Inhibition of bovine α-glucosidase by Castanospermum australe and its effect on the biochemical identification of heterozygotes for generalised glycogenosis type II (Pompe's disease) in cattle

All 18 2-year-old Brahman bulls grazing in a paddock containing Castanospermum australe trees were diagnosed as heterozygotes for Pompe's disease by measurement of mononuclear cell alpha-glucosidase activity. However, removal of the bulls to a paddock free of C. australe and retesting 2 months later indicated that 15 were homozygous normal. An in vitro assay demonstrated that a crude aqueous extract of seeds from these C. australe trees contained a potent inhibitor of mononuclear cell alpha-glucosidase. Two Hereford steers were dosed with 0.6 g C. australe seed/kg bodyweight for 6 days. The alpha-glucosidase activity in blood mononuclear cells declined to 5% of normal within 48 h of commencement of dosing. It was therefore assumed that the bulls had consumed C. australe seeds. A means of differentiating true heterozygotes from animals consuming the toxic seed, using the ratio of plasma alpha-glucosidase activity at pH 5.6 to that at pH 3.7, is proposed.