Basal H2-receptor stimulated and pH-dependent acid secretion from an isolated stomach mucosa preparation of the cod,Gadus morhua, studied using a modified pH-static titration method.

Gastric acid secretion from isolated cod stomach mucosa was measured using a pH-static titration method. A basal acid secretion rate (BASR) of 6.0±0.6 nEqH(+)min(-1)cm(-1) was measured when using 0.9% NaCl as luminal solution. There was a dose-dependent increase in response to histamine between 0.12 and 0.20 μM (EC50=0.15 μM), above which gastric acid secretion plateaued at 13.5±1.8 nEqH(+)min(-1)cm(-1). Ranitidine, a H2-receptor antagonist, completely blocked the stimulatory effect of histamine and reduced the BASR. The H1-receptor antagonist, clemastine, did not inhibit the response to histamine. Acid secretion rates decreased significantly when the pH of the luminal side of the mucosa was lowered from pH 5.75 to pH 4.50, indicating that a negative feedback mechanism was operating. Histological staining showed that oxynticopeptic cells were uniformly distributed throughout the cardiac stomach.It is concluded that the acid secretion in the isolated stomach mucosa of cod can be measuredin vitro with a pH-static titration method. The method was used to demonstrate that the BASR is downregulated by a decrease in pH. Furthermore, we conclude that the histamine receptor in the cod stomach mucosa resembles the mammalian H2-receptor and that histamine is secreted under basal conditions.