ECL cell histamine mobilization and parietal cell stimulation in the rat stomach studied by microdialysis and electron microscopy

Aim: Gastrin stimulates acid secretion by mobilizing histamine from enterochromaffin‐like (ECL) cells that occur predominantly at the base of the gastric glands. The parietal cells occur higher up in the glands nearer to the gastric lumen. The present study was performed to assess whether histamine is transported from the ECL cell via the microcirculation (endocrine route) or local diffusion (paracrine route). Methods: Totally isolated, vascularly perfused, rat stomachs were examined both in basal and gastrin‐stimulated state. Histamine concentrations, determined by radioimmunoassay in venous effluent and microdialysate from an indwelling probe in the submucosa, were monitored over a period of 240 min. Gastrin‐17 was infused through an arterial catheter for 120 min. The parietal cells were examined by electron microscopy, and the percentage of actively secreting parietal cells (displaying secretory canaliculi) in four regions along the glands (basal to surface, zones I–IV) was determined. Results: Gastrin stimulated acid secretion and histamine release as well as parietal cell activation. Upon gastrin stimulation, histamine concentration in the microdialysate was 2.5‐fold higher than in the venous effluent (P = 0.008). The parietal cells in the upper part of the gland (zone III) were found to be activated the most. Conclusion: As the histamine concentrations were higher in the tissue (microdialysate) than in blood, histamine seems to reach the parietal cells via the paracrine route. The fraction of active parietal cells seems to depend more on the age of the parietal cells than on the distance from the ECL cell.