Carcinoid - Cause

The cause of carcinoid, like other tumors, is still unclear. It has been noted that many symptoms of the disease are caused by the hormonal activity of the tumor. The most reliable evidence is that tumor cells secrete serotonin (5-hydroxytryptamine), a product of the conversion of the amino acid tryptophan, with its content in the blood reaching 0.1-0.3 μg/ml. Under the influence of monoamine oxidase, the bulk of serotonin is converted into 5-hydroxyindoleacetic acid, which is excreted in the urine. In the urine, the content of the final product of its conversion, 5-hydroxyindoleacetic acid (5-HIAA), is sharply increased in carcinoid and in most cases is 50-500 mg (with a norm of 2-10 mg).

The formation of serotonin from tryptophan is a complex enzymatic process that occurs in several phases. The biological functions of serotonin are known to be unusually wide. It participates in the regulation of the central nervous system, has vasoconstrictive properties, increases the tone of smooth muscles, blood clotting, regulates the blood supply to the kidneys, etc. In humans, the introduction of serotonin causes an increase in blood pressure, bradycardia, pronounced bronchospasm with asthmatic attacks, almost universal spasm of smooth muscles (miosis, pain and tenesmus of the intestines and bladder, in women - uterine contractions). The motility of the digestive tract, the secretion of all digestive juices, including saliva, are enhanced. In the body, serotonin is mainly in a bound form; most of it is fixed in platelets. Bound forms of serotonin are physiologically inert. Some proteins, lipids, and cellular polysaccharides are involved in the binding of serotonin.

The physiological activity of serotonin is manifested when it is in the blood in a free state. The release of serotonin by a tumor explains the complex set of reactions of the body observed during carcinoid (serotonin) attacks.

In recent years, it has been proven that the tumor also produces other biologically active substances: lysyl-bradykinin and bradykinin, formed as a result of the action of kallikreins on kininogens (related to plasma a2-globulins), histamine, prostaglandins and, as has been proven in recent decades, polypeptide P, i.e. it is multihormonal.

Argentaffin cells, from which carcinoid is formed, are also referred to in the literature as enterochromaffin, basal-granular (the basal part of the cells contains granules that, when examined histochemically, give argentaffin, chromaffin, acidic, alkaline and other reactions), yellow cells, intestinal argentaffinocytes (Kulchitsky cells), Heidenhain, Schmidt.

It was found that these cells are not only diffusely dispersed in the mucous membrane of the digestive tract, but are also found in other organs and perform an endocrine function. At first, it was proposed to call the system of these cells a "diffuse endocrine organ" or "diffuse endocrine system", and since 1954 the term "paracrine glands" has been used. Later, Pearse (1968-1972) developed the concept of the "APUD system", which includes a system of endocrine cells and has the ability to absorb amine precursors with subsequent decarboxylation and release of amines - oligopeptides (histamine, serotonin, choline, etc.), as well as polypeptide hormones. About 15 types of these intestinal argentaffinocytes have been differentiated (there may be more) and their classifications have been proposed.

The study of endocrine cells of the gastrointestinal tract is of great importance, in particular for a clearer understanding of the nature of carcinoid tumors and an explanation of the clinical symptoms of these diseases. Differences in endocrine ("general") symptoms of carcinoid tumors in patients are explained by the wide range of biologically active substances produced by the cells of these tumors.

The typical clinical picture of carcinoid syndrome is most characteristic of tumors originating from the jejunum and cecum.

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