Insulin-receptor binding in skeletal muscle of trout

Abstract

Two hundred rainbow trout (Oncorhynchus mykiss) age 0 +, weight range 11.3 - 11.5 g, were distributed randomly in two groups and maintained for five weeks on either 10% dextrin, or 20% dextrin diet. The fish were sampled 3-5 h and 18-20 h after the last feeding and insulin binding to partially purified insulin receptors in white and red skeletal muscles and to liver plasma membranes was assessed. Plasma insulin, plasma glucose, and liver glycogen content were analyzed in the same fish.Fish fed a diet with higher carbohydrate content (HC) had elevated insulin and glucose levels in peripheral blood, but lower liver glycogen contents compared to the fish fed a diet with lower carbohydrate content (LC). No growth retardation was observed in the fish from HC group.Three to five hours after the last feeding, insulin-receptor binding in white skeletal muscles was higher in HC group of fish, mostly because of an increase in number of high affinity binding sites. Eighteen to twenty hours after the last feeding this difference disappeared. In contrast, the specific binding of insulin to the liver plasma membranes appeared to be lower in the HC group of fish. The lower insulin binding to the liver plasma membranes observed 3-5 h after feeding, could be attributed to the lower quantity of binding sites, while the same phenomenon 18 h after feeding was likely a result of affinity changes. We conclude that higher glycemic levels observed in trout fed a HC diet as compared to LC group of fish, are not a consequence of impaired binding of insulin to its receptors in skeletal muscles.

Insulin regulates the expression of several metabolism-related genes in the liver and primary hepatocytes of rainbow trout (Oncorhynchus mykiss)

“…white muscle, liver and adipose tissues (Gutierrez et al, 1991;Navarro et al, 1999). Up-regulation of insulin binding and tyrosine kinase activity have been observed after insulin treatment and a carbohydrate-rich diet, respectively (Banos et al, 1998;Gutierrez et al, 1991;Parrizas et al, 1994a;Parrizas et al, 1994b). The persistent hyperglycemia in rainbow trout fed with carbohydrates despite the existence of insulin secretion and receptors suggests an insulin resistance state comparable to that observed in humans with type II diabetes.…”

“…Insulin receptors are also present in major insulin-responsive tissues in fish, i.e. white muscle, liver and adipose tissues (Gutierrez et al, 1991;Navarro et al, 1999). Up-regulation of insulin binding and tyrosine kinase activity have been observed after insulin treatment and a carbohydrate-rich diet, respectively (Banos et al, 1998;Gutierrez et al, 1991;Parrizas et al, 1994a;Parrizas et al, 1994b).…”

Effects of dietary arginine levels and carbohydrate-to-lipid ratios on mRNA expression of growth-related hormones in largemouth bass, Micropterus salmoides

“…Hilton et al [15], however, report that rainbow trout respond to high concentrations of digestible carbohydrates with elevated plasma insulin. An alternative hypothesis of impaired insulin-receptor binding in muscle is refuted by Gutiérrez et al [13]. Thus, the reason for the poor regulation of plasma glucose in fish is still in debate although other aspects than insulin have also been investigated widely [9,14].…”

Metformin improves postprandial glucose homeostasis in rainbow trout fed dietary carbohydrates: a link with the induction of hepatic lipogenic capacities?

“…Oral or intravenous administration of glucose or a carbohydrate-rich diet results in a persistent hyperglycaemia in various fish species, including rainbow trout (4,8,14,15,17,31,37), and is also associated with elevated insulin levels, very much like in mammals (8,17). Insulin receptors are present in major insulin-responsive tissues, including white muscle, liver, and adipose tissues (19,42,43,35). Upregulation of insulin binding and tyrosine kinase activities is observed after insulin treatment and carbohydrate-rich diets, respectively (2,19,42,43).…”