Relative Time Course Research Articles

Liposomal delivery of heat-shock protein 72 into the heart prevents endotoxin-induced myocardial contractile dysfunction

Background: The purposes of this study were to (1) determine whether functional heat-shock protein 72 (HSP-72) may be delivered into the heart, (2) determine whether HSP-72 itself is protective against endotoxin (lipopolysaccharide [LPS])-induced cardiodepression, and (3) compare relative protection and time courses required for protection for thermally induced HSP-72 versus liposomally introduced HSP-72. Methods: HSP-72 was introduced (liposomal HSP-72) or induced (heat shock, 42°C× 15 minutes, 24 hours before) in rat heart before LPS administration (0.5 mg/kg intraperitoneal or ex vivo coronary infusion). Western blot analysis for HSP-72 was used to confirm its expression. Left ventricular developed pressure (Langendorff) was used as an index of cardiac function. Results: Direct intracoronary perfusion of liposomal HSP-72 delivered functioning HSP-72 into the myocardium. LPS induced cardiodepression; however, heat shock pretreatment abolished LPS-induced contractile dysfunction. A direct connection was found between HSP-72 and protection derived from liposomal transfer experiments that similarly reduced LPS-induced cardiodepression. Conclusions: (1) HSP-72 prevents LPS-induced myocardial contractile dysfunction, (2) liposomal transfer of HSP-72 into the myocardium provides the first direct mechanistic connection between myocardial HSP-72 and protection against LPS, (3) HSP-72 induction requires 24 hours and liposomal transfer of HSP-72 requires 90 minutes, and (4) HSP-72 may offer a clinically acceptable means of protecting the heart. (Surgery 1999;126:135-41.)

Liposomal delivery of heat-shock protein 72 into the heart prevents endotoxin-induced myocardial contractile dysfunction

<h2>Abstract</h2> <b>Background:</b> The purposes of this study were to (1) determine whether functional heat-shock protein 72 (HSP-72) may be delivered into the heart, (2) determine whether HSP-72 itself is protective against endotoxin (lipopolysaccharide [LPS])-induced cardiodepression, and (3) compare relative protection and time courses required for protection for thermally induced HSP-72 versus liposomally introduced HSP-72. <b>Methods:</b> HSP-72 was introduced (liposomal HSP-72) or induced (heat shock, 42°C× 15 minutes, 24 hours before) in rat heart before LPS administration (0.5 mg/kg intraperitoneal or ex vivo coronary infusion). Western blot analysis for HSP-72 was used to confirm its expression. Left ventricular developed pressure (Langendorff) was used as an index of cardiac function. <b>Results:</b> Direct intracoronary perfusion of liposomal HSP-72 delivered functioning HSP-72 into the myocardium. LPS induced cardiodepression; however, heat shock pretreatment abolished LPS-induced contractile dysfunction. A direct connection was found between HSP-72 and protection derived from liposomal transfer experiments that similarly reduced LPS-induced cardiodepression. <b>Conclusions:</b> (1) HSP-72 prevents LPS-induced myocardial contractile dysfunction, (2) liposomal transfer of HSP-72 into the myocardium provides the first direct mechanistic connection between myocardial HSP-72 and protection against LPS, (3) HSP-72 induction requires 24 hours and liposomal transfer of HSP-72 requires 90 minutes, and (4) HSP-72 may offer a clinically acceptable means of protecting the heart. (Surgery 1999;126:135-41.)

On the Distinctiveness, Independence, and Time Course of the Brain Responses to Syntactic and Semantic Anomalies

We evaluated the distinctiveness, independence, and relative time courses of the event-related brain potentials (ERPs) elicited by syntactically and semantically anomalous words. ERPs were recorded from 13 scalp electrodes while subjects read sentences, some of which contained a selectional restriction violation (semantically anomalous), a verb tense violation (syntactically anomalous), or a doubly anomalous word that violated both selectional restriction and verb tense constraints. Semantic anomalies elicited a monophasic increase in N400 amplitude, whereas syntactic anomalies elicited a late positive shift with an onset around 500 msec and a duration of several hundred msec. Doubly anomalous words elicited both an increase in N400 amplitude and a late positive wave, and these effects summated in an approximately (but not perfectly) linear manner. These results are discussed with respect to the hypotheses that syntactic and semantic processes are separable and independent.

Effects of topical corticosteroids on inflammatory mediator–induced eicosanoid release by human airway epithelial cells

Background: Airway epithelial cells are among the first cells to come in contact with aerosolized corticosteroids. However, the relative potencies and time course of action of the several commonly used aerosolized corticosteroids on eicosanoid production by airway epithelial cells are unknown. Objectives: This study compared the effects of fluticasone, budesonide, and triamcinolone on eicosanoid output by human airway epithelial cells in vitro. We also determined the spectrum of eicosanoids affected and the mechanism for corticosteroid action. Methods: Cultured BEAS-2B airway epithelial cells (a transformed cell line) were exposed to corticosteroids (1 nmol/L to 1 μmol/L) for 2 to 48 hours and then assayed for basal- and bradykinin (BK)-stimulated eicosanoid output. The eicosanoid profile was identified by HPLC in tritiated arachidonic acid prelabelled cells, and PGE 2, the major eicosanoid product, was quantitated by RIA. The effect of corticosteroids on the immunoreactivity of key proteins involved in eicosanoid metabolism (ie, cyclooxygenase [COX], phospholipase A2 [PLA 2], and Clara cell protein, a PLA 2 inhibitor) was determined by Western blotting. Results: Eicosanoid output was largely confined to prostaglandins with values of 5 ± 2 and 82 ± 35 ng PGE 2/10 6 cells for basal- and BK stimulation, respectively (n = 8). All 3 corticosteroids inhibited basal- and BK-induced PGE 2 output in a dose- and time-dependent manner. Fluticasone and budesonide completely eliminated PGE 2 output in nanomolar concentrations in contrast to triamcinolone, which required micromolar concentration. The rank order of potency was: fluticasone = budesonide > triamcinolone. The time course of action for PGE 2 inhibition also differed, with budesonide acting more slowly than the other 2 corticosteroids ( P = .04). All 3 corticosteroids markedly reduced COX2 with little effect on COX1, cPLA 2 (Type IV), or iPLA 2 (Type VI) immunoreactivity or their relative distribution in cytosol versus membrane fractions. Clara cell protein immunoreactivity was undetectable in control and corticosteroid-treated cell lysates. Conclusion: These results show that in a human airway epithelial cell line, the 3 inhaled corticosteroids commonly used to treat asthma differ in onsets of action as inhibitors of prostaglandin synthesis and vary considerably in potency. All 3 corticosteroids act mechanistically in similar fashion by inhibiting COX2 synthesis. (J Allergy Clin Immunol 1999;103:1081-91.)

Thyroid hormone affects Schwann cell and oligodendrocyte gene expression at the glial transition zone of the VIIIth nerve prior to cochlea function.

All cranial nerves, as well as the VIIIth nerve which invades the cochlea, have a proximal end in which myelin is formed by Schwann cells and a distal end which is surrounded by oligodendrocytes. The question which arises in this context is whether peripheral and central parts of these nerves myelinate simultaneously or subsequently and whether the myelination of either of the parts occurs simultaneously at the onset of the cochlea function and under the control of neuronal activity. In the present paper, we examined the relative time course of the myelinogenesis of the distal part of the VIIIth nerve by analyzing the expression of peripheral protein P0, proteolipid protein and myelin basic protein. To our surprise, we observed that the expression of myelin markers in the peripheral and central part of the intradural part of the VIIIth nerve started simultaneously, from postnatal day 2 onwards, long before the onset of cochlea function. The expression rapidly achieved saturation levels on the approach to postnatal day 12, the day on which the cochlea function commenced. Because of its importance for the neuronal and morphological maturation of the cochlea during this time, an additional role of thyroid hormone in cochlear myelinogenesis was considered. Indeed, it transpires that this hormone ensures the rapid accomplishment of glial gene expression, not only in the central but also in the peripheral part of the cochlea. Furthermore, an analysis of the thyroid hormone receptors, TRaplha and TRbeta, indicates that TRbeta is necessary for myelinogenesis of the VIIIth nerve. Rapid thyroid hormone-dependent saturation of myelin marker gene expression in Schwann cells and oligodendrocytes of the VIIIth nerve may guarantee nerve conduction and synchronized impulse transmission at the onset of hearing. The thyroid hormone-dependent commencement of nerve conduction is discussed in connection with the patterning refinement of central auditory pathways and the acquisition of deafness.

RNA-binding proteins in mouse oocytes and embryos: expression of genes encoding Y box, DEAD box RNA helicase, and polyA binding proteins.

Growth and differentiation of early embryos depends almost entirely on information which is maternally inherited in the form of macromolecules accumulated by the female gamete during its growth phase. Most of the maternal mRNAs synthesized by growing oocytes are not immediately recruited onto polysomes but are stored as translationally dormant messenger ribonucleoprotein (mRNP) particles. mRNA binding proteins which have been associated with masked mRNP complexes in Xenopus oocytes fall into two main categories, those having affinity for a variety of RNA sequences (members of the Y box and DEAD box RNA helicase families) and those which interact more specifically with 3' polyA tails (the polyA binding proteins or PABPs). The objective of this study was to determine whether mouse oocytes and embryos express sequences encoding a Y box protein, (MSY1); on RNA helicase, (RCK/p54); and a universally expressed PABP and testis specific isoform (PABP1 and PABPt, respectively). RNAs were amplified by RT/PCR and the identities of targeted cDNAs were confirmed by restriction analysis and/or direct sequencing. Relative steady state levels and time courses of accumulation/decay were compared by Northern hybridization. All of the sequences are transcribed as maternal mRNAs. MSY1 transcripts accumulated during the growth phase appear to be degraded in parallel with the bulk of maternal mRNAs by the mid-late two-cell stage. RCK/p54 mRNAs are most abundant in growing oocytes; steady state levels decline in primary and secondary oocytes, and degradation appears to be complete by the mid-late two-cell stage. Zygotic transcription of MSY1 and RCK/p54 is evident in four-cell stage embryos. Most of the PABP1 message accumulated by growing oocytes decays during meiotic maturation with transcription resuming in two-cell embryos. PABPt is expressed at very low levels in oocytes and embryos. Based on the temporal patterns of expression and the reported activities of homologous sequences in other systems, we suggest that these RNA binding proteins may participate in the post-transcriptional regulation of gene expression during the period of maternal control of development in the mouse.

Cardiovascular consequences of bed rest: effect on maximal oxygen uptake.

Maximal oxygen uptake (VO2max) is reduced in healthy individuals confined to bed rest, suggesting it is independent of any disease state. The magnitude of reduction in VO2max is dependent on duration of bed rest and the initial level of aerobic fitness (VO2max), but it appears to be independent of age or gender. Bed rest induces an elevated maximal heart rate which, in turn, is associated with decreased cardiac vagal tone, increased sympathetic catecholamine secretion, and greater cardiac beta-receptor sensitivity. Despite the elevation in heart rate, VO2max is reduced primarily from decreased maximal stroke volume and cardiac output. An elevated ejection fraction during exercise following bed rest suggests that the lower stroke volume is not caused by ventricular dysfunction but is primarily the result of decreased venous return associated with lower circulating blood volume, reduced central venous pressure, and higher venous compliance in the lower extremities. VO2max, stroke volume, and cardiac output are further compromised by exercise in the upright posture. The contribution of hypovolemia to reduced cardiac output during exercise following bed rest is supported by the close relationship between the relative magnitude (% delta) and time course of change in blood volume and VO2max during bed rest, and also by the fact that retention of plasma volume is associated with maintenance of VO2max after bed rest. Arteriovenous oxygen difference during maximal exercise is not altered by bed rest, suggesting that peripheral mechanisms may not contribute significantly to the decreased VO2max. However reduction in baseline and maximal muscle blood flow, red blood cell volume, and capillarization in working muscles represent peripheral mechanisms that may contribute to limited oxygen delivery and, subsequently, lowered VO2max. Thus, alterations in cardiac and vascular functions induced by prolonged confinement to bed rest contribute to diminution of maximal oxygen uptake and reserve capacity to perform physical work.

Growth Hormone, Interferon-γ, and Leukemia Inhibitory Factor Utilize Insulin Receptor Substrate-2 in Intracellular Signaling

In this report, we demonstrate that insulin receptor substrate-2 (IRS-2) is tyrosyl-phosphorylated following stimulation of 3T3-F442A fibroblasts with growth hormone (GH), leukemia inhibitory factor and interferon-gamma. In response to GH and leukemia inhibitory factor, IRS-2 is immediately phosphorylated, with maximal phosphorylation detected at 15 min; the signal is substantially diminished by 60 min. In response to interferon-gamma, tyrosine phosphorylation of IRS-2 was prolonged, with substantial signal still detected at 60 min. Characterization of the mechanism of signaling utilized by GH indicated that tyrosine residues in GH receptor are not necessary for tyrosyl phosphorylation of IRS-2; however, the regions of GH receptor necessary for IRS-2 tyrosyl phosphorylation are the same as those required for JAK2 association and tyrosyl phosphorylation. The role of IRS-2 as a signaling molecule for GH is further demonstrated by the finding that GH stimulates association of IRS-2 with the 85-kDa regulatory subunit of phosphatidylinositol 3'-kinase and with the protein-tyrosine phosphatase SHP2. These results are consistent with the possibility that IRS-2 is a downstream signaling partner of multiple members of the cytokine family of receptors that activate JAK kinases.

Oxidative DNA Damage in Human Respiratory Tract Epithelial Cells. Time Course in Relation to DNA Strand Breakage

When human respiratory tract epithelial cells were exposed to 100 μM H2O2, there was rapid induction of DNA strand breakage and chemical modifications to all 4 DNA bases suggestive of attack by OH•. The major products were FAPy-adenine, FAPy-guanine, and 8-OH-guanine. Some of the base modifications were removed very quickly from the DNA (e.g., 8-OH-guanine), whereas others persisted for longer (e.g., thymine glycol), probably due to differential activity of different repair enzymes. By contrast, strand breaks continued to increase over the time course of the experiment, perhaps because strand breakage is also implicated in the repair process. One should therefore be cautious in using strand breakage as a sole measure of oxidative DNA damage, and when drawing conclusions about the pattern and biological significance of oxidative DNA damage in cells the relative persistence of different lesions must be considered.

Induction of clusterin in the immature brain following a hypoxic-ischemic injury.

A unilateral hypoxic-ischemic (HI) insult in the 21 day old rat has been used to assess the role of clusterin in nerve cell death. Both clusterin mRNA and protein levels were measured at various time points after moderate (15 min) and severe (60 min) HI insult using in situ hybridisation and immunocytochemistry respectively. The severe HI insult lead primarily to necrotic neuronal death and showed very little if any clusterin mRNA and protein induction on the ligated side of the brain. However, following the moderate HI insult there was a dramatic time-dependent accumulation of clusterin protein in neurons of the CA1-CA2 pyramidal cell layers in the hippocampus and cortical layers 3-5, regions undergoing delayed neuronal death. Clusterin mRNA expression, in contrast to neuronal protein accumulation, appeared to be glial in origin (probably astrocytes) with increases in mRNA in and around the hippocampal fissure and only a weak signal over the CA1-CA2 pyramidal cell layer. These results support the hypothesis that the clusterin protein is synthesised in the astrocytes, secreted and then taken up by dying neurons. Clusterin immunoreactivity and in situ DNA end-labelling performed on the same sections revealed that clusterin was accumulating in neurons destined to die by programmed cell death. However the relative time-courses of DNA fragmentation and clusterin immunoreactivity suggest that clusterin production was a result of the selective delayed neuronal death rather than being involved in the biochemical cascade of events that cause it.

Cellular Basis for the Electrocardiographic J Wave

The J wave is a deflection that appears in the ECG as a late delta wave following the QRS or as a small secondary R wave (R'). Also referred to as an Osborn wave, the J wave has been observed in the ECG of animals and humans for more than four decades, yet the mechanism underlying its manifestation is poorly understood. The present study investigates the cellular basis for the J wave using an isolated arterially perfused preparation consisting of a wedge of canine right or left ventricle. A 12-lead ECG was initially recorded in vivo. After isolation and arterial perfusion of the right or left ventricular wedge, transmembrane action potentials were simultaneously recorded from epicardial, M region, and endocardial transmural sites with three floating microelectrodes. A transmural ECG was recorded concurrently. A J wave was observed at the R-ST junction of the ECG in 17 of 20 adult dogs, usually in leads II, III, aVR, and aVF and the mid to lateral precordial leads. The J wave in the transmural ECG recorded across the wedge was closely associated with the presence of a prominent action potential notch in epicardium but not endocardium. The shape and amplitude of the J wave were found to depend on (1) the transmural distribution of the action potential notch amplitude, (2) the relative time course of the early phases of the action potential (width of notch) at different sites within the wall, (3) sequence of activation, and (4) conduction time across the wall. A highly significant correlation was demonstrated between the amplitude of the epicardial action potential notch and the amplitude of the J wave recorded during interventions that alter the appearance of the electrocardiographic J wave, including hypothermia, premature stimulation, and block of the transient outward current by 4-aminopyridine. Ventricular activation from endocardium to epicardium, with epicardium activated last, was also an important prerequisite for the appearance of the J wave. This sequence permits the establishment of a voltage gradient of the early phases of the action potential after activation (ie, the QRS) is complete. Our results provide the first direct evidence in support of the hypothesis that heterogeneous distribution of a transient outward current-mediated spike-and-dome morphology of the action potential across the ventricular wall underlies the manifestation of the electrocardiographic J wave. The presence of a prominent action potential notch in epicardium but not endocardium is shown to provide a voltage gradient that manifests as a J (Osborn) wave or elevated J-point in the ECG.

Hematopoietic differentiation of embryonic stem cells: an in vitro model to study gene regulation during megakaryocytopoiesis.

We are interested in the regulation of the tissue specificity of the megakaryocyte-specific platelet glycoprotein IIb gene. The murine embryonic stem (ES) cells are able to differentiate into erythroid, mast and granulomonocytic cells in appropriate culture conditions. Our goal is to optimize the production of myeloid cells including megakaryocytes (MKs) by ES cells. We have found that coculture with MS-5 stromal cells and the presence of a cocktail of hematopoietic growth factors (HGFs) [stem cell factor, interleukin 3 (IL-3), IL-6, IL-11, G-CSF and erythropoietin] had a high synergistic activity on differentiation of ES cells into pure and MK-containing myeloid colonies from day 12 embryoid bodies. Thrombopoietin increased the number of MKs only when added to the HGF cocktail in the presence of MS-5 cells. Interestingly, many MKs exhibited a "hairy" appearance evocative of pseudopodial proplatelet formation. Expression of genes specific for the megakaryocytic lineage, GPIIb, PF4, mpl and GPIIIa, was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) during differentiation of ES cells, and their relative time course was evaluated. This demonstrates that optimized culture conditions for the differentiation of ES cells into the MK lineage provide a useful tool for the study of the regulation of expression of genes during megakaryocytopoiesis.

Transient immunosuppressive treatment leads to long-term retention of allogeneic myoblasts in hybrid myofibers.

Normal and genetically engineered skeletal muscle cells (myoblasts) show promise as drug delivery vehicles and as therapeutic agents for treating muscle degeneration in muscular dystrophies. A limitation is the immune response of the host to the transplanted cells. Allogeneic myoblasts are rapidly rejected unless immunosuppressants are administered. However, continuous immunosuppression is associated with significant toxic side effects. Here we test whether immunosuppressive treatment, administered only transiently after allogeneic myoblast transplantation, allows the long-term survival of the transplanted cells in mice. Two immunosuppressive treatments with different modes of action were used: (a) cyclosporine A (CSA); and (b) monoclonal antibodies to intracellular adhesion molecule-1 and leukocyte function-associated molecule-1. The use of myoblasts genetically engineered to express beta-galactosidase allowed quantitation of the survival of allogeneic myoblasts at different times after cessation of the immunosuppressive treatments. Without host immunosuppression, allogeneic myoblasts were rejected from all host strains tested, although the relative time course differed as expected for low and high responder strains. The allogeneic myoblasts initially fused with host myofibers, but these hybrid cells were later destroyed by the massive immunological response of the host. However, transient immunosuppressive treatment prevented the hybrid myofiber destruction and led to their long-term retention. Even four months after the cessation of treatment, the hybrid myofibers persisted and no inflammatory infiltrate was present in the tissue. Such long-term survival indicates that transient immunosuppression may greatly increase the utility of myoblast transplantation as a therapeutic approach to the treatment of muscle and nonmuscle disease.

Time courses of changes in hepatic and skeletal muscle insulin action and GLUT4 protein in skeletal muscle after STZ injection.

To determine the relative time courses of changes in peripheral and hepatic insulin action and skeletal muscle GLUT4 protein levels after a streptozotocin (STZ) injection in rats, we performed hyperinsulinemic (14-18 nM), euglycemic (7.5 mM) clamps in control (n = 8) and diabetic rats at 1 (n = 7), 3 (n = 8), 7 (n = 8), and 14 (n = 6) days after intraperitoneal STZ (65 mg/kg). Basal plasma glucose concentrations increased from 8.1 +/- 0.2 mM in control rats to 23.5 +/- 1.2 mM 1 day after STZ (P < 0.01) and remained constant thereafter. Basal plasma insulin levels were approximately 35% of control levels in all STZ groups (P < 0.01). Insulin-stimulated whole-body glucose uptake decreased significantly as early as one day after STZ injection (P < 0.01), resulting predominantly from a decrease in whole-body glycolysis. Insulin action to suppress hepatic glucose output was normal on day 1 after STZ but impaired markedly on day 3 and thereafter (P < 0.01). Insulin-stimulated glucose uptake in individual skeletal muscles was not altered until day 7 after STZ, and the magnitudes of decreases in skeletal muscle insulin action on days 7 and 14 were not fully accounted for by the decreases in GLUT4 protein level measured from the same muscles. Our data indicate that there is a temporal hierarchy in the development of insulin resistance in STZ-induced diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

The psychological effects of exercise: a model

AbstractA model is put forward that seeks to describe the psychological consequences of exercise. The model indicates the relative time course of events and the interaction and feedback between different effects. It seeks to explain both the difficulties of beginning exercise and the phenomenon of exercise addiction and suggests intervention points for teachers and health educators.

Relative potencies and time course of changes in adenosine 5′-monophosphate airway responsiveness with inhaled furosemide and bumetanide in asthma

A randomized, double-blind, placebo-controlled study was conducted to compare the effects of two chemically unrelated “loop” diuretics, furosemide (40 mg) and bumetanide (2 mg) on the bronchoconstrictor response to inhaled adenosine 5′-monophosphate (AMP) in 12 subjects with asthma. In eight additional volunteers with asthma, we also carried out a separate randomized, double-blind study to examine in more detail the time course of change in bronchial reactivity to inhaled AMP after administration of nebulized furosemide and bumetanide. Inhaled loop diuretics significantly increased the provocative concentration of AMP causing a 20% fall in forced expiratory volume in 1 second (FEV 1) from the value of 21.2 mg/ml (range, 2.5 to 96.9 mg/ml) after placebo administration to 83.4 mg/ml (range, 11.3 to 345.0 mg/ml) (p < 0.01) and 33.8 mg/ml (range, 4.7 to 120.9 mg/ml) (p < 0.05) after administration of furosemide and bumetanide, respectively. After placebo administration, the provocative concentration of AMP causing a 20% fall in FEV 1 (PC 20 AMP) at 10, 30, and 120 minutes did not differ significantly; their geometric mean (range) values were 57.8 mg/ml (10.9 to 341.0 mg/ml), 55.0 mg/ml (13.2 to 304.1 mg/ml), and 52.8 mg/ml (14.4 to 252.2 mg/ml), respectively. When compared with placebo, inhaled furosemide significantly reduced the airway responsiveness to AMP at all time points; the PC 20 AMP values at 10, 30, and 120 minutes were 154.6 mg/ml (29.4 to 658.7 mg/ml) (p < 0.01), 142.6 mg/ml (25.5 to 639.9 mg/ml) (p < 0.01), and 103.9 mg/ml (12.5 to 605.5 mg/ml) (p < 0.05), respectively. The PC 20 values for AMP after pretreatment with bumetanide were significantly increased up to 110.2 mg/ml (25.9 to 639.0 mg/ml) (p < 0.01) and to 92.0 mg/ml (21.6 to 531.7 mg/ml) (p < 0.05) at 10 and 30 minutes, respectively. At 120 minutes, inhaled bumetanide failed to affect AMP airway responsiveness; the PC 20 AMP was not significantly different from that of placebo, with a value of 71.5 mg/ml (22.6 to 318.0 mg/ml). We conclude that comparable equidiuretic doses of furosemide and bumetanide are effective in attenuating the airway response to AMP, with furosemide being approximately 2.5 times more potent than bumetanide (p < 0.01). The time course of change in bronchial reactivity to AMP is similar for both drugs with a peak effect at 10 minutes. It is possible that the mechanism(s) underlying the protective effects of inhaled loop diuretics in asthma may be distinct from those responsible for their diuretic properties.

The relative time course of axonal loss from the optic nerve of the developing guinea pig is consistent with that of other mammals

The relative timing of a number of events during the development of the visual system has recently been suggested to be consistent across a number of mammalian species (Dreher & Robinson, 1988). Some conflicting reports, however, had suggested that the precocial guinea pig might represent an exception to the generalized scheme. A quantitative study was thus carried out on the development of the optic nerve and retina of the guinea pig. Consistent with the prediction of a stable relative time course of mammalian visual development, axons and growth cones were found in the optic stalk from the 24th postconceptional day (40% of the period from conception to eye opening--the cecal period), the peak number of axons was observed on the 32nd postconceptional day (56% of the cecal period), and the phase of rapid axonal loss extended to the 39th and 42nd postconceptional days (68-74% of the cecal period). The number of axons in the adult optic nerve (117,000) represented about 37% of the peak number of axons. Additional observations indicated that during development of the optic nerve the mean axonal diameter increased approximately threefold from 0.31 microns to 1.06 microns. As in other mammals studied so far, myelination was first noted after the period of rapid axonal loss and continued until in the adult 97% of axons were found to be myelinated. In the retina, the presence of pyknotic profiles in the ganglion cell layers extends throughout the periods of loss of the optic nerve axons. Finally, the presence of pyknotic profiles in the amacrine sublayer suggest that in the guinea pig, as in other mammalian species, there is a loss of displaced amacrine cells as well as ganglion cells from the ganglion cell layer.

Human immunodeficiency virus type 1 entry into T cells: more-rapid escape from an anti-V3 loop than from an antireceptor antibody.

The entry of human immunodeficiency virus type 1 into two T-cell lines has been analyzed to determine the relative time courses with which virus entry can be blocked (i) by washing, (ii) by adding a monoclonal antibody to the V3 loop of gp120 that neutralizes without blocking CD4 binding (0.5 beta), or (iii) by adding an antireceptor monoclonal antibody that competes for virus binding (leu3a). During entry into C8166 cells, 50% escape from the wash as well as the anti-V3 loop antibody required 20 min, whereas 50% escape from the leu3a block required 45 minutes. In contrast, during entry into H9 cells, 50% escape from the wash block required 50 min, 50% escape from the anti-V3 loop antibody required 110 min, and 50% escape from the antireceptor antibody required 190 min. These results demonstrate that the times required for entering virus to escape each of the blocks were cell type specific. They also demonstrate that V3 loop-dependent steps occur relatively early in entry and suggest that binding of gp120 to CD4 is important for late as well as early steps in human immunodeficiency virus type 1 entry.

Effects of hypoxia and hypercapnia on the force-velocity relation of rabbit myocardium.

The separate effects of hypoxia and hypercapnia on the force-velocity relation of rabbit myocardium were compared in 10 papillary or trabecular muscles superfused using control (95% O2-5% CO2), hypoxic (18% O2), and hypercapnic (20% CO2) physiological salt solutions. This level of hypoxia did not irreversibly damage the muscles and reduced peak isometric force by 53 +/- 11%. The level of hypercapnia was chosen to match the force depression (50 +/- 12%) produced by hypoxia. Multiple force-velocity points were measured by applying critically damped isotonic force steps at 90% of the time to peak isometric force and at the time to 50% peak isometric force. These points defined the force-velocity relation and maximum velocity of shortening, the extrapolated isometric force, and the maximum power of nonpotentiated and postextrasytolic potentiated contractions. Hypoxia and hypercapnia reduced maximum force and maximum power nearly equally. Maximum velocity of shortening decreased more during hypoxia (21 +/- 12%) than during hypercapnia (12 +/- 9%) (p less than 0.01). Postextrasystolic potentiation completely reversed the reduction of maximum velocity of shortening during hypercapnia but not during hypoxia. A 6% internal load could account for the reduction in maximum velocity of shortening during hypercapnia and all but 9% of the reduction in maximum velocity of shortening during hypoxia. The relative time course of the force-velocity relation was not altered by either hypoxia or hypercapnia. We conclude that hypercapnia reduces the effect of activation because increased activation (by postextrasystolic potentiation) restored the force-velocity relation and maximum velocity of shortening to control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Atherogenic Effects of Anabolic Steroids on Serum Lipid Levels

This article reviews the current body of literature linking anabolic steroids to atherogenic alterations in serum lipid levels. Anabolic steroids cause marked high-density lipoprotein2 levels [corrected] depression (weighted average, 52%) and severe depression of high-density lipoprotein b levels (weighted average, 78%) while raising low-density lipoprotein levels an average of 36%. The mechanism of these lipid changes, their time course in relation to anabolic steroid use, and their dependency on route of anabolic steroid administration are discussed. Interpretation of the observed lipid level changes in light of the epidemiologic data linking lipids to coronary heart disease risk is used to estimate the lipid-based increase in coronary heart disease risk due to anabolic steroid use.