The Gamete-Shedding Substances of Starfishes: A Physiological-Biochemical Study

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Abstract
A shedding substance, found in the radial nerves of 14 species of starfish, induced the release of gametes from intact animals as well as from whole or fragmented gonads. The shedding substance was not sex-specific, being present in the radial nerves of both males and females throughout the year, and, in general, was not species-specific. This neurosecretory-like polypeptide appeared to function by stimulating ovarian muscle to contract, and was calcium-dependent: it also stimulated the maturation of immature eggs. The shedding substance has been purified and its amino acid composition investigated. A second physiologically-active material, termed “shedhibin” because it inhibited shedding activity, was also found in the radial nerves of ripe sea stars. In the presence of shedhibin, normally-adequate quantities of shedding substance would not cause the release of gametes from isolated ovarian fragments. It appeared that although the level of shedding substance was constant throughout the year, the level of shedhibin fluctuated, possibly controlling the natural release of gametes from sea stars. The precise chemical nature of shedhibin has yet to be determined.

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