Serotonin and gastrin cells in rat gastrointestinal tract after thyroparathyroidectomy and induced hyperthyroidism

Thyroidectomy appears to reduce the serotonin content in the rat brain, whe reas hyperthyroidism has the opposite effect. As it is not known whether th e serotonin-producing cells of the gastrointestinal tract are influenced by these conditions. the effects of thyroparathyroidectomy and induced hypert hyroidism were studied experimentally, particularly as regards the serotoni n- and gastrin-immunoreactive cells of the gastrointestinal tract. Immunocy towchemical and quantification techniques were, used to localize and determ ine the numbers of serotonin and gastrin cells. In thyroparathyroidectomize d rats the intestine was significantly shorter and the mucosa thinner than in sham-operated and untreated controls, whereas the converse was found in the hyperthyroid rats. Following thyroparathyroidectomy, there were fewer g astrin-immunoreactive cells in antrum and the serotonin-immunoreactive cell s were significantly less dense throughout the gastrointestinal tract. In h yperthyroid rats, gastrin-immunoreactive cells were more numerous, as were the serotonin-immunoreactive cells in the small intestine, whereas these ce lls were fewer in antrum and caecum. In conclusion, the thyroid gland exert s a significant influence on the gastrointestinal tract and on the serotoni n and gastrin-immunoreactive cells. The observed alterations may reflect a direct effect of the thyroid hormones, although indirect factors must also be considered.