Biomedical subjects

T J McDonald

Publications and source records attributed to T J McDonald.

At least 19 recordsLinked to original sources

PubMed1992

Adenosine A1 receptors mediate inhibition of tachykinin release from perifused enteric nerve endings.

A perifused preparation of guinea pig myenteric nerve varicosities (synaptosomes) was used to determine the characteristics of evoked tachykinin release and the inhibition of such release by adenosine analogues. Release of substance P-like immunoreactivity (SP-LI) and neurokinin A-like immunoreactivity (NKA-LI) was evoked by elevated extracellular [K+] in a reversible and repeatable manner. This release was completely abolished in the absence of extracellular Ca2+. Perifusion in the presence of 5'-N-ethylcarboxamidoadenosine (NECA), a nonselective A1/A2 adenosine receptor agonist, decreased K(+)-evoked release of SP-LI and NKA-LI compared with that in the absence of the nucleoside. Similar decrements in peptide release were obtained with N6-cyclopentyl adenosine (CPA), a selective A1 agonist, and 2-[p-(2-carboxyethyl)]phenethylamino-5'-N-ethyl-carboxamidoadenosi ne (CGS 21680), a selective A2 agonist. Response to all nucleosides was graded. Potency order of adenosine analogues was CPA greater than NECA much greater than CGS 21680. Inhibition due to the nucleosides was diminished in the presence of the highly selective A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) while perifusion in the presence of DPCPX alone did not alter evoked release of either peptide. These findings provide direct measurements of inhibitory effects of adenine nucleosides on the release, from enteric nerve endings, of endogenous neuromediators SP and NKA. The findings also directly demonstrate the presence of functional adenosine receptors of the A1 subtype on enteric nerve endings coupled negatively to release of tachykinins. The presence of A2 receptors on enteric nerve endings is neither supported nor excluded.

Adenosine↗

PubMed1992

Effect of implantation of dexamethasone adjacent to the paraventricular nucleus on messenger ribonucleic acid for corticotropin-releasing hormone and proopiomelanocortin during late gestation in fetal sheep.

Glucocorticoids act upon the hypothalamic paraventricular nucleus (PVN) and anterior pituitary in a classic negative feedback loop to regulate ACTH biosynthesis and secretion. Evidence exists to indicate that glucocorticoid feedback may be attenuated during late gestation in the sheep fetus to allow the preterm rise in fetal plasma cortisol necessary for parturition in this species. The present studies were undertaken to determine the effect of glucocorticoids placed adjacent to the fetal PVN on messenger RNA (mRNA) for CRH in the PVN and mRNA for POMC in the anterior pituitary during late gestation. We performed our studies at two critical stages during late gestation to determine if gestational age related changes occur in the efficacy of negative feedback regulation of expression of CRH and subsequently POMC. Dexamethasone (DEX) implants were placed bilaterally 2 mm lateral to the fetal PVN at 105 to 107 days gestational age (dGA; group I, n = 4) and 121-123 dGA (group II; n = 4). Gestational-age matched, sham implanted fetuses were used as controls (CONT) for both groups (n = 4 per group). Fetuses were recovered at 126-128 (group I) and 136 dGA (group II). Fetal PVN were isolated by micropunching, and the anterior pituitary was separated from neurointermediate and posterior lobes after necropsy. Total RNA was subjected to Northern analysis using specific complementary DNA probes to CRH and POMC, and specific message was normalized to actin mRNA content in each individual sample. Anterior pituitary POMC mRNA was not different in DEX fetuses compared to CONT for either group I (78 +/- 26% of CONT; mean +/- SEM) or group II (84 +/- 17% of CONT). PVN CRH mRNA content was lower in DEX fetuses in group I (28 +/- 14% of CONT; P less than or equal to 0.01) and group II (65 +/- 12% of CONT; P less than or equal to 0.01). The degree to which DEX suppressed mRNA for CRH was greater in group I compared to group II (P less than or equal to 0.05). We conclude that 1) CRH expression in the PVN of fetal sheep is suppressible by glucocorticoids; 2) suppression can occur directly at the level of the PVN and 3) that the efficacy of negative feedback decreases with increasing gestational age. Furthermore, the lack of effect of hypothalamic administration of DEX on anterior pituitary POMC mRNA indicates that basal expression of POMC in fetal sheep may be independent from support from the PVN at this stage of gestation.

Animals↗

PubMed1992

Mitogenic action of gastrin-releasing polypeptide on isolated epiphyseal growth plate chondrocytes from the ovine fetus.

Gastrin-releasing polypeptide (GRP) has been implicated in the development of the human fetal lung. To determine whether GRP has a wider role in fetal development, its actions on DNA synthesis and cell replication by isolated epiphyseal growth plate chondrocytes obtained from ovine fetuses between 35 days gestation and near term (145 days) were examined. Chondrocytes were isolated using collagenase from the proximal tibia and cultured in monolayer. Synthesis of DNA was assessed from the incorporation of [3H]thymidine into previously growth-restricted cells after incubation in medium supplemented with GRP1-27 (40-1280 nM). Increase in cell number was assessed after incubation with test medium for 1 week. GRP caused a dose-dependent increase in both cell number and DNA synthetic rate compared to control incubations. Cell number was increased by 50% in the presence of a maximally effective 160 nM GRP and DNA synthesis by up to 800% utilizing chondrocytes obtained from animals of 75-80 days gestation. The mean (+/- SEM) half-maximal concentration of GRP for the stimulation of DNA synthesis was 97 +/- 12 nM (5 separate fetuses). Concentrations of GRP in excess of 160 nM caused a sharp reduction in both cell replication and DNA synthesis. To determine where within the cell cycle GRP exerted its mitogenic action, synchronized chondrocytes were transiently exposed to fetal bovine serum and cultured with GRP for increasing periods of time before pulse labeling with [3H]thymidine during S phase. GRP was as effective in stimulating DNA synthesis when present for the initial 4 h of G1 as when present for the entire G1 period. Since isolated fetal growth plate chondrocytes release insulin-like growth factor II (IGF II) and basic fibroblast growth factor (basic FGF) the possible mediation of GRP action by the release of these peptides or synergistic interactions were examined. Specific antibodies shown to negate the mitogenic actions of exogenous IGFs or basic FGF on chondrocytes did not alter GRP-stimulated DNA synthesis. The release of radioimmunoassayable IGF II by chondrocytes was not altered in the presence of GRP. Coincubation of GRP with submaximal concentrations of IGF I or basic FGF showed additive effects on DNA synthesis. When the actions of galanin were examined it was found to inhibit basal DNA synthesis by chondrocytes at a concentration of 167 nM. However, 66 nM or greater galanin was able to render 160 nM GRP inactive as a mitogen. These results suggest that GRP may potentially influence skeletal development in the ovine fetus and may interact with locally released peptide growth factors or other neuropeptides.

Analysis of Variance↗

PubMed1992

Effect of bilateral lesions of the ovine fetal hypothalamic paraventricular nuclei at 118-122 days of gestation on subsequent adrenocortical steroidogenic enzyme gene expression.

Fetal adrenal steroid hydroxylase activity and messenger RNA (mRNA) expression increases concurrent with the preterm rise in fetal plasma cortisol during late gestation in sheep. By placing bilateral lesions of the fetal paraventricular nuclei (PVN) we have previously demonstrated that the fetal PVN is necessary for the initiation of parturition, the late gestation preparturient increase in fetal plasma cortisol and ACTH, and ACTH secretion in response to fetal hypoxemia and hypotension. The purpose of this study was to determine the role of the fetal PVN in the late gestation increase in expression of mRNA for 17 alpha-hydroxylase (P-450(17)alpha), side-chain cleavage (P-450SCC), 11 beta-hydroxylase (P-450(11)beta), 21 hydroxylase (P-450C21), and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) in the fetal adrenal. Ovine fetuses were subjected to bilateral lesions of the PVN (Lx; n = 4) or sham lesions (Sh; n = 4) at 118-122 days gestational age (dGA). Lx fetuses were recovered by cesarean section at greater than or equal to 157 dGA; Sh fetuses were recovered immediately postbirth at normal term (146.5 +/- 0.9 dGA). In addition, uninstrumented fetuses were obtained at 145-147 dGA by cesarean section (n = 3). RNA obtained from individual fetal adrenals was subjected to Northern analysis. Lx of the fetal PVN decreased (P less than or equal to 0.05) mRNA for P-450(17)alpha and P-450SCC but did not affect adrenocortical mRNA for P-450C21, P-450(11)beta, or 3 beta-HSD compared to Sh. To determine if the differences observed between Lx and Sh for P-450(17)alpha and P-450SCC mRNA were due to the process of labor, we compared uninstrumented 145-147 dGA to Sh. No differences in adrenal mRNA content were observed for P-450(17)alpha or P-450SCC between these groups. We conclude that in late gestation fetal sheep an intact fetal PVN is necessary for normal gene expression of adrenocortical P-450(17)alpha and P-450SCC while P-450(11)beta, P-450C21, and 3 beta-HSD may be primarily regulated by factors not dependent upon a functional PVN.

3-Hydroxysteroid Dehydrogenases↗

PubMed1992

Hypothalamic paraventricular nuclear lesions delay corticotroph maturation in the fetal sheep anterior pituitary.

The purpose of this study was to determine whether normal morphological development occurs in pituitary corticotrophs deprived of products of the hypothalamic paraventricular nucleus (PVN), e.g. corticotropin releasing hormone and arginine vasopressin (AVP), after PVN lesions. In addition, we have attempted to ascertain if the neurophysin/AVP-positive fibers innervating the fetal sheep anterior pituitary are affected by PVN lesions. The experimental groups consisted of fetal sheep in which 1) hypothalamic PVN lesions were placed at 118-122 days gestation (dGA) and the fetuses subsequently harvested while still in utero at 157 dGA or more (PVNX; n = 5); 2) sham PVN lesions were placed at 118-122 dGA and subsequently harvested as newborn lambs immediately after birth at 146.5 +/- 0.9 (mean +/- SEM) dGA combined with two uninstrumented fetuses harvested at 144 dGA or more but not in labor (perinatal; n = 6); and 3) no instrumentation was placed, and the fetuses were harvested at 120 dGA (control; n = 4). Two ACTH-immunoreactive cell types were seen in the anterior pituitary: 1) fetal cells: large and variably stained, often columnar, occurring in clusters and arranged in palisades; and 2) adult cells: smaller, darkly staining, and angular, occurring singly or in small groups. Quantification of the distribution of the two ACTH cell types was performed by scanning sections from a one in six series from each pituitary and estimating the percent area of each section in the well that showed adult type staining only. The observer was blind to the treatment group assignment of the sections. The estimated percentages of the portion of the pituitaries of each group that contained adult-type cells only were as follows: PVNX, 42.8 +/- 10.0%; perinatal, 90.9 +/- 2.1%; and control, 3.7 +/- 1.1% (mean +/- SEM; P less than 0.05 for all comparisons). There were no qualitative differences between all groups in the appearance of neurophysin-positive fibers innervating the anterior pituitary. AVP staining was strong in the internal zone of the median eminence in all groups, but was absent in the external zone of PVNX fetuses only. The intermediate pituitary lobes stained darkly in all groups. We conclude that lesions of the PVN at 120 dGA delay development of fetal pituitary corticotrophs, but have no effect on the presence of neurophysin-positive nerve fibers in the anterior pituitary.

Adrenocorticotropic Hormone↗

PubMed1992

Effect of placement of dexamethasone adjacent to the ovine fetal paraventricular nucleus on adrenocortical steroid hydroxylase messenger ribonucleic acid.

The preterm rise in the concentration of ovine fetal plasma cortisol that initiates the events of parturition in sheep commences at approximately 125 days of gestational age (dGA; term = approximately 147 dGA). Concurrent with the rise in fetal plasma cortisol, adrenocortical steroid hydroxylase enzyme activity increases. The purpose of this study was 1) to quantitate changes in levels of mRNA for the steroid hydroxylases, 17-hydroxylase cytochrome P450 (P450(17)alpha), side-chain cleavage cytochrome P450 (P450scc), 11 beta-hydroxylase cytochrome P450 (P450(11)beta), and C21-hydroxylase cytochrome P450 (P450C21); and 2) examine the role of the fetal paraventricular nucleus (PVN) in the onset of adrenocortical steroid hydroxylase mRNA expression. Unperturbed fetuses were collected by cesarian section under halothane anesthesia at 105 (n = 4), 120 (n = 4), 126-128 (n = 4), and 136 dGA (n = 3); neonatal animals were collected within 2 h after birth. To examine the role of the fetal PVN in regulation of adrenocortical steroid hydroxylase mRNA expression, ovine fetuses were stereotaxically implanted bilaterally 2 mm lateral to the fetal PVN at 105-107 dGA with either cholesterol (n = 4) or dexamethasone (DEX; n = 3). Implanted fetuses were collected by cesarian section under halothane anesthesia at 126-128 dGA. mRNA for both cytochrome P450(17)alpha and P450scc declined 3-fold from 105 to 120 dGA (P less than or equal to 0.05), and then increased by 126-128 dGA compared to that on 120 dGA (P less than or equal to 0.05) and continued to increase through term. Cytochrome P450C21 increased at 126-128 dGA compared to that on 105 and 120 dGA (P less than or equal to 0.05) and remained elevated through term. Three distinct transcripts [approximately 6.2, 4.2, and 2.5 kilobases (kb)] were observed for cytochrome P450(11)beta; the 4.2-kb transcript was predominant. While total message for P450(11)beta declined over increasing gestational age, no differences were noted for the 4.2-kb transcript until after birth, when levels significantly declined (P less than or equal to 0.025). Placement of DEX adjacent to the fetal PVN prevented reemergence of expression of mRNA for P450(17)alpha and P450scc at 126-128 dGA, but had no effect on mRNA for P450C21 or P45011 beta. We conclude that mRNA for P450(17)alpha and P450scc undergoes a decline in expression concurrent with the previously described period of adrenal hyporesponsiveness from 105-126 dGA, followed by an increase in mRNA that accompanies the preterm rise in fetal plasma cortisol.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Cortex↗

PubMed1992

Gastrin releasing peptide immunoreactivity is present in ovine amniotic fluid and fetal and maternal circulations. MRC Group in Fetal and Neonatal Health and Development.

Using antisera directed towards the C-terminal region of gastrin releasing peptide (GRP), significant quantities of GRP-like immunoreactivity (GRPLI) were detected in ovine amniotic fluid and in the fetal and maternal circulations. The highest GRPLI levels were found in amniotic fluid (2135 +/- 829 fmol/ml, n = 12; mean +/- SEM), followed by those in ovine fetal (604 +/- 267 fmol/ml, n = 13) and maternal plasma (229 +/- 89 fmol/ml, n = 13). On gel filtration chromatography, the predominant GRPLI form in each fluid eluted in an identical position consistent with the entity being of apparently larger molecular size than porcine GRP1-27. Certain fetal plasma samples contained a second GRPLI peak eluting at the void volume. Hence, during ovine pregnancy a GRPLI entity circulates in fetal and maternal plasma; the entity is of apparently larger molecular size than GRP1-27 but contains a structure immunologically indistinguishable from the bioactive c-terminal region of GRP1-27. Given the recognized bioactivities of GRP, this entity may be an important hormone during ovine fetal life.

Amniotic Fluid↗

PubMed1992

Diminished insulinotropic effects of gastrin-releasing peptide in pregnant sheep are reproduced by progesterone treatment of nonpregnant animals.

Gastrin-releasing peptide (GRP) is insulinotropic in several species, but possible alterations in this action during pregnancy have not been explored. Therefore, changes in plasma insulin and glucagon concentrations were examined in response to exogenous GRP in nonpregnant and pregnant sheep that were feed restricted, fed ad libitum, or infused with glucose. Administered GRP provoked insulin and glucagon release in pregnant and nonpregnant fed animals. This effect was reduced with feed restriction and potentiated in the presence of glucose. The responses were less in pregnant than in nonpregnant animals. Interpretation of this result, however, was confounded by lower plasma immunoreactive concentrations of GRP achieved in pregnant than in nonpregnant sheep in response to the same infusion rate (picomoles per kg BW) of exogenous GRP. Therefore, nonpregnant ovariectomized sheep were treated with estradiol (E2) or E2 plus progesterone (P4), given to reproduce circulating steroid levels in pregnancy, in order to examine insulinotropic responses to GRP in the absence or presence of concurrent glucose administration. Similar plasma GRP and glucose concentrations were achieved by exogenous infusions in the different groups of nonpregnant animals treated with steroids and in control animals not receiving steroids. E2 alone did not alter the insulin response to GRP compared to control, but E2 plus P4 treatment attenuated these responses to values similar to those in pregnant animals. We conclude that GRP is insulinotropic in sheep, and this action is modulated by the circulating glucose concentration. The response to GRP is less in pregnant than in nonpregnant animals, and this attenuation is mimicked in nonpregnant animals treated with E2 plus P4. We suggest that in species such as sheep, GRP is a potentiator of glucose-stimulated insulin release. This action is diminished in response to the altered endocrine environment of pregnancy and may contribute to the metabolic changes that occur at this time.

Animals↗

PubMed1992

Pancreatic galanin: molecular forms and anatomical locations.

Galanin-like immunoreactivity (GalLI) was found to be present in extracts taken from human, canine, and porcine pancreata. The dominant gel filtration peak in each species co-elutes with standard synthetic porcine galanin (Gal), but an apparently smaller molecular weight Gal form was present in human pancreas and intestine and in dog intestine. Reverse-phase HPLC demonstrated identity of porcine pancreatic Gal immunoreactivity with synthetic intestinal Gal. Heterogeneity was seen on reverse-phase HPLC: Human pancreas and intestine had three peaks of immunoreactivity; the retention times were identical between the pancreas and intestinal extracts; and human Gal elutes at an earlier retention time than porcine Gal. Similarly, dog pancreatic GalLI eluted earlier than porcine Gal on reverse-phase HPLC. Immunohistochemical studies revealed the presence of specific staining for GalLI in varicose nerve fibers in the pancreas of the three species. In the dog pancreas an association between Gal-containing nerve fibers and islet cells was readily demonstrable. This was not the case with pig or human pancreas. We conclude that pancreatic Gal is present in the pancreas of the three species and that molecular heterogeneity is similar between intestinal and pancreatic forms. In the dog, a distinct anatomical relationship is demonstrable between Gal-containing nerves and islet cells.

Animals↗

PubMed1992

Monophosphoryl lipid A-induced immune enhancement of Brucella abortus salt-extractable protein and lipopolysaccharide vaccines in BALB/c mice.

A study was conducted to determine the effect of monophosphoryl lipid A (MPL) and trehalose dimycolate (TDM) as adjuvants on the protective responses in BALB/c mice vaccinated with Brucella abortus salt-extractable protein (BCSP) or proteinase-K-treated B abortus lipopolysaccharide (PKLPS). Mice were vaccinated with different doses of BCSP or PKLPS given alone or in combination with MPL or TDM. Mice were challenge-exposed 4 weeks later with virulent B abortus strain 2308. Two weeks after challenge exposure, the number of B abortus colony-forming units (CFU) per spleen, spleen weights, and spleen cell interleukin 1 production were measured. Serum IgG and IgM concentrations specific for vaccinal immunogens were measured before and after challenge exposure with B abortus. Spleen weights and mean B abortus CFU per vaccine group were significantly lower in BCSP- and PKLPS-vaccinated mice, compared with those of nonvaccinated control mice. Monophosphoryl lipid A enhanced the suppression of splenic infection when given with the BCSP vaccine, but not when given with the PKLPS vaccine. Trehalose dimycolate had no effect on mean CFU when given with BCSP, but incorporation of TDM resulted in a significant increase in mean CFU when given with PKLPS. Spleen weights in BCSP- or PKLPS-vaccinated mice were not different when these vaccines were combined with MPL or TDM. Because of the wide variation in the results, we could not conclude that vaccination with BCSP or PKLPS alone, or in combination with MPL altered spleen cell interleukin-1 production in B abortus-infected mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Adjuvants, Immunologic↗

PubMed1991

Bilateral destruction of the fetal paraventricular nuclei prolongs gestation in sheep.

At present the origin of the signal(s) to initiate parturition remains unknown. Experimental studies in sheep have shown that interruption of the fetal hypothalamohypophyseal-adrenal axis will prolong gestation but no studies have shown prolongation of gestation after destruction of fetal neural structures. In this study we placed bilateral lesions of the paraventricular nucleus in five fetal sheep at 118 to 122 days' gestation. Cortiocotropin-releasing factor staining in the median eminence of the hypothalamus was markedly decreased after fetal paraventricular nucleus lesions. Paraventricular nucleus lesions prevented the fetal adrenocorticotropic hormone rise in response to hypotension and the normal predelivery increase in fetal plasma adrenocorticotropic hormone and cortisol and resulted in impaired fetal adrenal growth relative to the rest of the fetus. Lesioned fetuses had not been delivered at 157 days' gestation when they were removed by cesarian section to obtain tissue for histology. Four control fetuses were delivered at 146.5 +/- 0.9 days' gestation (mean +/- SEM). These findings indicate that a structure in the fetal brain, the fetal hypothalamic paraventricular nucleus, is necessary for parturition to occur.

Adrenocorticotropic Hormone↗

PubMed1991

Metabolism of the heart and brain during hypothermic cardiopulmonary bypass.

The alterations in tissue metabolism induced by hypothermic cardiopulmonary bypass are not completely known. Phosphorus-31 nuclear magnetic resonance spectroscopy was used to determine the effect of hypothermic cardiopulmonary bypass on energy states and intracellular pH of the heart and brain. Sheep were instrumented for cardiopulmonary bypass and had a radiofrequency coil placed over either the heart or skull. The animals were placed in a 4.7-T magnet at 37 degrees C and spectra obtained. The animals were cooled on cardiopulmonary bypass to either 26 degrees C (n = 17) or 18 degrees C (n = 14) for brain studies and to 26 degrees C (n = 12) for heart studies. Hypothermia increased the phosphocreatine/adenosine triphosphate ratio in the heart (2.38 +/- 0.23 versus 3.18 +/- 0.37, 37 degrees versus 26 degrees C, respectively, p = 0.03). The brain phosphocreatine/adenosine triphosphate ratio increased from 1.70 +/- 0.09 at 37 degrees C to 2.00 +/- 0.12 at 26 degrees C (p = 0.009) and 2.10 +/- 0.07 at 18 degrees C (p = 0.0001). Intracellular pH increased during hypothermia (heart: 7.05 +/- 0.02 to 7.18 +/- 0.02, 37 degrees versus 26 degrees C, p = 0.0001; and brain: 7.07 +/- 0.02 versus 7.32 +/- 0.02, 37 degrees versus 18 degrees C, p = 0.0001). The adenosine triphosphate resonance position is known to be sensitive to magnesium binding as well as temperature and was shifted upfield (p less than 0.01) in both the heart and brain. This effect could be totally explained by the temperature dependence of this process.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗

PubMed1991

Galanin inhibition of vasoactive intestinal polypeptide release and circular muscle motility in the isolated perfused canine ileum.

The role of porcine galanin, infused arterially into isolated perfused canine ileal segments, in modulating the tonically elevated neural release of vasoactive intestinal polypeptide and possible concomitant motor actions dependent on vasoactive intestinal polypeptide modulation was studied. Galanin infusions (9-minute) inhibited vasoactive intestinal polypeptide release in a concentration-dependent manner (maximum during minutes 8-10) irrespective of the absence (quiescence) or presence of phasic circular muscle contractions induced by local electrical field stimulation of nerves. During quiescence, galanin induced phasic contractions in four of five segments beginning in the 8th minute of the infusion. During stimulated contractions, galanin inhibited phasic motor activity within 2 minutes of initiation of the infusion; this inhibition may result from direct smooth previously reported muscle inhibition. Thus galanin may inhibit both neural release of vasoactive intestinal polypeptide and circular muscle motility directly. The delayed period of phasic activity initiated by galanin during quiescence may be related to inhibition of vasoactive intestinal polypeptide release, freeing the muscle from tonic inhibition by vasoactive intestinal polypeptide. Because galanin and vasoactive intestinal polypeptide are colocalized in some enteric nerves, galanin may regulate vasoactive intestinal polypeptide release by negative feedback.

Animals↗

PubMed1991

Unresponsiveness of vaccinated BALB/c mice to a second inoculation of lipopolysaccharide from Brucella abortus strain 2308.

A study was conducted to determine whether the protection induced in mice by a primary inoculation of lipopolysaccharide from Brucella abortus would be enhanced by a second inoculation given at different time intervals. Protection was challenged by exposure of the mice to a virulent culture of B. abortus strain 2308. Reduced mean viable count and/or splenic weights were the criteria of protection. There was no significant difference (P greater than 0.05) in the protective responses among mice given a single inoculation. Vaccinated mice were significantly (P less than 0.05) better protected than were nonvaccinated mice. Mice given vaccinal inoculations simultaneous with challenge exposure were less protected (P less than 0.001) than were mice vaccinated prior to challenge, but were better protected (P less than 0.010) than were nonvaccinated mice.

Animals↗

PubMed1991

Relationship of cerebral and myocardial intracellular pH to blood pH during hypothermia.

The regulation of tissue pH during hypothermia is important for cellular homeostasis. The present study was undertaken to determine the relationship between blood pH and intracellular pH in the brain and heart during hypothermia in sheep and to compare these data with those in humans. Intracellular pH (pHi) was determined by 31P nuclear magnetic resonance (NMR) spectroscopic data collected from the heart and brain of sheep during cardiopulmonary bypass (CPB). Alpha-stat and pH-stat blood pH management schemes were compared. When the blood pH was held constant (pH stat), the pHi of the heart increased from 7.01 +/- 0.01 at 37 degrees C to 7.18 +/- 0.02 at 26 degrees C, and the pHi of the brain increased from 7.04 +/- 0.02 at 37 degrees C to 7.23 +/- 0.02 at 26 degrees C and to 7.32 +/- 0.04 at 20 degrees C. Alpha-stat pH management resulted in similar increases in pH to that found with pH-stat [heart: 7.00 +/- 0.02 at 37 degrees C to 7.19 +/- 0.03 at 26 degrees C; brain: 7.07 +/- 0.02 at 37 degrees C to 7.29 +/- 0.02 at 26 degrees C, and 7.32 +/- 0.03 at 20 degrees C]. The tissue pH of the heart in humans showed similar findings during blood pH-stat regulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Stimulation of glucagon secretion by gastric inhibitory polypeptide in patients with hepatic cirrhosis and hyperglucagonemia.

Porcine gastric inhibitory polypeptide (GIP) was infused iv (120 micrograms in 60 min) in seven patients with biopsy-proven hepatic cirrhosis who had surgical porta-caval anastomoses and hyperglucagonemia in the postabsorptive state. The infusions resulted in elevation of blood levels of immunoreactive GIP into the upper range of those observed after ingestion of large mixed meals. This was accompanied by significant increments in immunoreactive glucagon (IRG) in the plasma. Similar infusions in two cirrhotic patients with surgical porta-caval anastomoses who had normal plasma IRG levels in the postabsorptive state had no effect on the plasma IRG level. Ingestion of triglyceride (60 g) in hyperglucagonemic cirrhotic patients with porta-caval anastomoses also resulted in elevation of plasma immunoreactive GIP, and this was again associated with significant elevation of the plasma IRG level. Chromatography studies showed that the increments in plasma IRG after the administration of GIP or triglyceride were largely accounted for by increases in pancreatic-type glucagon. There were no significant effects of administration of GIP or triglyceride on the blood levels of glucose or immunoreactive insulin. It is concluded that porcine GIP is glucagonotropic in patients with cirrhosis of the liver who show elevated levels of IRG in the plasma in the postabsorptive state. This effect is not due to diversion of portal blood to the systemic circulation and may be attributable to hypersensitivity of the alpha-cells to stimulation by GIP.

Blood Glucose↗

PubMed1991

Establishment of dose-response relationships in BALB/c mice, using Brucella cell surface protein and lipopolysaccharide.

A study was conducted to determine the immune (increased antibody) and protective (reduced colony-forming units) responses induced in mice by a: (i) single vaccinal inoculation, using various concentrations of Brucella cell surface protein (BCSP) or lipopolysaccharide (LPS); (ii) primary inoculation, using various concentrations of BCSP, followed by a secondary inoculation, using a standard concentration of BCSP; and (iii) primary inoculation, using 1 concentration of BCSP or LPS, followed by a secondary inoculation, using various concentrations of BCSP or LPS. Four weeks after the primary inoculation, mice were challenge exposed with approximately 1 x 10(4) colony-forming units of Brucella abortus strain 2308 and all mice were euthanatized at 6 weeks. Reduced splenic weights and reduced colony-forming units in the spleens of vaccinated mice, compared with nonvaccinated mice, were the criteria of protection. Increase in serum IgM and IgG was defined as immunity. Both BCSP and LPS induced protective and immune responses that were proportional to the dose given up to an optimal limit. However, concentrations higher than optimal decreased the protective and immune responses. This was true for mice given either 1 or 2 vaccinal inoculations. Enhanced secondary protective responses were seen only when suboptimal doses were used in the primary inoculation. Excessive or optimal doses in the secondary inoculations prevented or obscured the protectiveness and immunity by primary inoculations. The protective effects appeared to be additive when suboptimal doses were used in the primary and secondary inoculations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Neuropeptide release from isolated myenteric nerve endings derived from the guinea pig myenteric plexus.

Isolated myenteric nerve varicosities prepared from the myenteric plexus of the guinea pig ileum were investigated as a suitable model system with which to study the release of several neuropeptide-like immunoreactivities (-LI). Basal release of substance P-LI, neurokinin A-LI, Leu-enkephalin-LI and Met-enkephalin-LI was determined, and clear depolarization-induced release of the enkephalin-LI's and neurokinin A-LI was obtained using this preparation, providing further support for their roles as putative mediators in the enteric nervous system. Evoked-release of these peptides was dependent on the presence in the incubation mixture of certain antagonists to known endogenous neuronal mediators. In the absence of such antagonists, no unequivocal evidence of release was seen. Clear evoked release of Leu-enkephalin-LI occurred only in the presence of the adenosine receptor antagonist 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX), atropine and naloxone. Release of Met-enkephalin-LI occurred in the presence of either atropine or naloxone. The release of neurokinin A-LI was evident in the presence of DPSPX. These findings suggest the existence of either distinct subpopulations of nerve varicosities or distinct neuronal pools containing each peptide and that these peptides may be under differential regulation by endogenous inhibitory mediators. It is concluded that, under suitable conditions, isolated myenteric nerve varicosities provide a useful model system for the study of release, and the modulation of release, of endogenous neuropeptides.

Animals↗