Segmental pulmonary vascular responses to changes in pH in rat lungs: role of nitric oxide.

BACKGROUND: Respiratory or renal failure is associated with changes in blood pH. Changes in pH may have profound effects on vascular tone and reactivity. Site of action of acidosis in the pulmonary vasculature and the role of nitric oxide production remain unclear. METHODS: We utilized isolated rat lung preparation perfused with autologous blood (Hct = 20%, flow rate = 33 ml/min), and investigated the effect of acidosis and alkalosis (induced by ventilation with high and low inspired CO2) on vascular resistance and the role of nitric oxide during resting and elevated tone conditions. Changes in resistance were described in terms of small and large arteries and veins, using the vascular occlusion technique. RESULTS: Acidosis (Pco2 = 66.7 +/- 0.7 mmHg, pH = 7.17 +/- 0.01, Po2 = 255 +/- 3 mmHg) caused vasoconstriction under resting and increased vascular tone conditions (U46619-induced). The changes in resistance occurred primarily in the small arteries. In contrast, alkalosis (Pco2 = 20.1 +/- 0.3 mmHg, pH = 7.61 +/- 0.01, Po2 = 244 +/- 3 mmHg) caused vasodilation only at elevated tone conditions. Nitro-L-arginine (LNA), an inhibitor of nitric oxide synthase, increased vascular resistance slightly but did not modulate the responses to pH, suggesting that such responses are not nitric oxide dependent. During KCl-induced contraction, the effects of pH were abolished. CONCLUSIONS: We conclude that in rat lung, acidosis causes an increase in pulmonary vascular resistance at normal and elevated tone conditions. Furthermore, the response is limited primarily to the small arteries, and is not mediated by nitric oxide. Alkalosis tends to cause the opposite effects. The effects of acidosis and alkalosis were abolished when vascular tone was elevated with a low dose of KCl, suggesting that vascular response to pH may involve changes in membrane potential.

Acidosis stimulates nitric oxide production and lung damage in rats.

Systemic hypotension during sepsis is thought to be due to nitric oxide (NO) overproduction, but it may also be due to acidosis. We evaluated in healthy rats the consequences of acid infusion on NO and blood pressure. Sprague-Dawley rats were anesthetized, and ventilated with room air. The animals were randomized into four groups. Group 1 (C, n = 10) received only normal saline at rates comparable to the other groups. Group 2 (A1, n = 10) received hydrochloric acid at 0.162 mmol in the first 15 to 30 min, followed by a continuous infusion of 0.058 mmol/h for 5 h. Group 3 (AG+A1, n = 6) was pretreated with aminoguanidine (AG, 50 mg/kg), and HCl was infused as above. Group 4 (A2, n = 7) received HCl at twice the rate used in A1. Nitric oxide concentration in the exhaled gas (ENO), blood gases, and mean arterial pressure were measured every 30 min. Acid infusion in A1 caused the pH to fall gradually from 7.43 +/- 0. 01 to 7.13 +/- 0.05. This moderate decrease in pH was associated with a marked increase in ENO (1.6 +/- 0.3 to 114.2 +/- 22.3 ppb), an increase in plasma nitrite/nitrate (17.3 +/- 3.7 to 35.2 +/- 4.3 microM), and a significant decrease in blood pressure (110.5 +/- 6.3 to 63.3 +/- 15.0 mm Hg). Furthermore, acidosis caused lung inflammation, as suggested by the increase in lung myeloperoxidase activity (282.2 +/- 24.7 to 679.3 +/- 57.3 U/min/g) and lung injury score (1.7 +/- 0.2 to 3.5 +/- 0.6). Acidosis after AG pretreatment was associated with a similar change in pH, but the increase in ENO, nitrite/nitrate, and systemic hypotension were prevented. Furthermore, lung injury was attenuated by AG, as suggested by a lower myeloperoxidase activity, though lung injury score was not altered. In this model, moderate acidosis causes increases in NO, hypotension, and lung inflammation. Lung inflammation and injury are due in part to acidosis and NO production. This is the first report to show a direct effect of chronic acidosis on NO production and lung injury. These results have profound implications on the role of acidosis on NO production and lung injury during sepsis.

Endotoxin-stimulated alveolar macrophage recruitment of neutrophils and modulation with exogenous surfactant.

OBJECTIVE: To determine whether endotoxin-stimulated alveolar macrophages would attract neutrophils and whether exogenous surfactant treatment would modulate this chemoattraction. DESIGN: Alveolar macrophages were harvested from bronchoalveolar lavage fluid and neutrophils from the blood of anesthetized guinea pigs. SUBJECTS: Hartley guinea pigs. INTERVENTIONS: Alveolar macrophages were suspended in RPMI 1640 and stimulated with 1 microg/mL of lipopolysaccharide (LPS), the supernatant removed and the alveolar macrophages were incubated in either RPMI or RPMI with surfactant at two different doses (292 microg/mL or 875 microg/mL) for 16 hrs. MEASUREMENTS AND MAIN RESULTS: The supernatant was extracted from the alveolar macrophages and placed in a chemotaxis plate and the migration of neutrophils was measured. Chemotaxis of all cell types to be tested was measured by a change of absorbance on a microplate reader set at 492 nm. Results were compared with alveolar macrophages not stimulated with LPS, RPMI alone, and N formyl-methionyl-leucyl-phenylalanine (FMLP). The supernatant of the stimulated alveolar macrophages increased neutrophil chemotaxis as compared with unstimulated alveolar macrophages, and RPMI (p < .05). Surfactant treatment with 292 microg/mL significantly decreased LPS-stimulated alveolar macrophages induced neutrophil chemotaxis. Treatment with 875 microg/mL of surfactant did not alter neutrophil chemotaxis. CONCLUSIONS: Alveolar macrophages stimulation with LPS increased the chemotaxis of neutrophils. Treatment with surfactant at a concentration of 875 microg/mL did not alter neutrophil migration; however, treatment with 292 microg/mL significantly decreased neutrophil chemotaxis suggesting that at low concentrations, surfactant inhibits chemokine release and may reduce pulmonary neutrophil sequestration in vivo.

Neutrophil sequestration in the lung following acute aortic occlusion starts during ischaemia and can be attenuated by tumour necrosis factor and nitric oxide blockade.

OBJECTIVES: To investigate the role of lower extremity ischaemia in acute lung injury with special emphasis on the role of tumour necrosis factor (TNF) and nitric oxide (NO) as mediators of neutrophil (PMN) chemotaxis in the lung. DESIGN: Prospective randomised study. MATERIALS AND METHODS: Sprague-Dawley rats were randomized into four groups: group 1 (x-clmap): aorta clamped just above the bifurcation for 3 h; group 2 (AG): 50 mg/kg aminoguanidine, a specific inducible NO synthase (iNOS) inhibitor, was administered prior to aortic occlusion; group 3 (Steroids): 1 mg/kg dexamethasone was administered prior to aortic occlusion; and group 4 (TNFbp): 2 mg/kg TNFbp, a PEGylated dimeric form of the high affinity TNF receptor I (R1) was administered prior to aortic occlusion to block TNF action. Groups 2, 3 and 4 were subjected to the same ischaemia time as group 1. NO concentration in the exhaled gas (ENO) was measured in 30 min intervals. At the end of the 3 h ischaemia, one lung was excised and fixed for routine histological evaluation, and the other underwent bronchoalveolar lavage (BAL). PMN chemotaxis towards the BAL fluid was then measured using the blindwell technique. RESULTS: ENO in group 1 increased from 0.9 +/- 0.3 ppb at baseline, to 41.3 +/- 9.2 ppb at the end of ischaemia. Animals in this group exhibited significant lung inflammation. Aminoguanidine, dexamethasone and TNFbp blocked NO production (peak ENO values of 7.2 +/- 1.9, 12.6 +/- 1.3 and 8.9 +/- 1.7 ppb for groups 2, 3 and 4 respectively), decreased PMN chemotaxis and sequestration in the lung, and attenuated lung inflammation. CONCLUSIONS: Acute lung injury resulting from distal aortic occlusion starts during ischaemia. TNF and NO blockade decrease PMN chemotaxis and sequestration and attenuate the lung injury process.

The use of near-infrared cerebral oximetry in awake carotid endarterectomy.

STUDY OBJECTIVE: To determine the utility of cerebral oximetry for monitoring the adequacy of cerebral blood flow (CBF) during carotid cross-clamp. DESIGN: Prospective study. SETTING: University hospital. PATIENTS: 16 consecutive ASA physical status III (or higher) patients for awake carotid endarterectomy (CEA). INTERVENTIONS: Regional cerebral oxygen saturation (SaO2) was monitored continuously during CEA, which was performed by the same surgeon, and with standard regional anesthetic, sedation, monitoring, and operative techniques. Data were recorded and analyzed using repeated measures analysis of variance (ANOVA). MEASUREMENTS AND MAIN RESULTS: 14 hemodynamically stable patients demonstrated significant decreases in cerebral SaO2 from baseline: 69 + 1.8% to 64 + 1.2% at carotid cross-clamp (p < 0.001). After 5, 10, and 15-minute cross-clamp time, cerebral SaO2 was 63 + 1.4%, 64 + 1.5%, and 63 + 1.4%, respectively (p < 0.001, vs. baseline). On cross-clamp removal, cerebral SaO2 rose significantly: 67 + 1.6% (p < 0.01 vs. 5, 10, and 15 min). Two hypotensive patients (mean arterial pressures of 40 and 43 mmHg) developed signs and symptoms of global cerebral ischemia, with a concomitant decrease in cerebral oximetry (40% and 48%, respectively). These changes resolved with correction of hypotension. CONCLUSION: Cerebral SaO2 decreased significantly on carotid cross-clamp in patients undergoing awake CEA. Hemodynamically stable patients demonstrated no evidence of regional brain failure when SaO2 decreased to 63% (mean decrease of 7.2%). Two hemodynamically unstable patients had evidence of global brain failure when SaO2 was less than 48% (mean decrease of 36%). Our findings suggest that cerebral oximetry reflects CBF, and it may be an effective, noninvasive method of monitoring regional cerebral oxygenation changes during CEA. Significant reductions in regional SaO2 may be tolerated without evidence of brain failure. Further studies are needed to define an SaO2 threshold that reflects regional brain failure.

Treatment of septic shock in rats with nitric oxide synthase inhibitors and inhaled nitric oxide.

OBJECTIVE: To evaluate the effect of treatment with a combination of nitric oxide synthase inhibitors and inhaled nitric oxide on systemic hypotension during sepsis. DESIGN: Prospective, randomized, controlled study on anesthetized animals. SETTING: A cardiopulmonary research laboratory. SUBJECTS: Forty-seven male adult Sprague-Dawley rats. INTERVENTIONS: Animals were anesthetized, mechanically ventilated with room air, and randomized into six groups: a) the control group (C, n=6) received normal saline infusion; b) the endotoxin-treated group received 100 mg/kg i.v. of Escherichia coli lipopolysaccharide (LPS, n=9); c) the third group received LPS, and 1 hr later the animals were treated with 100 mg/kg i.v. Nw-nitro-L-arginine (LNA, n=9); d) the fourth group received LPS, and after 1 hr, the animals were treated with 100 mg/kg i.v. aminoguanidine (AG, n=9); e) the fifth group received LPS and 1 hr later was treated with LNA plus 1 ppm inhaled nitric oxide (LNA+NO, n=7); f) the sixth group received LPS and 1 hr later was treated with aminoguanidine plus inhaled NO (AG+NO, n=7). Inhaled NO was administered continuously until the end of the experiment. MEASUREMENTS AND MAIN RESULTS: Systemic mean blood pressure (MAP) was monitored through a catheter in the carotid artery. Mean exhaled NO (ENO) was measured before LPS (T0) and every 30 mins thereafter for 5 hrs. Arterial blood gases and pH were measured every 30 mins for the first 2 hrs and then every hour. No attempt was made to regulate the animal body temperature. All the rats became equally hypothermic (28.9+/-1.2 degrees C [SEM]) at the end of the experiment. In the control group, blood pressure and pH remained stable for the duration of the experiment, however, ENO increased gradually from 1.3+/-0.7 to 17.6+/-3.1 ppb after 5 hrs (p< .05). In the LPS treated rats, MAP decreased in the first 30 mins and then remained stable for 5 hrs. The decrease in MAP was associated with a gradual increase in ENO, which was significant after 180 mins (58.9+/-16.6 ppb) and reached 95.3+/-27.5 ppb after 5 hrs (p< .05). LNA and AG prevented the increase in ENO after LPS to the level in the control group. AG caused a partial reversal of systemic hypotension, which lasted for the duration of the experiment. LNA reversed systemic hypotension almost completely but only transiently for 1 hr, and caused severe metabolic acidosis in all animals. The co-administration of NO with AG had no added benefits on MAP and pH. In contrast, NO inhalation increased the duration of the reversal in MAP after LNA, alleviated the degree of acidosis, and decreased the mortality rate (from 55% to 29%). CONCLUSIONS: In this animal model, LPS-induced hypotension was alleviated slightly and durably after AG, but only transiently after LNA. Furthermore, co-administration of NO with AG had no added benefits but alleviated the severity of metabolic acidosis and mortality after LNA. We conclude that nitric oxide synthase (NOS) inhibitors, given as a single large bolus in the early phase of sepsis, can exhibit some beneficial effects. Administration of inhaled NO with NOS inhibitors provided more benefits in some conditions and therefore may be a useful therapeutic combination in sepsis. NO production in sepsis does not seem to be a primary cause of systemic hypotension. Other factors are likely to have a major role.

Role of nitric oxide and tumor necrosis factor on lung injury caused by ischemia/reperfusion of the lower extremities.

PURPOSE: Acute aortic occlusion with subsequent ischemia/reperfusion (I/R) of the lower extremities is known to predispose to lung injury. The pathophysiologic mechanisms of this injury are not clear. In the present study, we studied the role of tumor necrosis factor (TNF) and nitric oxide (NO) in lung injury caused by lower extremity I/R. METHODS: A rat model in which the infrarenal aorta was cross-clamped for 3 hours followed by 1 hour of reperfusion was used. The rats were randomized into five groups: group 1, aorta exposed but not clamped; group 2, aorta clamped for 3 hours, followed by 1 hour of reperfusion; group 3, 1 mg/kg dexamethasone administered before the aorta was clamped; group 4, 25 mg aminoguanidine, a specific inducible NO synthase (iNOS) inhibitor, administered before the aorta was clamped; and group 5, 2 mg/kg TNFbp, a PEG-ylated dimeric form of the high-affinity p55 TNF receptor I (RI), administered before the aorta was clamped. NO concentration in the exhaled gas (ENO) was measured, as an index of NO production by the lung, in 30 minute intervals during I/R. Serial arterial blood samples for TNF assay were obtained during the course of the experiment. At the end of the experiment, the lungs were removed and histologically examined for evidence of injury. RESULTS: ENO in group 2 increased from 0.7 +/- 0.3 ppb at baseline to 54.3 +/- 7.5 ppb at the end of ischemia and remained stable during reperfusion (54.6 +/- 8.5 ppb at the end of reperfusion). ENO production was blocked by aminoguanidine, by dexamethasone, and by TNFbp given before aortic occlusion. Serum TNF in groups 2, 3 and 4 increased rapidly during early ischemia, reaching its peak value 60 minutes after occlusion of the aorta, then gradually declined to baseline levels at the end of ischemia, and remained low during reperfusion. TNFbp decreased serum TNF concentration significantly when it was given before aortic occlusion. Histologic examination of the lungs at the end of the experiment revealed that aminoguanidine, dexamethasone, and TNFbp had a protective effect on the lungs. CONCLUSIONS: Serum TNF increases rapidly during lower extremity ischemia and causes increased production of NO from the lung by upregulating iNOS. Increased NO is associated with more severe lung injury, and iNOS blockade has beneficial effects on the lung. TNF blockade before ischemia decreases NO production by the lung and attenuates lung injury. ENO can be used as an early marker of lung injury caused by lower extremity I/R.

Cardiac rupture due to blunt trauma.

Cardiac rupture due to blunt trauma has been recognized with increasing frequency over the past two decades. The mortality rate is high and the majority of patients die before they arrive at the emergency department. A high index of suspicion and prompt surgical intervention are crucial for survival. We report the management of two patients, one with a double right atrial tear and one with a single right atrial tear, after each was involved in a motor vehicle accident.

Increased nitric oxide in exhaled gas is an early marker of hypovolemic states.

Acute hemorrhage is associated with a variety of physiologic and metabolic alterations, including vascular hyporeactivity and endothelial cell dysfunction. The lung is a major target organ during hemorrhagic shock. The effect of acute hemorrhage on NO production in the lung is not well described. In the present study we examined the effect of acute hemorrhage on exhaled NO (NOe), and studied how changes in blood volume and flow affect NOe. Anesthetized and mechanically ventilated rabbits were used. The effect of acute hemorrhage by slow exsanguination on NOe was examined using chemiluminescence. Because hemorrhagic shock is associated with decreased pulmonary blood flow, we established an isolated lung preparation perfused with autologous blood (Hct = 17.4%) and studied the effect of pulmonary flow rate on NOe independent of metabolic changes. In order to separate the effect of flow from the effect of changes in blood volume, we examined the effect of flow in isolated lungs perfused with a blood-free albumin solution (PAS). In the isolated lung, ventilation was similar to that used in the intact animal, and temperature, pH, pCO2, and PO2 were kept normal. Prior to exsanguination, baseline NOe in the intact animal was 24 +/- 3 ppb. At 5, 10, 15, and 20 min after initiating the hemorrhage, NOe rose to 31 +/- 3, 51 +/- 7, 94 +/- 10, and 154 +/- 16 ppb, respectively (P < 0.05). During baseline conditions in the blood-perfused isolated lungs (200 ml/min), NOe was 35 +/- 3 ppb. When flow was decreased to 70 and 0 ml/min, NOe increased to 37 +/- 3 and 56 +/- 6 ppb, respectively (P < 0.001). During baseline conditions in the PAS-perfused lungs (70 ml/min), NOe was 94 +/- 13 ppb and was unaffected by changes in flow. The perfusion pressure in the isolated lungs was in the normal range. Reduction in blood flow rate in the isolated lung was associated with less than twofold increase in NOe. This was attributed to reduction in red blood cell volume and not due to changes in blood flow rate. Reduction in flow in the intact animal during hemorrhage generated more than threefold increase in NOe, suggesting that neurohumoral mediators, in addition to changes in flow, play an important role in determining. NOe in the intact condition. NOe began to rise immediately after exsanguination began, and therefore may be a useful early marker of acute hemorrhagic shock and hypovolemia. This information may be useful in the intensive care setting.

Objective tinnitus resulting from internal carotid artery stenosis.

Objective tinnitus represents sound wave energy that, by definition, may be heard or recorded by an examiner. It may occur as a result of either muscular contraction or turbulent blood flow. We report two cases of vascular objective tinnitus resulting from internal carotid artery stenosis. The first patient, a 74-year-old man, underwent ligation of the right internal carotid artery because of the distal extent of atherosclerosis. The second patient, a 75-year-old man, underwent a right carotid endarterectomy. Both patients noted complete relief of their tinnitus. The spectrum of vascular causes and treatment options are reviewed.

Determinants of nitric oxide in exhaled gas in the isolated rabbit lung.

Nitric oxide concentrations in the exhaled gas (NOe) increases during various inflammatory conditions in humans and animals. Little is known about the sources and factors that influence NOe. NOe at end expiration was measured by chemiluminescence in an isolated, blood-perfused rabbit lung. The average end-expiratory concentration over 10 breaths was used. The effect of positive end-expiratory pressure (PEEP), flow rate, pH, hypoxia, venous pressure, and flow pulsatility on NOe were determined. At constant blood flow, increasing PEEP from 1 to 5 cm H2O elicited a reproducible increase in NOe from 49 +/- 7 to 53 +/- 8 parts per billion (ppb) (p < 0.05). When blood pH was increased from 7.40 to 7.74 by breathing low CO2 gas, NOe rose from 45 +/- 7 to 55 +/- 7 ppb (p < 0.001). Hypoxia caused a dose-dependent decrease in NOe from 37 +/- 3 during baseline to 23 +/- 2 during ventilation with 0% O2 (p < 0.01). Venous pressure elevation from 0 to 5 and 10 mm Hg decreased NOe from 32 +/- 5, to 26 +/- 5 and 24 +/- 5 ppb, respectively (p < 0.05). Switching from steady to pulsatile flow (same man flow) resulted in a small, albeit significant reduction in NOe; 30 +/- 4 to 28 +/- 4 ppb (p < 0.05). Changes in flow rate between 200 and 20 ml/min were associated with small changes in NOe; however, when flow was stopped, NOe rose substantially to 56 +/- 6 ppb (p < 0.05). The changes in NOe were rapid (1 to 2 min) and reversible. The results suggest that NOe is influenced by ventilatory and hemodynamic variables, pH, and hypoxia. We suggest that caution must be taken when interpreting changes in exhaled NO in humans or experimental animals. Changes in total and regional blood flow, capillary blood volume, ventilation, hypoxia, and pH should not be overlooked.

Bilateral brachial artery fibromuscular dysplasia.

Fibromuscular dysplasia is a nonatherosclerotic, noninflammatory vascular disease that usually involves medium- and small-sized arteries. It is most commonly observed in the renal, carotid, and intracerebral arteries, although it has been reported in other arterial beds. The most common form is characterized by medial fibrosis, with or without smooth muscle cell hyperplasia, which can result in luminal narrowing and turbulent flow. There is often a secondary aneurysmal degeneration of the artery, which may or may not be associated with thrombosis or obstruction of flow. This accounts for the typical "string-of-beads" appearance seen on arteriography. We describe a patient who presented with ischemia of the right hand secondary to fibromuscular dysplasia of the brachial artery. Subsequent studies also demonstrated fibromuscular dysplasia in the other brachial artery as well as mild involvement of the right renal artery. The patient was treated on the symptomatic side with dilatation of proximal lesions, resection of the thrombosed segment, and reconstruction with a reversed saphenous vein graft. Distal pulses were fully restored postoperatively. Pathologic examination confirmed the arteriographic and clinical diagnosis of fibromuscular dysplasia. The salient features of this case are reviewed in addition to the other cases reported in the literature.

New RGD analogue inhibits human platelet adhesion and aggregation and eliminates platelet deposition on canine vascular grafts.

Platelet adhesion and aggregation are mediated by fibrinogen via the receptor glycoprotein IIb/IIIa, which recognizes the arginine-glycine-aspartic (RGD) amino-acid sequence. We investigated the ability of 8-guanidino-octanoyl-Asp-Phe (SC-49992), an intravenously infused, stable RGD analogue, to inhibit human platelet function in vitro and to reduce in vivo canine platelet deposition on prosthetic grafts. Human platelet aggregation induced by 10 mumol/L adenosine diphosphate was inhibited in a concentration dependent manner with an ED50 of 1 microgram/ml of SC-49992. Adenosine diphosphate-induced secretion, which is dependent on fibrinogen occupancy of the glycoprotein IIb/IIIa receptor, was reduced in a concentration dependent manner, also with an ED50 of 1 microgram/ml. Thrombin-induced secretion, which is independent of fibrinogen binding, was unaffected. Activation-dependent platelet adhesion to fibrinogen substrates was reduced in a concentration-dependent manner by SC-49992. Platelet adhesion to fibronectin substrates was also reduced by the analogue, but to a lesser extent. SC-49992 effectively eluted glycoprotein IIb/IIIa bound to RGD derivatized sepharose. Eight thrombosis-prone dogs had polytetrafluoroethylene femoral artery grafts placed. Dogs received the RGD analogue or a normal saline infusion during their first graft procedure. One week later a second contralateral femoral graft with infusion of the other agent was performed. Aggregometry during RGD analogue infusion demonstrated inhibition of induced aggregation, whereas normal saline infusion had no effect. As measured by the adherence of platelets labeled with indium III 8-guanidino-octanoyl-Asp-Phe reduced platelet deposition on vascular grafts by more than 90% (p = 0.0006, log transformed data, paired t test.(ABSTRACT TRUNCATED AT 250 WORDS)

Disseminated infection with Trichosporon beigelii.

Two cases of systemic infection with Trichosporon beigelii are reported. Both patients had acute leukemia and were receiving cytotoxic and antibiotic drug therapy, which included amphotericin B, at the time of sepsis. Although clinical isolates of the organisms were found to be sensitive to amphotericin B in vitro, both patients died from severe, widespread fungal infection. The pathologic findings in these two cases suggest that the host response to trichosporon infection is a granulomatous inflammation. Trichosporon is a virulent opportunistic pathogen that may originate from the gastrointestinal tract damaged by cytotoxic therapy in the patient with aplasia. Despite aggressive antifungal therapy, survival is most closely related to recovery of the host's hematopoietic system.

Diffraction from two-photon-excited thermal index gratings.

Two-photon absorption from crossed Gaussian laser beams creates a volume grating containing both a primary and a second-order sinusoidal index modulation. Unlike with linear excitation, the two-photon-induced grating exhibits two Bragg diffraction peaks having different decay rates. Comparison of diffracted orders from volume gratings allows the order of the excitation process to be determined.

Mouse erythrocyte formation. A marker for resting B lymphocytes.

The ability of peripheral blood lymphocytes to form rosettes with mouse erythrocytes was examined using lymphocytes from normal healthy individuals of various ages and of neoplastic lymphoid cells from patients with a variety of lymphoproliferative disorders. Our results indicated that only B lymphocytes form mouse rosettes (MR). The percentage of MR varied slightly according to the strain of mouse erythrocytes used in the assay. Little variation in the mean percentage of MR was observed when lymphocytes from various age groups of healthy individuals were studied. When neoplastic lymphoid cells were incubated with mouse erythrocytes only lymphocytes from patients with chronic lymphocytic leukemia formed an increased number of MR. Peripheral blood B lymphocytes lost their ability to form MR following incubation with pokeweed mitogen. These findings supported the view that the determinant on B lymphocytes which binds to mouse erythrocytes was present only at a resting stage of B cell maturation.