HEPATIC EXTRACTION OF CIRCULATING INSULIN AND GLUCAGON IN BROWN TROUT (SALMO-TRUTTA FARIO) AFTER GLUCOSE AND ARGININE INJECTION

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/100 g weight) injection was followed by a decrease in glucagon presented to the liver (11.7 ng/min vs. 34.3 ng/min) 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 ng/ml 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 ng/ml). 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, (C) 1993 Wiley-Liss, Inc.