NICHOLSON, G.S.*; JAMISON, M.; KELLEY, K.M.: Insulin-Regulated Glucose Transport in Muscle of the Goby, Gillichthys mirabilis

In the goby, a total pancreatic endocrine isletectomy (Ix) is followed by hyperglycemia and several additional symptoms typical of insulin-dependent diabetes mellitus (IDDM). Insulin treatment of Ix gobies normalizes serum glucose levels, with a significant glucose-lowering effect of the hormone observable by as early as 6 hr. In addition, glucose tolerance tests indicate that the Ix goby is impaired in its ability to clear glucose following injection of 250 mg/kg glucose, as compared with that in intact gobies, while injection of insulin significantly enhances glucose clearance rate. The degree to which these changes in serum glucose may be associated with alterations in peripheral glucose transport was assessed in part by measuring the rate of uptake of the non-metabolizable glucose analog, 3H-2-deoxyglucose, by muscle explants in vitro. Insulin treatment (1 IU/kg) of intact gobies results in a 2-fold greater rate of muscle glucose uptake as compared with that of controls, while in untreated Ix fish it was reduced by half. Furthermore, glucose transport in muscle from Ix gobies becomes resistant to direct insulin action in vitro, while insulin-replacement therapy of the Ix goby restores this response to normal. These data suggest the existence of a functional insulin-regulated glucose transport system in this teleost fish. [Support by NSF grant IBN-9600783 & NIH grant GM50089].