Effects of ergotamine and ergovaline on the electromyographic activity of smooth muscle of the reticulum and rumen of sheep.
OBJECTIVE
To investigate the effects of IV administration of ergotamine and ergovaline and intraruminal administration of ergotamine on electromyographic (EMG) activity of reticuloruminal smooth muscle in conscious sheep.


METHODS
3 sheep with indwelling electrodes in the musculature of the reticulum and rumen.


METHODS
In a crossover design study, reticuloruminal motility before and after IV administration of ergotamine (5, 10, 20, and 40 nmol/kg) or ergovaline (2.5, 5, and 10 nmol/kg) was evaluated; EMG effects were compared with those of corresponding control treatments (IV administration of saline [0.9% NaCl] solution or acetone, respectively) in sheep. Ergotamine (800 nmol/kg) or water was also administered intraruminally and their effects compared.


RESULTS
After IV administration of ergopeptides, vagally dependent cyclical A and B sequences of contraction of the reticulorumen were immediately inhibited, preceding increases in baseline EMG activity (tonus). The return of cyclical contractions was associated with an increase in contraction amplitude. The effects were dose dependent; administration of 40 nmol of ergotamine/kg resulted in responses that continued for 3 to 4 hours. The effects of intraruminal administration of ergotamine were variable; after 8 hours, EMG activity was increased from baseline for < 2 hours in 1 sheep, 10 hours in another, and > 15 hours in the third.


CONCLUSIONS
In sheep, the effects of ergotamine and ergovaline on reticuloruminal motility after IV administration and the duration of responses following intraruminal administration suggest that disruption of digestion may occur in animals grazing endophyte-infected pasture that has a high ergopeptide content.
McLeay
Lance M
LM
Department of Biological Sciences, School of Science and Engineering, The University of Waikato, Private Bag 3105, Hamilton, New Zealand.
Smith
Barry L
BL
D000818:Animals; D018592:Cross-Over Studies; D004576:Electromyography / Q000662:veterinary*; D004878:Ergotamine / Q000494:pharmacology*; D004879:Ergotamines / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D012417:Rumen / Q000187:drug effects / Q000502:physiology*; D012756:Sheep; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
D004879:Ergotamines; D014662:Vasoconstrictor Agents; C076760:ergovaline; D004878:Ergotamine