Separate and combined effects of dehydration and thirst sensation on exercise performance in the heat.

Using intravenous infusion, we separated the physiologic consequences of 3% body mass dehydration from the conscious awareness of fluid replacement on time trial (TT) performance in the heat. Eleven trained cyclists performed 90 min of steady-state (50% V ˙ O 2 peak ) cycling followed by a self-paced 20-km TT in a hot-dry (35 °C, 10% relative humidity, wind speed 3.0 m/s) environment while euhydrated-not thirsty (EU-NT), euhydrated-thirsty (EU-T), dehydrated-not thirsty (DH-NT), or dehydrated-thirsty (DH-T). Thirst was manipulated by providing (NT) or withholding (T) ad libitum 35 °C water oral rinse. Distinct hydration states existed, with 0.4 ± 0.5% dehydration following the 20-km TT (EU) compared with 3.2 ± 0.6% in DH (P < 0.001). Greater perceived thirst existed in T (7 ± 2 on a 1-9 scale) than NT (4 ± 2, P < 0.001) after the TT. No significant differences in power output existed during the TT between hydration (EU 202.9 ± 36.5 W vs DH 207.0 ± 35.9 W, P = 0.362) and thirst conditions (NT 203.3 ± 35.6 W vs T 206.6 ± 36.8 W, P = 0.548), nor were there differences in completion time (P = 0.832) or pacing profile (P = 0.690). Within the range of up to 3% body mass loss, neither the physiologic effects from lowered hydration status nor the perception of thirst, separately or combined, affected sustained submaximal exercise performance in the heat for a healthy and fit population.

Magmatic vapor source for sulfur dioxide released during volcanic eruptions: evidence from mount pinatubo.

Sulfur dioxide (SO(2)) released by the explosive eruption of Mount Pinatubo on 15 June 1991 had an impact on climate and stratospheric ozone. The total mass of SO(2) released was much greater than the amount dissolved in the magma before the eruption, and thus an additional source for the excess SO(2) is required. Infrared spectroscopic analyses of dissolved water and carbon dioxide in glass inclusions from quartz phenocrysts demonstrate that before eruption the magma contained a separate, SO(2)-bearing vapor phase. Data for gas emissions from other volcanoes in subduction-related arcs suggest that preeruptive magmatic vapor is a major source of the SO(2) that is released during many volcanic eruptions.

Complete remission in acute promyelocytic leukemia despite the persistence of the 15;17 translocation.

Acute promyelocytic leukemia (APL) is a morphologically distinct subtype of acute non-lymphocytic leukemia (ANLL) characterized cytogenetically by the presence of a translocation between chromosomes 15 and 17 (t(15;17]. In contrast to other subtypes of ANLL, morphologic examination of the bone marrow in the early postinduction period fails to identify patients adequately who have a high likelihood of entering remission. Remission has frequently been achieved in APL despite the failure to attain marrow aplasia or eliminate dysplastic progranulocytes after initial induction chemotherapy. In a patient with APL who failed to achieve cytoreduction after a single course of induction chemotherapy, serial cytogenetic studies demonstrated persistence of metaphases with the t(15;17) up to 23 days after induction. However, complete morphologic and cytogenetic remission was subsequently attained by day 29 without further therapy. In APL remission may occur even when induction therapy fails to achieve marrow aplasia or to eradicate replicative cells with abnormal karyotype promptly. In order to avoid excessive exposure to toxic therapy, new strategies may be necessary to identify, early in treatment, patients with APL who will require only one course of induction chemotherapy to enter remission successfully.

The effects of sulfhydryl inhibitors and cytochalasin on the cytoplasmic and cytoskeletal actin of human neutrophils.

To better understand the changes that occur in cytoplasmic actin during cell movement, we studied the effect of inhibitors of cell movement on the molecular conformation of actin and its incorporation into the Triton-insoluble cytoskeleton of human neutrophils. The sulfhydryl reactive compound N-ethylmaleimide caused an increase in cellular F-actin as measured by uptake of the F-actin specific fluorescent probe 7-nitrobenz-2-oxadiazole-phallacidin. However, N-ethylmaleimide reduced the amount of actin associated with the Triton-insoluble cytoskeleton. Dithiobisnitrobenzoic acid, a sulfhydryl reagent that does not cross cell membranes efficiently, did not alter the F-actin content of neutrophils. The effect of N-ethylmaleimide was blocked by the presence of dithiothreitol, a donor of sulfhydryl groups. N-ethylmaleimide did not affect the polymerization of actin in a cell-free system. Cytochalasin B did not alter F-actin content of neutrophils but did decrease actin in cytoskeletons of resting neutrophils. Cytochalasin inhibited the increase in F-actin initiated by the chemoattractant N-formylmethionylleucylphenylalanine. We propose that N-ethylmaleimide blocks the stabilization of G-actin in cytoplasm, interferes with the incorporation of F-actin polymer into the cytoskeleton, and depolymerizes the cytoskeleton. In contrast cytochalasin stabilizes G-actin in the presence of chemotactic peptide. These data suggest that reversible conversion of G-actin to F-actin and incorporation of F-actin into the Triton-insoluble cytoskeleton are important for neutrophil movement.

Maturation-associated changes in the peripheral cytoplasm of human neutrophils: a review.

The process of hemopoietic stem cell differentiation and proliferation leads to a large number of precursor cells committed to the neutrophil lineage. These precursor cells undergo a further limited degree of proliferation but, most importantly, undergo a dramatic process of maturation which alters the phenotype of the cell from a myeloblast, which is incapable of normal circulation and function into a segmented neutrophil capable of chemokinesis, chemotaxis, particle ingestion, microbicidal action, and other functions required to subserve the inflammatory process. This review describes the changes in the cell surface and cell cytoplasm that occur during precursor cell maturation and, to the extent possible, correlates molecular and macromolecular changes during maturation with the development of functional capacity.

Chemotactic peptide-induced changes in neutrophil actin conformation.

The effect of the chemotatic peptide, N-formylmethionylleucylphenylalanine (FMLP), on actin conformation in human neutrophils (PMN) was studied by flow cytometry using fluorescent 7-nitrobenz-2-oxa-1,3-diazole (NBD)-phallacidin to quantitate cellular F-actin content. Uptake of NBD-phallacidin by fixed PMN was saturable and inhibited by fluid phase F-actin but not G-actin. Stimulation of PMN by greater than 1 nM FMLP resulted in a dose-dependent and reversible increase in F-actin in 70-95% of PMN by 30 s. The induced increase in F-actin was blocked by 30 microM cytochalasin B or by a t-BOC peptide that competitively inhibits FMLP binding. Under fluorescence microscopy, NBD-phallacidin stained, unstimulated PMN had faint homogeneous cytoplasmic fluorescence while cells exposed to FMLP for 30 s prior to NBD-phallacidin staining had accentuated subcortical fluorescence. In the continued presence of an initial stimulatory dose of FMLP, PMN could respond with increased F-actin content to the addition of an increased concentration of FMLP. Thus, FMLP binding to PMN induces a rapid transient conversion of unpolymerized actin to subcortical F-actin and repetitive stimulation of F-actin formation can be induced by increasing chemoattractant concentration. The directed movement of PMN in response to chemoattractant gradients may require similar rapid reversible changes in actin conformation.