Studies on the photosensitisation of animals in South Africa. II. The presence of a lethal factor in certain members of the plant genus Tribulus

Abstract

"Geeldikkop" is a disease of South African sheep, associated with photosensitisation and icterus, caused by Tribulus terrestris and certain other plants. It is shown that a lethal factor is present in the fresh juice and aqueous extracts of Tribulus, which can cause death from asphyxia following intracorpuscular conversions of haemoglobin into methaemoglobin. The responsible agent is an inorganic nitrite, not present as such, but formed from pre-existing nitrate under the influence of an oxido-reductase. This, however, does not account for the naturally occurring " Geeldikkop, " since it does not account for the photosensitivity and icterus. Repeated dosing with sodium nitrite, hydroxylamine hydrochloride, hydrazine sulfate and ammonium carbonate failed to photosensitise sheep. Administration of sodium nitrite, nitrobenzol and amyl nitrite produced death from simple methaemoglobinaemia.