Rainbow trout, Oncorhynchus mykiss, were used to evaluate the effects of carbohydrate loading on plasma levels of pancreatic hormones and associated changes in metabolic indexes in a carnivorous fish. Glucose (3,000 mg/dl, 10 microliters/g body wt) was injected intraperitoneally into fish (mean wt 54 +/- 5 g) that were killed 0.5-24 h after administration. Glucose injection resulted in hyperglycemia with maximum glucose levels of 306 +/- 13 mg/dl observed 60 min after injection. Glucose administration also resulted in hyperlipidemia. Plasma fatty acids increased twofold in glucose-injected animals. Alterations in plasma metabolites reflected changes in energy stores. Although total lipid concentration was unaffected by glucose injection, lipolytic enzyme activity in the liver was enhanced. Biosynthetic capacity, as indicated by NADPH production from glucose-6-phosphate dehydrogenase, was decreased by glucose injection. Liver glycogen content was reduced in glucose-injected animals 1 h after injection. Glucose injection was attended by increases in the plasma levels of gene II somatostatin-25 (predominant form of pancreatic somatostatin in salmonids) and of glucagon. Insulin levels were initially suppressed after glucose injection. These results indicate that metabolic adjustments caused by glucose administration can be related to the regulatory action of pancreatic hormones. Furthermore, these results suggest that the somatostatin-secreting cells of the trout are sensitive to glucose and that somatostatin-suppressed insulin secretion contributes to the glucose intolerance of trout.

Experimental data obtained on cyclostomes and fish concerning the levels of plasma fatty acids (PFA), their biological role as an energetic substrate, various factors affecting PFA and mechanisms involved in the control of their level are reviewed.It was shown that PFA levels in lamprey and fish depend strongly on season, circadian rhythm, nutritional state, age, sex, intrinsic activity of individuals and are regulated by some metabolites as well as hormones. The question concermng the nervous control of PFA in cyclostomes and fish needs further elucidation on account of scarce information available at present.

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