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.
Animals—3 sheep with indwelling electrodes in the musculature of the reticulum and rumen.
Procedure—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 and Clinical Relevance—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.
Objective—To compare the effects of the ergot alkaloid
ergovaline with effects of ergotamine on blood
pressure, heart rate, respiratory rate, and body temperature
in conscious sheep.
Animals—3 sheep with indwelling arterial catheters.
Procedure—Ergotamine and ergovaline were injected
IV (20 nmol/kg), and their effects on arterial blood
pressure, heart rate, respiratory rate and pattern,
body temperature, and skeletal muscle electromyographic
activity were compared with control values
obtained following injections of saline (0.9% NaCl)
solution or acetone.
Results—Both ergopeptides caused immediate and
significant increases in blood pressure (50 to 75 mm
Hg) without concomitant increases in heart rate.
Ergovaline but not ergotamine significantly increased
pulse pressure (35 mm Hg). Both ergopeptides resulted
in decreased respiratory rate and increased respiratory
depth within the first hour of administration.
Body temperature was decreased slightly upon
ergopeptide administration but continued to increase
thereafter, with greater increases developing with
ergovaline than with ergotamine. Increased body
temperatures of 3.0 to 3.5 C were maintained for at
least 10 hours. Respiratory rate was increased to
rates as high as 210 to 220 breaths/min in association
with hyperthermia. Ergopeptides had no effect on
skeletal muscle electromyographic activity.
Conclusions and Clinical Relevance—In sheep,
ergovaline has similar effects to ergotamine on cardiovascular
and pulmonary function and body temperature
but is more potent. These effects are consistent
with clinical signs observed in the toxicoses
developed when ruminants ingest grass with high
concentrations of ergopeptides. (Am J Vet Res
Objective—To investigate effects and mechanisms of ergotamine and ergovaline and effects of peramine on reticulum motility of sheep.
Sample Population—3 sheep with indwelling electrodes in the reticulum and samples of reticulum collected from 126 sheep at an abattoir.
Procedures—In conscious sheep, motility was recorded as integrated electromyograms from the reticulum. Ergotamine was administered IV alone or in combination with the cholinergic muscarinic receptor antagonist atropine to sheep, and motility of the reticulum was assessed. In vitro, whole wall strips of the reticulum, cut in a direction to record longitudinal muscle activity via force transducers, were placed in 10-mL organ baths and superfused with Tyrode Ringer's solution at 37°C and oxygenated with 95% oxygen and 5% carbon dioxide. Testing involved incubation of reticulum strips with ergotamine, ergovaline, and peramine and measurement of motility of the reticulum tissues.
Results—Administration of ergotamine to sheep reduced the frequency of reticulum contractions and increased baseline electromyographic activity (tonus). Frequency was unaffected by atropine, whereas tonus was significantly reduced. In vitro, ergotamine and ergovaline increased tonic contractions and stimulated phasic contractions of reticulum tissues and potentiated electrically stimulated contractions. Atropine and tetrodotoxin re-duced tonic contractions, but stimulation of large-amplitude phasic contractions remained. Peramine had no effect on motility of reticulum tissues.
Conclusions and Clinical Relevance—Results of the study indicated that peripheral excitatory effects of the ergopeptides on motility of the reticulum appear to be mediated partly through myenteric neurons and muscarinic receptors and also through direct effects on the muscles.