Effects of adrenoceptor antagonists on vagally induced gastric and duodenal HCO₃^‐ secretions in the cat

Abstract

Experiments were performed on chloralosed cats with ligated adrenal glands. The cervical vagi were cut and arranged for electric stimulation. The gastric lumen was continuously perfused, and the secretions of H+ and HCO3- were calculated from pH/pCO2 measurements in the perfusate. Gastric motility was recorded as changes in hydrostatic pressure within the perfusion system. Mucosal HCO3- secretion into a duodenal segment, distal to the papilla of Vater and Brunners gland area, was titrated in situ by a pH-stat equipment. Animals pretreated with various adrenoceptor blockers or splanchnicotomy were compared with control animals with intact sympatho-adrenergic system. Basal gastric motor activity, H+ and HCO3- secretions, as well as duodenal HCO3- secretion were not influenced by prazosin, propranolol or splanchnicotomy. Yohimbine increased significantly basal gastric HCO3- secretion, but did not influence basal gastric motor activity, H+ secretion or duodenal HCO3- secretion. Vagal stimulation in yohimbine-treated or splanchnicotomized animals induced significantly larger gastric contractions, HCO3- secretory and duodenal HCO3- secretory responses than in the controls, whereas these responses to vagal stimulation were small in prazosin- or propranolol-treated animals. Vagally induced gastric H+ secretory responses were significantly larger in propranolol-treated animals than in controls, whereas prazosin-treated, yohimbine-treated or splanchnicotomized animals in this regard did not differ from the controls. The results suggest the existence of a sympathetic, probably alpha-2-adrenergic, inhibition of vagally induced gastric contractions as well as of the gastric and duodenal HCO3- secretions.

Bleeding‐induced decrease in duodenal HCO‐3 secretion in the rat is mediated via α2‐adrenoceptors

“…The present results suggest that reflex activation of the SNS, due to a 10% blood loss, releases catecholamines which inhibit duodenal HCO; secretion by an activation of mainly a,-adrenoceptors. These findings are in line with earlier observations in the cat, which suggest that the splanchnic nerves exert a depressive effect on gastroduodenal HCO; secretion via activation of peripheral a,-adrenoceptors (Fandriks I 986, Fandriks & Jonson 1987, Fandriks et al 1987. Bicarbonate secretion is considered to be important in the gastroduodenal mucosal defence (Flemstrom & Turnberg 1984).…”

“…An arterial bleeding of 0.6 ml per IOO g body wt, corresponding to 10% of the total blood volume (Lundin et al 1981), decreases the vagally induced duodenal HCO; secretion via an activation of the splanchnic nerves in the rat (Jonson & Fandriks 1987). Such a reflex activation of the sympathetic nervous system (SNS) is probably induced mainly via unloading of cardiovascular baro-and volume-receptors.…”

“…Thus, vagal stimulation increases HCO; secretion Uonson er al. 1986, Nylander et al 1987) whereas activation of the splanchnic nerves has an inhibitory action via activation of a,-adrenoceptors (Fandriks 1986, Fandriks et al 1987). In a previous study we showed that a minor blood loss, via an increased sympathetic activity conveyed in the splanchnic nerves, decreases the vagally induced duodenal HCO; secretion in rats (Jonson & Fandriks Correspondence : Claes Jonson, Department of Physiology, University of Goteborg, Box 330 3 I , S-400 33 Goteborg, Sweden.…”

Neural pathways regulating Brunner's gland secretion in guinea pig duodenum in vitro

“…Studies that examined regions of the duodenum devoid of Brunner's glands have demonstrated that bicarbonate secretion is regulated by both extrinsic and intrinsic pathways. These include vago-vagal reflexes (2,7,15,16,23), reflexes within the submucosal plexus of the enteric nervous system (12), C fiber efferent mechanisms (11,29), and inputs from the sympathetic nervous system (5,6,22). The interactions between these neural pathways have also been studied, and the findings suggest that secretomotor reflexes within the submucosal plexus are modified by vagal and sympathetic efferents that provide excitatory and inhibitory inputs, respectively, to submucosal neurons (6,22).…”

Vagal and sympathetic control of gastric and duodenal bicarbonate secretion

“…Activation of sympathetic nerves by applying negative pressure to the lower body, which increases venous pooling and mimics a hypovolaemic situation, decreases gastric bicarbonate secretion in man (0) (n = 6). Data from [25]. [22].…”