Delayed manifestation of ultraviolet reaction in the guinea-pig caused by anti-inflammatory drugs.

1. Exposure of depilated skin of guinea-pig to ultraviolet (u.v.) light for 20 s produces a prolonged inflammatory response.2. The erythaema becomes evident within 15-30 min after the exposure and progressively increases in intensity reaching its maximum by 4-6 hours. The erythaema persists over 24 hours.3. Increase in vascular permeability is biphasic with an early short-lived rise peaking at 0.5 h and a prolonged secondary response peaking at 9-12 h and lasting over 48 hours.4. In presence of aspirin, phenylbutazone and indomethacin, administered prior to u.v. exposure, the inflammatory reaction is partially suppressed, depending upon the dose. The drugs are ineffective in aborting or minimizing the response when given after the inflammation is established. Corticosteroids fail to influence the u.v. inflammation in this test. The significance of these findings is discussed.