Studies in neurosecretion. IX. Possibility of occurrence of a sodium-regulating hormone in the caudal neurosecretory system of teleosts.

The problem of osmoregulation in teleosts has been extensively studied by a number of workers to the effect that the basic plan of adaptive water and salt balance is figured out in its outline(Krogh, 1939; Baldwin, 1949; Black, 1951; Gaunt and Birnie, 1951; Fontaine, 1953, etc.). Several lines of evidences are available for physiological interpretation of observed osmotic phenomena in terms of the branchial, renal and/or dermal activities, but, despite much efforts hitherto made, the pattern of endocrine co-ordination responsible for the control of the gates for salt and water is yet only superficially understood. On the basis of recognition of the significant morphological characters of the caudal neurosecretory system in the terminal region of the spinal cord in various kinds of freshwater as well as marine teleosts(Enami, 1955; Enami and Imai, 1955, 1956 a, b), work has been directed to the inquiry of the role played by this possible endocrine source. The most recent experiments concerning the variability of the spinal neurosecretion in the loach, Misgurnus anguillicaudatus, are much demonstrable of the primary dependence of the phenomenon on prevailing osmotic relations between the fish body and the medium water(Enami, 1956). Such observation stimulated an attempt to investigate a possibility of production by the said neurosecretion of a certain hormonic principle concerned with the teleostean osmoregulation. Present report is rather of a preliminary nature, showing the outcomes of some of the experiments in vivo composing a part of such attempt.