PHOTO HENS EGG TEST - A MODEL FOR PHOTOTOXICITY

The aim of this investigation was to establish a new model for phototo xicity which is more advanced than the widely used cultures of yeasts, bacteria or cells of various origin, and at the same time to avoid an imal testing, We studied the extraembryonal vasculature of the incubat ed hen's egg. This model was originally introduced by toxicologists as an alternative to the rabbit's eye irritation test (Draize test). In the photo hen's egg test, substances are applied to the embryo's yolk- sac blood vessel system at a non-toxic concentration and are irradiate d with 5 J/cm(2) ultraviolet A (UVA) (320-400 nm). Promethazine, haema toporphyrin, ciprofloxacin and 8-methoxypsoralen were tested in this s ystem, Death of the embryo, membrane discoloration and haemorrhage are parameters for phototoxic damage, which were recorded during an obser vation period of 24 h. These well-known phototoxic substances induced pronounced damage of the yolk-sac membrane and blood vessels which was not found in the controls (test substance alone, UVA alone or untreat ed) using a 2 x 2 factorial test design. The photo hen's egg test serv es as a valid screening model for substances supposed to be photosensi tizers owing to a phototoxic mechanism.