Insulin and insulin-like growth factor I (IGF-I) receptors from carp ovaries were semipurified with wheat germ agglutinin at different moments of the reproductive cycle and their binding characteristics and tyrosine kinase activity were studied. Specific receptors for insulin and IGF-I were found. IGF-I receptors presented higher binding (23.8 ± 1.5%), number of receptors (965 ± 20fm/mg) and affinity (KD 0.24 ± 0.03nM) than those shown for insulin receptors (4.1 ± 1%, 530 ± 85fm/mg and 0.85 ± 0.1nM, respectively). Insulin and IGF-I receptors have a tyrosine kinase activity which is not different from that found in muscle of the same species. Seasonal changes were found in binding, with maximum values for insulin and IGF-I reached at the end of pre-spawning period (June). However, while IGF-I binding was observed in all stages, insulin binding decreased in autumn and disappeared in winter, which suggests a different role for the two peptides in ovarian physiology.

No abstract

To investigate whether nutritional state and induced changes of plasma hormone levels may affect hepatic extraction of hormones, plasma levels of insulin and glucagon were measured in the portal vein, hepatic vein, and caudal vessel of brown trout, Salmo trutta fario. In spring, when fish were actively feeding, glucose (30 mg/lOO g weight) injection was followed by a decrease in glucagon presented to the liver (11.7 ngimin vs. 34.3 ngimin) and in hepatic extraction of glucagon. As a result, systemic glucagon concentration remained unchanged. High circulation levels of insulin and its hepatic uptake remained unaffected by glucose. In autumn, when maturing fish were fasting, their systemic plasma insulin levels decreased from 6.9 ngiml to 1.8 ng/ml. Injected glucose increased both insulin quantity presented to the liver (81.3 ng/min vs. 43.6 ng/min) and systemic concentration of insulin (4.0 ng/ml vs. 1.8 ngiml). Glucagon levels and hepatic extraction of insulin and glucagon remained unchanged after glucose injection. Injection of arginine (139 mg/100 g) elevated plasma circulating levels of both peptides. However, their hepatic extraction (especially the extraction of glucagon) decreased as compared to the control fish. This resulted in very high levels of insulin (>20 ng/ml) and glucagon (3.8 ng/ml) in the systemic circulation of arginine-treated trout. We conclude that hepatic uptake of pancreatic hormones in fish is a dynamic process depending on experimental as well as nutritional conditions. o 1993 Wiley-Liss, Inc.

Previous work has shown that somatostatins (SS) affect teleost lipid metabolism indirectly by inhibition of insulin (INS) and directly by stimulation of hepatic lipolysis. In the present study, rainbow trout (Oncorhynchus mykiss) were used to characterize further the lipid-SS relationship by evaluating how lipid, contributes to SS secretion bothin vivo andin vitro. In vivo hyperlipidemia was induced for up to 3 h by short-term (2 min) infusion of a triacylglycerol (TG)-rich lipid emulsion (20% Intralipid(®)). Plasma total lipid concentration increased 118 and 155% over control levels 1 h and 3 h, respectively, after infusion; much of this increase was due to elevated plasma fatty acids (FA), which increased 39 and 520%, respectively, over the same time-frame. The hyperlipidemic pattern was attended by a significant increase in the plasma concentration of SS. The specific effects of fatty acids were evaluated on isolated Brockmann bodies. Palmitic acid and oleic acid stimulated SS release 378 and 82%, respectively, over baseline levels. These results indicate that lipids, and in particular fatty acids, modulate SS secretion in rainbow trout.