Measurement of phylloerythrin (phytoporphyrin) in plasma or serum and skin from sheep photosensitised after ingestion of Narthecium ossifragum.

OBJECTIVE

To establish a method for measuring phylloerythrin in plasma or serum and skin from lambs photosensitised after ingestion of the plant, Narthecium ossifragum, which induces an hepatogenous photosensitisation similar to the disease known as facial eczema in sheep.

METHODS

For two successive summers, lambs were grazed on uncultivated pastures containing N. ossifragum. Clinical photosensitisation was deemed to have occurred when symptoms such as restlessness, scratching, oedema and reddening of the skin were observed. Sixteen lambs that exhibited signs of photosensitisation were included in this study in the first year and five in the following year. A total of 16 clinically healthy lambs served as controls. Fluorescence emission and excitation spectra of phylloerythrin were measured in plasma or serum samples from the 21 photosensitised and 16 non-photosensitised lambs. In the first year of the study, skin samples were collected post mortem from the ear, lip, neck, nose, leg, belly, udder, back, vulva and perineal region, from all photosensitised and from seven non-photosensitised lambs, and examined by fixing them between two glass plates (each of 1 mm thickness) and placing them at a fixed angle in front of a fluorescence spectrofluorometer.

RESULTS

All plasma or serum samples obtained from the photosensitised lambs exhibited strong phylloerythrin-like fluorescence of identical spectra; maximum fluorescence was at 650 and 711 nm, and maximum excitation at 425 nm. Emission spectra obtained from plasma or sera from non-photosensitised sheep grazing the same N. ossifragum-containing pastures exhibited either no or only minor fluorescence. Phylloerythrin concentration in plasma or serum exceeded 0.3 microg/ml before clinical photosensitisation occurred, whereas the concentration in samples from clinically healthy lambs was <0.05 microg/ml. Fluorescence from skin samples from the photosensitised lambs showed emission peaks at 650, 670 and 711 nm, whereas the phylloerythrin emission peaks at 650 and 711 nm were not observed in skin from clinically healthy lambs.

CONCLUSIONS

Plasma concentrations of phylloerythrin in healthy sheep were <0.05 microg/ml. Clinical signs of photosensitisation were not observed until the concentration of phylloerythrin in plasma exceeded 0.3 microg/ml. This is the first reported spectroscopic method for analysis of phylloerythrin and the only one which does not involve exposure of the analyst to hazardous chemicals. It has the additional benefit of distinguishing between hepatogenous and primary photosensitisation.