The structure and catecholamine content of the carotid body.

The thesis reviews previous work on the ultrastructure and catecholamine content of the carotid body and describes areas of sparse available data. 1) The question of sub-populations of Type I cells on the basis of quantitative ultrastructure; 2) The reaction of the mitochondria and electron dense-cored vesicles of the Type I cells to physiological hypoxic stimuli; 3) The levels and type of catecholamines, stored within the carotid body; 4) The influence of sympathectomy on these levels; 5) The influence of hypoxia, hyperoxia and hypercapnia on catecholamine levels. The experimental data obtained has revealed that the rat carotid body contains only one cell population, whilst that of the cat contains two. Both organs show ultrastructural changes in the Type I cells in response to moderate hypoxia. The catecholamine content studies have shown that the rat stores predominantly dopamine in its Type I cells. In confirmation of previous studies hypoxia is shown to deplete dopamine levels; a new and potentially important finding is that hypercapnia and hyperoxia increase dopamine levels. The possible significance of these findings is discussed and a testable hypotheses suggested.