Involvement of the p53 tumor suppressor in repair of u.v.-type DNA damage

The tumor suppressor p53 plays a central role in the cellular responses to genotoxic stress. Besides its well known role in activation of the G1 checkpoint after exposure to agents like ionizing radiation and its role in apoptosis, the possibility exists that p53 may have additional roles, such as in DNA repair. For example, p53, is known to bind to single strand DNA such as would occur during repair events, and the proteins encoded by two p53-regulated genes have previously been found to bind to at least one protein involved in DNA damage processing including nucleotide excision repair (NER). NER is an important and versatile DNA repair mechanism, which is the major pathway for repair of u.v.-type lesions and damage by a variety of important carcinogens and mutagens. If components of the p53 pathway are involved in NER, then disruption of p53 function by mutations or expression of certain viral proteins could have important implications in carcinogenesis and cancer treatment. In the present study we show that disruption of normal p53 function in human colon carcinoma RKO cells with either the human papillomavirus E6 oncoprotein or a dominant-negative mutant p53 transgene results in reduced repair of u.v.-induced DNA damage. The E6 and mutant p53-containing cell lines demonstrated reduced repair of u.v.-induced DNA lesions in host cell reactivation experiments with reporter plasmids, and reduced repair in in vitro DNA repair assays. With this in vitro assay, extracts from the E6- and mutant p53-containing lines also showed loss of induced repair following cellular u.v.-irradiation. The reduced DNA repair activity of the transfected cell lines also correlated with reduced clonogenic survival following u.v.-irradiation. These results indicate that p53 and/or p53-regulated gene products function in the NER pathway and that this process is inducible by DNA damage.

Modulation of human sympathetic periodicity by mild, brief hypoxia and hypercapnia

We determined the influence of brief mild normocapnic hyperoxia, hypoxia, and hyperoxic hypercapnia on human muscle sympathetic nerve activity and R-R intervals, as quantified by both time- and frequency-domain analyses. We obtained measurements in nine healthy young adult men and women during uncontrolled and frequency (but not tidal volume) controlled breathing. Responses were evaluated with forward selection and backward elimination statistical models, with muscle sympathetic nerve activity as the dependent variable, and power spectral techniques. Hyperoxia and hypoxia did not alter arterial pressure; hypercapnia increased diastolic pressure modestly. Average R-R intervals tended to increase during hyperoxia, and decrease during hypoxia and hypercapnia. During uncontrolled breathing, changes of inspiratory gases exerted only minor effects on muscle sympathetic nerve activity; during controlled breathing, both hypoxia and hypercapnia tended to increase muscle sympathetic nerve activity. Statistical modeling suggested that chemoreceptor stimulation increased muscle sympathetic neural outflows, but that increases of sympathetic traffic were opposed by secondary increases of ventilation. Inspiratory gases modulated the frequency distribution of muscle sympathetic nerve activity strikingly: hypoxia increased sympathetic power at respiratory frequencies and hypercapnia increased sympathetic power at both respiratory and (primarily in one subject) cardiac frequencies. Our data suggest that mild brief hypoxia and hypercapnia increase human muscle sympathetic nerve activity, but that this tendency is opposed by chemoreflex-induced increases of ventilation. Our results suggest also that chemoreceptor activity exerts important influences on the frequency content, as well as the quantity of sympathetic neural outflow.

The effects of frontal- or temporal-lobe lesions on susceptibility to interference in spatial memory

Patients with unilateral frontal- or temporal-lobe lesions and normal control subjects studied multiple arrays of pictures and were tested for recall of the locations of the pictures. One condition consisted of three trials of the same pictures in different spatial arrangements, recall being tested immediately after each presentation. In a second condition (using different stimuli), the subject was given two trials with one set of pictures, but a new set of pictures was viewed on the third trial. All groups showed a build-up of proactive interference across trials using the same pictures, and a release of proactive interference when they studied new pictures. Patients with frontal-lobe lesions were more susceptible to proactive interference than were the other groups.

Hyperthermia nullifies the ameliorating effect of dizocilpine maleate (MK-801) in focal cerebral ischemia

The present study was inspired by two previous findings from the laboratory. The first was that dizocilpine maleate (MK-801) fails to reduce infarct size when the middle cerebral artery (MCA) is permanently occluded by an intraluminal filament technique in rats. In seeking the reasons for this we measured temperature and found that the body temperature of occluded animals increases to 39.0-39.5 degrees C during the first 2-3 h. In order to explore whether the rise in temperature was responsible for the lack of effect of MK-801, two groups of animals were studied, both containing animals which were subjected to 2 h of transient MCA occlusion and given MK-801 15 min before, as well as 6 and 24 h after ischemia. In one group, temperature was allowed to rise spontaneously during ischemia (39.0-39.5 degrees C). In the other, body temperature was maintained close to normal during ischemia, and for the first 6 h postischemically, by cooling of the ambient air. Infarct volume was assessed by triphenyltetrazolium chloride staining after 48 h of recovery. The results showed that MK-801 failed to reduce infarct size in animals whose body temperature rose during ischemia. In contrast, the drug markedly reduced infarct volume in temperature-controlled animals; in fact, 5/8 animals had no infarcts but selective neuronal damage only. The results suggest that amelioration of focal ischemic damage cannot be expected if body and brain temperature is allowed to rise above normal.

Genomic instability and the role of p53 mutations in cancer cells

The p53 tumor-suppressor gene encodes a cell-cycle checkpoint protein that functions in the G1 phase of the cell cycle. When DNA damage is incurred, p53 transactivates a number of downstream genes whose products, with diverse biologic activities, each make a contribution to the cellular response to DNA damage. One major p53-mediated stress response is the G1 cell-cycle arrest, or delay, which probably allows the cell time to repair DNA damage prior to S-phase entry. In cells lacking p53 function, which include most cancer cells, a condition of genomic instability results from checkpoint loss that culminates in gene amplifications, aneuploidy, and other chromosomal aberrations. These abnormalities contribute to the clonal evolution of cancer cells and tumor progression. The role of p53 in radioresistance and chemoresistance is discussed.

Forensic drug testing for opiates. VI. Urine testing for hydromorphone, hydrocodone, oxymorphone, and oxycodone with commercial opiate immunoassays and gas chromatography-mass spectrometry

Opiate testing for morphine and codeine is performed routinely in forensic urine drug-testing laboratories in an effort to identify illicit opiate abusers. In addition to heroin, the 6-keto-opioids, including hydromorphone, hydrocodone, oxymorphone, and oxycodone, have high abuse liability and are self-administered by opiate abusers, but only limited information is available on detection of these compounds by current immunoassay and gas chromatographic-mass spectrometric (GC-MS) methods. In this study, single doses of hydromorphone, hydrocodone, oxymorphone, and oxycodone were administered to human subjects, and urine samples were collected before and periodically after dosing. Opiate levels were determined in a quantitative mode with four commercial immunoassays, TDx opiates (TDx), Abuscreen radioimmunoassay (ABUS), Coat-A-Count morphine in urine (CAC), and EMIT d.a.u. opiate assay (EMIT), and by GC-MS. GC-MS assay results indicated that hydromorphone, hydrocodone, oxymorphone, and oxycodone administration resulted in rapid excretion of parent drug and O-demethylated metabolites in urine. Peak concentrations occurred within 8 h after drug administration and declined below 300 ng/mL within 24-48 h. Immunoassay testing indicated that hydromorphone, hydrocodone, and oxycodone, but not oxymorphone, were detectable in urine by TDx and EMIT (300-ng/mL cutoff) for 6-24 h. ABUS detected only hydrocodone, and CAC failed to detect any of the four 6-keto-opioid analgesics. Generally, immunoassays for opiates in urine displayed substantially lower sensitivities for 6-keto-opioids compared with GC-MS. Consequently, urine samples containing low to moderate concentrations of hydromorphone, hydrocodone, oxymorphone, and oxycodone will likely go undetected when tested by conventional immunoassays.

Characterization of human Gadd45, a p53-regulated protein

GADD45 (growth arrest and DNA damage) is a DNA-damage-inducible gene regulated in part by the tumor suppressor p53. A role in negative growth control has recently been suggested based on significant (more than 75%) reduction of colony formation following over expression of Gadd45. To better understand the role of Gadd45, we have developed specific rabbit and murine antibodies raised against the human recombinant protein. Using these antibodies, we have found that in ML-1 cells Gadd45 is predominantly a nuclear protein. MyD118, a protein induced by terminal differentiation sharing 57% homology with Gadd45, does not cross-react with any of the antibodies produced. As expected, the induction of Gadd45 protein by ionizing radiation (IR) was also found to be dependent on a wild type p53 phenotype. Interestingly, WI-L2-NS, a human lymphoid cell line, showed very high basal levels of Gadd45 mRNA and protein in addition to a high constitutive level of a mutated p53 protein. In this cell line, the high levels of GADD45 did not inhibit cellular growth in spite of the fact that no mutations were found in GADD45 sequence. These results indicate that some cell line(s) can tolerate high levels of Gadd45 and abrogate its growth suppression function.

Calbindin-D28k immunoreactivity within the cholinergic and GABAergic projection neurons of the basal forebrain

The purpose of this study was to determine whether the calcium binding protein calbindin-D28k was present within the cortically projecting basal forebrain neurons of various rodent species not previously examined. Double-label immunocytochemistry was performed using antibodies against calbindin-D28k and choline acetyltransferase (ChAT) to detect the presence of the calcium binding protein within the cholinergic basal forebrain neurons of various species (i.e., humans, rats, mice, gerbils, guinea pigs). Antibodies against calbindin-D28k, ChAT, and glutamic acid decarboxylase (GAD) were also used in combination with a cortically injected retrograde tracer (Fluoro-Gold) to determine whether calbindin-D28k immunoreactive (IR) neurons within the basal forebrain projected to the frontoparietal cortex. The nucleus basalis of rats was examined for the presence of calbindin-D27k IR within the GABAergic basal forebrain neurons. All species examined had cholinergic, GABAergic, and calbindinergic neurons within the basal forebrain; however, only the cholinergic neurons within the human nucleus basalis of Meynert were also immunoreactive for calbindin-D28k. Although all rodent species had both cholinergic and GABAergic basal forebrain neurons that contained the Fluoro-Gold dye, none of the calbindin-D28k IR neurons, detected using monoclonal and polyclonal antibodies, were found to contain the retrograde tracer. These results indicate that the cortically projecting cholinergic and GABAergic basal forebrain neurons within these rodent species do not contain calbindin-D28k. Therefore, age- and disease-related loss of nucleus basalis projection neurons may not be mediated by alterations in calbindin-D28k.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of retinoblastoma gene product in p53-mediated DNA damage response

The cellular response to DNA-damaging agents involves the activation of cell cycle checkpoints. Checkpoints provide a transient delay in cell cycle progression, presumably to allow time for the cell to repair the damage. A most important checkpoint, active in the G1 phase of the cell cycle, is mediated by the p53 tumor suppressor gene product. To investigate the role of downstream components of the cell cycle machinery in p53-mediated G1 arrest, the possible involvement of the RB gene product was examined. Rb and p53 proteins were studied by immunoprecipitation and Western blotting experiments in the presence and absence of DNA-damaging treatment. The phosphorylation status of Rb was altered following DNA damage in p53 wild-type cell lines, but was not altered in p53 mutant cell lines, nor in cell lines where p53 function was abrogated by viral gene products. These findings indicate that Rb probably plays a role in the activation of the p53-mediated checkpoint.

Interaction of the p53-regulated protein Gadd45 with proliferating cell nuclear antigen

GADD45 is a ubiquitously expressed mammalian gene that is induced by DNA damage and certain other stresses. Like another p53-regulated gene, p21WAF1/CIP1, whose product binds to cyclin-dependent kinases (Cdk's) and proliferating cell nuclear antigen (PCNA), GADD45 has been associated with growth suppression. Gadd45 was found to bind to PCNA, a normal component of Cdk complexes and a protein involved in DNA replication and repair. Gadd45 stimulated DNA excision repair in vitro and inhibited entry of cells into S phase. These results establish GADD45 as a link between the p53-dependent cell cycle checkpoint and DNA repair.

Language and behavior in children with Sotos syndrome

OBJECTIVE

To examine language and behavior in children with Sotos syndrome, an overgrowth syndrome involving advanced bone age, characteristic facies, and developmental disability.

METHOD

Twenty-seven children with Sotos syndrome were compared with 20 children with overgrowth, intellectual disability, and facies not characteristic of Sotos syndrome. Ages ranged from 5 to 16 years. Direct assessment was undertaken with standardized measures of intelligence and language abilities. Behavior was examined by parent and teacher report.

RESULTS

Children with Sotos syndrome had levels of intelligence in the severely disabled to average range, with the majority falling in the borderline range. Mean level of intelligence was significantly higher than that observed for children in the comparison group. Language abilities were developed to a level consistent with overall level of intelligence. Rates of parent- and teacher-reported behavior problems were significantly higher than normal, but, with the exception of temper tantrums, did not differ from those observed in children in the comparison group. Attention-deficit hyperactivity disorder was observed in 38% of children with Sotos syndrome. They were more irritable and had more stereotypic behavior and inappropriate speech than is expected in children with intellectual disabilities, and they were more withdrawn and had more stereotypic behavior than children in the comparison group.

CONCLUSIONS

Assessment of language abilities revealed no specific language impairment. High rates of behavior problems were observed, but these were not higher than those observed for other large, delayed, dysmorphic children.

Preischemic hyperglycemia leads to delayed postischemic hyperthermia

BACKGROUND AND PURPOSE

Temperature alterations are known to influence the outcome of transient ischemia, even when instituted in the postischemic period. Since preischemic hyperglycemia aggravates ischemic brain damage, the question of whether hyperglycemic animals become hyperthermic arose. To explore this possibility, we measured body temperature telemetrically in normoglycemic and hyperglycemic rats subjected to 10 minutes of forebrain ischemia at a body (and brain) temperature of 37 degrees C.

METHODS

Isoflurane-anesthetized animals were subjected to 10 minutes of forebrain ischemia under normoglycemic or hyperglycemic conditions. Temperature changes after ischemia were measured by means of a telemetric temperature coil.

RESULTS

In normoglycemic animals, temperature decreased to 35.6 +/- 1.1 degrees C (mean +/- SD) during the first 4 hours of recovery, after which it gradually increased to normal values (38 degrees C). Hyperglycemic animals behaved differently in that they remained normothermic for approximately 10 hours during recovery and later became hyperthermic, with core temperatures rising above 39 degrees C. The rise in temperature was not due to the osmotic load of the glucose administered because infusion of mannitol, which gave a comparable increase in plasma osmolality, failed to cause delayed postischemic hyperthermia. Excessive hypercapnia during ischemia in normoglycemic animals, which produces cerebral acidosis of a magnitude similar to that of hyperglycemia and is known to aggravate ischemic lesions, likewise failed to induce hyperthermia. When post-ischemic seizures ensued in hyperglycemic subjects, temperature was 39.8 +/- 0.6 degrees C. Animals with seizures invariably died. To evaluate the influence of postischemic hyperthermia on the outcome, an additional series of experiments was performed in which delayed hyperthermia was avoided by gentle cooling (n = 6) or by acetaminophen administration (n = 5). Although these procedures prevented delayed hyperthermia, they neither blocked seizure induction nor affected the fatal outcome. Postischemic seizures developed when the core temperatures of animals were 37.9 +/- 0.1 degrees C and 37.8 +/- 0.2 degrees C in the cooled and acetaminophen-treated groups, respectively.

CONCLUSIONS

The results suggest that both delayed hyperthermia and delayed seizures in hyperglycemic animals are caused by the aggravated damage incurred by these animals during or immediately after the ischemic insult.

The influence of plasma glucose concentrations on ischemic brain damage is a threshold function

To investigate whether aggravation of damage in hyperglycemic subjects is a continuous function of changes in intra- and extracellular pH during ischemia or whether there is a threshold value, preischemic plasma glucose was varied from 8.3-20.0 mM. 10 min forebrain ischemia was induced. The results showed that no animal with plasma glucose of < 13 mM developed seizures, and that all animals with glucose of > 16 mM died in status epilepticus. Half of the animals with plasma glucose in the range of 13-16 mM showed seizures and 50% of these died. In surviving animals, histological brain damage occurred in the hippocampal CA3 sector, cingulate cortex, thalamic nuclei and substantia nigra, structures normally not injured by 10 min ischemia. The data demonstrate that there is a glucose threshold of 10-13 mM, above which seizures develop and additional damage appears, and another one (> 16 mM), above which seizures are invariably fatal.

Structure and function of a mating-type gene from the homothallic species Neurospora africana

The homothallic Neurospora species, N. africana, contains sequences that hybridize to the A but not to a mating-type sequences of the heterothallic species N. crassa. In this study, the N. africana mating-type gene, mt A-1, was cloned, sequenced and its function analyzed in N. crassa. Although N. africana does not mate in a heterothallic manner, its mt A-1 gene functions as a mating activator in N. crassa. In addition, the N. africana mt A-1 gene confers mating type-associated vegetative incompatibility in N. crassa. DNA sequence analysis shows that the N. africana mt A-1 open reading frame (ORF) is 93% identical to that of N. crassa mt A-1. The mt A-1 ORF of N. africana contains no stop codons and was detected as a cDNA which is processed in a similar manner to mt A-1 of N. crassa. By DNA blot and orthogonal field agarose gel electrophoretic analysis, it is shown that the composition and location of the mating-type locus and the organization of the mating-type chromosome of N. africana are similar to that of N. crassa.

Hyperthermia complicates middle cerebral artery occlusion induced by an intraluminal filament

The present experiments were designed to study under what circumstances middle cerebral artery (MCA) occlusion by an intraluminal filament technique leads to hyperthermia and what the mechanisms are. We found that permanent MCA occlusion by this technique lead to a rise in body (core) temperature to 39.0-39.5 degrees C during the first 2-4 h, and to sustained hyperthermia thereafter (38.5-39.0 degrees C). After 2 h of transient MCA occlusion hyperthermia could only be avoided if anesthesia (with control of temperature) was maintained for 2 h of ischemia and 1 h of recirculation or, in unanesthetized animals, if external cooling was maintained for 2 h of ischemia and 2 h of recirculation. Control of temperature only during ischemia did not prevent a postischemic rise in temperature. One hour of MCA occlusion had less effect on body temperature. Results are presented which suggest that the hyperthermia observed is due to an interference, by the intraluminal filament, of circulation to hypothalamic centers regulating body temperature. It is speculated that the hyperthermia induced may blunt or obliterate the effect of drugs, normally considered to ameliorate brain damage due to focal ischemia.

Mitochondrial DNAs of the fungus Armillaria ostoyae: restriction map and length variation

A restriction-enzyme-site map is presented for the 147-kb mtDNA of North American Armillaria ostoyae. The locations of five structural genes, atp6, atp8, coxI, coxIII, and cob, along with the location and orientation of the large and small ribosomal RNA genes, were determined through Southern hybridizations with cloned genes from other fungal mtDNAs. Based on this map, the variation in mtDNA suggested geographic structure at two different levels. On a large geographic scale, 17 mtDNA types from North America were distinct, with respect to both size and restriction maps, from three mtDNA types from Europe. At the local scale, identical mtDNA types were evident among several different genetic individuals located no more than 1 km apart at a site in Michigan. No mtDNA type occurred more than once among genetic individuals from different regions of North America, although the occurrence of similar mtDNAs in isolates from distant regions suggested that this may occur at a low frequency with large sample sizes. Among the North American mtDNA types, analysis of discrete length variants was inconsistent with the hypothesis that the mtDNA of A. ostoyae evolves as a clonal lineage in which each length mutation represents a unique event. The two remaining hypotheses, that similar mutational events have occurred independently and that genetic exchange and recombination occurs among mtDNAs in natural populations of this species, remain to be tested.

Fitting of low-intensity wide-line spectra dominated by chemical shift anisotropy

How experimental parameters affect the appearance, and consequently the fitting, of signals having very wide lines is discussed. As these spectra usually have very low intensities, pulse sequences that remove acoustic ringing and other experimental artefacts have to be used. These pulse sequences introduce further spectral distortions. A FORTRAN 77 program was developed that accounts for these effects. The fitting of these broad spectra is demonstrated by application to 207Pb solid-state nuclear magnetic resonance (NMR) spectra.

Mechanisms of vasovagal syncope: relevance to postflight orthostatic intolerance

Orthostatic intolerance can present a very serious limitation to astronauts attempting any functions requiring the upright position. Vasovagal syncope is a common cause of fainting characterized by paradoxic bradycardia and vasodilation in the presence of decreasing arterial pressure. Several mechanisms have been proposed to mediate vasovagal syncope and it seems likely that redundant mechanisms exist both centrally and peripherally which can mediate these responses. Spaceflight alters reflex control of cardiovascular function in several ways which may influence susceptibility to vasovagal syncope provoked by the Bezold-Jarisch reflex.

Hyperthermia aggravates and hypothermia ameliorates epileptic brain damage

The influence of hyperthermia and hypothermia on epileptic brain damage was studied in rats, in which status epilepticus was induced by flurothyl. Histopathological changes were examined by light microscopy after 1 or 7 days of recovery. Two series of animals were studied. In the first, short periods of seizures (20 and 25 min) were employed to examine whether moderate hyperthermia (39.5 degrees C) would aggravate epileptic brain damage, and a longer period (45 min) was used to investigate whether moderate hypothermia (32.5 degrees C) would ameliorate the damage. The second series investigated whether brief periods of status epilepticus (10 min) would cause brain damage if hyperthermia were high or excessive. For this series, animals with body temperatures of 37.0, 39.0, and 41.0 degrees C were studied. Data from normothermic animals (37.5 degrees C) confirmed previously described neuronal damage. Although hyperthermic animals failed to show increased damage in the CA1 sector, or in the hilar region of the dentate gyrus, they showed enhanced damage in the neocortex and globus pallidus (GP). In substantia nigra pars reticulata (SNPR) four out of five hyperthermic animals had bilateral infarcts after 20 min of status epilepticus, whereas no normothermic animal showed such damage. Hypothermia seemed to ameliorate epileptic brain damage in the neocortex (n.s.) and GP (P < 0.05) following status epilepticus for 45 min. Three out of seven hypothermic animals had mild SNPR involvement compared to severe infarction of the nucleus in five out of six normothermic animals (P < 0.05). Thus, hyperthermia aggravated and hypothermia ameliorated epileptic brain damage both in regions showing selective neuronal necrosis (neocortex) and in regions developing pan-necrosis (GP and SNPR). The second series displayed an unexpected result of excessive hyperthermia. Animals subjected to only 10 min of status epilepticus at a temperature of 41 degrees C showed not only neocortical lesions, but also moderate to extensive damage to the hippocampus (CA1, subiculum, and dentate gyrus). It is concluded that at high body and brain temperature, brief periods of status epilepticus can yield extensive brain damage, primarily affecting the hippocampus.

Brain insults in rats induce increased expression of the BDNF gene through differential use of multiple promoters

The rat brain-derived neurotrophic factor (BDNF) gene consists of four short 5'-exons linked to separate promoters and one 3'-exon encoding the mature BDNF protein. Using in situ hybridization we demonstrate here that kindling-induced seizures, cerebral ischaemia and insulin-induced hypoglycaemic coma increase BDNF mRNA levels through insult- and region-specific usage of three promoters within the BDNF gene. Both brief (2 min) and longer (10 min) periods of forebrain ischaemia induced significant and major increases only of exon III mRNA in the dentate gyrus. Following hypoglycaemic coma (1 and 30 min), exon III mRNA was markedly elevated in the dentate gyrus and, in addition, exon I mRNA showed a moderate increase. Single and recurrent (n = 40) hippocampal seizures significantly increased expression of exon I, II and III mRNAs in the dentate gyrus granule cells. After recurrent seizures, including generalized convulsions, there were also major increases of both exon I and III mRNAs in the CA3 region, amygdala, piriform cortex and neocortex, whereas in the hippocampal CA1 sector marked elevations were detected only for exon III mRNA. The insults had no effect on the level of exon IV mRNA in the brain. The region- and insult-specific pattern of promoter activation might be of importance for the effectiveness of protective responses as well as for the regulation of plastic changes following brain insults.

Rapid adaptation of vagal baroreflexes in humans

We evaluated the time course of carotid baroreflex adaptation to arterial pressure elevations induced by phenylephrine infusion (1 microgram/kg per min) in 13 normotensive volunteers. Vagally-mediated carotid baroreceptor-cardiac reflex responses were assessed serially with a staircase pressure/suction sequence delivered to a neck chamber. Carotid baroreflex stimulus-response relations shifted up the response (R-R interval) axis and to the right on the stimulus (pressure) axis (determined as the carotid distending pressure at saturation) within 90-120 s (time between measurements) during the first 10 min. The shifts in position of the reflex relation were sustained throughout the infusion. The position of operational point pressure, relative to carotid distending pressure at saturation, was unchanged throughout the infusion period. These data suggest that human carotid baroreceptor reflex relations change within minutes to retain beat-to-beat pressure regulation as the prevailing pressure increases.

Acidosis induced by hypercapnia exaggerates ischemic brain damage

Although preischemic hyperglycemia is known to aggravate damage due to transient ischemia, it is a matter of controversy whether or not this is a result of the exaggerated acidosis. It has recently been reported that although tissue acidosis of a comparable severity could be induced in normoglycemic dogs by an excessive rise in arterial CO2 tension, short-term functional recovery was improved, rather than compromised. In the present experiments we induced excessive hypercapnia (PaCO2, approximately 300 mm Hg) in normoglycemic rats before inducing forebrain ischemia of 10-min duration. This reduced the brain extracellular pH to values normally encountered in hyperglycemic rats subjected to ischemia. The events induced by hypercapnia clearly enhanced ischemic brain damage, as assessed histologically after 7 days of recovery. We hypothesize that the decisive event was an exaggerated decrease in extra- and intracellular pH and that the results thus demonstrate an adverse effect of acidosis. However, since postischemic seizures did not occur in the hypercapnic ischemic rats, the results also demonstrate that changes in intra-extracellular pH and bicarbonate concentrations modulated ischemic damage in an unexpected way.