Effect of carbohydrates upon insulin secretion in Bufo arenarum (Amphibia : Bufonidae)

Pancreas pieces of Bufo arenarum were incubated with several sugars at basa l and stimulatory concentrations, and with inhibitors of their metabolism, measuring the insulin released by radioimmunoassay. Glucose, mannose, fruct ose, glyceraldehyde and dihydroxyacetone all at 8 mM, significantly enhance d the release of insulin elicited by basal concentrations of these carbohyd rates (2 mM). The nonmetabolizable sugars galactose and 2-deoxyglucose fail ed to enhance insulin secretion. N-Acetylglucosamine at 8 mM did not signif icantly affect the release of insulin. D-Glucose, but not L-glucose, at 8 m M stimulated insulin secretion above baseline (2 mM glucose). At 8 mM, the D-glucose a-anomer significantly increased insulin release, while this effe ct was not observed using the beta-anomer. Insulin release elicited by 2 mM of the alpha-anomer was significantly higher than that triggered by the be ta-anomer. Iodoacetate (5 mM), and dinitrophenol (0.3 mM) exerted an inhibi tory effect upon glucose-induced insulin secretion. The effect of these car bohydrates and metabolic inhibitors-tested for the first time in amphibians -was similar to that described in the mammalian pancreas, thus suggesting t hat such compounds play an important role in the metabolic control of insul in secretion in amphibians. (C) 1998 Elsevier Science inc. All rights reser ved.