RESUMEN
Non-insulin-dependent diabetes was obtained in rabbits following pancreatic duct ligation. The insulin responses to D-glucose and to L-arginine were studied in the isolated perfused pancreas of control, prediabetic, and diabetic rabbits. In controls, D-glucose or L-arginine caused biphasic insulin release that was qualitatively and quantitatively altered in both prediabetic and diabetic animals. Most secretagogues influence the islet response to other secretagogues by modifying the B-cell memory. In perfused control pancreas, the priming effect of D-glucose resulted in a time-dependent potentiation (TDP) of insulin release during subsequent L-arginine stimulus, whereas L-arginine induced a time-dependent inhibition (TDI) of insulin release during subsequent D-glucose stimulus. As compared with the controls, the TDP effect obtained was emphasized in prediabetic and strongly diminished in diabetic animals. In some prediabetic and diabetic cases, the TDI remained unchanged compared with the controls, and in others it diminished in prediabetic and disappeared in diabetic animals where the effect became one of TDP. The effects of TDP and TDI seem to evolve independently of the modifications of the responsiveness to B-cell secretagogues.
Asunto(s)
Arginina/farmacología , Diabetes Mellitus Tipo 2/fisiopatología , Glucosa/farmacología , Insulina/metabolismo , Islotes Pancreáticos/fisiopatología , Animales , Glucemia/metabolismo , Insulina/sangre , Secreción de Insulina , Islotes Pancreáticos/efectos de los fármacos , Cinética , Ligadura , Masculino , Conductos Pancreáticos/cirugía , Perfusión , ConejosRESUMEN
Ligation of the pancreatic duct in rabbits provokes a decrease in the insulin and glucagon content of the pancreas, and may lead to chronic hyperglycemia. The insulin secretory behavior of the perfused pancreas is perturbed in duct-ligated animals, and this is illustrated in several respects: 1. The steady-state insulin output evoked by L-leucine (10 mM) is higher in duct-ligated than control rabbits; 2. In the presence of the amino acid, the response to D-glucose is characterized by a delayed onset, the absence of an early secretory peak, and a sluggish return towards basal value upon removal of the hexose from the perfusate; and 3. Whereas control rabbits display a higher secretory response to alpha- than beta-D-glucose, such is no more the case in duct-ligated rabbits. The perturbation of the anomeric specificity in secretory response is most obvious in diabetic duct-ligated rabbits, in which case beta-D-glucose stimulates insulin release more efficiently than alpha-D-glucose. In both control and duct-ligated rabbits, however, the alpha-anomer is more potent than the beta-anomer in suppressing leucine-stimulated glucagon secretion. These findings are compatible with the view that chronic hyperglycemia leads to alteration in the anomeric preference of the pancreatic B-cell for alpha-D-glucose, possibly as a result of the nonenzymatic glycation of glycolytic enzymes in insulin-producing, but not glucagon-producing, islet cells.
Asunto(s)
Insulina/metabolismo , Páncreas/metabolismo , Animales , Glucagón/metabolismo , Glucosa/química , Glucosa/farmacología , Secreción de Insulina , Leucina/farmacología , Ligadura , Páncreas/efectos de los fármacos , Conductos Pancreáticos , Conejos , EstereoisomerismoRESUMEN
This work describes a perfusion technique adapted to the isolated rabbit pancreas allowing investigation of both the endocrine and exocrine function. The pancreas-duodenum-stomach-spleen complex is removed and perfused with a modified Krebs Ringer Bicarbonate medium. The surgical steps leading to the removal of the complex are described. The endocrine response is studied by measuring insulin release when the pancreas is submitted to successive glucose stimulations and the exocrine function is evaluated by the alpha-chymotrypsin activity of the pancreatic juice harvested during the perfusion.
Asunto(s)
Quimotripsina/metabolismo , Insulina/metabolismo , Islotes Pancreáticos/metabolismo , Páncreas/metabolismo , Jugo Pancreático/enzimología , Animales , Duodeno/cirugía , Fístula , Técnicas In Vitro , Secreción de Insulina , Masculino , Conductos Pancreáticos/fisiología , Conductos Pancreáticos/cirugía , Perfusión , ConejosRESUMEN
Kinetic studies of the histochemical and histoenzymatic behavior of rabbit pancreatic parenchymas were performed 5, 30 and 90 days after Wirsung duct ligation. In control pancreas, some enzyme activities (EA) were more prominent in Langerhans islets [glucose-6-phosphatase, glucose-6-phosphate dehydrogenase (DH), isocitrate DH, glycerol-3-phosphate DH, NADPH DH], others were strongly marked in acini and ducts (alkaline phosphatase, beta-glucuronidase, acid esterase aryl-sulfatase). Histochemical and enzyme abnormalities observed in experimental rabbits reflect the post-ligation degenerative and reactive processes in both exocrine and endocrine pancreas: (1) the decrease in Krebs cycle and pentose pathway linked EA and the increased lysosomal and acid phosphatase EA reflect early (day 5) degeneration and necrosis of islets and acini (day 30); (2) proliferative processes in developed ductal epithelia are shown by an increase in both glycolytic and lysosomal EA (days 30 and 90); (3) connective tissue neogenesis and interstitial fibrosis occurred as shown by activated beta-glucuronidase, aryl-sulfatase, alkaline phosphatase and increased ribonucleoproteins and glycoaminoglycans contents (day 30); (4) on day 90, the neoformed cell clusters presenting glucose-6-phosphatase positivity (B-cell marker) are seen in the pancreas remnant. At the same time, blood insulin level increases correlated with a decrease of hyperglycemia.