Prostaglandin biosynthesis from arachidonic acid by skin microsomal fraction preparation was enhanced by UV-irradiation at wavelengths of 254 and 360 nm. In the presence of 8-methoxy psoralen (8 MOP) and coal tar, prostaglandin biosynthesis was further enhanced approximately 2-fold by UV-irradiation at 254 nm. Stimulation was less by UV-irradiation at 360 nm. 8-MOP enhanced the conversion of PGE2 into PGF2-9-ketoreductase prepared from skin high speed supernatant fractions. UV-irradiation at 254 nm and 360 nm with or without the photosensitizers had no effect on the activity of the PGE2-9-ketoreductase. These data therefore indicate that the action of UV-irradiation, 8-methoxy psoralen and coal tar on the skin may in part be due to their regulation of the biosynthesis and metabolism of prostaglandins in this tissue.

SUMMARY Oxygenation of arachidonic acid in vitro by calf skin microsomal acetone powder was enhanced by UV‐irradiation at wavelengths of 254 and 360 nm. Further enhancement of the oxygenation reaction was observed in the presence of two photosensitizing cyclic antibiotics, tetracycline and demethylchlortetracy cline. To test whether or not the oxygenation of arachidonic acid was related to the biosynthesis of prostaglandins, [I‐14C]‐arachidonic acid was incubated with calf skin acetone powder in the presence of UV‐irradiation and the cyclic antibiotics. Prostaglandin biosynthesis from arachidonic acid by the calf skin microsomal acetone powder was enhanced after exposure to UV‐irradiation at 254 nm and moderately at 360 nm. Incubation in the presence of demethylchlortetracycline (0.2 mM) increased prostaglandin biosynthesis approximately 95% over control by UV‐irradiation at 254 nm. No significant stimulation of prostaglandin biosynthesis was observed at 360 nm. Non‐photosensitizing antibiotics had no effect either on the oxygenation of arachidonic acid or on the biosynthesis of prostaglandin with or without UV‐irradiation. Since a previous report from our laboratory had demonstrated that other photosensitizers also stimulate prostaglandin biosynthesis in vitro after exposure to UV‐irradiation and since these photosensitizing cyclic antibiotics have been associated with cutaneous inflammatory reactions such as erythema, it is reasonable to suggest from these data that the inflammatory reactions associated with these photoreactive antibiotics may in part, be via the biosynthesis and release of the prostaglandins which are known to produce cutaneous inflammatory reactions.