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  • Author or Editor: J. Carina Ingvast-Larsson x
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Objective—To investigate in vitro effects of isoeugenol on neuromuscular transmission in tissues obtained from rats.

Sample Population—Tissues (phrenic nerve and diaphragm) obtained from 15 male Sprague-Dawley rats.

Procedure—Rats were euthanatized, and tissues (phrenic nerves and diaphragm) were obtained. Phrenic nerve-diaphragm preparations were examined in vitro. The phrenic nerve was stimulated with weak electrical impulses. Muscle-twitch responses were recorded before and after the addition of drugs (pancuronium, neostigmine, isoeugenol, and benzocaine).

Results—Pancuronium and isoeugenol in low concentrations (10 to 206µM) caused a distinct decrease in twitch response, which could be reversed by the addition of neostigmine. The decrease in twitch response caused by benzocaine or high concentrations of isoeugenol could not be reversed by the addition of neostigmine.

Conclusions and Clinical Relevance—Isoeugenol caused a competitive blockade of neuromuscular transmission. Neostigmine restored this transmission by inhibiting acetylcholinesterase, which led to increased concentrations of acetylcholine. Because isoeugenol is used as an anesthetic in fish, further investigations are necessary to determine whether fish exposed to isoeugenol are sedated and unconscious or whether they are only paralyzed but have intact perception in afferent sensory nerves. (Am J Vet Res 2003;64:690–693)

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in American Journal of Veterinary Research


Objective—To determine pharmacokinetics of terbutaline in healthy horses and to relate serum terbutaline concentrations with the drug’s pharmacodynamic effects.

Animals—6 healthy horses.

Procedure—Horses were given terbutaline IV (10 µg/kg of body weight) and, 1 week later, PO (100 µg/kg). Responses to drug administration (eg, heart rate and serum lactate concentration) were measured. Serum terbutaline concentration was measured by means of gas chromatography with mass spectrometry. Protein binding was determined in vitro.

Results—Following IV administration, median maximum serum terbutaline concentration and mean residence time were 9.3 ng/ml and 30 minutes, respectively. Bioavailability following oral administration was < 1%. All horses developed sweating, trembling, excitement, and tachycardia during IV infusion. The 2 horses with the highest serum terbutaline concentrations developed severe tachycardia and CNS stimulation; 30 minutes after the IV infusion was completed, they were hyperventilating and lethargic. Heart rate and serum lactate concentration increased as serum terbutaline concentration increased.

Conclusions and Clinical Relevance—Results indicated that terbutaline is rapidly cleared from the bloodstream following IV administration to horses, suggesting that continuous IV infusion would be needed to maintain therapeutic serum concentrations. Oral administration of terbutaline to horses is not practical because of the low bioavailability. (Am J Vet Res 2000;61:761–765)

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in American Journal of Veterinary Research