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The effect of hypophysectomy on the gastrointestinal tract was studied in the rat 8 wk after operation, particularly regarding the frequency and distribution of serotonin, somatostatin and gastrin-immunoreactive cells. Body weight, the length of the intestine and the thickness of the mucosa of the antrum and small intestine were all reduced in the hypophysectomised rats compared with sham-operated and untreated controls. In the hypophysectomised animals the serotonin-immunoreactive cells were fewer in the antrum and caecum, whereas they were more numerous in the proximal large intestine. There were fewer gastrin-immunoreactive cells in the antrum, while the somatostatin-immunoreactive cells were more numerous in the antrum and caecum. The significant influence of hypophysectomy on the gastrointestinal tract could be direct, but could also be associated with the marked effect of pituitary deficiency on endocrine cells, known to exert both trophic and antitrophic actions. However, it could also be an indirect effect on metabolism, resulting in lower food intake, other endocrine cell systems, and growth factors.

The effects of bilateral adrenalectomy on the serotonin-, somatostatin-, and gastrin-immunoreactive cells in the rat gastrointestinal tract were studied four weeks after surgery. Body weight was reduced and the small intestine shorter in adrenalectomized animals compared with controls, while no changes were found in the histology of the mucosa. In the adrenalectomized animals the number of serotonin-immunoreactive cells was increased in the cecum and large intestine, while the somatostatin-immunoreactive cells were decreased in number in the antrum and increased in the corpus, cecum, and large intestine. The gastrin-immunoreactive cells in the antrum were not affected in number, but their nuclear size was enlarged, possibly indicating increased cellular activity.

Thyroidectomy appears to reduce the serotonin content in the rat brain, whereas hyperthyroidism has the opposite effect. As it is not known whether the serotonin-producing cells of the gastrointestinal tract are influenced by these conditions, the effects of thyroparathyroidectomy and induced hyperthyroidism were studied experimentally, particularly as regards the serotonin- and gastrin-immunoreactive cells of the gastrointestinal tract. Immunocytochemical and quantification techniques were used to localize and determine the numbers of serotonin and gastrin cells. In thyroparathyroidectomized 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 gastrin-immunoreactive cells in antrum and the serotonin-immunoreactive cells were significantly less dense throughout the gastrointestinal tract. In hyperthyroid rats, gastrin-immunoreactive cells were more numerous, as were the serotonin-immunoreactive cells in the small intestine, whereas these cells were fewer in antrum and caecum. In conclusion, the thyroid gland exerts a significant influence on the gastrointestinal tract and on the serotonin-and gastrin-immunoreactive cells. The observed alterations may reflect a direct effect of the thyroid hormones, although indirect factors must also be considered.

The effects of bilateral adrenalectomy on the serotonin-, somatostatin-, and gastrin-immunoreactive cells in the rat gastrointestinal tract were studied four weeks after surgery. Body weight was reduced and the small intestine shorter in adrenalectomized animals compared with controls, while no changes were found in the histology of the mucosa. In the adrenalectomized animals the number of serotonin-immunoreactive cells was increased in the cecum and large intestine, while the somatostatin-immunoreactive cells were decreased in number in the antrum and increased in the corpus, cecum, and large intestine. The gastrin-immunoreactive cells in the antrum were not affected in number, but their nuclear size was enlarged, possibly indicating increased cellular activity.

Values for the affinity constant were determined, in three kits, for seric gastrin, following the Scatchard plot and Michaelis-Menten representation. The determination of the affinity constant, K, is of great value for it defines the antigen-antibody complex stability and it gives information about some aspects of the analysis system: sensitivity and antibody saturation.