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The ouabain-like sodium pump inhibitor in mammals (so-called ''endogenous ouabain'') has been considered a subtle structural isomer of ouabain. Its structural investigation, however, has long been hindered by the paucity of sample material. Our recent purification of endogenous ouabain (3 g) from bovine hypothalamus allowed the measurement of its 1 H-NMR. The obtained spectrum as well as reexamination of past microscale structural studies on endogenous ouabain led us to identify the purified material as ouabain in an unusual manner. It turned out that the structural analysis had been complicated by a facile ouabainborate complexation in borosilicate glassware. In retrospect, it is not surprising that the polyhydroxylated ouabain molecule serves as a polydentate ligand to inorganic species. In its physiological environment, ouabain may exist as some unknown complex. The chemical species giving rise to the reported biological activities of hypothalamic inhibitory factor preparations remain to be clarified.

1. Conferred insect resistance arises from a mutualistic relationship between claviciptaceous endophytic fungi and various grasses. A number of secondary compounds are responsible for the insect resistance. This paper describes studies of the relationship between the endophytic fungus Acrernoniurn lolii Latch, Christensen & Samuels and the Argentine stem weevil Listronotus bonariensis (Kuschel) (Curculionidae) ; in particular, the effects on larval feeding behaviour, growth and survival.2. Larvae are stem borers. Tunnel length and distance bored into the basal sheath zone of ryegrass was reduced when the plants were infected by A.lo1ii.3 . Lolitrem B, a potent mammalian neurotoxin, levels were highest in A.lolii infected grasses and ranged from 2.61 to 7.08 pg/g dry wt, the higher value being recorded in summer. Lolitrem B extracted fromA . lolii-infected perennial ryegrass reduced larval growth rates and survival.5. Lolitrem B acted via the insect stomach rather than by absorption through the integument.6. The potential role of endophytic fungi in plants is discussed briefly in relation to herbivory.

Tremor dose-response curves were determined for mice dosed with the ryegrass neurotoxin lolitrem B, and the tremor-genic mycotoxin aflatrem. A family of characteristic curves was revealed for each tremorgenic, with lolitrem B eliciting a sustained tremor response persisting for over 24 h.

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