| Research Abstract |
1. We isolated atrial natriuretic peptide(ANP)and ventricular natriuretic peptide(VNP)from the eel atrium and ventricle, respectively and determined their amino acid seguences. We also determined cDNA sequence of eel VNP.
2. We established specific radioimm unoassay systems for eel ANP and VNP, and measured the levels in eel plasma, atria, ventricles and brains. The heart contains 3-fold greater level of ANP than that of VNP, but the plasma level of VNP was 3-foldgreater than that of ANP.
3. Protein A-goldimmunocytochemistry revealed many secretory granules which contain ANP, but VNP-containing. . granules in the ventricle was scarce.
4. Eel atrial myocytes in culture secrete a small amount of ANP into the medium but the amount stored in the cell is large. Eelventricular myocytes in culture secrete a large amount of VNP but store little VNP.
5. Based on these results, we hypothesized that ANP is principally synthesized in the atrium, stored in the granules, and secreted upon exogenous stimulus(regulatory pathway), whereas most of the VNP synthesezed in the ventricle is secreted soon without storage in the granules (constitutive pathway).
6. In order to substantiate this hypotheses, we are now conducting a pulse-chase experiment using labeled ^<32>S-Cysteine to examine the rate of secreion of ANP and VNP from eel atrium and ventricle in tissue culture. We also examine the expression of mRNA of ANP and VNP in the eel atrium and ventricle using a Northern blot analysis.
7. In the fetal rat, ANP is secreted from the atrium and ventricle viaregulatory pathway and constitutive pathway, respectively, although adult ventricles do not produce ANP in mammals. Thus, the data from eels and fetal rats illustrate that the Biogenic law of Haeckel, i. e., "Ontogeny is a recapitulation of phylogeny" appears to beapplicable to the mode of hormone secretion.
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