The relative importance of erythropoietin (Ep) and inhibition of erythropoiesis in the anemia of chronic renal insufficiency has been investigated. Sixty patients with varying degrees of renal insufficiency, 40 normal subjects and 40 patients with anemia and normal renal function, were studied. Erythroid (CFU-E) and granulocytic (CFU-GM) progenitor cell colony formation were assayed in fetal mouse liver and human bone marrow cultures, respectively. Erythropoietin was measured by radioimmunoassay. Hematocrit and plasma creatinine concentration correlated with the degree of serum inhibition of CFU-E formation (r = 0.69, P less than 0.001, and r = 0.62, P less than 0.001, respectively). Serum erythropoietin levels in patients with renal insufficiency (34.4 +/- 6.7 mU/ml) were slightly higher than normal values (23.1 +/- 0.98 mU/ml), but showed no relationship to plasma creatinine, hematocrit, or inhibition of CFU-E formation. In contrast, serum erythropoietin concentrations increased exponentially as the hematocrit decreased below 32% (r = 0.61, P less than 0.001), and CFU-E formation was stimulated by serum in anemia patients with normal renal function. Studies of granulopoiesis showed uremic sera supported in vitro CFU-GM growth more efficiently than sera from normal subjects. These results suggest that inhibition of erythroid, but not granulocytic, progenitor cell formation, in addition to a relative erythropoietin deficiency, are the primary factors responsible for the anemia of chronic renal failure.

During phagocytosis or in response to a soluble stimulus, polymorphonuclear leukocytes (PMN) undergo a burst of oxidative metabolism involved intimately in antimicrobial activity. Superoxide anion produced during the burst is bactericidal either directly or as an intermediate metabolite. In addition, stimulated PMN's emit light or chemiluminescence (CL). CL is a sensitive measure of PMN oxidative potential and correlates with antimicrobial activity. Because of the increased susceptibility to infection observed in patients on chronic hemodialysis (CHD), we studied superoxide anion production and luminol-amplified CL in PMN's from CHD patients and in age-matched controls in the resting state and in response to phorbol myristate acetate (PMA). Studies in autologous serum showed higher CL resting values in PMN's from CHD patients, and crossincubation studies indicated that this is a result of factor(s) in the patients' serum. In response to PMA, PMN's from patients on CHD in autologous serum had significantly (P less than 0.05) less of an increase (phorbol-stimulated minus resting values) in CL as compared with controls (peak time values, 60 +/- 5 x 10(3) cpm for patients vs. 76 +/- 5 x 10(3) cpm for controls). With crossincubation studies, these differences persisted, suggesting that there is a defect intrinsic to the patient PMN. Studies done after dialysis showed a significant reduction in resting values. The decreased response to PMA stimulation remained, however. No difference in superoxide anion production (superoxide-dismutase-inhibitable ferricytochrome c reduction) was seen in PMN's from patients on CHD compared with controls. This along with other studies indicating normal nitroblue tetrazolium (NBT) reduction in PMN's from CHD patients indicates that the decreased CL is due to superoxide-anion-independent mechanisms. Because CL correlates well with antimicrobial activity, the reduced response to PMA observed in neutrophils from patients on CHD may explain, at least in part, the increased susceptibility to infection in these patients.

Stimulated neutrophils exhibit a burst of oxidative metabolism which results in the formation of superoxide anion and other oxygen species that participate in bacterial killing. Chemiluminescence is also produced and is a sensitive measure of oxidative metabolism and correlates well with antimicrobial activity. Since infection is an important cause of morbidity and mortality in diabetic patients we examined chemiluminescence and superoxide production by leukocytes from diabetics in the resting state and in response to a soluble (phorbol myristate acetate) and to a particulate stimulus (opsonized zymosan). No significant difference in the resting chemiluminescence was observed. However, the resting superoxide anion production by patients' leukocytes was significantly higher in autologous serum; when patients' leukocytes were placed in normal serum, a significant reduction in the resting superoxide anion production was observed. Using phorbol myristate acetate as a stimulus, leukocytes from diabetic patients had a markedly reduced chemiluminescence response [controls 388 +/- 48, n = 22, patient 220 +/- 37, peak cpm X 10(3)/10(6)P leukocytes, n = 22, (P less than 0.01)] and reduced superoxide anion response [controls 30.1 +/- 3.8, n = 16, patients 13.3 +/- 2.6 nmol/15 min/10(6)P leukocytes, n = 16 (P less than 0.001)]. Significantly reduced chemiluminescence response (P less than 0.05) and superoxide production (P less than 0.05) by leukocytes from diabetic patients were also observed using opsonized zymosan as a stimulus. No significant effects on chemiluminescence or superoxide response to phorbol myristate acetate were observed with cross-incubation studies in which patients' leukocytes were placed in normal serum or control leukocytes in patient serum. In vitro addition of insulin (25 microU; 100 microU/ml) had no significant effect on patient cell response; similarly increasing the glucose concentration from 100 mg/dl to 200 mg/dl and 400 mg/dl had no significant effect on control cell response. Glucagon in a lower concentration (200 pg/ml) had no significant effect; only at a higher concentration (400 pg/ml), it caused an inhibition of the phorbol stimulated chemiluminescence and superoxide response of control leukocytes. These results show an impaired oxidative burst by leukocytes from diabetic patients which may contribute to impaired bacterial killing and may explain, in part, the morbidity and mortality in diabetic patients suffering from infection.

Parameters of erythropoiesis were studied in patients with endstage renal disease established on continuous ambulatory peritoneal dialysis (CAPD) and regular hemodialysis treatment (RDT). Serum erythropoietin was measured by radioimmunoassay, and erythroid progenitor cell (CFU-E) formation was assayed in fetal mouse liver cultures. Serum erythropoietin concentrations in both CAPD (35.3 +/- 4.0 mU/ml) and RDT (31.9 +/- 1.9 mU/ml) patients were significantly higher (P less than 0.01) than normal values (23.1 +/- 1.0 mU/ml). The serum erythropoietin concentration did not correlate with either hematocrit or inhibition of CFU-E formation in either group of dialysis patients. In both CAPD and RDT patients the hematocrit correlated significantly (P less than 0.001) with the degree of serum inhibition of CFU-E formation. CFU-E formation decreased from 74.5 +/- 2.5 to 62.5 +/- 3.5% of control with increasing concentrations of uremic serum in cell cultures from 5 to 20%. In RDT patients a single hemodialysis produced a decrease in the mean serum erythropoietin concentration from 31.8 +/- 2.1 to 27.4 +/- 1.8 mU/ml (P less than 0.01) but no significant change in CFU-E formation. In conclusion, although serum immunoreactive erythropoietin levels are elevated above the normal range in dialysis patients, the response remains inadequate for the severity of the anemia, and it is the degree of serum inhibition of erythropoiesis in both CAPD and RDT patients which correlates with and possibly determines the degree of anemia.

To evaluate glucose delivery and neuromuscular activity as modulators of glucose uptake in skeletal muscle, rat hindlimbs from pentobarbital-anesthetized rats were perfused in the presence of electrically stimulated muscular contractions. Glucose delivery was varied by altering non-cyclic perfusate flow. When flow was increased from 3 to 12 ml/min glucose disappearance increased from 1.1 +/- 0.2 to 4.0 +/- 0.2 mumol/min per 100 g rat (P less than 0.001). When glucose delivery was held constant, glucose disappearance was unaltered during muscular contractions. Insulin enhanced glucose disappearance, and its effect was unaltered during muscular contractions. Muscular contractions increased oxygen disappearance by two- to 3.5-fold and lactate appearance by 4.5- to fivefold (P less than 0.02). It was concluded that glucose delivery and insulin modulate glucose disappearance in isolated perfused rat hindlimbs. Electrical stimulation of muscle enhances lactate appearance and oxygen disappearance but does not alter glucose disappearance when flow is held constant. Because blood flow to muscle increases during exercise in vivo, increased glucose delivery may be a modulator of the augmented muscle glucose consumption observed under these conditions.

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