Differing ulcerogenic potential of dihydroxy and trihydroxy bile acids in canine gastric mucosa.

Although recent clinical reports suggest that greater than normal amounts of dihydroxy secondary bile acids appear in the gastric content of patients with postoperative alkaline reflux gastritis, the pathophysiologic significance of these observations is unclear. We addressed this problem by usiong chambered ex vivo wedges of proximal canine gastric wall. The effects of 1 and 2 mM concentrations of the dihydroxy secondary bile acid, taurodeoxycholic, were compared with those of its parent trihydroxy primary bile acid, taurocholic. The parameters of mucosal function evaluated included the net flux of hydrogen ion, the transmural electrical potential difference, mucosal blood flow determined by radiolabeled microsphere embolization, and the severity of mucosal damage induced in mucosa rendered ischemic by wedge-specific intra-arterial low-dose vasopressin infusin. The results indicate that at each concentration in both ischemic and nonischemic mucosa the dihydroxy secondary bile acid induced a greater depression in potential difference, a more profound increase in mucosal permeability to hydrogen ion, and in ischemic mucosa a more severe degree of gross mucosal damage than did the trihydroxy primary bile acid. These effects may be related to a greater lipid solubility and consequent capacity to disrupt cell membranes.

Arteriovenous acid-base balance during acute gastric mucosal ulcerogenesis.

The possibility that acute gastric mucosal ulcerogenesis induced by bile acid and ischemia is a consequence of inadequate tissue buffering of back-diffused intramucosal H+ was examined indirectly by measuring arteriovenous differences in acid-base parameters across vascularized chambered wedges of proximal canine gastric wall. During acute lesion formation gastric venous [HCO3-] and pH were significantly decreased, and a marked negative base excess developed. The data suggest that mucosal ulcerogenesis is a consequence of uncompensated tissue acidosis. Further, these derangements occur only in the presence of topical acid, suggesting that back-diffused H+ may be ultimately responsible.

Des-Asp1-angiotensin I: a metabolite of angiotensin I in the perfused feline adrenal.

The administration of radioactive angiotensin I to the retrogradely perfused feline adrenal gland caused a brisk discharge of catecholamines. Recovery of the labelled decapeptide and metabolites in the adrenal effluent fluid was complete in 5 min. Radioimmunoassay of this perfusate revealed that most of the peptide remained as angiotensin I, but chromatographic and electrophoretic evaluation indicated that greater than 68% of the peptide had been metabolized to des-asp1 -angiotensin I. The absence of des-asp1 -angiotensin II, angiotensin II or his-3H-leu in adrenal effluent fluid suggested minimal dipeptidyl carboxypeptidase activity in this preparation. In addition, the profile of angiotensin I metabolites from the perfused adrenal was not altered by treatment with a converting enzyme inhibitor B. jararaca nonapeptide. The des-asp1-angiotensin I peptide was a very weak secretagogue in the adrenal medulla. If metabolism of the decapeptide to the nonapeptide occurs in the medulla, this may represent a pathway to limit the secretory action of angiotensin I. These results suggest a high degree of adrenal aminopeptidase activity which may be primarily localized in the adrenal cortex.