MONOAMINERGIC MECHANISMS IN THE PANCREATIC α-CELLS

SUMMARY The occurrence of biogenic monoamines in the islets of Langerhans have been studied in different species and at different developmental stages. Great species and inter-individual differences were found. Dopamine is often stored within the islet cells especially in young and pigmented animals. In some species, dopamine and 5-hydroxytryptamine seem to occur simultaneously in varying proportions within one and the same cell. A monoamine storage in the α-cells have been found in the owl monkey, dog, cat, and the avain species, and in young pigmented rabbit and mouse. The α-cells, as well as the β-cells, store monoamines in the pig and new-born and foetal guinea-pig. In human foetus and adult guinea-pig, a storage has, so far, been observed only in the β-cells. No monoamines have been found in the endocrine cells in the rat, golden hamster, some strains of monkey, and albino and adult pigmented rabbit and mouse. The absence of demonstrable amounts of monoamines in islet cells does not exclude monoaminergic mechanisms from operating in such cells, since both the α-cells and the β-cells of albino mouse have a stereospecific uptake mechanism for l -dopa, which is then decarboxylated, stored, and deaminated within the islet cells. A transplantable islet cell tumour of golden hamster has been shown to contain dopamine, 5-hydroxytryptamine, and dopa, and also an unidentified substance, probably monoamine-like, capable of condensing with formaldehyde to fluorescent derivatives.