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Effects of macrocyclic lactone anthelmintics on feeding and pharyngeal pumping in Trichostrongylus colubriformis in vitro

Published online by Cambridge University Press:  17 January 2003

J. C. SHERIFF
Affiliation:
Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia CSIRO Division of Livestock Industries, 120 Meiers Road Indooroopilly 4068 Qld, Australia
A. C. KOTZE
Affiliation:
CSIRO Division of Livestock Industries, 120 Meiers Road Indooroopilly 4068 Qld, Australia
N. C. SANGSTER
Affiliation:
Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia
R. J. MARTIN
Affiliation:
Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University Ames, IOWA 50011, USA

Abstract

The effects of macrocyclic lactone anthelmintics (MLs) on feeding by Trichostrongylus colubriformis nematodes in vitro were examined using inulin uptake as a measure of ingestion and electropharyngeograms as a record of the electrical events associated with pharyngeal pumping. Inulin uptake was inhibited by the 4 MLs tested (EC50s 0.045–4.57 nM), with an order of potency of eprinomectin (most potent), ivermectin, ivermectin monosaccharide, and ivermectin aglycone. The MLs caused both the frequency and amplitude of pharyngeal electrical events to decrease. In individual worms the inhibition of pump frequency preceded the inhibition of pump amplitude. The order of potency of the MLs as inhibitors of frequency was ivermectin aglycone, ivermectin, ivermectin monosaccharide and eprinomectin. The difference compared with the inulin assay results are probably due to the dynamics of drug uptake in the two systems. It was possible that the nematodes in the electrophysiology experiments were effectively orally ligated by enclosure of the worm's head in the recording pipette which contained no drug. Despite this difference in relative potencies, both the ingestion assays and the electrical events indicate that MLs are potent inhibitors of the pharynx in T. colubriformis in vitro. The sequence of effects on pharyngeal electrical activity suggests that ML action involves an initial inhibitory effect on the rate of pharyngeal contractions, followed by a decrease in the amplitude of the potentials associated with pharyngeal pumping events.

Type
Original Article
Copyright
© 2002 Cambridge University Press

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