Biochemical and Structural Changes in Response to Abomasal Nematode Infections in Ruminants

Scott, Ian (1996) Biochemical and Structural Changes in Response to Abomasal Nematode Infections in Ruminants. PhD thesis, University of Glasgow.

Abstract

Four methods for estimating plasma pepsinogen concentrations were compared to determine the most suitable assay for routine use. Three of the methods were colorimetric assays which used glycine-buffered albumin, albumin, or haemoglobin as their substrates. The fourth method was a radial diffusion assay which used casein in agarose as its substrate. All four methods gave reproducible results when replicates were assayed on the same day. However, the first method had the least day-to-day variation and was the only method which gave a linear relationship with different concentrations of pepsinogen in a plasma pool. Two artificial pepsinogen containing solutions were created, the first was an entirely aqueous solution of porcine pepsinogen and the second was plasma with an identical pepsinogen concentration, achieved by adding an identical amount of porcine pepsinogen to ovine plasma instead of water. The ovine plasma chosen had zero intrinsic peptic activity. When the peptic activities of the two solutions were compared the activity of pepsinogen in plasma was significantly reduced. This was due either to an interference in enzyme reaction rates by the presence of plasma proteins, or to a more specific interference with activated pepsin by an inhibitor, as yet unknown, present in plasma. Either way this phenomenon represented a potentially significant source of variation when recording plasma pepsinogen concentrations by assays measuring proteolytic activity. The effects of excretory/secretory products (ES) of Ostertagia circimcincta on the release of pepsinogen and on smooth muscle function in vitro was investigated. ES was prepared by culture of O. circumcincta adults. Methods to monitor pepsinogen release from isolated, intact mucosal sheets and isometric contractions in abomasal smooth muscle were successfully developed and were both adequately responsive with the muscarinic agonist, carbachol. The addition of ES to tissues consistently resulted in the release of pepsinogen from mucosae and in smooth muscle contraction, but only in tissues obtained from animals with a history of previous exposure to helminth parasites. Tissues from known parasite-naive animals did not respond to the presence of ES. These responses were therefore considered to be hypersensitivity responses to antigens present in ES. The distribution of pepsinogen in abomasal tissues was investigated immunohistochemically and biochemically in the abomasa of parasite-naive cattle and sheep, and in animals with ostertagiasis and haemonchosis. In the parasite-naive animal the fundic chief cell was the major source of pepsinogen, as indicated by intensity of staining. Mucous neck cells also contained pepsinogen, but in lesser amounts. The pepsinogen content of surface mucous cells was variable in the bovine however this cell type did not contain pepsinogen in the normal ovine. Ostertagiasis was associated with focal hyperplasia around parasitised gastric glands and increased tissue pepsinogen content was detected within nodules. Normal epithelial cells, including chief cells, were replaced by hyperplastic mucous-type cells. These cells contained pepsinogen and hyperplasia resulted in an expanded population of cells producing the zymogen. Individual cells of the hyperplastic population contained less pepsinogen than did mature chief cells, but their greater numbers accounted for the increase in tissue pepsinogen content. In haemonchosis hyperplasia was generalised, and increased numbers of cells were positive for pepsinogen. However, overall tissue pepsinogen content was not increased by infection and it was observed that chief cell content was again reduced. Thus helminth infections were associated with an expanded zymogenic population and the inference was that pepsinogen secretion in infected animals was at least maintained in infection, if not increased.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Quintin McKellar
• Keywords: Veterinary science, Parasitology
• Date of Award: 1996
• Depositing User: Enlighten Team
• Unique ID: glathesis:1996-75845
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 17:44
• Last Modified: 19 Nov 2019 17:44
• URI: https://theses.gla.ac.uk/id/eprint/75845