Biol. Pharm. Bull. 29(6) 1286—1289 (2006)

macokinetic interactions with many drugs such as dihydropyridine calcium antagonists, including nifedipine (NFP). The plasma concentrations of the drugs increase significantly with GJ intake, and serious adverse reactions may possibly result. Most drugs interacting with GJ are substrates for small intestinal cytochrome P450 (CYP) 3A. That is, GJ– drug interactions are caused by the inhibition of CYP3Amediated drug oxidation during the intestinal absorption process. It has been demonstrated that furanocoumarin (FC) derivatives such as bergamottin (BG) and 6 ,7 -dihydroxybergamottin (DHB) in GJ induce drug interactions in vivo caused by the inhibition of CYP3A activity. In 1953, Lerner et al. reported that if 8-methoxypsoralen, one of the FCs, is exposed to UV irradiation, a decrease in optical density is obtained. Fowlks confirmed a similar loss of the characteristic peaks of the absorption spectrum of 5-methoxypsoralen, 8-methoxypsoralen, and psoralen after UV exposure. Furthermore, Knudsen et al. examined the reduction of the phototoxic effects of previously UV-irradiated 5-methoxypsoralen, 8-methoxypsoralen, and psoralen. Photodegradation of BG and bergaptol (BT), major FCs contained in GJ, were also reported. We considered that UV irradiation of GJ might eliminate FCs in the juice and decrease the ability to interact with drugs. However, the effects of UV light on the FCs in GJ and on GJ–drug interactions were not known. Therefore the effects of UV irradiation on the concentration of FCs in GJ were investigated using a comprehensive determination system of FCs in HPLC. Furthermore, NFP pharmacokinetics in rats administered untreated and UV-irradiated GJ were compared to assess the effects of UV irradiation in vivo.