The mycotoxic tremorgens penitrem, paxilline and lolitrem B had profound effects on electromyographic (EMG) activity of smooth muscle of the reticulorumen in conscious sheep, with a similar time course of action to their respective characteristic effects on the induction (1 to 2, 15 to 20 and 20 to 30 minutes) and the duration (1 to 2, 1 to 2 and 8 to 12 hours) of tremoring. Responses to penitrem revealed a greater sensitivity of smooth muscle than skeletal muscle. Effects included an inhibition of the vagally-dependent cyclical A and B sequences of contraction of the reticulorumen, an increase in their amplitude and an excitation of local intrinsic activity contributing to elevated baselines and the occurrence of chaotic activity of the reticulum. The excitatory local effects were partially blocked by atropine, indicating that stimulation of muscarinic cholinoceptors was involved. Increased local activity may mediate a reflex inhibition of cyclical contractions. A non-tremorgenic isomer of lolitrem B (31-epilolitrem B) had no effect on the reticulorumen. The intensity and duration of the effects of lolitrem B, up to 12 hours, indicate that severe disruption of digestion may occur in animals grazing endophyte-infected pasture.
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