Effect of adrenergic stimulation on insulin and proinsulin secretion. Study on patients with pheochromocytoma.

Two patients with pheochromocytoma predominantly secreting noradrenaline, were studied. Intravenous glucose tolerance tests were performed: in the preoperatory period, under alpha adrenergic blockade with pentolamine and one month after the tumor was removed. Serum glucose and insulin concentrations were determined. Proinsulin was separated from the insulin in Sephadex G-50 fine columns. In the preoperatory study, insulin secretion was less during the first 10 minutes after glucose administration, when comparing to that observed in two other studies. During pentolamine blockade, insulin secretion was at least three times higher than the preoperatory test; however, hypoglycemia was not observed. Proinsulin levels were similar to the observed in a normal individual in the pre and postoperatory test during pentolamine blockade, and were found significantly elevated. It is postulated that hypoglycemia was not produced during the late test because more than 50 per cent of immunoreactivity measured as insulin, corresponded to proinsulin whose biological activity is 10 times less than that of insulin.

Efecto de la estimulacion adrenergica sobre la secrecion de insulina y proinsulina. Estudio en pacientes con feocromocitoma. / Effect of adrenergic stimulation on insulin and proinsulin secretion. Study on patients with pheochromocytoma

Se estudiaron dos pacientes con feocromocitoma cuya secrecion predominante era noradrenalina. Se les practicaron pruebas de tolerancia endovenosa a la glucosa en el periodo preoperatorio, bajo bloqueo alfa adrenergico con pentolamina, y un mes despues de haber extirpado el tumor. Durante estas pruebas se determinaron las concentraciones sericas de glucosa e insulina. La proinsulina se separo de la insulina en columnas de Sephadex G=50 fino. Durante el estudio preoperatorio la secrecion de insulina fue menor durante los primeros 10 minutos despues de la administracion de glucosa, en comparacion con la observada en los otros dos estudios. Durante el bloqueo con pentolamina se produjo una secrecion de insulina por lo menos tres veces superior a la prueba preoperatoria a pesar de lo cual no se produjo hipoglucemia.Los porcentajes de proinsulina fueron normales en las pruebas pre y postoperatorias, en tanto que se encontraron anormalmente elevados durante el bloqueo con pentolamina. Se postula que no se produjo hipoglucemia durante esta ultima prueba porque mas de 50 por ciento de la inmunorreactividad medida como insulina correspondia a proinsulina cuya actividad biologica es 10 veces menor que la de la insulina