THE SEA URCHIN EGG AS A TESTING OBJECT IN TOXICOLOGY

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Abstract
The sea urchin egg offers unique properties for experimental work on the cellular and embryologic level. The developmental stages are well suited for the study of teratogenic effects exerted by drugs. The development of the sea urchin egg is holoblastic and resembles the early development of the human ovum considerably. The gametes and embryos of the regular sea urchin species Paracentrotus lividus and Psammechinus microtuberculatus have been used in a study of the teratogenic effects of chloramphenicol, nicotine, chlorpromazine, imipramine and thalidomide. All the substances tested were found to influence the fertilization, cleavage and differentiation of the larvae. The effects of the substances on the cellular and embryonic level are described and the possible mechanism of action is discussed.During the past decade the interest in substances inflicting malformations or general injuries in living organisms has gained an increasing interest. The extensive use of biocides and their repercussions on living organisms of immediate economic interest and on man created an extending research in this field. Of particular importance was, however, the discovery of the teratogenic properties of the sedative hypnotic drug thalidomide. In spite of the elaborate pharmacological methods applied in testing drugs before their adoption in clinical use thalidomide, if administered during pregnancy, was ascertained to cause congenital malformations in man. This was a surprise since thalidomide was regarded as a particularly safe drug and even the intake of large overdoses did not seem to cause any persisting ill effects. There is, however, some confusion about the teratogenic effect of thalidomide and its mode of action is still obscure.In the present investigation a number of substances with known or suspected teratogenic effect in man were studied on the cellular and embryonic level. As material served the gametes and larvae from the regular sea urchin Paracentrotus lividus (LAMARCK), which is the classic material for the study of fertilization, cleavage and development. Few organisms have been subjected to a more conclusive experimental work, and the main advantage with this material is that every ripe female delivers several millions of fairly uniform transparent eggs, particularly suited for microscopic examination in the living state. Subsequent to insemination the eggs develop within the course of a few days into self‐maintaining larvae. Cleavage and organogenesis are also easy to observe and even minor changes taking place after the addition of an active drug can be registered in the microscope.The fact that the cleavage and embryogenesis are so well investigated also makes it possible to study the specific effect on e.g. the ectoderm or the endoderm of a certain substance. The short period of time necessary for the embryo to reach the self‐maintaining pluteus stage also minimizes the influence of external experimental factors.