Ritmo diario da secreção de insulina por ilhotas pancreaticas isoladas de rato : correlação com permeabilidades a potassio e calcio

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

This thesis examines the insulin secretion and the t<" and Ca2+ effluxes in pancreatic islets at different times of the day. Insulin secretion was measured during a 60 min incubation (37°C) of islets from fed or 48 h-starved rats. The t<" and Ca2+ effluxes were determined by measuring the rate of Rb + and Ca2+ efflux, respectively, from islets preloaded with these tracers and incubated in Krebs solution containing different concentrations (O; 2.8; 5.6; 8.3; 11.1; 16.7 and 27.7 mM) of glucose. A diary rhythm was observed in insulin secretion, with the highest release occurring during the dark period in G 5.6 (Krebs containing 5.6 mM glucose) and G 8.3. The dark period insulin secretion curve in response to glucose was shifted to the left compared with the light period response and showed a lower stimulatory threshold. Thus, the lowest ECso for stimulation by glucose was observed at 12:00 a.m. (7.8 mM) and the highest at 8:00 a.m. (12.4 mM). During the day, a negative correlation was shown between the effect of the glucose withdraw from the Krebs, on the fractional efflux of the 86Rb and the levei of insulin secretion in G O. For the former, the maximum and minimum occurred at 4:00 p.m. and 4:00 a.m., respectively. Starvation for 48 h did not inhibit the occurrence of 86Rb efflux although there was a reduction in the absolute values and in the range of variation over a 24 h period. It also induced apparent shift of phase of the parameters that represents the effect of the glucose remova I from the perfusion medium. The maximum and minimum effects of 8.3 mM glucose in reducing the efflux rate were observed at 12:00 a.m. and 12:00 p.m., respectively. Over a 24 h period, there was a significant correlation between the levei of insulin secretion and the inhibition of 86Rb efflux induced by 8.3 mM glucose. Although the efflux of 45Ca in G 16.7 peaked at 8:00 p.m., there was no correlation between this parameter and the levei of insulin secretion in thisconcentration of glucose. These results indicate that in response to physiological concentrations of glucose, beta cells of the rar s isolated pancreatic islets release more insulin during the normal activity period of the species. This higher secretion may be related to an improved ability of glucose to reduce the permeability of these ceUs to potassium during the dark period. The glycopenia-mediated activation of t(" ATP channels in rat pancreatic beta ceUs is greater at the end of this species rest period. The feeding-starvation cycle appears to mask the daily rhythm of potassium efflux from beta ceUs

ASSUNTO(S)

insulina - secreção ritmos circadianos permeabilidade

ACESSO AO ARTIGO

Documentos Relacionados