1 Abdominal skin of 25 human subjects was irradiated with three times its minimal erythema dose of ultraviolet (u.v.) B radiation. Erythema appeared after 2 h, was of moderate degree at 6 h, and maximal at 24 and 48 h.
2 Exudate was recovered by a suction bulla technique from the subject's normal and erythematous skin either at 6, 24 or 48 h after irradiation.
3 Superfusion cascade bioassay of exudate showed increased prostaglandin (PG)-like activity, measured in PGE2 equivalents, at 6 and 24 h after irradiation. The maximum rise was at 24 h, coinciding with the peak of the erythema. However, prostaglandin concentrations were not significantly above that of controls at 48 h when the erythema was still maximal.
4 Radioimmunoassay for PGF2α yielded values in close agreement with the bioassay results.
5 Gel partition chromatography, after conversion of extracted residues from the exudate to 14C methyl esters, showed increased incorporation of radioactivity at 6 h, maximal at 24 h. At 48 h there was no significant difference from control levels. The major increased activity, maximal at 24 h, co-chromatographed with arachidonic acid and PGE2 and PGF2α. The materials provisionally identified as the latter three compounds also co-chromatographed with their corresponding methyl esters on t.l.c., although the arachidonic acid-like material contained at least two peaks. No evidence was obtained for the 1 or 3 series of PGs. On g.l.c. the material obtained from the PGF2α zone co-chromatographed with authentic PGF2α as the methyl ester trimethylsilyl ether. The PGE2 zone converted to methyl ester n-butyloxime trimethylsilyl ether also co-chromatographed with authentic PGE2, but with some distinct shouldering.
6 The evidence presented provides support for the presence of increased amounts of arachidonic acid, PGE2 and PGF2α-like compounds during the first 24 h of u.v.B erythema, with concordance of the erythema and prostaglandin levels. At 48 h this relationship could not be demonstrated.