An in vitro bioassay for a molluscan gonadotropin

Protein synthesis occurred at a high rate in the ovaries of maturing Octopus vulgaris and could be measured from the incorporation of [¹⁴C] leucine in vivo and in isolated groups of eggs in vitro. Removal of the optic glands in vivo 1 to 3 days prior to testing markedly reduced amino acid incorporation in vivo or in vitro. After 5 days in vivo incorporation stopped. The rate of incorporation in vitro was increased by the addition of optic gland extract. Analysis of the kinetics of leucine uptake and incorporation in vitro indicated that the hormone had an effect on the inward transport of leucine which was independent of its action on protein synthesis. Electron microscopic studies of the follicle cells and ova showed that the former were the site of protein synthesis. Changes in either uptake or incorporation into protein by the follicle cells could be used as a qualitative biological assay for the optic gland hormone. Uptake was very easy to measure but incorporation was the more sensitive parameter. Either is potentially suitable as a quantitative assay for this and possibly for other molluscan gonadotropins.