Pial microvascular hemodynamics in anemia

Isovolemic hemodilution and subsequent anemia increase cerebral blood flow (CBF). We hypothesized that pial microvascular pressure also increases with hemodilution and that arteriolar diameter varies concurrently as a myogenic autoregulatory response. First- and second-order arterioles (31-92 microns, n = 29) and large venules (65-215 microns, n = 17) were studied in thiopental-anesthetized rats. Microvascular pressure was determined using the servo-null technique, and vessel diameters were obtained directly from a video monitoring system. We measured the increase in CBF (radiolabeled microspheres) that accompanies hemodilution in a separate group of animals (n = 20). Hematocrit was reduced to 16-36% with homologous plasma (hemodilution group, n = 13) or held constant with homologous whole blood (control group, n = 4). In control animals, arteriolar and venular diameter varied +/- 1-2 microns from baseline values, and microvascular pressure remained unchanged from baseline. In the hemodilution group, CBF increased, but there was no systematic pial vasodilation. Furthermore, intraluminal pressure did not increase in pial microvessels, suggesting that proximal vasodilation was negligible even at the lowest hematocrit studied. Vascular resistance fell proportionately in both large vessel and microvascular segments. We conclude that experimental anemia does not produce alterations in microvascular pressure in rats, and the hyperemia accompanying hemodilution is largely viscosity mediated.

Haemophilus influenzae type B impairment of pial vessel autoregulation in rats

To examine the mechanisms of autoregulatory impairment in meningitis, we studied the effects of Haemophilus influenzae type b (Hib) on pial vessels during hemorrhagic hypotension in rats, using a cranial window technique. We prepared cranial windows in barbiturate-anesthetized, mechanically ventilated rats. Artificial cerebrospinal fluid or 10(5) Hib in cerebrospinal fluid (n = 7 each group) was suffused over the pial surface. Pial arteriolar diameter was measured hourly for 4 h. Autoregulation was assessed as the ability of pial arterioles to dilate in response to graded hemorrhagic hypotension at 2 and 4 h. Pial arterioles exposed to Hib dilated progressively to 149 +/- 27% of baseline at 4 h. Vessel diameter in the Hib group was significantly greater than in the control group beginning at 2 h. Autoregulation was progressively impaired in Hib-exposed rats compared with control rats [-5.85 +/- 1.38 versus -8.02 +/- 2.02 and -3.82 +/- 1.57 versus -8.53 +/- 1.72% dilation/kPa fall in mean arterial blood pressure at 2 and 4 h, respectively (p < 0.05)]. These data suggest that autoregulation is impaired in pial arterioles exposed to Hib because involved vessels have a finite dilatory capacity and are close to maximal dilation before hypotensive challenge.

Alternative splicing determines the carboxy terminus of the Epstein-Barr virus nuclear antigen 5 species expressed in the Burkitt's lymphoma cell line Daudi

The Daudi strain of Epstein-Barr virus (EBV) possesses a genomic deletion, relative to the B95-8 EBV prototype, that removes the entire Epstein-Barr virus nuclear antigen 2 (EBNA2) open reading frame (ORF) and the sequences encoding the carboxy terminus of EBNA5. Immunoblot analysis carried out in this study indicates that two species of EBNA5 (31K and 37K) are expressed in Daudi cells. Nucleotide sequence analysis of Daudi cDNA clones has confirmed that, as a consequence of the genomic deletion, exons usually appearing further downstream in EBNA messages (exons U or HF) are spliced directly onto the truncated EBNA5 ORF. Furthermore, the use of alternative splicing suggests that the two EBNA5 species expressed in Daudi cells possess different carboxy termini.

Circulatory dynamics during periodic intracranial hypertension in fetal sheep

The human fetal head is periodically compressed during labor. The resulting increase in intracranial pressure (ICP) may exceed the hydrostatic increase in mean arterial pressure (MAP), thereby decreasing cerebral perfusion pressure (CPP). We determined whether the cardiovascular system of near-term fetal sheep is capable of rapidly increasing MAP during periodic increases in ICP. In 12 chronically instrumented fetuses, we produced sinusoidal oscillations in ICP with a maximum of 52 +/- 1 mmHg (baseline MAP) and a minimum of 4 +/- 1 mmHg at a 3-min periodicity by ventricular fluid infusion and withdrawal. Phasic increases in MAP and decreases in electromagnetically determined renal blood flow tracked behind ICP by 0.3-0.5 min. By the sixth cycle, tonic peripheral vasoconstriction that occurred attenuated by the reduction in CPP during subsequent ICP oscillations. By the 10th cycle, plasma catecholamines and vasopressin increased 20-fold. To more closely simulate the pattern during labor, we produced an ICP triangular pulse train with 5-min periodicity and pulse duration of 1.5 min in six other fetuses. The MAP response was nearly out of phase with this more rapid rise of ICP. Thus the phasic component of the fetal pressor response is inadequate for maintaining CPP when ICP is increased to baseline MAP in less than 0.75 min. However, when the ICP pulse duration and frequency are sufficiently high, a tonic pressor response that may be humorally mediated acts to minimize transient cerebral ischemia.

Oxygen free radicals and the cerebral arteriolar response to group B streptococci

We used a cranial window preparation to observe the effects of direct application of group B streptococci to the surface of the brain in the adult rat. Continuous exposure to group B streptococci at concentrations of 10(3) and 10(5) organisms/mL caused progressive dilation of surface (pial) cerebral arterioles that became statistically significant (p less than 0.05) after 2.5 h. These results were reproduced with heat-killed organisms at the same concentration, but not with a bacteria-free filtrate of the growth medium. In separate studies, we found that infusion of alkaline cerebrospinal fluid (pH = 7.8) into the window did not reverse vasodilation, suggesting that it was not due to progressive cerebrospinal fluid acidosis. A solution of nitroblue tetrazolium infused into the window at the end of a 3-h exposure to the organism was promptly reduced, suggesting the presence of oxygen free radicals. Treatment with i.v. polyethylene glycol-superoxide dismutase and polyethylene glycol-catalase in doses of 10,000 and 20,000 U/kg, respectively, was itself without effect on pial arterioles, but treatment with these compounds before exposure to group B streptococci eliminated the vasodilation. These data support a role for oxygen free radicals in the pathogenesis of pial arteriolar dysfunction induced by exposure to group B streptococci.

Randomised controlled trial of day care for hypertension in pregnancy

Our aim was to assess the effect of the introduction of a day-care unit on the care of women with non-proteinuric hypertension in pregnancy. A randomised controlled trial was carried out on 54 women who presented at 26 weeks of pregnancy or later with non-proteinuric hypertension (systolic blood pressure 150-170 mm Hg and/or diastolic pressure 90-105 mm Hg on two occasions at least 15 min apart). 30 women were allocated to care by the day unit and 24 were managed according to the established practice of their clinicians without access to the day unit (control group). Women in the control group spent on average 4.6 times longer as inpatients (difference in mean stay 4.0 days [95% confidence interval 2.1-5.9 days]) than the day-unit group and were 8.8 times (95% CI 3.0-25.8) more likely to be admitted to hospital. Induction of labour was 4.9 times (95% CI 1.6-13.8) more likely in the control than in the day-unit group and the development of proteinuria 11.4 times (95% CI 1.8-71.4) more likely. The control group had a mean of 1.5 fewer hospital outpatient visits (95% CI 0.36-2.64). The groups did not differ in their use of antihypertensive drugs. Day-unit care for hypertension in pregnancy significantly reduced the need for and the length of antenatal inpatient admissions and the number of medical interventions, at the cost of an increase in outpatient attendances. Our results are further evidence that inpatient care does not improve outcomes or prevent the development of proteinuria in this disorder.

Cerebral blood flow response to hypercapnia in immature fetal sheep

We have reported recently that the cerebral blood flow (CBF) response to isocapnic hypoxic hypoxia is blunted in fetal sheep in utero at 93 days of gestation (term = 145-150 days), a time of rapid brain differentiation in this species. Cerebral O2 transport fell rather than being maintained, as it is in more mature fetuses. The reason for the blunted response was not clear. We hypothesized that the CBF response to hypercapnia also might be blunted. We studied 10 immature fetal sheep in utero at a mean gestational age of 92 days 24 h after catheters were placed into the superior sagittal sinus, axillary artery, and inferior vena cava. We raised the fetal arterial carbon dioxide tension (PaCO2) by changing the mother's inspired PCO2. CBF was measured before and during hypercapnia by the microsphere method. The overall increase in CBF in response to hypercapnia in immature fetuses was lower than in near-term fetuses. However, the difference was eliminated after correcting for differences in cerebral O2 consumption. This study failed to show any defect in the ability of cerebral vessels in immature fetal sheep to respond to carbon dioxide.

Characterization of the DNA polymerase gene of human herpesvirus 6

The construction of a recombinant bacteriophage lambda library containing overlapping clones covering 155 kbp of the 161-kbp genome of the Ugandan U1102 isolate of human herpesvirus 6 (HHV-6) is described. The use of degenerate-primer polymerase chain reaction allowed the isolation of a DNA probe for the DNA polymerase gene of HHV-6, which was subsequently used to isolate and position the pol gene on the physical map of the viral genome. A 4.4-kbp EcoRI DNA restriction fragment containing the pol gene was isolated and sequenced. The open reading frames flanking the pol gene code for the HHV-6 glycoprotein B gene and the human cytomegalovirus UL53 homolog. This arrangement is different from that seen in the alpha and gamma herpesvirus families, lending further support to the notion that HHV-6 is a member of the beta herpesvirus group.

Efficacy of Cushing response during development in sheep

Mean aortic pressure (MAP) increases (Cushing response) when intracranial pressure (ICP) approaches MAP. We elevated ICP to levels equivalent to normal baseline MAP with infusion of mock cerebrospinal fluid (CSF) into the lateral cerebral ventricles and contrasted responses in near-term fetal sheep, 1-wk-old lambs, and adult sheep anesthetized with pentobarbital sodium. With CSF infusion 1-wk-old lambs and adults produced sustained increases in MAP of 16 +/- 1 and 22 +/- 2 mmHg, respectively, over a 40-min period. However, cerebral blood flow fell 66 and 57%, and cerebral O2 uptake fell 34 and 37%, respectively. In the near-term fetus, MAP increased by 11 +/- 1 mmHg and cerebral blood fell 49% at 3 min of elevated ICP. However, by 15 min MAP had increased further (+17 +/- 2 mmHg) and cerebral blood flow was nearly restored. In contrast to postnatal sheep, cerebral O2 uptake was maintained throughout in the fetus. The mechanism of increased MAP differed among groups. In adults total peripheral resistance fell significantly, whereas in the fetus and lamb it remained constant. Cardiac output increased in each group, but, because of the fall in peripheral resistance, increased cardiac output was relatively more important to the rise in MAP in adults. In addition, marked vasoconstriction occurred in intestines and skin in the fetus. The Cushing response is well-developed in near-term fetal sheep. After birth it may lose its effectiveness in providing for the basal metabolic demand of the brain.

Simultaneous determination of clebopride and a major metabolite N-desbenzylclebopride in plasma by capillary gas chromatography-negative-ion chemical ionization mass spectrometry

A procedure for the simultaneous assay of clebopride and its major metabolite N-desbenzylclebopride in plasma has been developed. The method utilizes capillary gas chromatography-negative-ion chemical ionization mass spectrometry with selected-ion monitoring of characteristic ions. Employing 2-ethoxy analogues as internal standards, the benzamides were extracted from basified plasma using dichloromethane. Subsequent reaction with heptafluorobutyric anhydride produced volatile mono- and diheptafluorobutyryl derivatives of clebopride and N-desbenzylclebopride, respectively. The methane negative-ion mass spectra of these derivatives exhibited intense high-mass ions ideal for specific quantitation of low levels in biological fluids. Using this procedure the recovery of the drug and metabolite from human plasma was found to be 84.4 +/- 1.5% (n = 3) and 77.4 +/- 4.7% (n = 3), respectively, at 0.5 ng/ml. Measurement of both compounds down to 0.10 ng/ml with a coefficient of variation of less than 10.5% is described. Plasma levels are reported in four volunteers up to 24 h following oral administration of 1 mg of clebopride malate salt.

Haemostatic measurements in childhood nephrotic syndrome

Blood coagulation and platelet aggregation were assessed in children with nephrotic syndrome who were divided into the following groups: (1) relapse without treatment: (2) relapse on steroids; (3) early remission; (4) late remission and (5) steroid resistant. The renal histological findings were also recorded. Plasma anti-thrombin III (ATIII) levels were markedly reduced in groups 1 and 2, below normal in group 3 and were normal in groups 4 and 5. There was significant urinary loss of ATIII in groups 1 and 2 as well as in group 5. Plasma fibrinogen fluctuations exhibited the expected negative correlations with plasma ATIII. Reptilase time showed significant prolongation in groups 1, 2 and 3, and was near normal in groups 4 and 5. Platelet aggregation in response to arachidonic acid exhibited aggregation followed by disaggregation in groups 1, 2, 4 and 5, and was normal in group 3. Hyperaggregation in response to decreasing doses of ADP was noted in all patient groups as well as controls with no relationship to serum albumin levels. Aggregation responses to collagen and ristocetin were normal. It is concluded that: 1. The fluctuations in ATIII levels in childhood nephrotic syndrome are determined by the response to steroids and not by the renal histology per se. 2. An acquired fibrin polymerization defect (dysfibrinogenaemia) and an abnormality of the prostaglandin pathway of platelet activation, both reversible, are yet other haemostatic abnormalities in childhood nephrosis. 3. The discrepancies in the literature on haemostatic parameters, specially ATIII in childhood nephrosis, would not have arisen if their fluctuation in relation to steroid therapy as well as the renal histological features of nephrotic syndrome had been documented simultaneously.

The genome of human herpesvirus 6: maps of unit-length and concatemeric genomes for nine restriction endonucleases

More than 50 fragments resulting from complete digestion of the DNA of human herpesvirus 6 (HHV-6, strain U1102) with BamHI, EcoRI, HindIII, KpnI, NruI, SalI or SmaI have been isolated as clones in M13, plasmid, cosmid and lambda vectors. Using these clones, maps have been constructed for the fragments produced by nine restriction enzymes from unit-length virus genomes and from their concatemeric precursors. The unit-length genome is a linear, double-stranded molecule of 161.5 kbp composed of a central segment of a largely unique sequence of 141 kbp (U) with a sequence of 10 kbp duplicated in the same orientation at both 'left' and 'right' genomic termini (i.e. 'left' and 'right' copies of the direct repeat; DRL and DRR). Adopting as standard an orientation in which the major capsid protein gene is 'left' of the gene for alkaline exonuclease, then the 'right' genome termini and DRL. U junctions occur close to or within repetitive (GGGTTA)n sequences. Repetitions of short sequence motifs are present in at least two other regions of the genome. One of these regions consists of a simple repeat (TC/G) of approximately 1.5 kbp in length and is unstable as clones in bacterial vectors. The second region is stably maintained in such vectors and consists of a tandem array of at least 25 copies of a 110 bp sequence containing a single KpnI site. Comparisons of fragments arising from unit-length DNA with those from virus DNA from the nuclei of infected cells have shown that the concatemeric junctions in intracellular DNA contain head-to-tail dimers of the terminal duplications (i.e. ...U1.DRR1.DRL2.U2...). The gross structure established here for the genome from the U1102 isolate of HHV-6 resembles closely that suggested by Pellett and his colleagues for the Z29 isolate and differs from that of the five previously characterized human herpesviruses. This structure of HHV-6 DNA bears a superficial resemblance to that proposed for DNA from channel catfish virus and equine cytomegalovirus.

Effects of cocaine on pial arterioles in cats

We used the closed cranial window technique to observe the responses of pial arterioles to topical application of cocaine in 29 anesthetized cats. Alterations in arteriolar diameter were dependent on the concentration of cocaine applied. Cocaine dissolved in artificial cerebrospinal fluid at concentrations of 10(-8) or 10(-7) M was without effect. Concentrations of 10(-6) and 10(-5) M produced dilation (4.9 +/- 1.5% [mean +/- SEM] and 5.9 +/- 2.0%, respectively) in large arterioles (greater than 100 microns) but no significant change in the diameter of small arterioles (less than 100 microns). A concentration of 10(-4) M dilated both large and small arterioles (20.3 +/- 3.1% and 12.0 +/- 7.1%, respectively). Pretreatment with 1 mg/kg i.v. propranolol blocked the increase in pial arteriolar diameter after application of 10(-4) M cocaine and produced significant vasoconstriction in small arterioles (-8.3 +/- 3.1%). Cocaine produces vasodilation of cat cerebral arterioles. This effect appears to be mediated, at least in part, by mechanisms that depend on stimulation of beta-adrenergic receptors.

Inhaler and spacer use in obstructive airway diseases

The role of inhaled aerosols in the treatment of obstructive airway diseases is increasing for both immediate bronchodilation and prophylactic anti-inflammatory effects. Inhaled aerosol agents are available in metered-dose inhaler and nebulizer forms. Maximum therapeutic benefit from metered-dose inhalers is assured when the correct inhaler technique is used. Spacer devices may be helpful in some patients.

Myristylated polyomavirus VP2: role in the life cycle of the virus

The double-stranded genome of the small DNA tumor virus, polyomavirus, is enclosed in a capsid composed of a major protein, VP1, which associates as pentameric capsomeres into an icosahedral structure, and two minor proteins, VP2 and VP3, whose functions and positions within the structure are unknown. The N-terminal glycine of the VP2 coat protein has been shown to be cotranslationally acylated with myristic acid. To study the function of this modification and the role of VP2 in the life cycle of polyomavirus, the N-terminal glycine, critical to the myristylation consensus sequence, has been altered to a glutamic acid or a valine residue by site-directed oligonucleotide mutagenesis. The glycine----glutamic acid mutant DNA has been further studied. When transfected into cells permissive for the polyomavirus full lytic life cycle, this mutant DNA replicated at levels comparable to those of wild-type viral DNA, and small amounts of nonrevertant (mutant) virus could be harvested from the cultures. The virus particles viewed by electron microscopy appeared slightly distorted, but the ratio of full to empty particles was similar to that produced in a wild-type viral infection. Mutant virus was capable of reinfecting permissive cells but with a considerably reduced efficiency.

Effect of extracorporeal membrane oxygenation on cerebral blood flow and cerebral oxygen metabolism in newborn sheep

Extracorporeal membrane oxygenation (ECMO) supplies respiratory support to term or near-term infants with respiratory failure. Although infants requiring this therapy may have already sustained significant hypoxia and/or ischemia predisposing them to neurologic injury, the high incidence of neuroimaging abnormalities in the ECMO population raises concerns about the additional neurologic risk associated with the ECMO procedure itself. Our study was undertaken to evaluate the effects of ECMO on the normal neonatal cerebral circulation. Thirteen newborn lambs (1-7 d of age) were placed on normothermic venoarterial ECMO using a silicone membrane oxygenator and roller occlusion pump. Regional brain blood flows, cerebral oxygen consumption, fractional oxygen extraction, and oxygen transport were determined 30 and 120 min after initiation of ECMO. Neither cerebral blood flow (baseline, 60.2 +/- 23.6; 30 min, 56.1 +/- 18.1; 120 min 56.1 +/- 12.9 mL/100 g/min) nor oxygen metabolism (cerebral oxygen consumption: baseline, 4.48 +/- 1.48; 30 min, 3.86 +/- 1.53; 120 min, 4.10 +/- 1.32 mL/100 g/min and oxygen extraction: baseline, 0.52 +/- 0.09; 30 min, 0.47 +/- 0.14; 120 min, 0.46 +/- 0.14 mL/100 g/min) changed after the initiation of ECMO. Regional and left/right blood flow differences were not noted. These findings suggest that in healthy newborn lambs, initiation of ECMO does not alter cerebral blood flow or oxygen metabolism.

Effect of acute hypoxemia on brain blood flow and oxygen metabolism in immature fetal sheep

Studies of cerebral blood flow and oxygen metabolism during acute hypoxic hypoxia in fetal sheep have been confined to late gestation, a time when brain development in this species is largely complete. There is no systematic study of cerebral vascular responses to acute hypoxic hypoxia in immature fetal sheep or, indeed, in immature brains of any species. We studied 13 fetal sheep in utero at 93 +/- 1 days gestation (term = 145-150 days), 48 h after intravascular catheters were placed into the superior sagittal sinus, axillary arteries, and inferior vena cava. We measured brain blood flow by the microsphere method. Cerebral oxygen consumption was calculated with the use of blood flow to the cerebral hemispheres (cerebrum, diencephalon, mesencephalon) and arterial and sagittal sinus values for oxygen content. Fractional oxygen extraction was calculated as the ratio between oxygen consumption and oxygen transport. We altered fetal oxygenation by changing the mother's inspired oxygen concentration. As in the near-term fetus, acute hypoxic hypoxia resulted in increased blood flow to cerebral hemispheres, cerebellum, and pons-medulla; furthermore, the increase in blood flow was sufficient to sustain cerebral oxygen consumption. However, in contrast to near-term fetuses, the increase in blood flow to the cerebral hemispheres was not sufficient to maintain convective oxygen transport. Cerebral oxygen consumption was therefore sustained in part by an increase in fractional extraction. Blunted hypoxic vasodilation in immature fetuses might reflect either immature regulatory mechanisms or an inability of cerebral vessels to respond to the usual stimuli. It is also possible that hypoxic vasodilation was blunted by reflex stimulation of the sympathetic nervous system.

Hypocapnia does not alter collateral ventilation in sheep

Hypocapnic constriction has been proposed as a mechanism by which collateral pathways might rapidly alter ventilation to match perfusion. We studied the changes in response to hypocapnia with age in sheep, a species with collateral resistance (Rcoll) similar to those measured in humans. Measurements of Rcoll were made with either 5 or 10% CO2 and with air (hypocapnia) in 29 anesthetized sheep, ages 6 mo to 10 yr, with the wedged bronchoscope technique. Rcoll was 0.42 +/- 0.12, 0.58 +/- 0.18, 0.32 +/- 0.18, and 0.17 +/- 0.04 (SE) cmH2O.ml-1.min in 6-mo- and 1-, 2-, and 10-yr-old animals, respectively. These values were unchanged with hypocapnia. Despite the lack of a change in Rcoll with hypocapnia, administration of histamine aerosol (8 animals) through the bronchoscope increased Rcoll by 151 +/- 35% (P less than 0.05). These data suggest that although collateral pathways exist in sheep and are capable of constriction, they do not respond to hypocapnia. Furthermore, the response to hypocapnia is not influenced by age.

Localized ileus of the proximal jejunum: a new sign for acute appendicitis

A focal dilatation of a loop of small bowel has been identified in the left upper quadrant in a series of individuals with suspected appendicitis. Retrospective review of 100 cases of surgically proven appendicitis demonstrated this sign in 51. No previous description of this sign has been found. This finding is believed to be an early sign of appendicitis and may be a valuable adjunct in combination with a clinical history without other radiologic signs of appendicitis. The more conventional signs of appendicitis such as appendicolith and focal ileus of the terminal ileum reinforce the diagnosis.

Chemodenervation does not alter cerebrovascular response to hypoxic hypoxia

We tested the hypothesis that sinoaortic chemodenervation would alter the increase in cerebral blood flow (CBF) during isocapnic hypoxic hypoxia in 1- to 7-day-old lambs. Lambs were anesthetized with pentobarbital and studied during moderate (arterial O2 content [CaO2] = 10 vol/100 ml) and severe (CaO2 = 6 vol/100 ml) hypoxic hypoxia. Regional brain blood flows were measured with the radioactive microsphere technique. Cerebral oxygen consumption (CMRO2) was calculated as the product of forebrain blood flow and the difference in oxygen contents between arterial and sagittal sinus blood. Lambs were then subjected to either sham surgery (n = 6) or to carotid chemodenervation and cervical vagotomy (n = 6). Chemodenervation was verified by abolition of the transient increase in blood pressure after intravenous injection of sodium cyanide in intact subjects. Neither sham surgery nor chemodenervation had an effect on CMRO2 or CBF during hypoxic hypoxia. These data thus do not support the hypothesis that arterial chemoreceptors play any substantial role in the regulation of cerebral vascular tone during hypoxic hypoxia in the 1- to 7-day-old anesthetized lamb.

Reverse transcription of mRNA by Thermus aquaticus DNA polymerase

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Hemodilution causes size-dependent constriction of pial arterioles in the cat

Cerebral blood flow (CBF) rises as hematocrit (Hct) falls. We previously attributed this rise in CBF to two independent factors of equal importance, decreased arterial O2 content and decreased blood viscosity. We hypothesized that decreased arterial O2 content would dilate cerebral arterioles and that the magnitude of the vasodilation would depend on the magnitude of the passive fall in vascular resistance attributable to decreased viscosity. The present study was designed to test the hypothesis that anemia is accompanied by cerebral vasodilation. Using a closed cranial window, we measured the diameters of 42 pial arterioles (35-305 microns) in 7 cats as serial isovolemic hemodilution lowered Hct by 44% from 31 +/- 4 to 17 +/- 3%. Hemodilution increased CBF (microsphere technique) but did not change mean arterial blood pressure or arterial blood gases. Anticipated vasodilation did not occur; instead, pial arterioles constricted as Hct fell. Maximum vasoconstriction was observed when Hct reached 65-70% of the initial value. Vasoconstriction lessened as Hct was lowered further, but arteriolar diameters at the lowest Hcts remained less than base-line levels. Constriction was greater in small (less than 100 microns) than in large (greater than or equal to 100 microns) arterioles. The initial constriction of pial arterioles may represent myogenic vasoconstriction in response to flow-induced vasodilation of more proximal portions of the cerebrovascular bed and/or to washout of an endogenous vasodilator. Arteriolar relaxation with more profound hemodilution may reflect superimposed metabolic vasodilation.

EBV gene expression in an NPC-related tumour

A nasopharyngeal carcinoma tumour (designated C15) propagated in nude mice has been used to generate a large cDNA library that we have analysed for Epstein-Barr virus (EBV) gene expression. No gross alterations exist in viral DNA from C15 relative to other human isolates and the large deletion present in the B95-8 'prototype' viral strain established in marmoset cells is not found; C15 contains no linear virion DNA. In the cDNA library, of the six EBV nuclear antigens (EBNAs) expressed in latently infected B-lymphocytes, only clones for EBNA-1 are found. These data are confirmed by immunoblotting. Sequence analysis shows the EBNA-1 mRNA splicing pattern in the carcinoma to differ from that observed in B-lymphocytes. Further, contrary to observations with B-cell lines, most viral transcription in the tumour is localized onto the 'rightmost' region of the conventional EBV physical map. Transcripts identified corresponding to known genes include those for the latent membrane protein (LMP), the alkaline DNA exonuclease and probably the terminal protein; major transcripts are also derived from the BamHI D fragment and the region deleted in B95-8 EBV DNA. Novel transcripts have also been identified that proceed in an anti-sense direction to genes encoding functions associated with replication, such as the viral DNA polymerase. They contain a large, hitherto unidentified, open reading frame in the viral genome that is complementary to the putative function known as BALF3 and a smaller open reading frame complementary to BALF5 (the DNA polymerase gene). From the present studies we can conclude that: (i) EBV transcription patterns in the epithelial cells vary markedly from those identified previously in B-cells, reflecting differential use of promoters or splicing patterns. (ii) Transcription is tightly regulated and restricted in the C15 tumour with many latent genes, notably EBNAs 2-6, being 'switched off.' (iii) A family of cytoplasmic RNAs are transcribed in an antisense direction to a number of existing open reading frames in the EBV genome. (iv) There are a number of mutations in C15 transcripts relative to the B95-8 genome, some of which could result in amino acid alterations in proteins.

Assessing the need for transfusion of premature infants and role of hematocrit, clinical signs, and erythropoietin level

There are no clear criteria for administration of blood to premature infants. In the past, indications for transfusion have included tachypnea, tachycardia, poor weight gain, apnea, bradycardia, pallor, lethargy, decreased activity, or poor feeding. Some have suggested that erythropoietin levels may also be useful in determining the need for transfusion. Data were studied from 11 premature infants with birth weights less than 1500 g collected throughout 469 hospital days. During that period the infants received a total of 37 blood transfusions. No overall relationship was found between hematocrit of 19% to 64% and heart rate, respiratory rate, or the occurrence of bradycardia; ie, these variables proved to be clinically unreliable as indicators of hematocrit. Furthermore, no predictable effect of transfusion could be identified on heart rate, respiratory rate, or on the incidence of apnea or bradycardia. It was anticipated that frequent episodes of apnea or bradycardia might increase serum erythropoietin concentration. To the contrary, more frequent bradycardia was associated with the low erythropoietin levels because those infants tended to receive transfusions for "symptomatic" anemia. The data are consistent with the concept that "anemia of prematurity" is not predictably associated with symptoms classically attributed to anemia. Possible reasons for this are that the premature infant has a different inherent response to anemia; that it is inappropriate to extrapolate symptoms of severe acute anemia to persons with mild or moderate chronic anemia; or, most likely, that other determinants of heart rate, respiratory rate, and apnea/bradycardia are of more importance than mild or moderate anemia.

Cerebral blood flow and metabolism during and after prolonged hypocapnia in newborn lambs

We studied the effects of prolonged (6 hours) hypocapnia and the abrupt termination thereof on cerebral blood flow and metabolism in six paralyzed, sedated (but not anesthetized) newborn lambs. Thirty minutes after institution of hyperventilation to an arterial carbon dioxide pressure of 15 +/- 2 torr, hyperventilation, cerebral blood flow had returned to baseline. Abrupt termination of hyperventilation after 6 hours resulted in a 110 +/- 71% increase in cerebral blood flow over baseline after 30 minutes of normocapnia. This cerebral hyperemia persisted for at least 90 minutes after hyperventilation was discontinued. Cerebral oxygen consumption did not change throughout the study. The posthypocapnia hyperemia noted in these animals after abrupt normalization of arterial carbon dioxide pressure may contribute to the increased risk of intracranial hemorrhage in newborn infants who are treated similarly in the management of pulmonary hypertension.

Cerebral blood flow, oxygenation, and carbohydrate metabolism in immature fetal sheep in utero

Studies of cerebral blood flow (CBF) and metabolism in fetal sheep have been largely confined to late gestation, a time when brain development in this species is largely complete. Few studies have been done at a time when the fetal sheep brain is in the midst of rapid differentiation and development. We studied seven fetal sheep in utero at 91 days of gestation (term = 145-150 days) 24 h after catheters were placed into the sagittal sinus, axillary artery, and inferior vena cava. We measured CBF by the microsphere method and used arteriovenous differences of O2, lactate, and glucose to calculate cerebral O2 consumption (CMRo2), fractional O2 extraction, glucose consumption, O2-glucose index (OGI), and cerebral lactate production. Compared with near-term fetal sheep, we found lower CBF (33.9 +/- 5.3 ml.100 g-1.min-1), lower glucose consumption (8.5 +/- 1.25 mumol.100 g-1.min-1), and lower CMRo2 (41.8 +/- 8.8 mumol.100 g-1.min-1). Fractional O2 extraction was 0.29 +/- 0.04, which is similar to near-term fetal sheep. There was consistent cerebral lactate production (2.45 +/- 1.58 mumol.100 g-1.min-1). The OGI was 81 +/- 16%, i.e., oxidative metabolism could account for 81% of glucose uptake. Lactate production accounts for virtually all glucose uptake exceeding that required for oxidation.

Cerebral and peripheral circulatory responses to intracranial hypertension in fetal sheep

Fetal head compression during normal labor can increase intracranial pressure (ICP). We studied the cerebral and peripheral blood flow responses to ICP elevation in utero in chronically catheterized fetal sheep using the radiolabeled microsphere technique. ICP was elevated, stepwise, in increments of 6 +/- 1 mm Hg by infusion of artificial cerebrospinal fluid into a lateral ventricle. When ICP was raised to within 28 mm Hg of baseline mean arterial blood pressure (i.e., ICP above 22 mm Hg), arterial pressure began to increase. Above this ICP level, up to 41 mm Hg, mean cerebral perfusion pressure was maintained by equivalent increases in arterial pressure. Cerebral blood flow and O2 uptake at the highest ICP levels were not different from baseline values. Changes in peripheral organ blood flow were graded according to the level of ICP. At the highest level (ICP = 41 mm Hg), renal, gastrointestinal, and skin blood flow decreased by 68%, 69%, and 65%, respectively. Myocardial and adrenal blood flow doubled, whereas heart rate and cardiac output were unchanged. Placental blood flow increased in proportion to arterial pressure. Arterial plasma epinephrine, norepinephrine and arginine vasopressin increased by nearly two orders of magnitude. Therefore, as ICP approaches baseline mean arterial pressure, fetal lambs are capable of sustaining cerebral perfusion by initiating profound visceral vasoconstriction without curtailing placental blood flow. Since cerebral O2 uptake was maintained, there is no evidence that stimulation of the peripheral response requires pronounced cerebral ischemia. This highly developed Cushing response may be important for ensuring cerebral viability when the fetal head is compressed during parturition.

Hypercapnia and response of cerebral blood flow to hypoxia in newborn lambs

Individual effects of hypoxic hypoxia and hypercapnia on the cerebral circulation are well described, but data on their combined effects are conflicting. We measured the effect of hypoxic hypoxia on cerebral blood flow (CBF) and cerebral O2 consumption during normocapnia (arterial PCO2 = 33 +/- 2 Torr) and during hypercapnia (60 +/- 2 Torr) in seven pentobarbital-anesthetized lambs. Analysis of variance showed that neither the magnitude of the hypoxic CBF response nor cerebral O2 consumption was significantly related to the level of arterial PCO2. To determine whether hypoxic cerebral vasodilation during hypercapnia was restricted by reflex sympathetic stimulation we studied an additional six hypercapnic anesthetized lambs before and after bilateral removal of the superior cervical ganglion. Sympathectomy had no effect on base-line CBF during hypercapnia or on the CBF response to hypoxic hypoxia. We conclude that the effects of hypoxic hypoxia on CBF and cerebral O2 consumption are not significantly altered by moderate hypercapnia in the anesthetized lamb. Furthermore, we found no evidence that hypercapnia results in a reflex increase in sympathetic tone that interferes with the ability of cerebral vessels to dilate during hypoxic hypoxia.

Cerebral blood flow and evoked potentials during Cushing response in sheep

We determined how alterations in systemic hemodynamics, characteristic of the Cushing response, are related to changes in cerebral blood flow (CBF), cerebral metabolic rate of O2 (CMRO2), and brain electrical conductive function, as assessed by somatosensory-evoked potentials (SEP) and brain stem auditory-evoked responses (BAER). In three groups of eight pentobarbital-anesthetized sheep, intracranial pressure was gradually elevated to within 50, 25, or 0 mmHg of base-line mean arterial pressure and then held constant for 40 min by intraventricular infusion of mock cerebrospinal fluid. Microsphere-determined CBF fell when cerebral perfusion pressure was less than 50 mmHg. CMRO2 fell when CBF fell greater than 30-40%. Mean aortic pressure and cardiac output increased when CBF fell greater than 40%, i.e., at approximately the level at which CMRO2 fell. Furthermore, the magnitude of the increase in arterial pressure and cardiac output correlated with the reduction of CMRO2. SEP latency did not increase unless CBF fell greater than 55-65%, corresponding to a 20-30% reduction of CMRO2. Increased latency of BAER wave V was associated with a fall in midbrain blood flow of greater than 65-70%. Thus increase in SEP and BAER latencies required reductions of flow greater than those required to elicit a systemic response. This demonstrates that there is a range of intracranial pressure over which the increase in arterial pressure preserves sufficient CBF to sustain minimal electrical conductive function. The best predictor of the onset and magnitude of the Cushing response in adult sheep is the decrease in CMRO2.

A compartmental model for oxygen transport in brain microcirculation

A compartmental model is formulated for oxygen transport in the cerebrovascular bed of the brain. The model considers the arteriolar, capillary and venular vessels. The vascular bed is represented as a series of compartments on the basis of blood vessel diameter. The formulation takes into account such parameters as hematocrit, vascular diameter, blood viscosity, blood flow, metabolic rate, the nonlinear oxygen dissociation curve, arterial PO2, P50 (oxygen tension at 50% hemoglobin saturation with O2) and carbon monoxide concentration. The countercurrent diffusional exchange between paired arterioles and venules is incorporated into the model. The model predicts significant longitudinal PO2 gradients in the precapillary vessels. However, gradients of hemoglobin saturation with oxygen remain fairly small. The longitudinal PO2 gradients in the postcapillary vessels are found to be very small. The effect of the following variables on tissue PO2 is studied: blood flow, PO2 in the arterial blood, hematocrit, P50, concentration of carbon monoxide, metabolic rate, arterial diameter, and the number of perfused capillaries. The qualitative features of PO2 distribution in the vascular network are not altered with moderate variation of these parameters. Finally, the various types of hypoxia, namely hypoxic, anemic and carbon monoxide hypoxia, are discussed in light of the above sensitivity analysis.

Fetal cerebral responses to ventilation and oxygenation in utero

Previous studies have shown that cerebral oxygen consumption (CMRO2) increases by nearly 50% at birth. The perinatal factors responsible for this increase are unknown; however, one possibility is that fetal CMRO2 is constrained by the normal intrauterine arterial PO2 (PaO2) of approximately 20 mmHg. We investigated this possibility in seven near-term chronically instrumented fetal sheep (131-138 days gestation) in which we inserted vascular catheters and an endotracheal tube. After 1-3 days recovery, we measured cerebral blood flow (CBF) with radiolabeled microspheres and calculated CMRO2. Measurements were made in utero under three conditions for each fetus: 1) nonventilated control; 2) ventilation with 3% O2-5% CO2-92% N2; and 3) ventilation with an inspired oxygen concentration sufficient to raise fetal PaO2 to normal newborn levels (mean 73 mmHg). A calf lung surfactant extract (CLSE) was instilled into the endotracheal tube of the fetus before ventilation to ensure adequate levels of alveolar surfactant and to maintain stable pH and arterial PCO2. The results showed that increasing fetal arterial PO2 to postnatal levels did not consistently increase CMRO2. CBF decreased as arterial O2 content (CaO2) rose, with an inverse hyperbolic response similar to that previously found to relate CBF to CaO2 during fetal hypoxic hypoxia. This indicates that the normally low intrauterine PaO2 does not intrinsically limit CMRO2 and implies that the rapid increase in CMRO2 at birth reflects the activation of specific cellular and physiological processes at (or near) this unique developmental event.

Determination of clebopride in plasma by capillary gas chromatography-negative-ion chemical ionization mass spectrometry

A procedure for the analysis of clebopride in plasma using capillary gas chromatography-negative-ion chemical ionization mass spectrometry has been developed. Employing an ethoxy analogue as internal standard, the two compounds were extracted from basified plasma using dichloromethane. Subsequent reaction with heptafluorobutyryl imidazole produced volatile monoheptafluorobutyryl derivatives whose ammonia negative-ion mass spectra proved ideal for selected-ion monitoring. The recovery of clebopride from plasma at 0.536 nmol/l was found to be 85.5 +/- 0.9% (n = 3) whilst measurement down to 0.268 nmol/l was possible with a coefficient of variation of 7.9%. Plasma levels of the compound are reported in two volunteers following ingestion of 1 mg of clebopride as the malate salt.

Bony overgrowths and abnormal calcifications about the spine

The common phenomenon of osteophyte formation about the vertebral margins and on the vertebral bodies in certain instances connotes underlying disk degeneration. The classification and mechanism of formation of these bony excrescences are not totally clear in all instances, but there is frequent association with degenerative disk change. Distorted alignment of the spinal column as in scoliosis, and functional demands on the spine, play major roles in these abnormalities. The true degree of anatomic abnormality is greater than can be appreciated on the radiographs. Syndesmophytes are vertically orientated outgrowths of trabecular bone forming in the outer margins of the annulus fibrosus and related to repeated episodes of inflammation and repair. They are classically seen in ankylosing spondylitis and colonic spondyloarthropathy. Bulky paravertebral excrescences are more likely to be found in psoriatic arthritis and Reiter's syndrome. Other bony excrescences in the spine were also discussed. OPLL is a progressive disease that can result in severe radicular and myelopathic symptoms. Although OPLL appears to have an unexplained predilection for Asians, it affects all races. Classically diagnosed on lateral radiographs of the cervical spine, it is best imaged with CT. Proper evaluation of the extent of the entire ossified mass and its effect on the spinal cord is crucial in the planning of adequate therapy.

A highly conserved repetitive DNA sequence, (TTAGGG)n, present at the telomeres of human chromosomes

A highly conserved repetitive DNA sequence, (TTAGGG)n, has been isolated from a human recombinant repetitive DNA library. Quantitative hybridization to chromosomes sorted by flow cytometry indicates that comparable amounts of this sequence are present on each human chromosome. Both fluorescent in situ hybridization and BAL-31 nuclease digestion experiments reveal major clusters of this sequence at the telomeres of all human chromosomes. The evolutionary conservation of this DNA sequence, its terminal chromosomal location in a variety of higher eukaryotes (regardless of chromosome number or chromosome length), and its similarity to functional telomeres isolated from lower eukaryotes suggest that this sequence is a functional human telomere.

Base-line O2 extraction influences cerebral blood flow response to hematocrit

We have shown that the fall in cerebral blood flow (CBF) as hematocrit (Hct) rises is due to the independent effects of increasing red blood cell (RBC) concentration and arterial O2 content (CaO2). In the present study, we tested the hypothesis that the magnitude of the effect of RBC concentration depends on the base-line cerebral fractional oxygen extraction (E). E is the ratio of O2 demand (cerebral O2 consumption, CMRO2) to supply (cerebral O2 transport: OT = CBF x CaO2) and is assumed to be inversely related to tissue O2 availability. Pentobarbital-anesthetized 1- to 7-day-old sheep were first exchange transfused with plasma to lower Hct to 20%. Base-line E was set to either high or low levels by induction of hypocarbia [arterial CO2 partial pressure (PaCO2) = 15.3 +/- 0.7 mmHg, means +/- SE; n = 7] or hypercarbia (PaCO2 = 62.7 +/- 1.1 mmHg; n = 5), respectively. A second isovolemic exchange transfusion with pure methemoglobin-containing adult sheep red cells then raised Hct (to 38.5 +/- 0.5%) with no significant increase in CaO2. PaCO2 was maintained and other variables (oxyhemoglobin affinity, pH, mean arterial blood pressure) with potential effect on CBF did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and molecular characterization of a highly polymorphic centromeric tandem repeat in the family Falconidae

An abundant tandem repeat has been cloned from genomic DNA of the merlin (Falco columbarius). The cloned sequence is 174 bp in length, and maps by in situ hybridization to the centromeric regions of several of the large chromosomes within the merlin karyotype. Complementary sequences have been identified within a variety of falcon species; these sequences are either absent or in very low copy number in the family Accipitridae. The cloned merlin repeat reveals highly polymorphic restriction patterns in the peregrine falcon (Falco peregrinus). These polymorphisms, which have been shown to be stably inherited within a family of captive peregrines, can be used to differentiate the Greenland and Argentina populations of this endangered raptor species.

Cerebral blood flow autoregulation during intracranial hypertension in hypoxic lambs

We tested the hypothesis that hypoxic hypoxia interferes with cerebral blood flow (CBF) autoregulation when intracranial pressure (ICP) is elevated in pentobarbital-anesthetized lambs (3 to 9 days old). Cerebral perfusion pressure (CPP) was lowered stepwise from 73 to 23 mmHg in eight normoxic lambs and from 65 to 31 mmHg in eight other hypoxic lambs by ventricular infusion of artificial cerebrospinal fluid. In normoxic lambs, CBF measured by microspheres was not significantly changed over this range of CPP. In animals made hypoxic [arterial O2 tension (PaO2) of 28 Torr; 47% arterial O2 saturation], base-line CBF was twice that of normoxic lambs. CBF was unchanged as CPP was reduced to 31 mmHg. Lower levels of CPP were not attained because a pressor response occurred with further elevations of ICP. No regional decrements in blood flow to cortical arterial watershed areas or to more caudal regions, such as cerebellum, brain stem, or thalamus, were detected with elevated ICP. Cerebral O2 uptake was similar in both groups and did not decrease when CPP was reduced. These results demonstrate that normoxic lambs have a considerable capacity for effective autoregulation of CBF when ICP is elevated. Moreover, cerebral vasodilation in response to a level of hypoxia approximating that normally seen prenatally does not abolish CBF autoregulation when ICP is elevated during the first postnatal week.