The term "neurosecretion" refers to the fact that certain nerve fibers release biologically active substances into the blood stream which are then able to influence the activities of distant target organs. The lower portion of the spinal cord of fishes contains such a neurosecretory system. The nerves synthesize two peptides (small proteins) known as urotensin I and urotensin II. The urotensins were first isolated from bony fishes (teleosts) but despite intensive study, their importance in the physiology of these fish is not understood. The laboratories of Dr. Conlon and Hazon are proposing a new animal model in which to investigate the physiological roles of the urotensins. We will purify urotensin I and II from an extract of the spinal cord of a cartilaginous fish, the European common dogfish and determine their chemical structures. We will then synthesize several milligrams of the peptides in order to determine their biological actions in the dogfish. Using free swimming fish that have been fitted with a cannula in an artery, we will investigate the effects of the dogfish urotensins on blood pressure and on the production of steroids. The blood of the dogfish, like other members of the shark family, contains a very high concentration of urea which is important in maintaining an equilibrium between the fish's body fluids and the surrounding sea water. We will investigate the effects of the urotensins upon the levels of urea and other blood constituents in the dogfish. We will prepare strips of smooth muscle from the various organs and blood vessels of the dogfish and study the abilities of the urotensins either to relax or contract these muscles. Finally, we hope to gain insight into the sites of action of the urotensins by tagging the molecules with a radioactive label and determining which organs in the dogfish recognize and bind the peptides. In this way, we hope to build up an overall picture of the roles of the urotensins in regulating the physiology of a cartilaginous fish. This knowledge will be valuable in future investigations that will assess the roles of the urotensins in other classes of vertebrate.
