Aquaculture, 95 ( 199 1) 179-l 88 Elsevier Science Publishers B.V., Amsterdam 179 Plasma kinetics of growth hormone in the Japanese eel, Alzguilla japonica Cunming Duan and Tetsuya Hirano Ocean Research Institute, University of Tokyo, Nakano, Tokyo 164. Japan (Accepted 27 August 1990) ABSTRACT Duan, C. and Hirano, T., 1991. Plasma kinetics of growth hormone in the Japanese eel, Anguilfa japonica. Aquaculture, 95: 179-l 88. Plasma kinetics of growth hormone (GH) were examined in chronically cannulated eel after administration of recombinant eel GH by various routes. When eel GH was injected intra-arterially (30 rig/g body weight) into freshwater eels, GH, as measured by a homologous radioimmunoassay, disappeared from the circulation within 6 h. The plasma half-life and metabolic clearance rate were 15 min and 169 ml/h kg-‘, respectively. Similar values were obtained in eels adapted to 80% seawa- ter. An intramuscular injection of eel GH (30 rig/g)) resulted in a rapid increase in plasma GH levels (maximum level of 25 ng/ml, 1 h post injection), and was undetectable 6 h post injection. A similar uptake and clearance pattern was seen after intraperitoneal injection. No increase in plasma GH levels was seen over a period of 48 h after an intragastric administration of GH at 30 rig/g,, whereas a slight increase (8 ng/ml) was seen 4 h after administration of a higher dose (2 /Ip/g). In contrast, rectal administration of GH (2 pgp/g) resulted in a rapid and marked increase in plasma GH levels, suggest- ing that GH is absorbed by the posterior intestine. These results are discussed in relation to dietary application of GH in the eel. INTRODUCTION Growth hormone (GH) secreted from the pituitary is known as a potent endogenous anabolic hormone enhancing growth in all vertebrates. In the past decade, GHs have been isolated and characterized from several teleost spe- cies: tilapia, Oreochromis mossumbicus (Farmer et al., 1976 ), sturgeon, Aci- penser guldenstadti (Farmer et al., 198 1)) chum salmon, Oncorhynchus keta (Komourdjian and Idler, 1979; Wagner et al., 1985; Kawauchi et al., 1986)) carp, Cyprinus carpio (Cook et al., 1983), Japanese eel, Anguilla japonica (Kishida et al., 1987; Yamaguchi et al., 1987), yellowtail, SerioZu quinqueru- diata (Kawazoe et al., 1988), bonito, Kutsuwonuspelumis (Noso et al., 1988), Atlantic cod, Gadus morhua (Rand-Weaver et al., 1989) and tuna, Thunnus albucares (Kariya et al., 1989). Recently, cDNA of GHs has been cloned from chum salmon, rainbow trout (0. mykiss) and Japanese eel, and the recom- 0044-848619 l/$03.50 0 199 1 - Elsevier Science Publishers B.V.