Phylogenetic study on regulation of water balance by biologically active peptide.

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1. In the central nervous system of the amphioxus, six separate neuronal systems were found showing immunoreactivity for vasopressin (VP), oxytocin (OT), angiotensin II, cholecystokinin, urotensin I, and FMRFamide, respectively.2. Evidence was provided for the intragranular colocalization of immunoreactive endothelin-1 (ET-1) and neurohypophysial hormones in the axon terminal of the rat neural lobe.3. Plasma levels of immunoreactive ET-1 were not altered following hemorrhage or dehydration, whereas those of immunoreactive VP were remarkably increased. In the neural lobe, the immunoreactive ET-1 contents decreased by about 50% after dehydration, but increased nearly three-fold in hemorrhaged rats.4. ET-1-immunoreactivity was found in the preoptic nucleus and the neurohypophysis of the bullfrog. Immunoreacted neurons corresponded to a subpolpulation of 0T-immunoreactive neurons.5. Putative receptors for ET were localized autoradiographically in the bullfrog neurohypophysis using [^<125>I]ET-1 as a lignad. The highest densities were found on the axon membrane of two types of the axon, and within these axons.6. The distribution of ET-like immunoreactivity was studied in the bullfrog adenohypophysis. ET-3-immunoreactive cells were found to correspond to somatotrophs. ET-1-like immunoreactivity was not detected.7. Brain natriuretic peptide elicited a significant increase in water intake, when administered intraperitoneally or intracerebro-ventricularly, in the water-replete Japanese quail. Intraperitoneal injection of ET-1 slightly enhanced water intake.8. Immunohistochemical distribution of nine peptides, which are able to affect drinking behavior, was investigated in the rat subfornical organ (SFO). Fibers immunoreactive for substance P or Leu-enkephalin were found in the anterolateral area of the SFO, whereas fibers immunoreactive for neurotensin and LH-releasing hormone were detected in the dorsocaudal region of the SFO.