METABOLISM OF SAPONINS FROM NARTHECIUM-OSSIFRAGUM - A PLANT IMPLICATED IN THE ETIOLOGY OF ALVELD, A HEPATOGENOUS PHOTOSENSITIZATION OF SHEEP

One sheep was dosed over 4 consecutive days with 2.1 kg of leaves and Bower stems of Narthecium ossifragum before it was killed. Sarsasapoge nin and smilagenin glycosides, in the ratio 9:1, were the dominant sap onins present in the dosed plant material. CC-MS analyses of the free and conjugated sapogenin content of samples recovered from the sheep i dentified three distinct regions of metabolic activity. In the first m etabolic region, in the rumen and omasum, the ingested plant saponins were hydrolysed to the parent sapogenins, before being oxidized at C-3 and reduced to give the epi analogues of the ingested sapogenins, The second metabolic region consisted of the duodenum, jejunum, the liver and associated ducts. Sapogenins appear to be absorbed in the jejunum and may be transported via the portal vein to the liver, where 3 alph a-OH-5 beta-H sapogenins (epismilagenin and episarsasapogenin), but no t 3 beta-OH-5 alpha-H sapogenins (smilagenin and sarsasapogenin), are conjugated and excreted into the bile as episarsasapogenin and epismil agenin conjugates in the ratio 4:1. In the third metabolic region, in the caecum and the colon, the epi-sapogenin conjugates were hydrolysed to free epi-sapogenins. The absence of free and/or conjugated sapogen ins in urine, collected 24 h after dosing commenced, indicates that sa ponins and their metabolites are not likely to be implicated in the ki dney disease occurring in ruminants ingesting N. ossifragum.