The possible occurrence of endogenous anti-inflammatory substances in the blood of injured rats.

1 Using the carrageenin rat paw oedema test as an assay, an attempt has been made to confirm the presence of anti-inflammatory activity in the blood of rats with a chronic inflammatory lesion induced by a polyester sponge, and to relate such activity to the systemic anti-inflammatory effect exerted in situ by the lesion. In addition, plasma from rats given acetic acid intraperitoneally has been examined for anti-inflammatory properties. 2 The activity of serum obtained from sponge-bearing adrenalectomized Wistar rats did not differ significantly from that obtained from animals without implants. Furthermore, implanted sponges exerted no systemic anti-inflammatory effect. 3 Similar experiments were performed in sponge-bearing adrenalectomized Sprague-Dawley rats, plasma instead of serum being examined for anti-inflammatory activity. The plasma removed from such animals possessed no anti-inflammatory activity, whilst implanted sponges exerted a small, yet significant, systemic inhibitory effect. 4 When the irritancy of sponge implants was augmented with croton oil, more marked systemic anti-inflammatory effects were observed. However, the plasma obtained from rats injured in this manner exerted no anti-inflammatory effect. 5 No anti-inflammatory activity could be detected in plasma samples obtained from rats treated with doses of acetic acid capable of producing pronounced systemic anti-inflammatory effects. 6 It was concluded that the induction of these inflammatory lesions in rats does not appear to lead to a detectable release of endogenous anti-inflammatory substances into the circulation.