Detection of singlet oxygen in blood serum samples of clinically healthy lambs and lambs suffering from alveld disease

Alveld is a disease in lambs of domestic sheep ( Ovis aries L.), characterized by a combination of photosensitivity and liver damage. Generation of singlet oxygen play a major role in phototoxicity reactions. The compound phylloerythrin (phytoporphyrin) is so far assumed to be the main photodynamic agent in hepatogenous photosensitivity diseases in sheep. Phylloerythrin is a potent photosensitizer and an efficient source of singlet oxygen. The compound accumulates in the peripheral circualtion upon liver damage. Liver dysfunction is also likely to cause an increase in the blood level of bilirubin. Formation of singlet oxygen by bilirubin is reported. In the present work the photosensitizing potential of serum has been measured and related to the bilirubin- and phylloerythrin levels in lambs suffering from alveld and in clinically healthy controls. The singlet oxygen level of the serum was taken as a measure of the photosensitizing potential. The observed singlet oxygen values in serum from alveld lambs were significantly higher than the corresponding values observed in clinically healthy control lambs. This indicates that the serum of the alveld lambs contains an elevated concentration of photosensitizer. The singlet oxygen level was not correlated to the concentration of bilirubin or phylloerythrin. The results indicate that the photosensitizing mechanism is quite complex and may involve other sensitizer(s) than phylloerythrin.