Gastric emptying and secretion in the calf on duodenal infusion of tryptophan, tryptamine and 5‐hydroxytryptamine

Abstract

SUMMARY1. Gastric emptying, gastric acid and pepsinogen secretion were assessed simultaneously in the conscious calf using the test meal and duodenal perfusion technique (Bell & Mostaghni, 1975).2. When 60 mM-HCl was infused into the duodenum, gastric emptying was arrested but both acid and pepsinogen secretion continued at a low level. Duodenal infusion with isotonic NaHCO3 caused rapid exponential emptying of the test meal and acid and pepsinogen output was more than doubled.3. Duodenal infusion of amino acids in isotonic NaHCO3 did not affect the rapid emptying, except infusion with tryptophan, which caused a measureable degree of inhibition of emptying, with concomitant effects on acid and pepsinogen secretion 4. Tryptamine and 5-hydroxytryptamine (5-HT) incorporated in low concentration into isotonic NaHCO3 also produced depression of gastric emptying, acid and pepsinogen levels comparable to the response initiated by acid infusate. Tryptophan was effective only in non-physiological amounts while 5-HT and tryptamine were active in smaller doses.5. Our results suggest that the inhibition of gastric emptying following duodenal infusion of tryptophan noted by Stephens, Woolson & Cooke (1975) may be due to the duodenal synthesis of its biogenic amine derivatives tryptamine and 5-HT.6. The level of activity of the three gastric functions, emptying, acid secretion and pepsinogen secretion appears to be linked. A single stimulus, therefore, could evoke a duodenal receptor or receptors to mediate or suppress activity of the gastric smooth muscle and secretary cells through interrelated mechanisms. The effect of some duodenal infusates, however, produces some variability in response which suggests differential activation of different receptors with consequent variable motor activity on effector cells.

The interplay between hydrogen ions, bicarbonate ions and osmolarity in the anterior duodenum modulating gastric function in the conscious calf

“…Duodenal infusion of NaCl at a constant osmolality of 300 m-osmole/kg, but with pH ranging from 2-0 to 12-0, did not alter the high level of gastric emptying and secretion already reported for isotonic NaCl or NaHCO3 alone (Bell & Mostaghni, 1975;Bell & Webber, 1979). Gastric function, therefore, is either unaffected by gastric chyme at pH 2-0-12-0 entering the duodenum, or else isotonicity is dominant over pH in activating duodenal receptors which increase motor activity.…”

“…In man (Hunt & Knox, 1969) and the calf (Bell & Razig, 1973b), as the concentration of HCl in a meal increases so emptying of the stomach decreases. In contrast to the inhibitory effect of duodenal acidification, alkalinization by isotonic NaHCO3 is an effective stimulant of gastric emptying and secretion (Bell & Webber, 1979). The stimulatory effect of certain isotonic solutions is believed to be mediated through duodenal osmoreceptQrs (Hunt & Knox, 1969;Bell & Razig, 1973b).…”

“…It is recognized that HCl of the gastric chyme modulates gastric functions such as emptying (Hunt & Knox, 1972;Bell & Webber, 1979), secretion (Andersson, Nilsson & Sjodin, 1976;Bell & Webber, 1979) and blood flow (Benyo, Saindor & Szabo, 1979) through duodenal receptors. In man (Hunt & Knox, 1969) and the calf (Bell & Razig, 1973b), as the concentration of HCl in a meal increases so emptying of the stomach decreases.…”

“…Various types of surgical pouches of the stomach have been used to study gastric acid secretion but they cannot be utilized to measure gastric emptying alone or combined with secretion. The duodenal re-entrant preparation in the calf overcomes these difficulties and allows a continual controlled stimulus, with simultaneous collection of gastric effluent without contamination of the duodenal infusate (Bell & Mostaghni, 1975;Bell & Webber, 1979). We have sought to measure the effects on gastric function of discrete amounts of acid and alkali introduced directly into the duodenum.…”

Communications

“…Department of Medicine, Royal Veterinary College, London NW1 OTU The presence of gastric hydrochloric acid in the duodenal chyme is known to be a powerful determinant of gastric function in many species, including man (Hunt & Knox, 1969) and calf (Bell & Webber, 1979). The greater the duodenal concentration of acid the greater the reduction in gastric empt-ing and secretion.…”