Karl Johan Öbrink

Gastrin-histamine as a normal sequence in gastric acid stimulation in the rabbit.

In a suspension of isolated gastric glands the effect of secretagogues on the oxyntic cells can only be detected by direct stimulation. An indirect stimulus like gastrin inducing one type of cell to liberate histamine which then acts on the oxyntic cells will not be detectable because of the very high dilution of the liberated substance. Thus the isolated gland preparation presents a means by which two steps in a sequential stimulation can be separated. There is no evidence that gastrin acts directly on the oxyntic cells but it does liberate histamine in a dose-effect relationship, which would in an intact stomach give histamine concentrations sufficient to effectively stimulate the acid secretion. Thus in the rabbit histamine seems to be a normal physiological mediator for gastrin stimulation.

Session 1: Histamine and Gastric Acid Secretion: A Review

Obrink KJ. Histamine and gastric acid secretion. Scand J Gastroenterol 1991, 26(suppl 180), 4–8Histamine was found to be a potent stimulus for acid secretion in 1920. It was then for about 20 years considered to be identical to the antral factor gastrin. It stimulates the parietal cells—the site of acid production—via an H2-receptor in a dynamic manner—that is. there is a continuous turnover of histamine at the receptor site. Cyclic AMP is formed by the receptor stimulation, but how this is coupled to the proton transport is unknown. It could even be possible that the main function of the histamine action is to initiate the drastic morphologic transformation of the parietal cells which occurs in connection with acid secretion. Possible sites for some acid inhibitors are elucidated.

The antidiuretic hormone as an inhibitor of gastric secretion.

Male Heidenhain pouch dogs were used to evaluate the antidiuretic hormone as a physiological inhibitor of gastric acid secretion. The dogs were stimulated to a constant gastric secretion by food and 40-minute ADH infusions of different concentrations took place. The inhibition was expressed as a percentage and plotted against the dose of ADH. The physiological significance of these doses is discussed and evaluated against already published data on normal concentrations. In our experiments we found that 30 muU/kg min markedly influenced the gastric secretion, which means that this inhibition may well occur under physiological conditions.

Potassium in Gastric Juice under Non-Steady-State Conditions

In a Heidenhain pouch dog the K(+) concentration of the gastric juice was analyzed after continuous intravenous injections of histamine. The steady states of the secretion rates and the changing over from different steady states were studied. The old observation that the K(+) concentration is independent of the secretion rate in the steady state was confirmed, but it was also found that during an increase of the secretion rate the K(+) concentration in the juice showed a transient increase. In changing the secretion rate to a lower steady level the K(+) concentration showed a similar deviation in the opposite direction before returning to its steady-state level. It is suggested that this phenomenon is due to a loss and uptake of K(+) by the mucosa when stimulation is started or stopped.

Sodium Secretion as Part of the Formation of Gastric Juice

Experiments with Heidenhain pouch dogs showed the well known high sodium concentrations at low secretion rates and low sodium concentrations at high ones after stimulation with a continuous intravenous injection of histamine. It was previously thought that the primary secretion did not contain any sodium, but that all the sodium present in the gastric juice appeared as a result of diffusion. A more detailed analysis of the experimental data showed, however, that there is in fact sodium present also in the primary juice in the small concentration of 3-5 mEq/l. The origin of the secreting volume containing this concentration of sodium is unknown.

LOSS OF HYDROGEN IONS IN DIFFERENT PARTS OF THE NON-STIMULATED STOMACH

Publisher Summary This chapter discusses the loss of hydrogen ions in different parts of the nonstimulated stomach. The experiments described in the chapter analyzed the permeability of H+ ions in different parts of the cats stomach. Cats were starved and anesthetized with chloralos-nembutal. The stomach was tied with ligatures at the esophagus and the pylorus. In some experiments, plastic partition was tied in between the antrum and the fundus. Through cannulas, the chambers thus formed could be filled and emptied. Before the beginning of the actual experiments, it was controlled that the stomachs were in complete secretory rest. When hydrochloric acid of primary acidity strength (170 mM) is instilled into such a resting stomach, the acidity will decrease with time without volume changes. This decrease can be mathematically treated as the result of a diffusion process and the permeability coefficient (k) can be determined. The results suggest that the permeability for hydrogen ions is much higher in the antrum than in the fundus. This may be because of a larger microscopic diffusion area compared to the macroscopic one in antrum or to a greater specific permittivity or to something else.