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Biomedical subjects

A J Watson

Publications and source records attributed to A J Watson.

At least 163 records · Page 9Linked to original sources
PubMed1992

Expression of bovine trophoblast interferon in conceptuses derived by in vitro techniques.

Expression of the trophoblast interferon, bovine trophoblast protein-1 (bTP-1), has been studied in embryos produced by in vitro maturation-in vitro fertilization (IVM-IVF). No bTP-1 production was noted until after embryos had reached the expanded blastocyst stage and had begun to hatch (Days 8-9 post-fertilization). Single blastocysts comprising 115 +/- 22 cells released 1.0 +/- 0.1 units of interferon activity/24 h. Amplification of conceptus mRNA by reverse transcription-polymerase chain reaction procedure with bTP-1-specific oligonucleotides confirmed that bTP-1 transcripts were present in blastocysts but were not detectable at earlier stages. Although cultured blastocysts produced by IVM-IVF procedures continued to secrete bTP-1 for a few days, they failed to attach to the substratum and form outgrowths, and soon lost structural integrity. However, when Day 8 blastocysts/morulae were transferred to the uteri of synchronized cows, recovered 4 days later, and placed into individual cultures, they attached and formed outgrowths that produced large amounts of bTP-1 (greater than 2000 units/culture/24 h after 14 days). Embryos thus first expressed bTP-1 when a functional trophectoderm was first formed, and induction did not require a period of in vivo development. However, continued viability of the blastocyst and bTP-1 production were not sustained in vitro and may require some exposure to the uterine environment.

Animals↗
PubMed1992

Dominant role for osmolality in the efficacy of glucose and glycine-containing oral rehydration solutions: studies in a rat model of secretory diarrhoea.

The effect of osmolality on the efficacy of oral rehydration solutions (ORS) and the contribution of the amino acid glycine to water absorption from ORS have been studied in an animal model of secretory diarrhoea. After exposure to pure cholera toxin, rat small intestine (excluding the duodenum) was perfused in situ with seven different ORS. All ORS were derived from a "basic" solution containing Na 50, K 25, Cl 75 and glucose 50 mmol/l to which 25 or 50 mmol/l of glycine, glucose, or mannitol was added. All ORS reversed water secretion to absorption, but maximum water absorption was obtained with the "basic" solution with an osmolality of 200 mOsm/kg. When the osmolality of the "basic" solution was raised to 225 and 250 mOsm/kg by adding mannitol, water absorption decreased. At each of these osmolalities, substitution of mannitol by glycine or glucose resulted in similar increases in water absorption, but all modifications compared unfavourably with the "basic" solution. Net sodium secretion occurred with all ORS tested, despite net water absorption. These findings in a perfusion model of rat small intestine suggest that osmolality is a key factor influencing the efficacy of ORS and that addition of a second substrate, such as glycine, has no beneficial effects. Our results suggest that there is a maximal rate for water absorption from the small intestine which is inversely related to the osmolality of the perfusate.

Animals↗
PubMed1992

Mechanism of action of a repressor of dioxin-dependent induction of Cyp1a1 gene transcription.

A dominant mutant of Hepa-1 cells, c31, expresses a repressor that prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-dependent stimulation of Cyp1a1 transcription. The repressor acts via the xenobiotic-responsive elements (XREs), which are the DNA-binding sites for the aryl hydrocarbon (Ah) receptor-TCDD complex during transcriptional activation of the gene. High-salt nuclear extracts prepared from c31 cells grown with TCDD contained normal levels of the Ah receptor which bound the XRE with normal affinity, as judged by in vitro gel mobility shift assays. Furthermore, extracts prepared from these cells, grown either with or without TCDD, contained no novel XRE-binding proteins compared with extracts from wild-type Hepa-1 cells. However, in vivo genomic footprinting demonstrated that TCDD treatment leads to binding of the Ah receptor to the XREs in Hepa-1 but not mutant cells. This finding suggests that the repressor associates with the Ah receptor to prevent its binding to the XREs and that high-salt treatment either causes dissociation of the receptor/repressor complex or fails to extract the repressor from nuclei. The results underscore the importance of using both in vivo and in vitro assays for analyzing DNA-protein interactions.

Animals↗
PubMed1991

Modulation by verapamil of vincristine pharmacokinetics and sensitivity to metaphase arrest of the normal rat colon in organ culture.

The in-vitro pharmacokinetics of vincristine (VCR) in normal rat colonic mucosa were studied. Two complementary approaches were adopted using an explant organ-culture system. Firstly [G-3H]vincristine (3HVCR) accumulation, retention and efflux were characterized under basal conditions and compared with measurements made either under energy-depleted conditions, or in the presence of VRP. Secondly, a histological method--the postmetaphase index (PMI)--was used to compare the sensitivity of explants to VCR in the presence or absence of verapamil (VRP). This latter technique involves the measurement, by counting, of the proportion of mitotic figures escaping from metaphase arrest. The studies yielded the following results: 3HVCR accumulation in colonic mucosa showed no evidence of saturability up to the maximum dose studied (130 nM), at a dose of 52 nM accumulation was enhanced in energy-depleted conditions by a factor of 1.8, and in the presence of VRP (6.6 microM) by a factor of 1.4. In the presence of VRP (6.6 microM) retention of 3HVCR was increased by a factor of 1.3 and efflux was reduced by a factor of 0.8 after 2 hr. VRP (6.6 microM) reduced the PMI of colonic mucosal epithelial cells exposed to 11 nM VCR from 18.8% to 11.4% (i.e. 40% reduction) indicating sensitization of the cells to this property of VCR. These results provide evidence that the sensitivity of normal colonic mucosa to vincristine is, at least in part, regulated by drug transport. Qualitatively our observations resemble those described in multidrug resistance. Given that P-glycoprotein has been demonstrated by several groups in colonic mucosal cells, the results support a normal role for this membrane transport molecule in the protection of intestinal cells from plant alkaloids and other xenobiotic agents ingested in the diet.

Animals↗
PubMed1991

Molecular cloning and expression of a cDNA encoding the rabbit ileal villus cell basolateral membrane Na+/H+ exchanger.

A cDNA clone encoding a rabbit ileal villus cell Na+/H+ exchanger was isolated and its complete nucleotide sequence was determined. The cDNA is 4 kb long and contains 322 bp of 5'-untranslated region, 2451 bp of open reading frame and 1163 bp of 3'-untranslated area, with 70%, 91% and 40% identity to the human sequence, respectively. Amino acid sequence deduced from the longest open reading frame indicated a protein of 816 residues (predicted Mr 90,716) which exhibits 95% amino acid identity to the human Na+/H+ exchanger. The two putative glycosylation sites in the human Na+/H+ exchanger are conserved in this protein, suggesting that it is a glycoprotein. Stable transfection of the cDNA into an Na+/H+ exchanger deficient fibroblast cell line, established Na+/H+ exchange. The Na+/H+ exchanger was stimulated by serum and a phorbol ester but not by 8-Br-cAMP. In Northern blot analysis, the cDNA hybridized to a 4.8 kb message in rabbit ileal villus cells, kidney cortex, kidney medulla, adrenal gland, brain and descending colon and to a 5.2 kb message in cultured human colonic cancer cell lines, HT29-18 and Caco-2. In immunoblotting, a polyclonal antibody raised against a fusion protein of beta-galactosidase and the C-terminal 158 amino acids of the human Na+/H+ exchanger identified a rabbit ileal basolateral membrane protein of 94 kd and only weakly interacted with the ileal brush border membrane. In immunocytochemical studies using ileal villus and crypt epithelial cells, the same antibody identified basolateral and not brush border epitopes. Restriction analysis of genomic DNA with a 462 bp PstI-AccI fragment of the rabbit Na+/H+ exchanger strongly suggests the existence of closely related Na+/H+ exchanger genes. The near identity of the basolateral Na+/H+ exchanger and the human Na+/H+ exchanger plus the ubiquitous expression of this message suggests that the ileal basolateral Na+/H+ exchanger is the 'housekeeping' Na+/H+ exchanger.

Amino Acid Sequence↗
PubMed1991

Effects of maturation and co-culture treatments on the developmental capacity of early bovine embryos.

A total of 901 cumulus-oocyte complexes (COCs) were collected from bovine ovaries obtained at a local abattoir. COCs randomly assigned to Treatment I (n = 451), were cultured in TCM-199 + 10% fetal bovine serum (FBS) and hormones, while oocytes in Treatment II (n = 450) were cultured in TCM-199 + 20% estrous cow serum (ECS). Assessment of maturation revealed that 91.3% (42/46) of oocytes in Treatment I had reached metaphase II of meiosis, which was greater (P less than 0.05) than the 73.3% (33/45) in Treatment II. Following in vitro fertilization, 203 oocytes from Treatment I were co-cultured on bovine granulosa cells (Treatment IA) while the remaining 202 oocytes were co-cultured on bovine oviductal cells (Treatment IB). Similarly, 203 oocytes from Treatment II were co-cultured on granulosa cells (Treatment IIA) or oviductal cells (Treatment IIB, n = 202). Co-culture was maintained for 8 days. The proportion of cleaved zygotes was higher (P less than 0.05) in Treatment IB (86.6%) compared to Treatments IA (78.8%), IIA (58.1%), and IIB (64.8%). The proportion of cleaved zygotes that progressed beyond the 16-cell stage was also greater (P less than 0.001) in Treatment IB (71.4%) compared to Treatments IA (50.0%), IIA (35.4%) and IIB (55.8%). Treatment IB also produced the highest proportion of blastocysts (P less than 0.0001) (41.1%) versus 24.6% (IA), 11.3% (IIA) and 18.3% (IIB). The proportion of day 6 morulae that progressed to form day 8 blastocysts was similar for both co-culture treatments (IA, 70.1%; IB 70.2%; IIA, 51.5%; IIB 50.8%) and varied only between in vitro maturation groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Organ culture as a model for investigating the effects of antimetabolites and nucleoside transport inhibitors on rodent colonic mucosa.

The in-vitro effects of hydroxyurea 5-FU and 5-FUdR have been extensively studied in experimental systems employing cell-line techniques. In this study we investigated the effects of these drugs on the levels of incorporation of labeled nucleosides into DNA in explants of intact rat colonic mucosa maintained in organ culture. The effects of the nucleoside transport inhibitors nitrobenzylthioinosine (NBMPR) and dipyridamole--which are modulators of antimetabolite cytotoxicity--on the incorporation of tritiated thymidine ([3H]TdR) into DNA were also studied. The incorporation of tritiated TdR into DNA was reduced by hydroxyurea but was not altered by either 5-FU or 5-FUdR. The levels of tritiated deoxyuridine were reduced by 5-FU and 5-FUdR in separate experiments; this is in keeping with thymidylate synthase inhibition. NBMPR and dipyridamole also reduced 3H-TdR incorporation into DNA. These results can be explained in terms of the known mechanisms of action of these drugs. This experimental model is therefore useful in assessing the effects of antimetabolites and nucleoside transport inhibitors in intact colonic mucosa.

Animals↗
PubMed1991

Genetic and molecular analysis of the Ah receptor and of Cyp1a1 gene expression.

The Ah receptor is a soluble protein complex that mediates carcinogenesis by a wide range of environmental pollutants, including polycyclic aromatic hydrocarbons, heterocyclic amines, and polychlorinated aromatic compounds. The best understood activity of the receptor concerns its role in the induction of cytochrome P450IA1. We undertook a somatic cell genetic analysis of P450IA1 induction using the mouse hepatoma cell line, Hepa-1. Clones of Hepa-1 were isolated that are defective in induction of P450IA1. Evidence was obtained that the clones are mutational in origin. Cell fusion experiments demonstrated that a few of the mutants are dominant, while the majority are recessive. The dominant mutants were shown to synthesize a repressor of P450IA1 transcription. The recessive mutants were assigned to 4 complementation groups (probably corresponding to 4 different genes). Complementation group A corresponds to the P450IA1 structural gene. Mutations in the B, C and D genes all affect functioning of the Ah receptor. A 'reverse selection procedure', whereby cells that express P450IA1 inducibility can be selected from a majority population of cells lacking inducibility, was developed. The reverse selection procedure was used to isolate transfectants of representative recessive mutants in which the mutational defects are complemented by exogenously applied genomic DNA. A human DNA-derived transfectant of a C- mutant was used to clone the human C gene. The C gene is not the ligand-binding subunit of the Ah receptor but is a protein that is required for translocation of Ah receptor-ligand complexes from cytoplasm to nucleus. In analogous experiments the dominant gene from one of the dominant mutants was transfected into wild-type Hepa-1 cells. Success in transfecting the dominant gene should provide the means for cloning it.

Animals↗
PubMed1991

Experimental stray light in retinal densitometry.

The effects of stray light upon retinal pigment densitometric measurements were evaluated by adding specified amounts of stray light to fundus reflections. To allow for interpolations and extrapolations, a computer simulation was devised and validated against the empirical data. The results demonstrate that measured density is greatly decreased by increases in stray light but the time constant of pigment regeneration is little affected.

Computer Simulation↗
PubMed1991

Effects of gastrointestinal peptides on azoxymethane-treated colonic mucosa in vitro.

An organ-culture system has been used to investigate the effect of certain gastrointestinal peptides on the morphology and cell proliferation of explants of azoxymethane (AOM)-treated colonic mucosa. Our aim was to ascertain whether such factors play a direct part in the maintenance of hyperplastic changes in the large intestine. Explants of AOM-treated colonic mucosa from 15 animals were maintained in a serum-free medium in the presence of either gastrin-17 (250 pg/ml and 250 ng/ml), peptide YY (80 pmol/l and 160 pmol/l) epidermal growth factor (EGF) (10 ng/ml and 100 ng/ml) or the C-terminal fragment of glucagon-37 (30 pmol/l) for a period of up to 7 days. Other explants (controls) received fresh medium only each day. After 1, 2, 3, 5 and 7 days of culture both experimental and control explants received vincristine (4 micrograms/ml) for 3 h prior to fixation. The proportion of vincristine-arrested metaphases within the explants was determined together with crypt length. Neither gastrin nor peptide YY was found to influence cell division at either concentration. Despite an initial inhibitory effect, both concentrations of EGF exerted a trophic effect which increased with time. The glucagon-37 fragment caused an immediate increase in proliferation which then declined as time progressed. None of these factors, however, were able to maintain the hyperplastic changes seen in the pre-culture samples of AOM-treated mucosae.

Animals↗
PubMed1991

Search for the ideal oral rehydration solution: studies in a model of secretory diarrhoea.

In situ perfusion of whole rat small intestine was used to compare the efficacy of five oral rehydration solutions in promoting water and sodium absorption in normal intestine and secreting intestine after exposure to cholera toxin. Solutions varied in their sodium (35-90 mmol/l) and glucose (111-200 mmol/l) concentrations, molar ratio of glucose:sodium (1.2-5.8), and osmolality (281-331 mOsmol/kg), and contained either bicarbonate (18-30 mmol/l) or citrate (10 mmol/l). In normal intestine all solutions promoted net water absorption. Cholera toxin induced reproducible water secretion but all solutions reversed this to absorption. Water absorption was greatest with solutions containing sodium 60 mmol/l and glucose 111 or 140 mmol/l, and with a glucose:sodium ratio approximately 2, in both normal and secreting intestine. All solutions promoted net glucose absorption in both normal and secreting intestine. Net sodium absorption occurred with solutions containing greater than or equal to 60 mmol/l sodium in normal intestine but sodium secretion occurred from all solutions in secreting intestine. Sodium movement was directly related to the sodium concentration of the solution and sodium secretion occurred despite net water and glucose absorption. We consider that these studies may guide future development of oral rehydration solutions.

Animals↗
PubMed1991

Acetate uptake by intestinal brush border membrane vesicles.

The mechanism of acetate absorption in the small intestine is not yet established. One possible mechanism is by carrier mediated Na(+)-acetate cotransport since acetate, like glucose, stimulates intestinal Na+ and water absorption in vivo. Uptake of radioactive carbon acetate by small intestinal brush border membrane vesicles was not saturable or Na+ dependent and did not respond to osmotic shrinkage of the vesicles. This suggests that acetate binds to the membranes but is not transported into the intravesicular space and argues against carrier mediated Na+ acetate cotransport. These results are consistent with acetate absorption by a non-mediated diffusion and suggest that the stimulation of water and Na+ absorption by acetate in vivo is largely due to osmotic forces and solvent drag.

Acetates↗
PubMed1991

Kinetics and regulation of a polarized Na(+)-H+ exchanger from Caco-2 cells, a human intestinal cell line.

The kinetics and regulation of Na(+)-H+ exchange were studied using BCECF to measure pHi in Caco-2 cells grown on membrane filters. Na(+)-H+ exchange was defined as a Na(+)-dependent H+ efflux in response to an acid load imposed by an NH4Cl prepulse in the absence of added CO2. Na(+)-H+ exchange was present exclusively on the basolateral membrane, had a Kt (Na+) of 21 +/- 2 mM, and an ID50 for amiloride dependent on medium [Na+] with an apparent Ki for amiloride of 3 microM. Na(+)-H+ exchange rates had a greater than first-order dependence on intracellular [H+], suggesting the presence of an internal proton modifier site. Results also suggest that Na(+)-H+ exchange is kinetically inactivated at resting pHi (7.35 +/- 0.02), since neither removal of Na+ nor addition of amiloride affected resting pHi, although monensin alkalinized cells to pHi 7.6. To evaluate regulation of Na(+)-H+ exchange, cells were exposed to either forskolin, 1,9-dideoxyforskolin (a noncyclase-activating forskolin derivative), 8-BrcAMP, E. coli STa toxin, ionomycin, phorbol dibutyrate, or cellular shrinkage in hypertonic medium. Only forskolin and 1,9-dideoxyforskolin caused a significant change (inhibition) in Na(+)-H+ exchange rate. Experiments performed with the Ussing chamber-voltage clamp technique verified that forskolin, 8-BrcAMP, E. coli STa toxin, ionomycin, and phorbol dibutyrate increased transepithelial Isc, verifying that all the regulatory pathways tested were functional and responsive to agonists. Results suggested that the Isc was due to Cl- secretion, since no net transcellular Na+ or Cl- flux was detected in basal conditions, and the Isc response to forskolin was abolished by omission of serosal Cl-. Because forskolin, but not 1,9-dideoxyforskolin, increased both cellular cAMP and Isc, the inhibition of Na(+)-H+ exchange by forskolin derivatives was mediated by a mechanism not involving activation of adenylyl cyclase. In conclusion, Caco-2 cells use a basolateral Na(+)-H+ exchanger to regulate pHi, but this exchanger is not affected by cell shrinkage or second messenger pathways that regulate Na(+)-H+ exchangers in other cell systems.

Amiloride↗
PubMed1991

Characterization of the synergistic interaction of Escherichia coli heat-stable toxin and carbachol.

STa, the heat-stable enterotoxin of Escherichia coli, is a specific activator of membrane-bound guanylyl cyclase and stimulates secretion of Cl- in a human colonic carcinoma cell line (T84). We investigated the effect of the cholinergic agent carbachol on the secretory response to STa. T84 cell monolayers were studied under voltage-clamped conditions in modified Ussing chambers. Simultaneous addition of STa and carbachol resulted in a biphasic synergistic response characterized by a brief peak in short-circuit current (Isc) followed by a prolonged plateau phase lasting up to 90 min. A synergistic response was also seen with sequential addition of the agonists, and was altered by the order and timing of agonist addition. Pretreatment with STa enhanced the synergistic response to carbachol, while the reverse order of additions produced synergy only when STa was added during or immediately after the Isc response to carbachol. Synergy occurred only with a concentration of STa sufficient to produce an Isc response alone. However, a concentration of carbachol that caused neither an increase in Isc nor intracellular Ca2+ mobilization was sufficient to evoke a synergistic response. Addition of 8-bromoguanosine 3',5'-cyclic monophosphate also produced a synergistic Isc response with carbachol, although maximal synergism was seen with simultaneous addition. Augmentation of the intracellular Ca2+ response to carbachol by STa is not the mechanism of synergy. Although the mechanism of synergy is not understood, these studies suggest that STa-induced cGMP interacts with other second messengers to produce the synergistic response, and that multiple intracellular mediators may influence the ability of STa to cause disease.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Expression of a human O6-alkylguanine-DNA-alkyltransferase cDNA in human cells and transgenic mice.

A truncated human O6-alkylguanine-DNA-alkyltransferase (ATase) cDNA was ligated into an expression vector under the control of the mouse metallothionein-1 gene promotor and upstream of part of the human growth hormone gene to provide splice and polyadenylation signals. Transfection of this construct into human cells resulted in very high levels of ATase expression (more than 300 fmoles/mg protein versus less than 2 fm/mg protein in parent vector transfected control cells). Microinjection of a 4.2 kb fragment of this vector into B6D2F2 mouse embryos and implantation of survivors into pseudopregnant females has so far generated 35 offspring. Southern analysis of tail tip DNA has shown that 11 of the offspring are transgenic for the human ATase gene, between 1 and at least 30 copies of the gene being detected. Human ATase transcripts were detected in total RNA extracted from liver obtained from two male transgenic mice by partial hepatectomy. Cell free extracts of liver samples from five transgenic mice showed up to 4 times higher ATase levels than control livers.

Animals↗
PubMed1990

Cell polarity and development of the first epithelium.

In the 4 1/2 to 5 days between fertilization and implantation, the mouse conceptus must gain the abilities to implant and produce an embryo. Each of these is the sole developmental responsibility of one of two cell types forming the blastocyst, trophectoderm and inner cell mass (ICM), respectively. Trophectoderm is a polarized transporting epithelium while the ICM is an aggregate of non-epithelial pluripotent stem cells. These two cell types originate from the division of polar blastomeres when their cleavage furrows parallel their apical surfaces. Blastomeres polarize in response to asymmetric cell--cell contact, and understanding the mechanism of this induction is regarded as the key to understanding the origin of trophectoderm and ICM. Here we propose a model based on transcellular ion current loops for the induction of cell polarity during the development of the first epithelium, trophectoderm.

Animals↗
PubMed1990

Expression of Na,K-ATPase alpha and beta subunit genes during preimplantation development of the mouse.

Na,K-ATPase is a plasma membrane enzyme that plays a critical role in eutherian blastocoel formation (cavitation) by pumping Na+ into the extracellular space enclosed by the trophectoderm. Previous experiments with the mouse had shown that the alpha (catalytic) subunit of the enzyme becomes detectable by immunocytochemistry in the late morula, just prior to the onset of cavitation. In the present study we have used cDNAs corresponding to three mRNA isoforms of the alpha subunit and a beta subunit to determine which genes are expressed during preimplantation development and to explore the timing of their expression. Of the three alpha subunit cDNAs tested by Northern blot hybridization with blastocyst RNA, only alpha 1 produced a hybridization signal, recognizing a single mRNA about 4 kb in length. This mRNA is relatively abundant in zygotes but barely detectable by the 2-cell stage and then accumulates steadily thereafter to reach its preimplantation maximum in blastocysts. The beta 1 cDNA detected mRNA of about 2.6-2.8 kb. This mRNA is present in zygotes but could not be detected in 2-, 4-, or 8-cell stages; it is present at a low level in late morulae and is abundant in blastocysts. The temporal profile of accumulation of beta 1 mRNA thus matches more closely than does alpha 1 the timing of appearance of the catalytic subunit. This suggests that the beta subunit may regulate production of the holoenzyme and hence the timing of cavitation.

Animals↗