Effect of the H2-receptor antagonist metiamide on carbachol- and histamine-induced gastric acid secretion in the Atlantic cod,Gadus morhua

Autonomic control of glands and secretion: a comparative view

The autonomic nervous system together with circulating and local hormones control secretion from glands. This article summarizes histochemical and functional studies on the autonomic innervation and control of secretory glands in non-mammalian vertebrates, including secretion of saliva in the mouth and gastric acid in the stomach, secretion of enzymes and bicarbonate from the pancreas and gut wall, secretion of mucus in the gut epithelium and onto the skin, and salt secretion from salt glands and rectal glands. Cholinergic and adrenergic nerves, directly or indirectly, in combination with different types of peptidergic and other nerves appear to innervate gland tissues and affect secretion in all investigated species.

In vitro evaluation of gut contractile response to histamine in rainbow trout (Oncorhynchus mykiss Walbaum, 1792)

The contractile response of intestinal strips in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) to the administration of histamine was assessed by means of the organ bath technique. Intestinal strips were isolated from 16 clinically healthy fish and mounted in organ baths. Histamine was compared with the full agonist serotonin, to evaluate their contractile efficacy and potency. Serotonin elicited a concentration-related contraction in all examined intestinal strips, whereas histamine induced the contraction only in 14 exemplars. Of these, seven exhibited a concentration-related response. A sigmoidal curve was fitted from data (R(2) = 0.55) and its best fit values were compared with those of serotonin. Interestingly, histamine exhibited the same efficacy (E(max)) as serotonin (F-test, p > 0.05), but showed lower potency (by an order of magnitude) (F-test, p < 0.01). Moreover, the effect of the H1 antagonist, pyrilamine, has been tested to exclude aspecific contraction due to other agonists eventually released in situ following histamine administration. Pyrilamine showed a marked concentration-related antagonist action on the contractility induced by histamine with complete contractility antagonism at 10(-4)M. The authors suggest that the responses to histamine measured in the present study reflect a less sensitive response to an exogenous source of histamine, possibly due to bacterial metabolism.

A review of causal factors and control measures for bloat in farmed salmonids with a suggested mechanism for the development of the condition

A mechanism for the development of bloat in salmonids is proposed and explained in terms of the physiology of digestion and osmoregulation in fish. Understanding the causal factors for bloat enables control measures to be identified. In farmed salmonids, the chyme produced during the digestion of nutrient-rich pelleted foods that rapidly disintegrate in the stomach will be a potent activator of a negative feedback mechanism (enterogastric control), which slows stomach emptying to protect the small intestine from nutrient overload. In saline environments salmonids continuously drink sea water to replace fluid lost across the gills. Fluid loss is increased during periods of stress caused by factors such as low oxygen levels, elevated temperature or high salinity. When ingestion of nutrient-rich food results in prolonged activation of enterogastric control, slowed stomach emptying leads to decreased absorption of water, thirst and increased drinking. This further exacerbates stomach distention. The proposed mechanism for the development of bloat is supported by on-farm experience where measures to control bloat include reducing food intake, altering the composition of the diet and using appropriate strategies to reduce stress.

The effect of cimetidine on basal gastric acid secretion in the rat

1. The effect of cimetidine on the basal gastric acid secretion of the rat has been investigated in an anaesthetized lumen-perfused preparation. 2. Six rats previously given large doses of cimetidine orally showed no significant difference in basal gastric acid secretion when compared with six control rats. 3. Intravenous administration of 1 mg and 8 mg of cimetidine failed to inhibit significantly basal gastric acid secretion. 4. Although rats with a basal gastric acid secretion above 2.5 micro Eq/10 min. showed a consistent small reduction in basal gastric acid secretion after intravenous cimetidine, this was not seen in rats with a basal gastric acid secretion below 2.5 micro Eq/10 min. 5. THese results contrast sharply with the pronounced inhibition of basal gastric acid secretion by cimetidine in man and the possible reasons for this are discussed. 6. The results are also contrasted with previous work on gastric fistula rats which showed higher basal gastric acid secretion and significant inhibition by cimetidine.

Stimulation of gastric acid secretion and suppression of VIP-like immunoreactivity by bombesin in the Atlantic codfish, Gadus morhua

Cods were equipped with cannulae for drainage of the stomach and for separate perfusion of the stomach (pure sea-water) and intestine (diluted sea-water). Acidity and volume of gastric effluence were measured. Plasma immunoreactive gastrin and vasoactive intestinal polypeptide (VIP) were assayed in some experiments. The high rate of "basal" acid secretion was further elevated by i.m. administration of bombesin, but not by pentagastrin. Exogenous VIP inhibited acid secretion. Following 5 h of bombesin infusion, plasma gastrin-IR was unaffected while VIP-IR was depressed compared to saline-treated controls. The possibility that bombesin stimulates acid secretion by inhibiting VIP-release is discussed.

Effect of vagotomy and glucose administration on gastric acid secretion in the Atlantic cod, Gadus morhua

Cods were prepared for measurement of gastric acid secretion. Cannulae were implanted for drainage of the stomach and for separate perfusion of the stomach and intestine. Fishes, intestinally perfused with diluted sea-water (33% SW) exhibited high rates of acid secretion. This "basal" secretion was abolished (96% inhibition) by bilateral vagotomy. Perfusion of the stomach with isosmotic glucose (5.5%) diminished the amount of titratable acid in the gastric effluence, and induced oral ingestion of water. Only part of the decrease could be explained by neutralization by ingested sea-water. Perfusion of the intestine with 5.5% glucose, containing sea-water to raise the osmolality to that of 50% SW, depressed gastric acid secretion compared to 50% SW-perfused controls, without significantly affecting oral intake of water. I.m. administration of glucose, increasing plasma glucose to the same level as intraluminal administration, did not affect acid secretion or oral water ingestion. The study demonstrates the existence of a potential intestinal mechanism for inhibition of gastric acid secretion, and indicates that vagal activity is independent of the blood glucose level in the cod.

The ultrastructure of the gastric glands and its relation to induced secretory activity of cod, Gadus morhua (Day)

Light and electron microscopic studies have been performed on different parts of cod stomach. The studies have been concentrated on the gastric glands of the gastric mucosa. The glands consist of only one cell type. This cell contains an apically located, comprehensive tubular system as well as zymogen granules and therefore probably secretes both acid and zymogen. The high degree of development of certain organelles and their mutual localization shows a structural organization which appears suitable for an effective secretion. What appears to be intermediate organelle forms are common. When acid secretion is increased by continuous intramuscular infusion of histamine or of carbachol the most marked structural changes are increases in the size of the gland lumen and in the cell membrane facing the lumen. Histamine in particular causes the appearance of numerous long and slender cell processes in an enlarged gland lumen. When the acid secretion, increased by histamine, had reached a plateau, metiamide was infused. This histamine H2-receptor antagonist caused a decrease in acid secretion as well as in the size of the gland cell surface to values characteristic of untreated cod.

Gastric acid secretion and drinking in the Atlantic cod (Gadus morhua) during acidic or hyperosmotic perfusion of the intestine

Cods were equipped with cannulae for drainage of the stomach and for separate perfusion of the stomach and intestine. Acidity, volume, and osmolality of the gastric outflow were measured. During perfusion of the intestine with a near-isosmotic saline (1 part sea-water, 2 parts distilled water, '33% SW') and the stomach with pure ('100%') SW, gastric acid output was high and volume output slightly above the infused volume. The osmolality of the gastric perfusate decreased during passage of the stomach. It was concluded that no drinking occurred, and that the decreased osmolality was due to dilution by gastric secretions and osmotically lost water. When substituting the isosmotic intestinal perfusion to a dehydrating perfusion (100% SW), gastric acid secretion was depressed but volume output was unaffected. Also perfusion of the intestine with acidified 33% SW depressed gastric acid secretion and in addition increased volume and osmolality of the gastric outflow. The results suggest that perfusion of the intestine depress the drinking reflex and that this depression is surmounted by intestinal acidification. Possible mediators of the intestinal feed-back mechanism for the inhibition of gastric acid secretion are discussed.

Gastric acid secretion and water balance in the marine teleost Gadus morhua

Gastric acid secretion was measured in unanaesthetized codfish surgically equipped with a catheter draining the stomach. The pylorus was ligated. Without perfusion of the intestine, or during perfusion with pure sea water (100% SW) or slightly diluted (67%) SW, gastric acid secretion was low ( less than 10 mumol H+/kg.h) and the fishes became dehydrated during the experiment. Perfusion of the intestine with 50% or 3% SW enabled the fishes to compensate for the water loss to the environment and greatly enhanced gastric acid secretion. Acid secretion was elevated also in fishes in which the dehydration was prevented by an intra-muscular infusion of saline. Perfusion of the intestine (8.5 ml/h) decreased the hourly effluent volume ('drinking rate') from the stomach to almost zero within 2 h. The effect was independent of the degree of dilution of the perfusing SW, but was less pronounced when the perfusion rate was lowered. Intra-muscular saline also depressed 'drinking rate'. The acid secretion prevailing during perfusion of the intestine with SW at a dilution preventing dehydration--suggested to represent the basal acid secretion of the codfish--was inhibited by atropine, hexamethonium, and metiamide.

Effect of atropine and SC-15396 on stimulated gastric acid secretion in the atlantic cod, Gadus morhua

Gastric acid secretion was measured in swimming codfish surgically equipped with a catheter draining the stomach. Gastric acid secretion was stimulated by histamine (5 or 15 microgram/kg-h) or by carbachol (5 microgram/kg-h). Pretreatment with atropine (1 mumol/kg-h) completely prevented the acid secretion induced by carbachol, but did not influence the secretion induced by histamine. Atropine had marked effects on the motor functions of the stomach, and seriously reduced the volume draining from the stomach. Infusion of phenol red indicated that the decrease in volume was due to a decrease in recovery of ingested water. SC-15396, "antigastrin", significantly depressed acid secretion induced by histamine, and reduced carbachol-stimulated secretion, although the later was statistically insignificant. The effects of SC-15396 is discussed with reference to the absence of receptors for gastrin related to gastric acid secretion in the codfish stomach.