Abstract
The mycotoxins lolitrem B (responsible for ryegrass- staggers), and paxilline have a common moiety and are well known for their ability to cause tremoring in animals. Little is known of their other effects in ruminants and we investigated these in sheep, on electromyographic (EMG) activity of gastrointestinal smooth muscle of the reticulum, rumen, abomasal antrum and duodenum and on blood pressure, heart rate, respiration and body temperature. Both mycotoxins induced tremor and caused marked increases in respiratory rate, heart rate and blood pressure, but had relatively little effect on body temperature. Increases in blood pressure preceded substantial rises in heart rate, indicating a peripheral vasoconstrictive effect. Both mycotoxins had variable excitatory and inhibitory effects on the antrum and duodenum, but had consistent and profound effects on activity of the reticulorumen with a similar time course to their characteristic effects for paxilline and lolitrem B respectively, on the induction (2 and 30 minutes) and the duration (2-3 h and 8-12 h) of tremoring. The effects included an inhibition of the vagallydependent cyclical A and B sequences of contraction of the reticulorumen and an excitation of intrinsic activity including "chaotic" activity of the reticulum. Excitatory effects of the tremorgens were partially blocked by atropine, indicating some but not all, excitatory effects on the reticulorumen arise from stimulation of muscarinic cholinoceptors and it is possible this and other excitatory effects may be mediated through calcium-activated high conductance potassium channels. It is concluded tremorgens have widespread effects on the respiratory, cardiovascular and digestive systems. The intensity and duration of the effects with lolitrem B, indicate substantial disruption of digestion may occur with its ingestion on grazing endophyte-infected pasture. Keywords: cardiovascular, electromyograph activity, endophyte, gastrointestinal, lolitrem B, mycotoxins, paxilline, respiration, reticulorumen, temperature
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