A redução da síntese e da secreção de catecolaminas observada em diabéticos é conseqüência da hiperglicemia?

Abstract

The diabetes reduces the catecholamine secretion with hypoglycemic episodes, to turning worse the metabolic disorder of diabetic people. Several studies have shown that hyperglycemia has pivotal role in diabetic complication development. This work studied the effect of diabetes on catecholamine synthesis and secretion and the effects of insulin treatment. Methods and results: 60 days old, male Wistar rats were used. The diabetes was induced by a single intravenous injection of streptozotocin (50mg/Kg body weight). The control group received buffer injection. To establish the protocol of insulin treatment the food consumption and the blood glucose levels were measured during 24h from hour to hour. The insulintreated diabetic rats received human NPH insulin at 1pm (1U) and 7pm (4U). After 15 days of the streptozotocin injection, the rats were sacrificed and the adrenal glands withdrew. To evaluate the effect of diabetes and the insulin treatment, fructosamine, triglycerides, total cholesterol, HDL, LDL and VLDL were measured. The total catecholamine content of adrenal gland and the basal and stimulated catecholamine secretion was quantified. The experiments of stimulated catecholamine secretion were performed with high potassium, carbachol and caffeine. The catecholamines measurement was done by fluorimetric method. The expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis, was analyzed by western blotting. The glicemia was 82.82 ± 1.24 mg/dl, 405.74 ± 23.35 mg/dl and 103.72 ± 6.79 mg/dl in control, diabetic and insulin-treated diabetic groups, respectively. The body mass of diabetic rats was reduced in 6.1 ± 3.84g and increased on control and insulin-treated diabetic rats, in 36.34 ± 1.8g and 43.32 ± 3.79g, respectively. The diabetes changed total cholesterol, LDL and VLDL plasma levels, alteration reversed by insulin treatment. The triglycerides, fructosamine and LDH levels were not affected by diabetes. The insulin-treated rats showed significant reduction of fructosamine levels. The diabetic rats presented a significant reduction, 21.14% on the catecholamine content when compared to the control group, p<0.05. The insulin treatment recovered the catecholamine stores. The TH expression was similar in all three experimental groups. The diabetes reduced the basal and stimulated catecholamine secretion by 24.3%, 42.28% (high K+) e 28.9% (carbachol).The catecholamine secretion stimulated by mobilization of intracellular Ca2+ pools was not affected by diabetes or insulin treatment. Our results show that diabetes reduces the catecholamine secretion, and this is not consequence of reduction on cell catecholamine stores and it is not reversed by insulin therapy.