatin reduced the discharges of non-noxious and of noxious movements to about 55% and 52%, respectively. Injections of somatostatin with lower concentrations (10−6 mol, 10−8 mol) i.a. close to inflamed joints revealed shorter and less pronounced reductions of the responses to noxious movements. In a proportion of afferents, substance P (10−4 mol) and bradykinin (10−4 mol) were able to increase these responses again. These data indicate that the mechanosensitivity of articular afferents in normal joints may also be regulated by several neuropeptides based on a balance of pro-inflammatory peptides such as substance P, and anti-inflammatory peptides such as somatostatin. In an inflamed joint, pro-inflammatory peptides seem to predominate resulting in a sensitization of the peripheral nerve fibers. In this case, an application of somatostatin or its analogues could be used clinically to compensate this effect....