HYPERBARIC OXYGEN AND EMBRYONIC DEVELOPMENT IN ARBACIA PUNCTULATA

¹ Department of Anatomy, Tulane University School of Medicine, New Orleans, Louisiana 70112, and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543

The effects of hyperbaric oxygen (HBO) upon the embryonic development of Arbacia were studied from fertilization to the time of formation of the pluteus larva. Fertilized eggs were incubated in sea water at 16° C in air or in 3 atmospheres absolute (AA) pure oxygen in a hyperbaric chamber. Pressure control experiments using 1 atmosphere oxygen and 2 atmospheres nitrogen demonstrated that the changes observed were caused by elevated pressure of oxygen, and not merely to high ambient pressure. Animals exposed continuously to hyperbaric oxygen for 48 hours were arrested in the gastrula stage; the archenteron was observed to form at 30-32 hours, but to regress, resulting in an unorganized mass of cells within the blastocoel. If removed from HBO at 48 hours, over 90% of these inhibited embryos proceeded to form normal prisms and plutei within 144 hours following removal. In respect to reversibility, therefore, HBO differs significantly from many chemical inhibitors of differentiation.

Embryos reared in HBO following development in air for the first 12 hours after fertilization failed to form plutei by 72 hours, whereas controls did so within 48 hours. Embryos in which exposure to HBO was delayed 18 or 24 hours were delayed in reaching the prism or pluteus stage, and showed evidence of disaggregation within 72 hours post-fertilization. Embryos exposed to HBO following 36 hours of development escaped both the inhibitory and lethal effects of HBO and proceeded to form normal plutei by 48 hours. The inactivation by HBO of sulfhydryl-containing enzymes which normally are maximally active during gastrulation in the sea urchin may contribute to the failure of embryos treated with hyperbaric oxygen to complete gastrulation.