Biomedical subjects

D W Walker

Publications and source records attributed to D W Walker.

At least 91 records · Page 5Linked to original sources

PubMed1994

Effect of two weeks of continuous light on the development of the circadian melatonin rhythm in newborn lambs.

We have investigated the effect of exposure of newborn lambs to continuous light during the first 2 weeks after birth on the subsequent development of the phase and amplitude of the plasma melatonin rhythm during the next 8 weeks. During the first 2 weeks after birth, the mean plasma melatonin concentrations were significantly lower (P < 0.001) in lambs exposed to continuous light (58 +/- 15 pmol/l, n = 7) than in lambs exposed to LD 12:12 (i.e., "normal" lighting: 189 +/- 38 pmol/l, n = 9). Between 3 and 4 weeks of age, plasma melatonin concentrations during the daily light and dark periods were also significantly lower in the lambs exposed to continuous light during the first 2 weeks after birth. There was no effect of time of day on plasma melatonin in either group of lambs during the first 2 weeks after birth but between 3 and 10 weeks of age there was a significant (P < 0.001) effect of light and dark and time of day on plasma melatonin concentrations which was the same in both groups of lambs. Plasma melatonin concentrations were higher in the dark period than in the light period and between 2100 and 0700 than between 0900 and 1700 at all ages after week 2. We have therefore demonstrated that exposure of the lamb to 2 weeks of continuous light after birth results in a suppression of melatonin secretion that extends beyond the end of the exposure to continuous light.

Animals↗

PubMed1994

Monoamine concentrations in cerebrospinal fluid of fetal and newborn sheep.

Monoamine concentrations were measured in cisternal cerebrospinal fluid (CSF) of unanesthetized fetal (115-135 days gestation) and newborn (2-34 days old) sheep. Norepinephrine (NE) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations decreased with gestational age; NE CSF concentrations were significantly higher in the newborn (336.4 +/- 61.7 pg/ml; n = 5) compared with the 131- to 135-day-gestation fetuses (104.0 +/- 46.3 pg/ml, n = 3; P < 0.05). Dopamine (DO), homovanillic acid (HVA), and serotonin (5-HT) concentrations in fetal CSF did not change with gestational age, and epinephrine (Epi) was undetectable in most fetal and newborn samples. Hypoxia, induced by giving the ewe 9% O2 in N2 to breathe for 30 min, resulted in a 10.78 +/- 3.94-fold (n = 5) increase of NE concentration in fetal CSF (P < 0.05); DO and DOPAC concentrations did not change. Hypoxia did not increase NE concentrations in CSF of newborn lambs. Inhibition of prostaglandin (PG) synthesis by intravenous infusion of indomethacin significantly reduced plasma prostaglandin E2 concentrations from 7.8 +/- 1.0 (n = 6) to 2.5 +/- 0.2 nmol/l (n = 3; P < 0.05), and was associated with an increase of CSF DOPAC concentrations from 2,156.3 +/- 504.5 (n = 9) to 5,453.6 +/- 1,091.3 pg/ml (n = 5; P < 0.05); NE and DO concentrations did not change significantly. These results show that catecholamines and indoleamines are released in the brain and enter the CSF of fetal sheep from at least 115 days gestation. The data also show that concentrations of some monoamines in CSF are changed by fetal hypoxia or prostaglandin synthesis.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1993

Modulation of ethanol neurotoxicity by nerve growth factor.

Dorsal root ganglion (DRG) neurons were cultured with varying concentrations of ethanol and NGF. At low concentrations of NGF (0.1 ng/ml) moderate initial ethanol levels (250 mg/dl) significantly suppressed neurite outgrowth. Higher NGF concentrations (5 ng/ml) protected against this neurotoxicity. At this higher NGF concentration, neuronal survival was not significantly affected by exposure to 0.25-4 g/dl ethanol, although survival was significantly diminished at 5 and 6 g/dl. Neurite outgrowth was a more sensitive indicator of ethanol neurotoxicity in this population, with significant decreases in process extension seen with 1 g/dl ethanol. When cultures were supplemented with 10 ng/ml NGF, however, process elaboration was significantly greater at 1 g/dl ethanol than that measured with 5 ng/ml NGF, and in fact did not differ from NGF controls. These studies indicate that NGF can provide neuroprotective effects against ethanol toxicity under these conditions. The results are discussed in relation to other recent reports of trophic factor neuroprotection.

Animals↗

PubMed1993

Effect of chronic ethanol on the septohippocampal system: a role for neurotrophic factors?

The mechanisms by which chronic ethanol exposure produces neuronal damage have not been established. Potentially ethanol may reduce normal neurotrophic influences necessary for neuronal survival, growth, and function. We hypothesized that chronic ethanol exposure might produce a decrease in the synthesis, availability, upregulation, delivery, and/or the biological activity of normally occurring neurotrophic factors, or may alter the capacity of target neurons to respond to these factors. The available evidence leading to this hypothesis and supporting data from our laboratory are discussed.

Alcoholism↗

PubMed1993

Effects of intracisternal monoamines on breathing movements in fetal sheep.

The effects of intracisternal administration of tyramine on fetal breathing movements (FBM), electrocortical (ECoG) and nuchal muscle activities, and cerebrospinal fluid (CSF) monoamine concentrations have been studied in unanesthetized fetal sheep (124-140 days gestation) in utero. In 18 trials (8 fetuses) infusion of 50 or 100 micrograms/kg tyramine increased the incidence of FBM from 32.2 +/- 2.0 to 79.4 +/- 4.7%/h (P < 0.05) and increased mean breath amplitude from 6.4 +/- 0.4 to 11.8 +/- 1.6 mmHg (P < 0.05). FBM incidence during high-voltage ECoG activity increased from 3.3 +/- 0.6 to 22.5 +/- 3.6%/h (P < 0.05). Tyramine infusion (100 micrograms/kg) significantly increased (P < 0.05) the CSF concentrations of dopamine from 129.5 +/- 26.2 to 10,222.4 +/- 1,103.6 pg/ml, of norepinephrine from 74.7 +/- 11.0 to 2,238.6 +/- 143.5 pg/ml, and of serotonin from 1,824.5 +/- 340.7 to 3,888.7 +/- 1,335.2 pg/ml. Intracisternal injection of dopamine or norepinephrine (10-20 micrograms) caused the rapid onset of large-amplitude FBM, which often continued throughout high-voltage ECoG activity. In contrast, serotonin (20-40 micrograms) caused cessation of FBM and change of the ECoG from low- to high-voltage activity. These results indicate that neuronal release of catecholamines in the CNS has excitatory effects on FBM.

Animals↗

PubMed1993

Melatonin and the light-dark cycle separately influence daily behavioral and hormonal rhythms in the pregnant ewe and sheep fetus.

We have studied the effects of independently altering the time of darkness and the phase of the daily melatonin rhythm during a 12-h photoperiod on the diurnal rhythms of fetal breathing movements (FBMs), low voltage electrocortical activity, and maternal and fetal plasma concentrations of PRL. Thirteen pregnant ewes were pinealectomized at 99-100 days gestation and held under a normal lighting regime (12-h photoperiod, lights off at 1900 h) until 135 days gestation. All ewes were then exposed to an altered lighting regime (12-h photoperiod, lights off at 1100 h) until 145 days gestation. Six of these ewes were infused with melatonin (12-15 micrograms/h iv) from 1100 h for 12 h each day between 125 and 135 days gestation while in the normal lighting regime, and from 1900 h while in the altered lighting regime. The remaining seven ewes were infused with saline at corresponding times. Infusion of melatonin produced a significant daily rhythm in maternal and fetal melatonin concentrations; concentrations were highest throughout the 12-h infusion period in each lighting regime. In the normal lighting regime (i.e. lights off at 1900 h) the peak incidence of FBM occurred at between 1000 and 1300 h in the ewes infused with saline or melatonin. Under the altered lighting conditions there was no 24-h variation in the incidence of FBMs in the saline-infused group, but a significant daily variation was present in the melatonin-infused group with peak incidence occurring at 1900-2200 h. The daily variation in maternal PRL concentrations was not affected by changes in the time of onset of melatonin infusion but was different in each of the two lighting regimes. In the normal lighting regime, PRL concentrations were highest at 2100 h (56.2 +/- 21.6 ng/ml) whereas in the altered lighting conditions the peak in maternal PRL occurred at 1700 h (90.4 +/- 25.1 ng/ml). The daily variation in fetal PRL concentrations was also not affected by changes in the time of onset of melatonin infusion but was different in the two lighting regimes; in the normal lighting regime, fetal PRL reached a peak (13.0 +/- 3.7 ng/ml) at 0100-0300 h whereas in the altered lighting regime the peak (29.2 +/- 9.8 ng/ml) occurred at 1700-2100 h. We have presented evidence therefore that the daily melatonin rhythm may entrain the daily rhythm in fetal breathing activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Chronic ethanol consumption reduces the neurotrophic activity in rat hippocampus.

The effect of chronic ethanol treatment (CET) for 21-26 weeks on the neurotrophic activity contained in the rat hippocampus (HPC) was determined with a bioassay in cultures of dissociated dorsal root ganglion cells (DRG) obtained from E7-8 chick embryos. Extracts of the HPC from CET or pair-fed control rats were used as experimental media, and neuronal survival and neurite-outgrowth of DRG cultures were determined. Both neuronal survival (-25%) and neurite-outgrowth (-50%) were reduced in the presence of HPC extracts from CET rats relative to controls. These data suggest that CET reduces the neurotrophic content of the HPC which may result in damage to septohippocampal neurons.

Animals↗

PubMed1992

Developmental changes in hindlimb muscles and diaphragm of sheep.

In this study, plasma thyroxine, contractile and histochemical (adenosinetriphosphatase and NADH) characteristics of soleus (SOL), medial gastrocnemius (MG), and extensor digitorum longus (EDL) were examined in 140-day-gestation fetal sheep and in 2-, 5-, and 30-day-old lambs and adult ewes. Electrophoretic separation of myosin heavy chains was also done on all muscles and the diaphragm. There were no differences in the twitch contraction and relaxation times of MG and EDL at the different ages; in contrast SOL contraction times were significantly shorter in the fetus and newborn than in the adult. Fast glycolytic fibers first appeared in EDL, MG, and diaphragm at 5, 30, and 5 days after birth, respectively. The proportion of slow oxidative fibers decreased after birth and with postnatal development in EDL, whereas they increased in MG and diaphragm. Plasma thyroxine concentrations were higher in the fetus and day-old lambs than in 2-, 5-, and 30-day-old lambs or adult sheep. It is suggested that contractile specialization of the fast-twitch diaphragm, MG, and EDL is largely achieved in utero and is probably mediated by thyroid hormone. In contrast, SOL changed postnatally, probably influenced by the altered neural drive.

Aging↗

PubMed1991

Binding of [125I]-insulin-like growth factor-1 (IGF-1) in brains of Alzheimer's and alcoholic patients.

Patients with chronic alcoholism and/or Alzheimer's disease suffer from degenerative changes in the cerebral cortex and hippocampus. To investigate possible changes in IGF-1 receptor binding sites in brain tissue of patients with these pathological conditions, the binding of [125I]-IGF-1 was determined in tissues obtained from control, Alzheimer's and/or patients with a history of alcoholism. The four experimental groups examined consisted of patients from similar age groups. Specific binding of [125I]-IGF-1 to cerebral cortical membranes from Alzheimer's patients had significantly more binding sites than age-matched controls, alcoholic patients and alcoholic patients with Alzheimer's disease. Regression analyses indicated that there were no significant differences in [125I]-IGF-1 binding in cerebral cortex with regard to age of patients (1.1% of total variance with a range of 52 to 92 years). Likewise, the time interval between death and autopsy contributed only 1.4% to the total variance in IGF-1 binding. No statistical differences in [125I]-IGF-1 binding were noted in hippocampal tissue from the various patient groups. Thus, human IGF-1 binding sites in cerebral cortex and hippocampus appear to be relatively stable for a number of variables. The increase in cerebral cortical [125I]-IGF-1 binding sites could be due to upregulation of IGF-1 receptors resulting from a decrease in IGF-1 levels in Alzheimer's patients.

Alcoholism↗

PubMed1991

Effect of feeding on the diurnal rhythm of plasma cortisol and adrenocorticotrophic hormone concentrations in the pregnant ewe and sheep fetus.

The effects of two different feeding regimes on the 24 h profiles of maternal and fetal plasma cortisol and adrenocorticotrophic hormone (ACTH) concentrations were studied in eight pregnant ewes between 123 and 144 days of gestation. Once daily-fed ewes (n = 4) received 1 kg of lucerne-chaff at 11.00 h, and multi-fed ewes (n = 4) received 100-200 g of lucerne-chaff at 09.00, 11.00 and 13.00 h and then 150 g until 09.00 h the following day. There were significant differences between the two feeding groups in the 24 h profile of maternal plasma osmolality; once daily feeding at 11.00 h was associated with a peak in maternal plasma osmolality at 15.00 h whereas maternal plasma osmolality reached plateau levels at around 17.00 h in the multi-fed group. There were also differences between the two feeding groups in the 24 h profiles of maternal and fetal plasma glucose. Maternal and fetal plasma glucose reached peak concentrations at 19.00 h in the once daily-fed ewes in contrast to the multi-fed group, where a plateau in maternal and fetal plasma glucose was reached between 19.00 h and 09.00 h the following day. A significant diurnal variation in the plasma concentrations of cortisol was present in the once daily-fed ewes from 123 days gestation and in their fetuses after, but not before, 135 days gestation. Plasma cortisol peaked at 11.00 h in the ewes and at 13.00 h in the fetuses of this group. In the once daily-fed group there was also a significant diurnal variation in maternal and fetal plasma ACTH; plasma ACTH concentrations were highest at 11.00 h in the ewes aged between 123 and 144 days and in fetuses after 135 days gestation. In the multi-fed group, whilst ACTH was highest at 09.00 h in the ewes and at 13.00 h in the fetuses, there was no significant diurnal variation in the plasma concentrations of cortisol in the ewes or fetuses of this group at any stage between 123 and 144 days gestation.

Adrenocorticotropic Hormone↗

PubMed1991

Effects of different lighting regimes on daily hormonal and behavioural rhythms in the pregnant ewe and sheep fetus.

1. We have studied the effect of altering the time of darkness during a 12 h photoperiod on the diurnal rhythms of maternal and fetal plasma melatonin and prolactin concentrations and fetal breathing movements (FBMs) in the late pregnant sheep. 2. Four ewes were exposed to a 'normal' 12 h light-12 h dark regime with lights off at 19.00 h. Eight ewes were exposed to an 'altered' 12 h light-12 h dark regime with lights off at 11.00 h. FBMs were recorded continuously and 2 hourly maternal and fetal blood samples taken during 24 h experiments between 120 and 138 days gestation. 3. Plasma melatonin concentrations were higher during the hours of darkness in the ewes and fetuses in both the normal and altered groups; i.e. altering the time of darkness was associated with a shift in the timing of the daily increase in melatonin concentrations in the mother and fetus. 4. In the fetuses, the mean 24 h plasma prolactin concentration was higher in the altered lighting group (28.8 +/- 6.1 micrograms/l) compared to the normal lighting group (13.0 +/- 3.9 micrograms/l). There was no difference, however, between groups in the daily variation of fetal plasma prolactin concentrations, which were higher at 17.00-01.00 h than at 05.00-19.00 h. Thus, altering the time of darkness did not change the timing of the daily plasma prolactin rhythm in the fetus. 5. Under the normal lighting regime maternal plasma prolactin concentrations were higher at 17.00-19.00 h (i.e. from 2 h before lights off) than at 09.00-11.00 h. In contrast, under altered lighting, plasma prolactin concentrations were higher at 01.00-07.00 h (i.e. 2-8 h after lights on) than at 09.00 h. 6. In the normal lighting group the incidence (min/h) of FBMs were highest at 16.00-21.00 h and reached a minimum at 05.00-06.00 h. In contrast, in the altered lighting group the incidence of FBMs was lowest at 19.00-20.00 h and reached a maximum at 11.00-12.00 h. 7. The results suggest that the light-dark cycle influences the diurnal modulation of FBMs, but not the daily variation of fetal plasma prolactin concentrations. The role of plasma melatonin concentrations, and evidence for a photo-inducible phase of increased prolactin secretion in the fetus, is discussed.

Animals↗

PubMed1990

Characterization of a human apolipoprotein E gene enhancer element and its associated protein factors.

An enhancer element in the 5' flanking region of the human apolipoprotein E gene, known as upstream regulatory element 1 (URE1), has previously been implicated in the expression of this gene. The URE1 element, which spans nucleotides -193 to -124 of the 5'-flanking region of the human apolipoprotein E gene, contains two sequences that bind to nuclear proteins, as determined by the DNase I footprinting assay. In the present study of URE1, we have characterized these sequences further. Deletion of one of the footprint sequences, at nucleotides -161 to -141, reduced URE1 enhancer activity substantially. A 30-base pair oligonucleotide that included this protein-binding sequence was able, by itself, to act as an enhancer. This sequence, termed the positive element for transcription (PET), was demonstrated by gel retention analysis to bind at least two protein factors, one of which is the transcription factor Sp1. Sp1 appeared to be the only protein required for the enhancer activity of PET to be manifested. In vitro transcription assays showed that the PET sequence was necessary for efficient transcription directed by the apoE promoter and that the PET sequence was the dominant regulatory element in the apoE promoter. Gel filtration chromatography and PET oligonucleotide-affinity chromatography were used to isolate a second PET-binding factor, a Mr = 55,000 protein, from HeLa cell nuclear extracts. It appeared to compete with Sp1 for a common binding site in the PET sequence, but it was not required for enhancer activity. The second footprint sequence in URE1, at nucleotides -184 to -173, also bound Sp1, but it was not required for enhancer activity. A third Sp1-binding region was located at a proximal GC box element (nucleotides -54 to -45). This region had no enhancer activity, but it was required for maximum transcriptional activity of the apoE promoter. Thus, the regulation of apoE gene expression is influenced by different protein-binding sequences, with transcription factor Sp1 playing major roles in both basal promoter activity and enhancer activity.

Animals↗

PubMed1990

Maternal pinealectomy alters the daily pattern of fetal breathing in sheep.

We have investigated the effect of pinealectomy of the pregnant ewe on the 24-h pattern of fetal breathing activity during late gestation. Fetal breathing movements were recorded during 24-h periods on 18 occasions in 5 pinealectomized ewes and on 24 occasions in 6 pineal-intact ewes between 120 and 145 days gestation. All ewes were fed once daily between 1000 and 1300 h and were kept under a light-dark cycle 12:12 h. There was no significant difference in the mean hourly incidence of fetal breathing movements between the pineal-intact (27.2 +/- 0.5 min/h) and pinealectomized (25.5 +/- 0.6 min/h) groups. However, there was a significant difference in the 24-h profiles of fetal breathing movements in the two groups. The peak incidence of fetal breathing occurred between 1900 and 2000 h in the pineal-intact ewes and between 1200 and 1300 h in the pinealectomized ewes. We conclude that maternal pinealectomy alters the daily pattern of a fetal behavioral pattern and that maternal melatonin may therefore provide the fetus with information about time of day.

Animals↗

PubMed1990

Effect of feeding regimen on diurnal variation of breathing movements in late-gestation fetal sheep.

There is a diurnal variation in the mean incidence and amplitude of fetal breathing movements (FBMs) in sheep after approximately 120 days gestation. To determine whether this variation is caused by diurnal fluctuations in plasma glucose or prostaglandin (PG) concentrations, we studied two groups of pregnant sheep fed either once daily at 1100 h or every 2 h for 24 h. Maternal and fetal blood samples were taken every 2 h from 0900 to 0900 h the next day for assay of plasma glucose and PGE2 and PGF2 alpha concentrations. FBMs were recorded throughout the 24 h. The mean fetal plasma glucose concentrations of the once-daily and multifed groups were not different, but there was a significant difference between the two groups in the 24-h pattern of fetal glucose concentrations. In the once-daily fed group, plasma glucose concentrations reached a peak 8 h after maternal feeding and then declined, whereas in the multifed group, fetal plasma glucose concentrations reached a plateau and were constant from 1300 to 0900 h the next day. Fetal plasma PGE2 and PGF2 alpha concentrations did not show a significant change with time of day in either group. There was a significant diurnal variation in the incidence and amplitude of FBMs in each of the two feeding groups, and the 24-h pattern of FBMs did not differ significantly between groups. Therefore it would appear that the diurnal variation of FBMs is not a consequence of the maternal feeding regimen or diurnal changes in plasma glucose or PG concentrations.

Animals↗

PubMed1990

Catecholamine neurons in fetal brain: effects on breathing movements and electrocorticogram.

We investigated the effect of increasing the synaptic concentration of catecholamines released from central pathways on breathing movements and electrocortical (ECoG) activity in fetal sheep in utero. In 11 trials (9 fetuses) intravenous infusion of the noradrenergic uptake inhibitor desipramine (DMI) resulted in an initial increase in the incidence of breathing movements from 47.8 +/- 2.2%/h to a maximum of 77.9 +/- 5.5%/h (P less than 0.05) followed by a subsequent decrease to 18.8 +/- 2.7%/h (P less than 0.05), which was associated with a decrease in the incidence of low-voltage ECoG activity. Mean breath amplitude also increased after DMI infusion from 5.8 +/- 0.2 mmHg to a peak of 8.9 +/- 0.9 mmHg (P less than 0.05). In five fetuses, intravenous injection of the alpha 1-receptor antagonist prazosin 30 min after the start of the DMI infusion blocked the increase of breath amplitude observed when DMI was given alone. Intracisternal infusion of 6-hydroxydopamine (6-OHDA, which causes an initial displacement of transmitter stores followed by a neurotoxic action) in six fetuses caused an increase in mean breath amplitude from 6.6 +/- 0.3 mmHg (control) to 22.3 +/- 5.5 mmHg (P less than 0.05) and a prolonged episode of breathing movements (168.5 +/- 47.2 min). The incidence of low-voltage ECoG activity was also increased significantly. A second infusion of 6-OHDA, 2 days after the first, had no effect on breathing movements or ECoG activities. The two treatments with 6-OHDA also resulted in a significant reduction in the response to intravenous infusion of DMI, indicating that endogenous release of norepinephrine had been reduced by the neurotoxin. These results suggest that 1) there is normally some tonic release of norepinephrine from central pathways, but this release is insufficient to stimulate sustained fetal breathing, and 2) accumulation in the synaptic cleft of catecholamines from central neurons is able to stimulate fetal breathing and promote low-voltage ECoG activity. Possible mechanisms that normally limit the activity of central catecholamine pathways before birth are discussed.

Animals↗

PubMed1990

Effect of hyperthermia on thyroid structure in the late gestation fetal lamb.

This study examined the effect of hyperthermia in late gestation on fetal thyroid structure. Mild heat stress (increase of ewe's rectal temperature to 40.4 degrees C) caused significant changes of fetal thyroid structure. Intra-follicular colloid area was significantly larger in the heat-stressed group (2,532 +/- 181 microns2) compared to a control group where rectal temperature of the ewe was within the normal range (1,660 +/- 188 microns2; p less than 0.01). Epithelial cell height was significantly reduced (2.5 +/- 0.19 vs. 4.8 +/- 0.26 microns; p less than 0.01). Fetal plasma glucose concentrations were significantly lower in the heat-stressed group (0.7 +/- 0.07 mmol/l) compared to the non-heated group (1.0 +/- 0.11 mmol/l; p less than 0.05). We suggest that the fetal thyroid gland in sheep is responsive to environmental temperature changes and is important in the neuroendocrine regulation of fetal body temperature. Fetal hypoglycaemia may also contribute to the changes in fetal thyroid gland by altering the peripheral utilization of thyroid hormone. Such changes, if prolonged, may contribute to the decreased rate of fetal growth and maturation associated with chronic heat stress in sheep.

Animals↗

PubMed1990

Polypeptides constituting the antigenic basis for identification of Rickettsia sibirica species by the standard serotyping method for spotted fever group rickettsiae.

The antigens of Rickettsia sibirica, Rickettsia rickettsii, and Rickettsia conorii were examined by Western immunoblots and the standard immunofluorescent serotyping assay with mouse anti-Rickettsia sibirica serum that is used for determining the species identification of spotted fever group rickettsiae. Serum was employed prior to absorption and after absorption with purified native or heated Rickettsia sibirica. The unabsorbed antiserum, the antiserum absorbed with heated Rickettsia sibirica and the antibodies eluted from native Rickettsia sibirica recognized two antigenic polypeptides of Rickettsia sibirica (130 and 118 kDa), Rickettsia rickettsii (151 and 133 kDa), and Rickettsia conorii (136 and 113 kDa), respectively when examined in native state, not denatured by heat. The antiserum absorbed with native Rickettsia sibirica reacted most strongly with one polypeptide of Rickettsia sibirica (118 kDa), Rickettsia rickettsii (133 kDa), and Rickettsia conorii (136 kDa); at the endpoint of the immunofluorescence assay there was minimal reactivity with the 130 kDa polypeptide by immunoblotting. Both Western immunoblots and immunofluorescence assay showed that the antiserum absorbed with native Rickettsia sibirica reacted with homologous and heterologous antigens at a much lower titer than did the antiserum that was not absorbed. However, the titers of reaction with Rickettsia sibirica, Rickettsia rickettsii, or Rickettsia conorii were not diminished by absorption of the native antiserum with heated Rickettsia sibirica. The antibody eluted from native Rickettsia sibirica reacted by immunofluorescence with all the rickettsiae at a higher dilution than the antibody eluted from heated Rickettsia sibirica.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Effect of hyperthermia on the plasma concentrations of prolactin and cortisol in the fetal lamb and pregnant ewe during late gestation.

Exposing pregnant sheep to an ambient temperature of 43 +/- 1 degree C for 8 h was associated with a 1-1.5 degrees C increase of maternal and fetal core temperatures, and a 11-fold and 3-5 fold increase in maternal and fetal plasma prolactin concentrations respectively. Hyperthermia did not change maternal or fetal plasma cortisol concentrations. We conclude that maternal and fetal hyperprolactinaemia may occur in late pregnancy during hyperthermic conditions and that the increase in fetal plasma prolactin is due to either increased secretion or decreased metabolic clearance of prolactin in the feto-placental compartment.

Animals↗