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The reactions of the previously described neuro-epithelial bodies (NEB)(Lauweryns et al., 1969, 1970, 1972a, b, 1973a, b, c 1974, 1975) in young rabbits to: (1) hypoxia with normoxaemia in the arteria pulmonalis on the one hand, and (2) hypoxaemia in the arteria pulmonalis with normoxic aeration on the other hand, has been investigated by means of cross-circulation experiments and light microscopical, electron microscopical and morphometrical techniques. Hypoxically aerated young rabbits, which received normoxaemic blood in their arteria pulmonalis from a donor rabbit by means of an arterio-arterial cross-circulation with mutal exchange transfusion, revealed an increased exocytosis of the dense-core vesicles of their NEB. Normoxically aerated young rabbits which received hypoxaemic blood in an identical manner, did not exhibit an increased exocytosis. It is concluded that the NEB apparently react directly to the hypoxia of the inhaled air and not to the hypoxaemia of the pulmonary blood. By the release of serotonin and a polypeptide substance, they may produce a local vasoconstriction in hypoxically aerated lung areas, enabling an intrapulmonary regulation of the V/Q ratio. This is regarded as additional proof that the NEB--while being modulated by the CNS--probably are intrapulmonary chemoreceptors with local secretory activities, reacting to the composition of the inhaled air.

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The intrapulmonary lining epithelium of rabbits contains newly identified corpuscles composed of argyrophil, argentaffin, yellow fluorescent, ultrastructurally granulated and innervated epithelial cellular organs. These are proved, by electron microscopic cytochemistry and microspectrography, to be a source for intrapulmonary production of serotonin. Probably they are intrapulmonary neuroreceptor organs modulated by the central nervous system which exhibit local secretory activities.