RESUMEN
The glucagon-secreting potency of 22 amino acids was investigated in the rat isolated perfused pancreas. Arginine and the structurally related amino acids were the most potent A2-cell stimulators that induced a biphasic and sustained glucagon release. Dose-response curver were different for L(+) and D(+)arginine, and the suppressor effect of glucose on the response to L(+) arginine was not detected in the presence of D(+) arginine or homoarginine. Citrulline was the only exception among the arginine-related amino acids; it displayed neither stimulatory nor inhibitory potency on glucagon release. The A2-cell response to D(+) amino acids and artificial analogues of arginine is a strong case for the theory of amino acid receptors' triggering the release of the hormone before (or in the absence of) further metabolism. The prominent rank of arginine and ornithine amont stimulatory amino acids and some other physiologic evidence suggest that A2-cell may play a regulatory role in the metabolsm of ammonia by the liver.
Asunto(s)
Aminoácidos/farmacología , Glucagón/metabolismo , Páncreas/metabolismo , Animales , Arginina/análogos & derivados , Arginina/farmacología , Citrulina/farmacología , Relación Dosis-Respuesta a Droga , Técnicas In Vitro , Masculino , Ornitina/farmacología , Páncreas/efectos de los fármacos , Ratas , Estimulación QuímicaRESUMEN
A correlated morphological study, employing endocrine cell stains, immunofluorescence, and electron microscopy, was performed on biopsy specimens taken from a pancreatic tumor and liver metastases in a woman with hypoglycemic symptoms and high fasting insulin levels. The study revealed the tumor to be composed of two different endocrine cell populations, irrespective of the primary or metastatic growth. The first cell type fulfilled all the morphological characteristics of the islet B cells. The second was argyrophil (with the Grimelius silver method) and showed the morphological pattern of polypeptide-hormone-producing cells. With the lack of a detectable symptomatology, normal blood levels of the hormones other than insulin, and the negative results of a large number of immunofluorescence tests, we were unable to indetify the specific nature of the second type of cells.