The Repellent Effect of Gastric Contents from Uninfected Calves for Sheathed and Exsheathed Larvae of Ostertagia ostertagi

Abstract

Stringfellow (1974, J. Parasitol. 60: 293297; 1977, Proc. Helminthol. Soc. Wash. 44: 76-81) studied the histochemistry of abomasa from uninfected calves and those infected with Ostertagia ostertagi. Chief cells were denuded of their pepsinogen granules. Carbonic anhydrase activity was not detected histochemically in parietal cells from infected calves. These observations, as well as biochemical evidence, suggested a mechanism whereby pepsinogen was released directly into the blood from chief cells. They also provided a mechanism for the rise in pH of the ,gastric contents during ostertagiasis. (Stringfellow and Madden, 1979, Proc. Helminthol. Soc. Wash. 46: 233-239). Those studies described the worm's environment at both the tissue and biochemical level in abomasa from both uninfected and infected calves. The present paper reports further analyses of selected components in the gastric contents of abomasa from uninfected calves. It compares the response of both sheathed and exsheathed larvae of 0. ostertagi to components of both calf origin and from commercial sources. Six 3-mo-old, helminth-free calves were taken off feed 12 hr before they were stunned with a captive bolt gun. Their throats were then slit. The anterior part of the fundus and the pylorus were tightly tied with string which retained the gastric contents and prevented the leaking of omasal and duodenal contents. The abomasum was slit and its contents were drained into a bucket with little or no bleeding. The contents were filtered through gauze, measured, and centrifuged. The clear supernatant was recovered and stored in vials on dry ice. The pH of the gastric contents was measured electrometrically immediately with standard buffers. Sodium and potassium ions were measured with a Corning 450 flame photometer with suitable standards. Chloride ion was measured electrometrically with Markson specific ion electrodes (liquid membrane type) and compared with a suitable calibration curve. Albumin and globulins were determined with Harleco kits on a Clinicard spectrophotometer. Pepsin (E.C. 3.4.4.1) was measured according to Edwards et al. (1960, Br. Med. J. 1: 30-32). Sigma Fraction V albumin was incubated at pH 2 for 24 hr at 37 C. The products were estimated with FolinCiocalteau reagent, and the samples were read in a Spectronic 20 spectrophotometer at 540 nm. Standard tyrosine (0.2 mmol) and a water blank served as references. Results are expressed as milliunits in Table I (Reid et al., 1967, Vet. Rec. 80: 1-4). Lipase (E.C. 3.1.1.3) was measured with the procedure of Cherry and Crandall (1965, In The practical manual for clinical laboratory procedures, Chemical Rubber Company [ed.], pp. 30-31). The response of 0. ostertagi larvae to test agar blocks was bioassayed on agar petri plates. Each petri plate had a background pH of either 2.3 or 7. The agar was adjusted to pH 2.3 with concentrated HC1. It was allowed to cool without adjustment to attain pH 7. A value of 2.3 represented the pH of the gastric contents from an uninfected calf. The pH 7 represented gastric contents from severe, advanced infections with this abomasal worm (Stringfellow and Madden, 1979, loc. cit.). Selected data at background pH 7 are presented in Figure 1. Only data with a common background pH were compared statistically. The test components were incorporated into 2% agar at the concentrations shown in Table I. Defined gradients were established as explained by Ward (1973, Proc. Nat. Acad. Sci. 70: 817-821). The agar background was adjusted with an appropriate compound such that only the substance in the agar block could be detected. Less defined components were prepared as follows: Fundic tissue (wet weight: 0.1-0.2 g) was homogenized with 10 ml of deionized, distilled water. Three milli-