Decreased response of plasma catecholamine to stress in diabetic rats.

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Abstract
The heart norepinephrine concentration was markedly increased in diabetic rats. To further study the relationship between a disturbance in the autonomic nervous system and catecholamine metabolism in diabetes mellitus, the plasma catecholamine response to stress and catecholamine concentration of heart and adrenals were measured. Wistar male rats were made diabetic by streptozotocin and kept for 13 wk. A silicon catheter was placed in the superior vena cava 1 wk prior to the experiment. Insulin was injected s.c. for 3 days once daily. After an overnight fast and without anesthesia, 1 ml of blood, a control sample, was obtained and then the animals were exsanguinated. The blood was mixed with 1 mM EGTA [ethyleneglycol bis(.beta.-aminoethyl ether)N,N,N'',N''-tetraacetic acid] at a final concentration and centrifuged. The tissue was homogenized with 0.4 N perchloric acid containing 1 mM EGTA and centrifuged at 10,000 .times. g for 20 min. Catecholamines were determined by high performance liquid chromatography. Normal rats responded to blood withdrawal stress, and plasma catecholamines were markedly increased, but almost no increase or an actual decrease was observed in diabetic rats. These abnormal responses were improved by insulin treatment. Heart norepinephrine was increased significantly in the diabetic rats compared with the control rats and was reduced significantly by insulin injections. Adrenal epinephrine was also significantly increased in the diabetic rats compared with the control rats, but was not significantly reduced by insulin. A possible disturbance of catecholamine secretion in the diabetic rats was suggested.