Effects of cyproheptadine on the rat yolk sac membrane and embryonic development in vitro.

Electron-microscopic examinations of rat embryonic yolk sacs treated in vitro with 1.5 X 10(-5) M cyproheptadine showed proliferation of the lysosomal structures; other organelles remained unaffected, and also overall yolk-sac growth and vascularization were comparable to non-treated samples. Radioactive measurements with 125I-labelled albumin showed that yolk sacs and embryos of the cyproheptadine-treated group incorporated less radioactivity than the controls. Embryos inside the yolk sacs, treated either for 24 or 48 h, were severely retarded in growth and differentiation (approximately 50% of the controls). It is suggested that the specific action of cyproheptadine on yolk-sac lysosomal structures, combined with reduced macromolecular transport, is the cause of inhibited embryonic development.