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Biomedical subjects

A H Taylor

Publications and source records attributed to A H Taylor.

51 records · Page 3Linked to original sources
PubMed1991

Hypoxanthine phosphoribosyl transferase deficiency, haematopoiesis and fertility in the mouse.

We have looked for effects of deficiency in hypoxanthine phosphoribosyl transferase (HPRT) in the mouse comparable to non-behavioural consequences of HPRT-deficiency in humans. HPRT-deficient humans show abnormalities in haematopoiesis and, in heterozygotes, there is strong selection in haematopoietic tissues against HPRT-deficient cells arising as a result of X-chromosome inactivation. We have examined two situations in mice in which HPRT- and HPRT+ cells occur in the same individual. First, in chimaeras resulting from the injection of HPRT- embryonal stem cells into HPRT+ blastocysts the fate of HPRT- and HPRT+ cell populations was monitored by their expression of different isozymes of glucose phosphate isomerase and also, in those chimaeras that resulted from injecting the male ES cells into female blastocysts, by in situ hybridisation using a Y-chromosome-specific repetitive DNA probe. There was a small statistically significant selection against the HPRT- population in haematopoietic tissues in both XX in equilibrium with XY and XY in equilibrium with XY chimaeras. Second, in female mice doubly heterozygous for HPRT-deficiency and for an electrophoretic variant of the X-linked enzyme phosphoglycerate kinase, there was a similar small statistically significant selection against the HPRT- population in haematopoietic tissues. While further work is required to establish whether this selection is a consequence of the HPRT mutation, it is clear that any selection against cells in the haematopoietic system as a consequence of HPRT-deficiency is at most small compared with the effect seen in humans. In HPRT-deficient human males surviving beyond the normal age of puberty, there is testicular atrophy. However, we find no effect of HPRT-deficiency on the fertility of either male or female mice. Thus, as with effects on behaviour, the consequences of HPRT-deficiency for haematopoiesis and testis development in the mouse are at most small compared with those in the human. We conclude that the reason for the difference in effects between the two species lies in a difference in purine-related intermediary metabolism per se, rather than in its interaction with brain amine biochemistry.

Animals↗
PubMed1990

Interaction of vasopressin and oxytocin with human breast carcinoma cells.

The arginine vasopressin and oxytocin content of normal and cancerous human breast tissue were measured using radioimmunoassay. Both peptides were present in amounts greater than that found in the circulation, but no difference between normal and malignant tissues was found. Binding of [3H]oxytocin and [3H]vasopressin were characterized in human breast carcinoma cells (MCF7 cells). Binding of both hormones to MCF7 cells was specific and saturable, the vasopressin receptor found to be of the V1 subtype. Scatchard analyses of the data were linear, indicating a single high affinity, low capacity binding site for each hormone (vasopressin: KD = 47.4 +/- 1.6 nmol/liter, Bmax = 27,300 +/- 6,500 sites/cell; oxytocin: KD = 51.3 +/- 0.4 nmol/liter, Bmax = 87,000 +/- 4,000 sites/cell). The effects of vasopressin and oxytocin on the growth of MCF7 cells were assessed using protein accumulation and cell numbers. Vasopressin at 10-1000 pmol/liter was mitogenic for MCF7 cells, but higher doses (10 nmol/liter) were growth inhibitory. Oxytocin was also mitogenic for MCF7 cells but to a lesser extent than vasopressin. In conclusion, we suggest that vasopressin and possibly oxytocin may be important modulators of the growth of some human breast carcinomas.

Arginine Vasopressin↗
PubMed1990

Structure-function relationships among highly diverse T cells that recognize a determinant from influenza virus hemagglutinin.

We have analyzed the structural and genetic basis for T cell recognition of the complex formed between antigen and class II products of the major histocompatibility complex by performing sequence analysis of T cell receptors (TCRs) induced in response to the helper T cell site 1 of the influenza virus hemagglutinin. The results demonstrate, first, that structurally highly diverse TCRs can be utilized in recognition of the same antigen/I-Ed complex: 12 of 13 TCRs utilize unique V alpha/V beta gene segment combinations, suggesting that approximately 70 different V alpha/V beta combinations are available to BALB/c mice in response to this determinant. Second, comparison of these sequences with the ability of each hybridoma to recognize a panel of peptide analogues suggests that alpha and beta chains of these TCRs frequently determine specificity for the NH2-terminal and the COOH terminal portions, respectively, of the site 1 determinant.

Amino Acid Sequence↗
PubMed1990

Modulation of the biological activity of thyrotrophin by anti-human thyrotrophin monoclonal antibodies.

The mechanism by which monoclonal antibodies enhance the biological activity of a number of hormones is poorly understood. One such antibody (GC73), which binds to human but not bovine TSH, enhances the bioactivity of human TSH in vivo. We have investigated whether GC73 enhancement of TSH bioactivity involves potentiation of hormone-receptor activation assessed by the cyclic AMP (cAMP) responses of both primary human thyrocyte cultures and a TSH-responsive human thyrocyte cell line (SGHTL-45). GC73 had no effect on basal cAMP production. In contrast to its enhancement of the bioactivity of human TSH in vivo, it markedly inhibited the cAMP response to 1 and 10 mU human TSH/ml in primary thyrocytes. This effect was dose-dependent with neutralization of the bioactivity of TSH occurring at 2 mg GC73/ml. GC73 had no effect on the bioactivity of bovine TSH. In contrast, a second anti-TSH monoclonal antibody (TC12), which binds to both human and bovine TSH, inhibited the bioactivity of both species of TSH. Similar results were obtained using SGHTL-45 cells, although the peak concentrations of cAMP were lower. We conclude that binding of GC73 to human TSH resulted in inhibition rather than enhancement of the in-vitro biological activity of human TSH. We suggest that GC73 enhancement of human TSH bioactivity seen in vivo does not result from a mechanism involving potentiation of receptor activation by human TSH.

Antibodies, Monoclonal↗
PubMed1990

Binding of 125I-labelled thyrotrophin to transfected human thyrocytes (SGHTL-34 cells).

The binding of 125I-labelled bovine TSH to a human thyroid cell line (SGHTL-34) has been studied. Binding to hormonally responsive cells was time dependent, specific and reversible. Scatchard analysis of the binding data indicated the presence of a single binding site with high affinity (intrinsic dissociation constant (Kd) = 0.25 +/- 0.08 nmol/l; mean +/- S.E.M.; n = 4) and low capacity (maximum binding (Bmax) = 104 +/- 29 fmol/mg protein; mean +/- S.E.M.; n = 4). Hill plots confirmed the presence of a single site. Kinetic data demonstrated close agreement between the Kd and Bmax obtained from the competition data (Kd = 0.23 +/- 0.35 nmol/l; Bmax = 161 +/- 83 fmol/mg protein; n = 6).

Cell Line↗
PubMed1989

Cytotoxic effects of amiodarone and desethylamiodarone on human thyrocytes.

Since recent in vivo evidence suggests that the benzofuran antiarrhythmic drug amiodarone has a direct toxic effect on the human thyroid gland, we have investigated the effects of both amiodarone and its metabolite desethylamiodarone on a novel immortalized functional human thyrocyte line (SGHTL-34 cells). Desethylamiodarone markedly reduced cell number as assessed from both DNA and protein content. Few cells were left after 24 hr exposure to 12.5 micrograms/ml; the concentration producing death of 50% of cells (EC50) was 6.8 +/- 1.1 micrograms/ml (mean +/- SE, N = 15). Amiodarone was much less potent, producing a maximum decrease in cell number of approximately 25% at concentrations up to 50 micrograms/ml. The effect of desethylamiodarone was seen within 24 hr of culture. T3 in concentrations up to 0.75 micrograms/ml had no effect on the action of amiodarone or desethylamiodarone on SGHTL-34 cells. Light microscopy demonstrated vacuolation of SGHTL-34 cells after 4-day culture with either the drug or its metabolite. Studies using primary cultures of human retroorbital fibroblasts demonstrated that the greater cytotoxicity of desethylamiodarone was not confined to thyrocytes. When SGHTL-34 cells were incubated with 2.5 micrograms/ml desethylamiodarone for 4 days, 71.7 +/- 0.9% was taken up by the cells; there was no detectable conversion to amiodarone. Incubation of thyrocytes with 50 micrograms/ml amiodarone for 4 days resulted in the uptake of 80.1 +/- 2.1% by the cells. In addition, 5.0 +/- 0.1% of the amiodarone was converted to material with the same retention time as desethylamiodarone standard; of this material, 72.9 +/- 2.8% was taken up by the cells. We conclude that desethylamiodarone, at concentrations near those found in the plasma of patients on long-term amiodarone therapy, exerts a direct cytotoxic effect on human thyroid cells in short-term culture. This effect may play a role in the aetiology of clinical thyroid disease during amiodarone therapy. We suggest that, since the effect is not restricted to thyrocytes, desethylamiodarone may play a role in the aetiology of amiodarone toxicity which occurs clinically in many tissues.

Amiodarone↗
PubMed1989

The interaction of arginine vasopressin and oxytocin with bovine adrenal medulla cells.

Binding of [3H]arginine vasopressin (AVP) and [3H]oxytocin to primary monolayer cultures of bovine adrenal chromaffin cells was time-dependent, and the binding sites for each peptide were specific and saturable. Studies with the V1 AVP antagonist d(CH2)5Tyr(Me)2-AVP, the V2 agonist 1-deamino-8-D-AVP and the V2 antagonist d(CH2)5D-Leu2,Val4-AVP indicated that the AVP receptor was V1 in specificity. Scatchard plots showed that each ligand interacted with a single high-affinity, low-capacity binding site: oxytocin dissociation constant (Kd) 0.29 +/- 0.02 nmol/l, maximum binding capacity (Bmax) 7.6 +/- 0.2 fmol/10(6) cells (or 4500 +/- 102 sites/cell) (n = 3); AVP Kd 0.09 +/- 0.02 nmol/l, Bmax 5.1 +/- 0.63 fmol/10(6) cells (or 3050 +/- 318 sites/cell) (n = 3). Although forskolin in concentrations from 1 nmol/l to 1 mmol/l stimulated cyclic AMP (cAMP) production in isolated chromaffin cells, this did not result in detectable catecholamine release. Neither AVP nor oxytocin in concentrations between 10 pmol/l and 10 mumols/l stimulated cAMP production in these cells. Vasopressin in concentrations as low as 10 pmol/l stimulated a sixfold increase in total inositol phosphates; the dose-response curve was triphasic. Oxytocin had little effect on total inositol phosphate accumulation at low concentrations, but concentrations above micromolar stimulated total inositol phosphate production approximately fourfold. There was no measurable release of catecholamines in response to either peptide. The physiological consequences of these AVP-induced changes in inositol phosphate concentrations remain to be elucidated.

Adenylyl Cyclases↗
PubMed1988

Hemagglutinin polymorphism as the basis for low- and high-yield phenotypes of swine influenza virus.

Single amino acid substitutions at the rim of the receptor binding site of the hemagglutinin molecule of swine influenza virus markedly influence the replicative capacity of the virus in chicken embryos, Madin-Darby canine kidney cells (MDCK), and swine as well as its antigenic phenotype. Mutants of low-yield (L) phenotype replicate poorly in chicken embryos and produce small plaques in MDCK cells but are highly infective for swine. Such mutants have lysine at position 153 and glycine at position 155 of the hemagglutinin (residues 156 and 158 in the H3 model). High-yield (H) mutants have the converse replicative characteristics and can be antigenically distinguished from L mutants (and from each other) based on their differential reactivity with two monoclonal antibodies, 9C8 and Sa-13. H mutants differ from L mutants in that the H mutants express glutamic acid at either position 153 or 155. L and H mutants act in an allelic fashion in effecting predictable one-step adaptation to different hosts. Selection for replication (e.g., high-yielding) phenotype results in concordant pleiotropic change in antigenic phenotype and in genotype. Conversely, immunoselection leads to change in replicative phenotype. Although the mechanism by which these mutations affect viral replication has not yet been defined, they may reflect differences in the affinity of each mutant for different host receptors.

Animals↗
PubMed1984

Rotavirus-specific antibodies in fetal bovine serum and commercial preparations of serum albumin.

Rotavirus-specific antibodies were detected in fetal bovine serum, bovine serum albumin, and human serum albumin by radioimmunoprecipitation with the NCDV strain of bovine rotavirus as the detecting antigen. Fetal bovine sera neutralized bovine rotavirus in a plaque reduction neutralization test to titers of 1:20 or greater. Immunoglobulins purified from fetal bovine serum by protein A-agarose affinity chromatography precipitated rotavirus antigens but did not neutralize bovine rotavirus. Rotavirus antibodies in fetal bovine serum and in purified serum albumin preparations may interfere with diagnostic assays for the detection of rotavirus antigens or antibodies.

Animals↗
PubMedDate not supplied

C-terminal truncation of WT1 delays but does not abolish hematopoiesis in embryoid bodies.

The effect of mutations that truncate the WT1 protein on in vitro hematopoietic differentiation from embryonal stem cells has been examined by CFU-A assay, o-dianisidine staining for heme, and RT-PCR analysis of the expression of fetal and adult globins. In two independently isolated ES cell lines the mutations delay but do not abolish hematopoiesis. Analysis of replated CFU-A colonies indicates that the delay occurs prior to the formation of hematopoietic stem cells. The results demonstrate a role for WT1 at the onset of hematopoiesis.

Animals↗
PubMedDate not supplied

Effect of arginine vasopressin and oxytocin on acetylcholine-stimulation of corticosteroid and catecholamine secretion from the rat adrenal gland perfused in situ.

The effects of acetylcholine, arginine vasopressin (AVP) and oxytocin (OXT) on both catecholamine and steroid secretion have been investigated using the isolated rat adrenal gland perfused in situ. Significant stimulation of steroid (aldosterone and corticosterone) secretion occurred with 1 mumol/l acetylcholine; the ED50 was approximately 20-fold higher (circa 20 mumol/l) than that for catecholamine secretion. The highest concentration of acetylcholine used (100 mumol/l) stimulated aldosterone secretion eight-fold; corticosterone secretion four-fold; noradrenaline and adrenaline secretion three-fold. AVP at 100 nmol/l but not at 1 nmol/l significantly stimulated the secretion of both steroids and catecholamines. OXT had no significant effect on corticosteroid or catecholamine secretion at either concentration. The effects on aldosterone secretion of simultaneous administration of acetylcholine and AVP were additive. No similar effect was seen on corticosterone or catecholamine secretion where the degree of stimulation was the same as for acetylcholine alone. OXT (100 nmol/l) inhibited acetylcholine-stimulated aldosterone secretion but had no effect on acetylcholine-stimulated catecholamine secretion. Carbachol was equipotent with acetylcholine in stimulating steroid secretion from the perfused gland. Our results support the hypothesis that acetylcholine may play a role in the control of steroid secretion by the rat adrenal cortex. They fail to support a role for AVP and OXT in modulating catecholamine secretion by the adrenal medulla except at high concentrations.

Acetylcholine↗