Microalbuminuria in Type I diabetes involves a cell membrane abnormality and is associated with a large increase in cardiovascular risk. The hypothesis that the membrane abnormality alters granule exocytosis in neutrophils, which could contribute to the increased incidence of cardiovascular disease, was investigated. PMA-stimulated expression of CD11b and CD69 on neutrophils from normal controls (NC), long-term uncomplicated Type I diabetic control patients (DC) and diabetic nephropathy patients (DN) was determined by fluorescence activated cell scanning. Neutrophils from DN were faster than neutrophils from either NC or DC to exocytose primary granules with CD69 following initial expression of the adhesion molecule CD11b. However, a larger proportion of neutrophils from DN failed to withdraw CD11b from the cell membrane after 90min incubation. The protein kinase C (PKC) inhibitor, bisindolylmaleimide (BIM), showed that a larger proportion of neutrophils from DN, compared with DC or NC, exocytosed primary granules independent of PKC. The calpain inhibitor, E64d, showed that a larger proportion of neutrophils from both groups of diabetic patients, compared with NC, exocytosed primary granules independent of calpain. Cytoskeletal disruption with cytochalasin D had an effect on CD11b and CD69 exocytosis similar to that of BIM and E64d. The pathways controlling granule exocytosis in neutrophils from diabetic patients are abnormal. A change characteristic of DN causes rapid exocytosis of primary granules, and also causes the adhesion molecule CD11b to persist on an increased proportion of neutrophils. This will make an important contribution to increased vascular damage in these patients.
1. The metabolic clearance rate of arginine vasopressin was determined using a constant infusion technique in normal subjects and patients with chronic renal failure immediately before commencing dialysis. Endogenous arginine vasopressin was suppressed in all subjects before the infusion with a water load. 2. Plasma arginine vasopressin concentrations were determined using a sensitive and specific radioimmunoassay after Florisil extraction. The detection limit of the assay was 0.3 pmol/l, and intra- and inter-assay coefficients of variation at 2 pmol/l were 9.7% and 15.3%, respectively. 3. In normal subjects, the metabolic clearance rate was determined at two infusion rates producing steady-state concentrations of arginine vasopressin of 1.3 and 4.4 pmol/l. In the patients with renal failure, a single infusion rate was used, producing a steady-state concentration of 1.5 pmol/l. 4. At comparable plasma arginine vasopressin concentrations, metabolic clearance rate was significantly reduced in patients with renal failure (normal 1168 ± 235 ml/min versus renal failure 584 ± 169 ml/min; means ± sd ; P< 0.001). 5. Free water clearance was significantly reduced in normal subjects during the arginine vasopressin infusion from 8.19 ± 2.61 to −1.41 ± 0.51 ml/min ( P <0.001), but was unchanged in the patients with renal failure after attaining comparable plasma arginine vasopressin concentrations. 6. In normal subjects there was a small but significant fall in metabolic clearance rate at the higher steady-state arginine vasopressin concentration (1168 ± 235 ml/min at 1.3 pmol/l versus 1059 ± 269 ml/min at 4.4 pmol/l; P = 0.016). 7. Our results show that the metabolic clearance rate of arginine vasopressin is reduced by approximately 50% in severe chronic renal failure. This alone may account for the raised plasma concentrations of the hormone seen in this condition.
1. It has been proposed that raised erythrocyte sodium-lithium countertransport activity in type 1 diabetic patients is associated with an increased risk of developing diabetic nephropathy. Diabetic patients with established nephropathy would therefore be expected to have high activity. 2. Standard sodium-lithium countertransport activity, sodium affinity ( K m ) and maximum velocity ( V max. ) were measured in type 1 diabetic patients at different stages of diabetic nephropathy and in appropriately matched uncomplicated diabetic patients and normal control subjects. 3. A small proportion (15%) of patients with nephropathy had standard sodium-lithium countertransport activity higher than the control range. However, mean standard sodium-lithium countertransport activity in the diabetic patients with nephropathy [mean ± sem , 0.26 + 0.12 mmol of Li + h −1 (l of cells) −1 ] was not significantly higher than in the uncomplicated diabetic patients [0.27 ± 0.03 mmol of Li + h −1 (1 of cells) −1 ] or in the normal control subjects [0.25 ± 0.02 mmol of Li + h −1 (l of cells) −1 ]. 4. There were marked changes in the kinetic characteristics of the sodium-lithium countertransport in the diabetic patients with nephropathy so that there were decreases in both K m and V max . 5. These kinetic changes could not be attributed to an effect of either renal failure per se or the duration of diabetes. 6. The characteristic kinetic changes in sodium-lithium countertransport may indicate underlying alterations in membrane function with the onset of nephropathy in type 1 diabetes.