Effects of Thyrotrophin‐releasing Hormone, and Methionine‐enkephalin on Gastric Acid and Pepsin Secretion in the Cat

Abstract

upon Tyne NEI 7RU1 The effect of intravenous administration of thyrotrophin-releasing hormone (TRH) and methionine-enkephalin on gastric acid and pepsin secretions was investigated in conscious cats prepared with chronic gastric fistulae.2 TRH, 20 jig kg-' h-', did not influence unstimulated gastric acid secretion, nor gastric acid secretion stimulated by submaximal doses of pentagastrin or histamine. Pepsin secretion stimulated by pentagastrin was not influenced by TRH. 3 TRH, 20 pg kg-' h-, significantly reduced the gastric acid and pepsin responses to intravenous infusion of insulin. TRH also significantly reduced the degree of hypoglycaemia seen in response to insulin. TRH, 20 pg kg-' h-V, but not 5 Mg kg-1 h-V, infused alone resulted in a significant hyperglycaemia. 4 It is concluded that the reduction of insulin-stimulated gastric secretion by TRH is not dependent on the hyperglycaemic action of the peptide. The mechanism of action of TRH on insulin-stimulated secretion is discussed with respect to its site of action. 5 Methionine-enkephalin or the potent analogue, D-Ala2, Met-enkephalinamide were without effect on unstimulated gastric secretion, or secretion stimulated by pentagastrin, histamine, and insulin. The opiate receptor antagonist, naloxone, did not significantly alter the gastric acid or pepsin response to insulin. 6 It is concluded that there is no evidence that opiates stimulate oxyntic glands directly, nor that the oxyntic cells may possess high affinity binding sites for opiates, nor that endogenous opiates are involved in the control of gastric secretion.

Modulation of Acid Secretion from Enriched Guinea Pig Parietal Cells by Opioid Receptors

“…27], and man [2,17], In contrast, stimu latory effects occurred in the dog [10; these workers also reported inhibition] and man [6,19]. Finally, Gascoigne et al [8] found no influence of opioids on gastric acid secretion in the cat in vivo, and Canfield and Spencer [3] observed no effect in the isolated stomach of rats.…”

Stereospecific Inhibition by Naloxone of Histamine-Stimulated Acid Secretion in Isolated Guinea Pig Parietal Cells

“…It is still a matter of debate whether opioids have an effect on gastric acid secre tion and if so, whether they stimulate or inhibit, and whether the effect is elicited in the gastric mucosa or centrally [3,4,6,8,9,11,12,14,17,21,23], In a previous paper [10], we have demonstrated for the first time that the opioid peptide D-ala2-Z)-leu5-enkephalin (DADLE) [25] enhanced acid secre tion stimulated by histamine in isolated and enriched guinea pig parietal cells. The effect was blocked by the competitive opioid antag onist naloxone, suggesting a specific effect on opioid receptors.…”