PubMed Health⌕ Search

Biomedical subjects

G W Tregear

Publications and source records attributed to G W Tregear.

At least 73 records · Page 4Linked to original sources
PubMed1986

The nucleotide sequences of baboon chorionic gonadotropin beta-subunit genes have diverged from the human.

The placental glycopeptide hormone chorionic gonadotropin (CG) is involved in establishing and maintaining pregnancy. The hormone consists of two different non-covalently associated subunits termed alpha and beta. In man there are seven closely linked genes coding for beta CG-like peptides, but only three of these appear capable of expression in the placenta. The organization of beta CG-like genes in man and baboon appears to be similar. We demonstrate here that the baboon genome contains multiple copies (at least five) of beta CG-related genes, and that these genes are closely linked in the genome. Nucleotide sequence data from several beta CG cDNA clones indicates that at least two of these beta CG-related genes are expressed in the baboon placenta. Analysis of beta CG sequences from baboons and human subjects demonstrates that these genes have diverged markedly between species. In contrast, these sequences are remarkably homogeneous within their respective genomes. Gene conversion events may be responsible for retaining the high degree of identity among the various beta CG gene family members. Knowledge of beta CG sequences from baboon may lead to development of a long-term antipregnancy vaccine. The ability of CG antibodies to interfere with the maintenance of pregnancy can now be investigated within a homologous system.

Animals↗
PubMed1986

Location of the major antigenic sites involved in rotavirus serotype-specific neutralization.

Antigenic sites on the rotavirus major outershell glycoprotein were identified by using mutant viruses selected for resistance to neutralizing (serotype-specific) monoclonal antibodies. The glycoprotein genes from these mutants were sequenced to determine the position and nature of the resultant amino acid substitutions in the protein. Three regions (A, B, and C) were identified (amino acids 87-96, 145-150, and 211-223, respectively), of which region C appears to be the most important. A mutation in region C caused a 10-fold increase in resistance to neutralization by polyclonal antiviral antiserum. The results of this study, together with other data, indicate that the three-dimensional folding of the native protein is such that regions A and C are in close proximity.

Amino Acid Sequence↗
PubMed1986

Effect of long-term infusion of ovine corticotrophin-releasing factor in the immature ovine fetus.

Synthetic ovine corticotrophin-releasing factor (oCRF) was infused continuously into the jugular veins of six ovine fetuses for 5-11 days. Two fetuses receiving 0.1 and 1.0 microgram oCRF/h from gestational days 134 and 135 respectively, lambed prematurely on days 141 and 140 respectively. Three out of four fetuses receiving oCRF at 2.4 micrograms/h, from 125 days of gestation, delivered spontaneously at 131, 131 and 136 days, whilst one died in utero at 132 days. Two fetuses receiving vehicle only or oCRF intra-amniotically, were born at 148 and 145 days respectively, whilst six fetuses chronically cannulated but not infused were born at 149.8 +/- 2.1 (S.D.) days. In ewes lambing at term, maternal plasma progesterone concentrations were 41.4 +/- 11.4 (S.E.M.; n = 5), 28.8 +/- 7.8 (n = 6), 17.1 +/- 4.8 (n = 5) and 7.9 +/- 1.1 (n = 4) nmol/l on 3, 2, 1 and 0 days respectively before the lambs were born. No such decrease in maternal plasma progesterone concentrations was seen in the oCRF-infused fetuses. Fetal plasma concentrations of immunoreactive ACTH were maintained above normal in oCRF-infused fetuses, but some desensitization to bolus oCRF injections occurred in these fetuses. Four of the five fetuses born prematurely were sufficiently mature to survive, being able to stand, breathe and suckle. It is concluded that continuous oCRF infusions into immature fetuses can accelerate maturation of a number of organs and systems culminating in the premature delivery of viable lambs.

Adrenocorticotropic Hormone↗
PubMed1985

Hybridization histochemistry.

In this review we have used our own recent work as a flagship to illustrate the recent renaissance of interest in hybridization histochemistry. A trickle of papers followed the initial key excursion into the in situ labeling of tissue sections (48-50). Our own entry into this field started in 1978 and since then a confluence of important questions and technical advances has served to make hybridization histochemistry much more attractive as a research tool. Hybridization histochemistry is able to solve some problems for which there is no other suitable technique at this time. Hybridization histochemistry provides the location of anatomical sites of gene expression, and viral replication, with uniquely high specificity. We have taken 32P-labeled probes to what appears to be their limit of resolution, which is single cells in thin sections. While 32P has clear disadvantages, exposure time is relatively short and the use of fast-X-ray film to preview the results and estimate exposure time for emulsion has been turned to advantage. Our introduction (27) of the use of whole-mouse sections in hybridization histochemistry has great potential in hormonal, enzymatic, and growth factor gene expression and will no doubt prove of great use in developmental studies and examination of viral infection. The use of synthetic DNA (synthetic oligonucleotides) unshackles the technique from the need for an associated molecular biology laboratory and at once widens the horizon of application of the technique. Although hybridization histochemistry is a valuable research tool which will soon find a niche in many fields, in a short time it should become a key diagnostic aid. It may well become the method of preference for detection of the expression of oncogenes and other cancer-related genes and for viruses which for other reasons are difficult to detect.

Animals↗
PubMed1985

Antibodies elicited by influenza virus hemagglutinin fail to bind to synthetic peptides representing putative antigenic sites.

A number of peptides of the hemagglutinin (HA) of X-31 influenza virus have been synthesised. The amino acid sequences of some of these peptides represent regions of HA which have been postulated [Wiley et al., Nature, Lond. 289, 373-378 (1981)] to form the antigenic sites of this molecule. Animals were immunized with free peptide or peptide conjugated to a carrier and the resulting antisera examined for their capacities to bind to homologous peptide, whole HA, reduced and alkylated HA, and intact virus. Not all peptides examined in this way were immunogenic. Only antibodies raised against the C-terminus of HA1 peptide displayed binding to virus. This antiserum bound to the intact HA but not to the reduced and alkylated form of the molecule. These results raise questions as to the feasibility of using synthetic peptides of the influenza HA in short linear sequences to elicit neutralising antibody.

Amino Acid Sequence↗
PubMed1985

Vasopressin-neurophysin II gene expression in the ovary: studies in Sprague-Dawley, Long-Evans and Brattleboro rats.

The neurohypophysial hormones oxytocin and arginine vasopressin (AVP) have been identified on immunological criteria in the ovary. Confirmation of extraneuronal synthesis requires the demonstration in the tissue of the specific messenger RNA (mRNA) for the preprohormone. Using a synthetic pentadecamer nucleotide probe, highly specific for the 5' region of rat neurophysin II (NP II), we have demonstrated the presence of AVP-NP II mRNA in the ovary of Sprague-Dawley, Long-Evans and Brattleboro rats, with an apparent molecular weight identical to that seen for hypothalamus. These findings, together with the presence of immunoreactive AVP in the ovaries but not hypothalami of Brattleboro rats, suggest that tissue-specific differences in AVP-NP II gene expression occur at the translational as well as transcriptional level.

Animals↗
PubMed1985

Development of the hypothalamic-pituitary-axis in the ovine fetus: ontogeny of action of ovine corticotropin-releasing factor.

In samples from twenty chronically cannulated ovine fetuses the plasma immunoreactive adrenocorticotrophin (ACTH) concentrations were 12.5 +/- 3.2(8), 15.2 +/- 4.1(9) and 21.2 +/- 5.6(8) pg/ml at periods, prior to parturition, of -30 to -35, -25 to -29 and -20 to -24 days respectively. Values are mean +/- SEM (number of samples). These values were not significantly different from each other but were significantly lower (P less than 0.02) than values in the next two age groups -36.0 +/- 4.9(7) pg/ml at -19 to -15 days, and 39.6 +/- 6.6(11) pg/ml at -14 to -9 days. A further significant increase (P less than 0.05) occurred in the -8 to -3 day period, ACTH being 53.9 +/- 5.4(12) pg/ml. On day of delivery two samples had values of 325 and 360 pg/ml. A single injection, intravenously of 1.0 microgram ovine corticotrophin-releasing factor (O-CRF), caused a significant increase in fetal plasma ACTH concentrations in fetuses of -6 to -23 days prior to delivery but not in fetuses -24 to -35 days prior to parturition. The maximum values of ACTH after O-CRF were significantly greater in fetuses -2 to 0 days prior to parturition than in younger fetuses (P less than 0.01). In 6 experiments in 4 fetuses (parturition -1 to -13 days) the effect of 1.0 microgram O-CRF persisted for at least 2.5 h. The results support the hypothesis that the pituitary release of ACTH changes sensitivity to hypothalamic O-CRF at least twice during the last fifth of gestation; an increasing sensitivity is seen as term approaches.

Adrenocorticotropic Hormone↗
PubMed1984

Handling of phosphate by a parotid gland (ovine).

The handling of phosphate by the sheep's parotid gland was investigated by examining the effects on the composition of saliva of phosphate depletion, secretomotor nerve stimulation, enrichment of phosphate in the blood supply, and parotid arterial infusion of parathyroid hormone (PTH) and calcitonin. Experiments were performed in anesthetized sheep after vascular isolation of the parotid gland. In phosphate depletion arterial plasma phosphate fell from 1.50 +/- 0.12 to 0.73 +/- 0.08 mM. In phosphate repletion salivary phosphate ion was concentrated 8- and 16-fold compared with parotid arterial and venous plasma, respectively. In depletion salivary phosphate concentration was unchanged at slow salivary flow rate but was significantly lower at high flow rate. Enrichment of phosphate in the arterial blood increased salivary phosphate concentration in both situations. Synthetic bPTH (1-34), highly purified bPTH (1-84), and bovine parathyroid extract were equipotent in increasing salivary phosphate concentration in phosphate repletion and had no effect in phosphate depletion. They also increased parotid blood flow. The rise in phosphate with PTH was conditional on the rise in blood flow, but the same rise in blood flow alone did not reproduce the effect of PTH on salivary phosphate. PTH increased work done and oxygen consumption by the gland but arterial phosphate enrichment did not. Increases in salivary phosphate were associated with decreases in salivary bicarbonate, and the sum [HCO-3] + [Cl-] + (HPO2-4] remained almost constant. Micropuncture studies have shown that ovine parotid ducts do not normally reabsorb phosphate and therefore PTH probably increases phosphate secretion in the endpieces.

Animals↗
PubMed1984

Synthetic ovine corticotropin-releasing factor stimulates adrenocorticotropin release in the ovine fetus over the last fifth of gestation.

Synthetic ovine corticotropin-releasing factor (0.1-1.0 micrograms) was injected intravenously to 6 chronically cannulated ovine fetuses between 104 and 149 days of gestation (term 142-152 days). Arterial plasma immunoreactive adrenocorticotropin was first elevated by this procedure if the fetuses were between 118 and 130 days of gestation, and an increased response occurred later in gestation. This suggests that a progressive reset of the hypothalamic-pituitary-adrenal feedback relationship occurs over the last 2-3 weeks of gestation in the ovine fetus.

Adrenocorticotropic Hormone↗
PubMed1984

Evaluation of the biological properties of parathyroid hormone and analogues in a vascularly isolated parotid gland-based assay.

Infusion of bovine parathyroid hormone (bPTH) preparations into the arterial blood supply of the vascularly isolated parotid gland in anaesthetized sheep increases salivary phosphate concentration and gland blood flow rate with rapid onset and offset of action. These responses have been used as a bioassay for PTH and PTH analogues and for assessing the properties of an in-vitro inhibitory analogue [Nle-8, Nle-18, Tyr-34]bPTH-(3-34)amide. [Nle-8, Nle-18, Tyr-34]bPTH-(1-34)amide at 10(-9) to 10(-8) mol/l was four to five times more potent than bPTH(1-34) on both salivary phosphate and blood flow assays. Human PTH(1-34) was not significantly more potent than bPTH(1-34). The [Nle-8, Nle-18, Tyr-34]bPTH-(3-34)amide analogue had very slight agonist activity at 3 X 10(-7) mol/l and at a 100:1 ratio of analogue to PTH it completely inhibited the action of bPTH(1-34) on phosphate secretion and gland blood flow. It caused partial inhibition at 10:1 and had no evident effect at 1:1. These results differ from previous in-vitro results and indicate that the preparation may be valuable for evaluation of agonist and antagonist analogues of PTH. The vascularly isolated parotid gland of the sheep permits repeated random testing of analogues in a control-test-control sequence and the results indicate high sensitivity to PTH in a rapidly reactive in-vivo system with two responding parameters.

Animals↗
PubMed1984

Stress, ACTH, salt intake and high blood pressure.

Epidemiological evidence supports the thesis that high salt intake is involved in the aetiology of hypertension. If sodium intake is not causal, it appears other factors do not cause high blood pressure in unacculturated societies with low sodium intake. In this context, it is potentially important that stress causing ACTH release, as well as other neurohumoral effects, causes increased salt appetite and can impair renal sodium excretion.

Adrenalectomy↗
PubMed1984

The effect of intracerebroventricular infusions of CRF, sauvagine, ACTH (1-24) and ACTH (4-10) on blood pressure in sheep.

This study reviews the effects of intracerebroventricular (i.c.v.) infusion of corticotrophin releasing factor (CRF) and adrenocorticotrophic hormone (ACTH) (1-24) on blood pressure in conscious sheep. The effects of sauvagine, a peptide with 50% homology with CRF and ACTH (4-10) and other analogues of ACTH were studied. Intracerebroventricular infusion of CRF for 24 h at 10 and 100 micrograms/h increased blood pressure and heart rate. Sodium (Na) excretion also increased. Sauvagine at 10 micrograms/h also increased blood pressure. Both peptides raised body temperature and produced 'arousal' behaviour. ACTH (1-24) at 0.8 microgram/h for 48 h raised blood pressure and body temperature but had no significant effect on Na excretion or behavior. ACTH (4-10) and other related analogs (alpha-MSH, alpha gamma 1-MSH) at up to 10 micrograms/h for 48 h had no effects. These studies show that neuropeptides involved in the physiological response to 'stress' may have central effects on blood pressure.

Adrenocorticotropic Hormone↗
PubMed1982

Circular dichroism studies of relaxin and insulin peptide chains.

The circular dichroism (CD) spectra of pig relaxin and pig insulin are similar, reflecting the known structural similarities between the two hormones. However, the conformational characteristics of the separate chains of insulin and relaxin show significant differences. The S-sulfo forms of insulin A and B chains and S-sulfo relaxin A chain have CD spectra consistent with largely unordered structures whereas the S-sulfo form of relaxin B-chain has at least 90% beta--structure. This beta-structure may explain the unusual solubility and adsorptive properties of the relaxin B-chain and the poor combination yields with A-chain. The relaxin B-chain changes to a largely unordered conformation if the peptide is shortened at the carboxyl terminus by six amino acid residues. This conformational change has important implications in planning relaxin synthesis strategy. Significant interactions and conformational changes are observed between the oxidized forms of the A and B chains of both relaxin and insulin. In using CD to monitor chain recombination of native relaxin peptides it was found that the spectra obtained after depending on whether the reduced chains are separated or not separated from the reaction mixture prior to reoxidation. Although the spectra differ the biological activity was 20% in both cases. The remainder of the reoxidized but inactive material contains beta-structures which make a greater contribution to the CD spectrum when the chains have been separated and processed than when they are reoxidized in situ.

Amino Acid Sequence↗
PubMed1982

Local action of parathyroid hormone (1-34) and (1-84) at the parotid gland of sheep.

Administration of bovine parathyroid hormone (PTH) preparations increased the phosphate concentration in the parotid saliva of sheep. Data on the site of action of PTH (1-84) were obtained by (a) equimolar infusions of PTH (1-84) and (1-34) directly into the arterial blood supply of the vascularly isolated parotid gland in anaesthetized sheep, (b) intravenous infusion of PTH (1-84) at a similar rate and (c) intra-arterial infusion of PTH (1-84) with complete drainage of the venous effluent from the gland during the infusion. Results showed substantial time- and dose-response identity of the two peptides, at 10(-9) to 4 X 10(-9) mol/l in arterial blood, in raising salivary phosphate concentration. The effect of PTH (1-84) was not due to recirculated fragments because the response was obtained when recirculation was prevented by complete venous drainage and little or no response occurred when the same infusion was given i.v.

Animals↗
PubMed1982

Angiotensin production and metabolism in sheep.

1. The arterial and central venous concentrations of angiotensin I, II and III have been determined in Na replete and Na depleted conscious sheep. 2. During Na deficiency the arterio-venous ratios of angiotensin I, II and III were 0.48, 1.30 and 1.52 respectively. 3. During infusion of angiotensin II or III, the arterio-venous ratios were 2.1 for angiotensin II and 2.2 for angiotensin III. 4. The blood clearance rate of angiotensin II and III in Na depleted sheep were 135 and 140 l/h respectively; values similar to those found in Na replete animals. 5. The angiotensin III concentration in arterial blood is 42% of that found for angiotensin II. 6. A steady state model of angiotensin production and metabolism has been constructed and shows that 55% of arterial angiotensin II and 40% of angiotensin III are derived in the peripheral vascular bed. These are minimal estimates.

Angiotensins↗