Blood serotonin

Enterochromaffin cells are interspersed with mucosal cells mainly in the stomach and small intestine. In the blood, serotonin is present at high concentrations in platelets, which take up serotonin from the plasma by an active transport process. Serotonin is released on platelet activation. In the central nervous system, serotonin serves as a transmitter. The main serotonin-containing neurons are those clustered in form of the Raphe nuclei. Serotonin exerts its biological effects through the activation of specific receptors. Most of them are G-protein coupled receptors (GPCRs) and belong to the 5-HTr, 5-HT2-, 5-HT4-, 5-HTs-, 5-HT6-, 5-HT7-receptor subfamilies. The 5-HT3-receptor is a ligand-operated ion channel. 

Hanna, G.L., Himle, J.A., Curtis, G.C., Koram, D.Q., Weele, J.V.V., Leventhal, B.L., and Cook, E.H., Jr. (1998) Serotonin transporter and seasonal variation in blood serotonin in families with obsessive-compulsive disorder. Neuropsychopharmacology 18 102-111. 

Abrahamson, R.K., Wright, H.H., Carpenter, R., Brennan, W., Lum-puy, O., Cole, E., and Young, S.R. (1989) Elevated blood serotonin in autistic probands and their first-degree relatives./ Autism Dev Disorder 19 397-407. 

Hoshino, Y., Yamamoto, T., Kaneko, M., Tachibana, R., Wantabe, M., Ono, Y., and Kumashiro, H. (1984) Blood serotonin and free tryptophan concentration in autistic children. Neuropsychobiology 11 22-27. 

Ritvo, E.R., Yuwiler, A., Geller, E., Ornitz, E.M., Saeyer, K., and Plotkin, S. (1970) Increased blood serotonin and platelets in early... 

Salazar D, Chaikin P, Swanson B, et al. The effects of nefazodone and fluoxetine on platelet serotonin uptake and whole blood serotonin. Clin Pharmacol Ther 1994 55 137. 

Raleigh MJ, Brammer GL, Ritvo ER, Geller E, McGuire MT, Yuwiler A. Effects of chronic fenfluramine on blood serotonin, cerebrospinal fluid metabolites, and behavior in monkeys. Psychopharmacology (Berl) 1986 90 503-508. 

Hyperserotonemia has been a consistent finding in subjects with autism, which may be due to activity of serotonin-associated platelet proteins (Hranilovic et al., 2008, 2009). Interestingly, 99% of blood serotonin is contained in platelets (Anderson et al., 1987) and studies have shown that there is an approximate 50% increase in blood-levels of serotonin in subjects with autism vs. controls (McBride et al., 1998). Hypotheses for increased serotonin include increased synthesis of serotonin by tryptophan hydroxylase (TPHl), increased uptake of serotonin into platelets via serotonin transporters (5-HTT), diminished release of serotonin from platelets via serotonin 2A receptor, and decreased breakdown of serotonin by monoamine oxidase (MAOA) (Hranilovic et al., 2008). A study by Hranilovic et al. (2008) identified polymorphisms of tryptophan hydroxylase and MAOA with increased serum serotonin levels. Similarly, haplotype analysis has shown a significant association between polymorphisms of TPHl and increased serotonin in whole blood (Cross et al., 2008). 

Anderson GM, Freedman DX, Cohen DJ, Volkmar FR, Hoder EL, McPhedran P, Minderaa RB, Hansen CR, Young JG (1987) Whole blood serotonin in autistic and normal subjects. 1 Child Psychol Psychiatry 28 885-900... 

Serotonin can be measured in whole blood, serum, platelet-rich plasma, platelet-poor plasma (i.e., platelet-free plasma), isolated platelet pellets, urine, and CSF. Most blood serotonin is stored in the platelets and is easily released during sample preparation. For whole blood serotonin, venous blood (10 mL) is drawn into a tube containing potassium EDTA as an anticoagulant, gently mixed, placed on ice, and transferred to a storage tube. An aliquot of blood is then removed for a platelet count alternatively, a simultaneous EDTA blood sample can be collected. Antioxidants such as ascorbic acid or metabisulfite are conveniently added to the storage tube when a fluorometric detection system is used. Blood serotonin samples are stored frozen at -20 °C, preferably within 2 hours after collection. 

Carling RS, Degg TJ, AUen KR, Bax ND, Barth JH. Evaluation of whole blood serotonin and plasma and urine 5-hydroxymdole acetic acid in diagnosis of... 

Bhagavan, H. N., Coleman, M., and Coursin, D. B., The effect of pyridoxine hydrochloride on blood serotonin and pyridoxal phosphate contents in hyperactive children, Pediatrics, 55(3), 437, 1975. 

Ferguson, FI. B., Pappas, B. A., Trites, R. L., Peters, D. A., and Taub, FI., Plasma free and total tryptophan, blood serotonin, and the hyperactivity syndrome No evidence for the serotonin deficiency hypothesis, Biol. Psychiatr., 16(3), 231, 1981. 

The neurohypophyseal hormones oxytocin and vasopressin are involved in autism. Elevated levels of blood serotonin occur in one third to two thirds of persons with autism. Parents of autistic children often have elevated blood serotonin levels, as well as an increased incidence of depression, obsessions, and compulsions. 

Serotonin In blood serotonin is predominantly located in the platelets, with levels in plasma being 100-fold lower. Most analysts interested in serotonin measurements have concentrated on determining serotonin in whole blood or platelet rich plasma. The presence of monoamine oxidase enzymes in blood necessitates the use of an enzyme inhibitor, e.g., pargyline to prevent the conversion of serotonin to 5-HIAA prior to analysis. Similar chromatographic conditions to those used for catecholamines can be used, e.g., CIS reversed-phase columns and electrochemical detection at an oxidation potential of -I-0.75 V or fluorescence detection. Sample... 

Schmid, E., Scheiffarth, F. and Zicha, L., Blood-serotonin in rheumatic disease. Lancet 1959, p. 354. 

Studies on MAO-A deficiency are limited to one family and only urine has been analysed. It is probable that elevated whole blood serotonin and plasma catecholamines would also point to this condition. 

B. Whole Blood Serotonin Levels after Infusion ... 

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