ABSTRACT
In this chapter, the authors review the action of that secretion and its active fraction--pardaxin--on elasmobranchs under laboratory conditions. They explain two elasmobranch species--the Atlantic sharpnose and the dogfish shark --in their experiments. Pardaxin administered to the head region instantly caused the shark to struggle and to open its mouth as if to gasp. Although the opercular rate initially dropped from 40-42/min to 8-11/min, it recovered substantially, despite the continuing presence of pardaxin. Raising the seawater temperature from 15°C to 25°C itself caused a substantial increase in the permeability of dogfish gills to urea without, however, producing the behavioral responses characteristic of pardaxin's action. The invivo gill permeability studies in the dogfish shark show that the pardaxin-induced increased permeability to urea and to sodium was reversible. The rapid behavioral responses may be due to pardaxin's action on the sensory cells located on the surface of the shark's gills.
