Haemonchus contortus: Abomasal transmural potential difference and permeability changes associated with experimental infection in sheep

Abstract

Measurements of abomasal potential difference (PD), pH, and ionic concentrations of abomasal contents were made in four lambs fitted with permanent abomasal cannulae and infected twice at 39-day intervals with 25,000 Haemonchus contortus larvae. Within 10 to 15 min after intraruminal administration of larvae, the abomasal transmural PD increased from −12.9 ± 2.6 to −25 ± 3.1 mV and then returned progressively to basal values in 48 hr. A similar but slower increase was observed from 6 to 9 days after infection, the maximal PD values reaching −22.6 ± 0.8 mV. During the period of egg laying by the parasite, the transmural PD remained higher (55%) than normal. It returned to control levels following this period. After each infection, the transmural PD variations were positively correlated ( r = 0.82, P < 0.01) with the Na + concentration of abomasal contents but not with K + and Cl−. We conclude that H. contortus infection in sheep was characterized by an increase in the abomasal transmural PD occurring immediately after infection and we suggest that it was related to the changes in ionic permeability of the gastric wall.