J. Marchelidon

Long-Term Inhibitory Effects of Somatostatin and Insulin-Like Growth Factor 1 on Growth Hormone Release by Serum-Free Primary Culture of Pituitary Cells from European Eel (Anguilla anguilla)

To investigate the ability of hypothalamic and peripheral factors to directly regulate growth hormone (GH) release in a primitive teleost, the European eel (Anguilla anguilla L.), we used primary cultures of dispersed pituitary cells. When cultured for 12 days in a serum-free medium, pituitary cells continuously released large amounts of GH, which exceeded the initial cellular content. Somatotropin-release inhibiting hormone (SRIH-14) dose-dependently inhibited GH release (EC50 0.75 nM) up to a maximal inhibitory effect of 95%. No desensitization of somatotropes to SRIH was observed over the 12 days of culture. Use of receptor subtype-selective SRIH agonists suggests the existence on eel somatotropes of SRIH receptor(s) related to the mammalian sst2/sst3/sst5 class rather than to the sst1/sst4 class. Insulin-like growth factor 1 (IGF1) dose-dependently inhibited GH release (EC50 0.03 nM) up to a maximal inhibitory effect of 85%, without desensitization. IGF1 and IGF2 were equipotent in inhibiting GH release, whereas insulin was 1,000 times less active, suggesting the implication of a receptor related to the mammalian IGF type 1 receptor. These results indicate that eel somatotropes are active in vitro without any specific additional factors, and suggest the existence of a dominant inhibitory control of GH release in vivo. Two potential candidates for this chronic negative regulation are a neurohormone, SRIH and a circulating factor, IGF1. These data underline the early evolutionary origin of the molecular and functional SRIH-GH-IGF1 neuroendocrine axis in vertebrates.

Amino acid contents of the brain and the muscle of young salmon (Salmo salar L.) at parr and smolt stages

Abstract 1. 1. During the parr-smolt transformation of Salmo salar L. in fresh water, variations in the concentration of some free amino acids in the brain and the muscle are observed. 2. 2. An increase of threonine and glutamine in the brain and a decrease of the total free amino acids—particularly glycine and taurine—in the muscle are especially important. 3. 3. The results are discussed in relation with the migratory behaviour and hydromineral regulation.

Mise en évidence et propriétés des sites de liaison spécifique pour la gonadotropine de carpe dans des préparations membranaires d'ovaire d'Anguille (Anguilla anguilla L.)

Abstract Membrane preparations from silver eel ovary bind specifically labeled carp gonadotropin (cGTH 125 I); similar preparations from kidney, liver, brain, and muscle exhibit either no or negligible specific binding. cGTH and partially purified eel pituitary extract, but neither hCG nor bTSH, inhibit cGTH 125 I specific binding in a dose-dependent way. However, a high membrane concentration can bind hCG 125 I and this binding is partly inhibited by excess hCG, thus suggesting the existence of a relatively small number of sites able to recognize this hormone. Studies of either cGTH inhibition of cGTH 125 I specific binding or cGTH 125 I dose-dependent binding have permitted, according to Scatchard, the binding parameters to be determined. Specific binding seems to have two components: one with low affinity and high capacity, and the other with high affinity ( K d = 1.2 10 −10 M ) and low capacity ( N = 0.2 fmol/mg ovary).