Release of 5‐hydroxytryptamine (serotonin) from the dog's gastro‐intestinal tract

Abstract

provided (1) for the spontaneous release of a substance similar to 5-hydroxytryptamine from the gastro-intestinal tract, (2) for the specific release of such a substance from the perfused stomach. METHODSDogs which had fasted overmght were anaesthetized with pentobarbitone (Nembutal).Collection of blood. Owing to the fragility of platelets, the following precautions were taken in the collection of blood samples. All glass cannulae and centrifuge tubes were treated with silicone. Each tube contained 0-2 ml. of a 1 % solution of heparin, and 15 mg of 'Versene' (di-sodium salt of ethylene diamine tetraacetic acid) in 0 3 ml. of water to give a final concentration of 0.1 % in 15-16 ml. of blood. In order to separate the plasma the blood samples were centrifuged at 3000 rev/min for 20 min.Arterial blood was collected from a cannulated femoral artery. For the collection of portal blood the following operation was performed. The spleen was removed and a branch of the splenic vein was cannulated. A loose ligature was placed around the portal vein near its entrance into the liver. By pulling on this ligature the portal vein was occluded and portal blood diverted into the cannulated splenic vein.Plasma contains unknown substances which interfere with assays for 5-hydroxytryptamine on the rat's isolated colon. This difficulty was overcome either by dialysing plasma and using the dialysates for the assays or by extracting the plasma with acetone and assaying the acetone extracts.Dialysis of plawma. 5 ml. of plasma was placed in a cellophane bag and dialysed against 10 ml. of a saline solution of the same composition as that used in the assay of serotonin on the rat's * Part of this work was performed at

The release of 5‐hydroxytryptamine from rabbit small intestine in vitro

“…Hence, it can be assumed that under the 'Normal' and 'Niamid' conditions the endogenous 5-HT was released directly into the serosal fluid and that release into the lumen with subsequent absorption did not occur. The evidence that endogenous 5-HT is released into the serosal fluid adds further support to the view that blood 5-HT is derived from the intestine (Toh, 1954;Erspamer & Testini, 1959;Adams, 1960;Bertaccini, 1960;Stacey & Young, 1964).…”

“…The uptake of 5-HT by platelets in vivo has also been demonstrated (Erspamer, 1956;Weissbach, Bogdanski & Udenfriend, 1958). There is also considerable evidence that the gastrointestinal mucosa is the main, if not the only, source of platelet 5-HT (Toh, 1954;Haverback & Davidson, 1958;Rosenberg, Davis, Moran & Zimmermann, 1959;Bertaccini, 1960). The large amounts of 5-HT in the enterochromaffin cells and the elevation M. C. E. GWEE AND T. S. YEOH of blood 5-HT in patients with carcinoid tumours (Sjoerdsma, Weissbach & Udenfriend, 1956) indicate that platelet 5-HT has its origin in the enterochromaffin cells (Barter & Everson-Pearse, 1953, 1955Erspamer, 1955).…”

Common Drugs Inhibit Human Organic Cation Transporter 1 (OCT1)-Mediated Neurotransmitter Uptake

“…Dopamine uptake by OCT1, although significant, is again unlikely to be germane to the liver because of the low circulating levels of this neurotransmitter. Serotonin, however, is found at high concentrations in the gut; consequently, portal blood levels are significantly higher than arterial blood, reportedly as much as 3-fold (Toh 1954;Gershon and Tack, 2007), making it the best candidate of the three neurotransmitters to be transported by OCT1 in vivo. Because of this, and the data suggesting that serotonin was the superior neurotransmitter substrate for OCT1, serotonin was selected as the model endogenous substrate for further study.…”

Biogenesis of 5-Hydroxytryptophan

“…However platelets take up 5-HT from solution (Humphrey and Toh, 1954) and there are many sites (e.g., the intestinal tract; Toh, 1954) where the presence of large amounts of 5-hydroxytryptophan decarboxylase suggests that the circulating platelets may acquire their 5-HT. There is, however, no evidence that the 5-hydroxytryptophan is formed at the same sites at which it is decarboxylated.…”