Mode of Action of some Stimulants of the Hatching Enzyme Secretion in Fish Embryos *

Mode of action of two stimulants of the hatching enzyme secretion, electric current (AC) and potassium cyanide, was analyzed by applying them to Medaka embryos in the presence or absence of suppressants of nervous system‐mediated secretion, tetrodotoxin or MS–222. Electric current (AC) stimulated the secretion of the hatching gland of the embryos that had been treated with these suppressants, while potassium cyanide did not. These results strongly suggest that electric current acts as a stimulant of hatching enzyme secretion directly on the gland cell itself, while potassium cyanide stimulates the secretion indirectly, probably through nervous system of the embryo. In the present experiments, it was also shown that Ca 2+ and ionophore, X‐537A, when applied directly to the hatching gland extracellularly, induced a marked secretion‐associated morphological change of the gland cells instantaneously. However, it was found that chum salmon prolactin did not induce the secretion‐associated morphological changes in the hatching gland cells when it was applied directly to the gland cells in situ or indirectly through embryonic circulation.