THE ROLE OF CIRCULATING CATECHOLAMINES IN THE REGULATION OF FISH METABOLISM - AN OVERVIEW

The physiological role of the catecholamines (CA), adrenaline and nora drenaline in fish has been frequently reviewed, but the metabolic cons equences of these hormones have received less attention. The purpose o f this review is to examine the recent literature dealing with CA acti ons on whole fish and tissue metabolism. The CA increase glucose produ ction both in vivo and in vitro, at least in isolated hepatocytes. Alt hough the data are less clear, lipid mobilization is also a consequenc e of elevated circulating CA. The difficulty with using the whole fish for such studies is that CA may alter other circulating hormone level s, CA turnover in the circulation quickly, and it is difficult to defi ne precisely the tissue being affected. Much of our understanding is d erived, therefore, from the study of isolated tissues, and especially the hepatocyte. Catecholamines stimulate both glycogenolysis and gluco neogenesis in hepatocytes isolated from a large number of fish species . This review examines the steps involved in the signal transduction s ystem, from the binding of CA to alpha- and beta-adrenoceptors to the ultimate effects of specific enzyme phosphorylation. Recent literature demonstrates that the complexity of the adrenoceptor system noted for mammals, also is expressed in fish. Adrenoceptor subtypes are specifi c to species, to tissues and to function of the tissues, and these iss ues are discussed especially as they are related to external and to in ternal stressors. Future research will pursue better definitions of th e adrenoceptor systems, molecular biology of the components of these r eceptor systems and development of alternative cell models. There stil l remains a poor explanation of the reason for the diversity of adreno ceptor systems, and there are a number of fish systems that may provid e unique opportunities to understand this question. (C) 1998 Elsevier Science Inc. All rights reserved.