The vagus regulates histamine mobilization from rat stomach ECL cells by controlling their sensitivity to gastrin

Abstract

The ECL cells in the oxyntic mucosa secrete histamine in response to gastrin, stimulating parietal cells to produce acid. Do they also operate under nervous control? The present study examines histamine mobilization from rat stomach ECL cells in situ in response to acute vagal excitation and to food or gastrin following vagal or sympathetic denervation. Applying the technique of microdialysis, we monitored the release of histamine by radioimmunoassay. Microdialysis probes were placed in the submucosa on either side of the stomach, 3 days before experiments. The rats were awake during microdialysis except when subjected to electrical vagal stimulation. One-sided electrical vagal stimulation raised serum gastrin and mobilized gastric histamine. However, gastrin receptor blockade prevented the histamine mobilization, indicating that circulating gastrin accounts for the response. Vagal excitation by hypoglycaemia (insulin) or pylorus ligation did not mobilize either gastrin or histamine. The histamine response to food was almost abolished by gastrin receptor blockade, and it was halved on the denervated side after unilateral subdiaphragmatic vagotomy. While the histamine response to a near-maximally effective dose of gastrin was unaffected by vagotomy, the response to low gastrin doses was reduced significantly. Abdominal ganglionic sympathectomy failed to affect the histamine response to either food or gastrin. In conclusion, gastrin is responsible for most of the food-evoked mobilization of ECL-cell histamine. The histamine response to electrical vagal stimulation reflects the effect of circulating gastrin rather than a direct action of the vagus on the ECL cells. Vagal denervation was accompanied by an impaired histamine response to food intake, probably reflecting the right-ward shift of the serum gastrin concentration-histamine response curve. The results suggest that the vagus controls the sensitivity of the ECL cells to gastrin.

Figure 1. Effect of refeeding on histamine mobilization from the ventral and the dorsal side of the stomach in fasted rats

The rats were fitted with microdialysis probes on both sides of the stomach. After 24 h of food deprivation they received standard rat chow (time zero). Access to food is indicated by straight line. Microdialysate samples were collected simultaneously from the two sides of the stomach. Mean values ± s.e.m. (n = 7).

Figure 2. Effect of vagal stimulation on gastric histamine mobilization

In A and B, the ventral vagus nerve of fasted rats was exposed below the diaphragm and stimulated electrically with 1 ms impulses of 5 V at 1, 5 or 20 Hz. In A, the serum gastrin concentration was determined 30 min before and 15 min after start of electrical stimulation (blood sampling from the tail). In B, the microdialysate histamine output during 30 min of electrical stimulation was integrated and compared with the integrated output during 30 min before stimulation. In C, a histamine response was noted on both the stimulated (asterisks above the curve) and the non-stimulated side (asterisks below the curve) of the stomach in response to electrical stimulation (5 Hz, horizontal line) of the ventral vagus nerve (n = 5). The integrated histamine response (pmol (30 min)⁻¹) (not shown) was 2-fold greater on the stimulated than on the non-stimulated side (P < 0.05). In D, it is shown that pretreatment with the gastrin receptor antagonist YF476 (300 μmol kg⁻¹, administered as a single subcutaneous dose 24 h before the experiments) virtually abolished the response to electrical stimulation (horizontal line) (results from vehicle-treated rats are given for comparison). Finally, the effects of insulin injection (E) and pylorus ligation (F) on the microdialysate histamine concentration in fasted rats were assessed. Insulin was given as a single subcutaneous injection (0.6 IU kg⁻¹) at time zero (arrow) (n = 8). The pylorus was ligated at time zero (arrow): the ligation was maintained for 4 h (experiment terminated) (n = 6). Neither insulin injection nor pylorus ligation mobilized histamine. Mean values ± s.e.m. Statistical significance was assessed by ANOVA, followed by Dunnett's multiple comparison test (*P < 0.05, **P < 0.01, ***P < 0.001).

Figure 3. Effect of refeeding on gastric histamine mobilization in fasted rats

Unilateral (ventral or dorsal) vagotomy had been performed 3 days before microdialysis (microdialysis probes on both sides of the stomach). One group of vagotomized rats received a maximally effective dose of the gastrin receptor antagonist YF476 (300 μmol kg⁻¹, as a single subcutaneous injection, Kitano et al. 2000a) 24 h before the experiments (A). Rats were given standard rat chow at time zero (refeeding indicated by horizontal line) and microdialysate samples were collected simultaneously from the ventral side and the dorsal side. In B, the histamine response to refeeding (4 h) is integrated from data in A. Mean values ± s.e.m. The number of rats is indicated. Statistical significance was assessed by ANOVA followed by Dunnett's multiple comparison test (*P < 0.05, ***P < 0.001).

Figure 4. Effect of vagotomy on gastric histamine mobilization

A, gastric histamine mobilization in response to an intravenous infusion of gastrin (5 nmol kg⁻¹ h⁻¹) in unilaterally vagotomized rats. Ventral vagotomy was performed on 5 rats 3 days before the experiments. Gastrin infusion (3 h) is indicated by horizontal line. Mean values ± s.e.m. The histamine response (integrated over 3 h) to different doses of gastrin (given by intravenous infusion) (B) and to the resulting serum gastrin concentrations (C) was assessed in 28 rats subjected to ventral vagotomy. Microdialysate samples were collected simultaneously from both the ventral (vagally denervated) and the dorsal (vagally intact) side in all rats. The gastrin dose–response and concentration–response curves for the vagally intact side and the vagally denervated side were compared. In B, each point is the mean of 4–7 rats. Each rat received one dose of gastrin only. Bars give s.e.m. The P value for the difference between the histamine response of the vagally intact and the denervated side at a gastrin dose of 0.15 nmol kg⁻¹ h⁻¹ was 0.06. Integrated values for the histamine output versus the serum gastrin concentration are given for each individual rat in C: •, the histamine output on the vagally intact side; the output on the vagotomized side of the stomach. The two sides were compared within the serum gastrin concentration range of 40–550 pmol l⁻¹ (indicated by vertical lines). The statistical significance of the difference between the two sides was assessed by ANOVA followed by Dunnett's multiple comparison test (B) or by Student's paired t test (C). *P < 0.05. Dose–response and concentration–response curves were constructed by the GraphPad PRISM program. In C, the drawn curve represents the intact side while the dotted curve represents the denervated side.

Figure 5. Effect of surgical sympathectomy on food-evoked (A) and gastrin-evoked (B) gastric histamine mobilization in fasted rats

Duration of refeeding or intravenous gastrin infusion (5 nmol kg⁻¹ h⁻¹) is indicated by horizontal lines. Mean values ± s.e.m. (n = 5).