LONDRAVILLE, R.L.*; DUVALL, C.S.: Fish Respond to Murine Leptin Injections by Increasing Intracellular Fat Metabolism.

Green sunfish (Lepomis cyanellus) were injected (i.p.) with murine leptin over the course of two weeks to test the hypothesis that fish respond to leptin in a manner similar to mammals. Leptin is a 16 kDa protein hormone that controls metabolic rate and storage of body fat in mammals; we recently demonstrated the presence of leptin in fishes. If leptin signaling in fishes is similar to that in mammals, then administering leptin should lead to loss of body weight, decrease of appetite, and increase in fatty acid metabolism. Fish were divided into three groups of 10 each; the first group received 10 �g leptin per day for 9 days and 20 �g for 5 days (IP injection); the second group received an equal volume of phosphate-buffered saline, and the third group was simply handled. All groups lost weight, but total weight, % dry weight, % body fat, cardiosomatic index and hepatosomatic index were not different among groups. However, two indicators of fatty acid metabolism approximately doubled in the leptin treated group: CPT in liver(carnitine palmitoyl transferase; 0.57 � 0.10; 0.28 � 0.10; 0.25 � 0.08 U/gm wet weight; LEPTIN, PBS, HANDLED, respectively; p<0.05) and FABP in heart (fatty acid-binding protein; 85.6 � 6.1; 53.2 � 10.1; 32.6 � 4.1 % relative signal strength; LEPTIN, PBS, HANDLED, respectively; p<0.05). These data indicate that the leptin signaling pathway is present in fish, and that it triggers an increase in fatty acid oxidation. Sponsored by OhioSeaGrant #735489 and NIH #1R15DK5811301 grants to RLL.