Hormonal control of parietal cell function

AM and PM measurement of gastric potential difference and prostacyclin production in humans: effects of ranitidine

It has been previously documented that aspirin induced gastric injury of healthy male volunteers was greater in the morning than in the evening. We have also reported that fasting gastric acid secretion rates and gastric retention times for solids were lower in the morning hours of the circadian cycle. We hypothesized, therefore, that defensive factors in the human stomach may exhibit circadian rhythmicity with greater vulnerability to noxious agents during the morning hours. It has also been hypothesized that an antisecretory agent, with reported protective effects, such as Ranitidine, would affect gastric defense mechanisms differently at different times in the circadian cycle. Transmural electrical potential difference (PD) and prostacyclin (PGI2) production by mucosal biopsy specimens were chosen as putative indicators of gastric defensive status. Accordingly, morning (1000) and evening (2200) studies were performed on 10 fasting healthy male subjects with and without oral Ranitidine (150 mg) given 3 hr before oro-gastric intubation for the measurement of PD and the removal of mucosal biopsy samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Porcine ileal polypeptide causes an increase in cytoplasmic Ca2+ in both parietal and chief cells resulting in acid and pepsinogen secretion

Porcine ileal polypeptide, an enterooxyntin isolated from distal small intestinal mucosal epithelium, has been observed to stimulate gastric acid secretion in vivo as well as in vitro (Wider, M.D. et al. (1984) Endocrinology 115, 1484-1491, Wider M.D. et al. (1986) Endocrinology 118, 1546-1550). We report here that porcine ileal polypeptide stimulates both acid (aminopyrine accumulation) and pepsinogen secretion in isolated, enriched populations of guinea pig parietal and chief cells in a dose-dependent manner. Further, 10(-9) M porcine ileal polypeptide caused an increase in cytoplasmic Ca2+ concentration in both parietal and chief cells similar in magnitude to that observed with gastrin-17 (10(-8) M) (as measured by both fura-2 and aequorin) and cholecystokinin octapeptide (CCK-OP) (10(-8) M), respectively. Porcine ileal polypeptide has been observed to cause no stimulation of cAMP production in gastric glands from guinea pigs (Gespach, C., personal communication) nor is there any effect of medium Ca2+ depletion on acid production observed with guinea pig gastric mucosal sections. It is concluded that porcine ileal polypeptide, at concentrations similar to circulating levels observed in plasma of normal pigs (5 x 10(-9) M), acts directly on the parietal and chief cells to cause the mobilization of intracellular Ca2+ from the stores resulting in acid and pepsinogen secretion. These experiments demonstrate that this peptide is a potent enterooxyntin and chief cell secretagogue which acts via the same signal transduction mechanisms as gastrin and cholecystokinin.

Effects of some polycyclic drugs on gastric secretion and on the healing of duodenal ulcers

Polycyclic drugs such as the dibenzazapine trimipramine have been shown to accelerate the healing of gastric and duodenal ulcers, possibly by inhibiting gastric secretion. We have therefore compared the effects of three polycyclic drugs (trimipramine, mianserin and quisultidine) on nocturnal and pentagastrin-stimulated gastric secretion. The patterns of the effects of the three drugs on gastric secretion differed. Although pentagastrin-stimulated secretion of acid was inhibited by trimipramine (13%), mianserin (38%), and quisultidine (29%), overnight gastric secretion was inhibited by mianserin (37%) and quisultidine (78%) but increased by trimipramine (16%). In view of its gastric inhibitory actions, the effects of mianserin on the healing of duodenal ulcers have been studied. In a pilot open trial seven out of eight duodenal ulcers healed after four weeks of treatment with mianserin 60 mg at night. A controlled, randomized long-term study is now scheduled in order to assess the role of mianserin in the management of ulcer disease.

The effect of stimulation and blocking of histamine H2 receptors on the turnover of the serotonin in different parts of the alimentary tract and the brain of the rat

In the experiments performed on Wistar rats it was found that histamine (0.05 and 0.5 mg/kg i.p.) caused an acceleration of the turnover of serotonin (5-HT) in the stomach. After the lowest dose of ranitidine (3 mg/kg i.p.) a decrease in the rate of 5-HT turnover in the stomach was observed, whereas the higher doses (15.0 and 30 mg/kg i.p.) accelerated the turnover of this amine. In the duodenum, both doses of histamine accelerated the turnover of 5-HT, however, ranitidine in all doses induced a reduction in the rate of 5-HT turnover in this part of the alimentary tract. In the intestine, both doses of histamine enhanced the turnover of 5-HT but after all doses of ranitidine a decrease of the turnover was observed. The blockade of histamine H2 receptors with ranitidine did not completely abolish the effects of histamine on the 5-HT system, in the parts of the rat digestive system studied which suggests also an indirect activity of other receptors in presented observations. In the rat brain, an acceleration of the turnover of 5-HT after both doses of histamine was found. However, ranitidine only reduced the rate of 5-HT turnover at the lowest dose. In animals treated with ranitidine (15 mg/kg i.p.) for three days, histamine did not produce any change in the turnover of 5-HT in rat brain. These experiments show, that in the alimentary tract a relationship exists between histaminergic and serotoninergic systems.

Muscarinic cholinergic receptors in human gastric mucosa

Muscarinic cholinergic receptor sites in human gastric mucosa were analyzed directly by using radioligand binding techniques with the specific muscarinic antagonist 3H-quinuclidinyl benzilate (QNB) as ligand. Specific binding of 3H-QNB to membrane preparations from human gastric mucosa was saturable, of high affinity (Kd = 4.17 +/- 1.94 nM, Bmax = 0.37 +/- 0.04 pmol/mg protein) and selectively inhibited by muscarinic antagonists (atropine, scopolamine) and agonists (acetylcholine, pilocarpine). These findings provide direct evidence for the existence of muscarinic cholinergic receptors in human gastric mucosa. The specific 3H-QNB binding to its receptor was blocked by atropine but not by histamine, cimetidine, pentagastrin, or synthetic human gastrin. The muscarine and histamine H2-receptor, or muscarine and gastrin receptor, probably do not share the same locus.