The activity and function of gastric urease in the cat

Abstract

The in vivo hydrolysis of urea was determined from the expiration of (Cl4) CO2 after intravenous injection of (Cl4) urea into fasted, anaesthetized cats, whose ureters were tied. When cats secreted gastric acid, there was an increase in rate of urea breakdown, due to the activity of gastric urease. The gastric juice secreted contained, on average, 0.60 mM urea and 4.2 mM ammonia, and suspensions of the gastric mucosae contained urea-splitting staphylococci. The activity of gastric urease could not be elicited by the presence of acid in, nor by variations in the blood flow through, the stomach. It was evoked when the stomach secreted a nonacid juice. By forcing (Cl4) urea solution at pH 1.5 or 6.8 through the gastric mucosa from stomach lumen to blood, it was shown that the activity of gastric urease was dependent upon flow of urea-containing liquid past the enzyme, which is located in the stomach at sites protected from inactivation by acid. The enzymic hydrolysis of (C14) urea was abolished by treating cats for 4 days with a mixture of penicillin, Terramycin and sulfaguanidine, which was shown not to inhibit gastric urease either in vitro or in vivo but to act by removing urea-splitting bacteria from the cats. These cats were free of gastric urease activity, and secreted gastric juice containing, on average, 3.0 mM urea and no detectable (<0.05 mM) ammonia. This confirms that the ammonia of the gastric juice was derived from the hydrolysis of urea by gastric urease. From the quantities of (C14) CO2 liberated into the blood, and the ammonia secreted in the gastric juice, it was calculated that gastric urease hydrolyzed 12-23 u moles of urea/hr., i.e. about 0.2%/hr. of the total urea in the cat. The ammonia thus produced could neutralize less than 2% of the acid secreted during this time. Apparently gastric urease is of bacterial origin, and plays no essential role in the physiology of the stomach.