Degree Type

Dissertation

Date of Award

1982

Degree Name

Doctor of Philosophy

Department

Veterinary Physiology and Pharmacology

Abstract

The in vitro effects of E. coli heat-stable enterotoxin (ST) on isolated jejunum of 3-week-old piglets were studied using everted gut sac and isolated enterocyte techniques. ST increased chloride secretion and chloride absorption in the everted gut sac studies. VIP (2 (mu)g/ml) increased chloride secretion but had no effect on chloride absorption. Neither VIP nor pilocarpine (10('-5) M) had any additive effect to ST. ST secretory effects were not blocked by atropine (2 x 10('-5) M), clonidine (10('-6) M), or morphine (1.2 (mu)g/ml). Phenylephrine (10('-5) M), an alpha-1 adrenergic agonist, enhanced ST secretory effects;Three fractions of cells were isolated from pig jejunum: upper villus, lower villus, and crypt cells. ST increased chloride efflux rates from all three fractions. These effects were not blocked by atropine or clonidine. Morphine significantly reduced chloride efflux rate from mature villus cells with no significant effect on immature epithelial cells. ST did not have any effect on calcium efflux rate from isolated enterocytes;Metabolic activity studies performed by using ('14)C-glucose and ('14)C-glutamic acid as substrates revealed no significant effect of ST on ('14)CO(,2) production. Ouabain (1 mM) blocked ('14)CO(,2) production from ('14)C-glucose but not from ('14)C-glutamic acid. The results indicated that isolated enterocytes maintained metabolic activity in the presence of enterotoxin;The results suggest that ST produces loss of fluid and electrolytes primarily by stimulating secretion rather than impairing absorption. This action is exerted directly on both mature villus and immature crypt cells and is not inhibited by alpha-adrenergic agonists or cholinergic antagonists. Opiate agonists may inhibit secretion, in part, by a direct action on mature enterocytes.

DOI

https://doi.org/10.31274/rtd-180813-5918

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Wara Panichkriangkrai

Language

en

Proquest ID

AAI8221216

File Format

application/pdf

File Size

180 pages

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