Effects of in vitro PUVA treatment on adenylate cyclase responses of epidermis

We investigated the effect of 8-methoxypsoralen (8-MOP) plus long wave ultraviolet irradiation (PUVA) on the pig skin epidermal cyclic AMP (cAMP) system. Following PUVA treatment in vitro, pig skin squares were incubated in RPMI 1640 medium, and the cAMP accumulation by various adenylate cyclase stimulators was determined. A significant increase of the beta-adrenergic adenylate cyclase response was observed as early as 6-h following PUVA treatment; the maximal effect was reached at 24-h and lasted at least for 72-h. This augmentation effect of PUVA treatment was potentiated by increasing the 8-MOP concentration (0.5–160 μg/ml) and UVA irradiation dose (0.05–1.4 J/cm²). At higher irradiation doses (2.1–2.8 J/cm²), the beta-adrenergic augmentation effect was less marked. There were no significant differences in the adenosine-and histamine-adenylate cyclase response up to 1.4 J/cm² irradiation; however, the latter was decreased at a higher irradiation dose (2.8 J/cm²). Although UVA irradiation alone had no effect on the beta-adrenergic response, 8-MOP treatment alone increased this receptor response at higher concentrations; this effect was much weaker than that induced by PUVA treatment. Cyclic AMP phosphodiesterase activities were not affected by PUVA treatment. These results indicate that epidermal adenylate cyclase response is affected by in vitro PUVA treatment.