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T Wells

Publications and source records attributed to T Wells.

At least 19 recordsLinked to original sources
PubMed2006

Comparative analysis of the effects of ghrelin and unacylated ghrelin on luteinizing hormone secretion in male rats.

Ghrelin, the endogenous ligand of GH secretagogue receptor type 1a, has emerged as pleiotropic modulator of diverse biological functions, including energy homeostasis and, recently, reproduction. Although inhibitory actions of ghrelin on LH secretion and puberty onset have been reported previously, the receptor mechanisms mediating these actions, and the potential gonadotropic effects of the unacylated isoform of ghrelin (UAG), remain unclear. In this work, the effects of single and repeated administration of ghrelin or UAG on LH secretion were compared in pubertal and adult male rats. In addition, the effects of ghrelin were assessed in models of transient or persistent hypergonadotropism. Daily injection of ghrelin or UAG throughout puberty similarly decreased LH levels and partially delayed balanopreputial separation. Likewise, chronic infusion of ghrelin or UAG to adult males resulted in significant decreases in circulating LH and FSH concentrations. Moreover, acute injection of ghrelin induced a transient reduction in LH levels in freely moving males, an effect that was fully mimicked by administration of UAG. Yet in contrast to ghrelin, UAG failed to modify GH secretion. Finally, injection of ghrelin moderately, but significantly, reduced the duration of LH secretory responses to the potent gonadotropin secretagogue kisspeptin-10, whereas ghrelin infusion in a model of chronic elevation of serum gonadotropin levels (the transgenic growth retarded male rat) evoked a significant reduction of LH concentrations. Altogether our present results further substantiate the inhibitory effect of ghrelin on basal and stimulated LH secretion in a wide array of experimental conditions. Moreover, our data are the first to demonstrate the ability of UAG, originally considered an inert form of the molecule, to mimic the actions of acylated ghrelin on LH release. These observations reinforce the contention that ghrelin, as putative signal for energy insufficiency, may operate as negative modifier of male puberty and LH secretion, an effect that might be, at least partially, conducted through a GH secretagogue receptor type 1a-independent mechanism.

Animals↗
PubMed2006

Hypothalamic expression of human growth hormone induces post-pubertal hypergonadotrophism in male transgenic growth retarded rats.

Growth hormone (GH) is known to regulate peripheral components of the hypothalamo-pituitary gonadal (HPG) axis, but it remains unclear whether GH exerts a significant influence on the activity of the hypothalamo-pituitary components of the HPG axis. In this study, we investigated the development of HPG axis function in the male transgenic growth retarded (Tgr) rat, a model of moderate systemic GH deficiency caused by hypothalamic expression of human (h)GH. Impaired postnatal somatotroph expansion and moderate GH deficiency in male Tgr rats were accompanied by a two- to three-fold increase in pituitary gonadotrophin content, but without a significant change in the pituitary gonadotroph population. A three- to nine-fold elevation in basal circulating luteinising hormone concentration was seen in postpubertal Tgr rats, with a smaller increase in follicle-stimulating hormone. Despite this hypergonadotrophism, there was no corresponding increase in steroidogenic (circulating testosterone and seminal vesicle weights) or gametogenic (spermatozoa counts in seminiferous tubules) activity in the postpubertal Tgr testis. Following puberty, the plasma leptin concentration also became progressively elevated in Tgr males. Circulating gonadotrophin and leptin levels were normalised in Tgr rats by peripheral physiological replacement of rat GH, but plasma testosterone concentration was unaffected. These results confirm that hGH exerts a positive influence on the central control of gonadotrophin secretion in the Tgr rat, but the absence of a corresponding elevation in the steroidogenic or gametogenic function of the Tgr testis implies that the peripheral GH/insulin-like growth factor I axis may also exert a permissive influence on testicular function. The relative contribution of somatogenic and lactogenic mechanisms and the potential influence of elevated leptin and decreased sensitivity to androgen feedback to the development of postpubertal hypergonadotrophism in Tgr males remain to be determined.

Animals↗
PubMed2006

Reducing transfer times for coronary angiography in patients with acute coronary syndromes: one solution to a national problem.

BACKGROUND: Patients with acute coronary syndrome (ACS) are at high risk of further cardiac events and benefit from early intervention, as reflected by international guidelines recommending early transfer to interventional centres. The current average waiting time of up to 21 days contravenes evidence based early intervention, creates geographical inequity of access, wastes bed days, and is unsatisfactory for patients. METHODS: A regional transfer unit (RTU) was created to expatriate access of ACS patients referred from other centres to the revascularisation service. By redesigning the care pathway patients arriving on the RTU undergo angiography within 24 hours, and then leave the RTU the following day, allowing other ACS patients to be treated. RESULTS: During the first six months of the RTU, the mean waiting time from referral to procedure decreased from 20 (SD 15) days (range 0-51) to 8 (SD 3) days (range 0-21) for 365 patients transferred from a district general hospital. Ninety seven per cent of patients underwent angiography within 24 hours, 61% having undergone percutaneous coronary intervention at the same sitting, and 78% were discharged home within 24 hours. CONCLUSIONS: Delivering standards laid out in the National Service Framework, reducing inequalities of care across the region, and facilitating evidence based strategies of care represents a challenging and complex issue. For high risk patients suffering ACS who need early invasive investigation, a coordinated network wide approach together with the creation of an RTU resulted in a 62% reduction in waiting times for no extra resources. Further improvements can be expected through increased capacity of this verified strategy.

Angioplasty, Balloon, Coronary↗
PubMed2004

Manipulating sorting signals to generate co-expression of somatostatin and eGFP in the regulated secretory pathway from a monocistronic construct.

Targeted overexpression of biologically active peptides represents a powerful approach to the functional dissection of neuroendocrine systems. However, the requirement to generate separate, biologically active and reporter molecules necessitates the use of internal ribosome entry site (IRES) technology, which often results in preferential translation of the second cistron. We report here a novel approach in which the proteolytic processing machinery of the regulated secretory pathway (RSP) has been exploited to generate multiple mature proteins from a monocistronic construct that encodes a single precursor. This was achieved by duplication of the pre-pro cleavage sites in pre-prosomatostatin cDNA. The duplicated site included 10 flanking amino acids on either side of the Gly-Ala cleavage position. This enabled the incorporation of a foreign protein-coding sequence (in this case, enhanced green fluorescent protein (eGFP)) between these sites. The pre-eGFP-prosomatostatin (PEPS) construct generated co-localized expression of fully processed eGFP and somatostatin to the RSP of transiently transfected AtT20 cells. This approach represents an advance upon bicistronic and other extant approaches to the targeting of multiple, biologically active proteins to neuroendocrine systems, and, importantly, permits the co-expression of fluorescent markers with biologically active neuropeptides. In this study, our demonstration of the fusion of the first 10 amino acids of the prosomatostatin sequence to the N-terminus of eGFP shows that this putative sorting sequence is sufficient to direct expression to the RSP.

Animals↗
PubMed2003

Morphological determinants of femoral strength in growth hormone-deficient transgenic growth-retarded (Tgr) rats.

UNLABELLED: The extent to which childhood GHD affects adult fracture risk is unclear. We measured femoral strength in adult transgenic growth-retarded rats as a model of GHD. Long-term, moderate GHD was accompanied by endocrine and morphometric changes consistent with a significant reduction in femoral strength. INTRODUCTION: Childhood growth hormone deficiency (GHD) is associated with osteopenia, but little is known about its effects on subsequent adult bone strength and fracture risk. MATERIALS AND METHODS: We have therefore measured femoral strength (failure load measured by three-point bending) in a new model of moderate GHD, the transgenic growth-retarded (Tgr) rat at 15, 22-23, and 52 weeks of age, and have quantified potential morphological and endocrine determinants of bone strength. RESULTS: Skeletal growth retardation in Tgr rats was accompanied by a sustained reduction in the anterior-posterior diameter of the femoral cortex, whereas mid-diaphyseal cortical wall thicknesses were largely unaltered. Total femoral strength was significantly impaired in Tgr rats (p < 0.01), and this impairment was more pronounced in males than females. Compromised bone strength in Tgr rats could not be accounted for by the reduction in mechanical load (body weight) and was not caused by impairment of the material properties of the calcified tissue (ultimate tensile stress), despite marked reductions in femoral mineral density (areal bone mineral density; p < 0.001). Microcomputerized tomographical analysis revealed significant modification of the architecture of trabecular bone in Tgr rats, with reductions in the number and thickness of trabeculae (p < 0.05) and in the degree of anisotropy (p < 0.01). The marked reduction in plasma insulin-like growth factor-1 in Tgr rats was accompanied by the development of high circulating leptin levels (p < 0.01). CONCLUSION: These results show that the changes in endocrinology and bone morphology associated with long-term moderate GHD in Tgr rats are accompanied by changes consistent with a significant reduction in the threshold for femoral fracture.

Age Factors↗
PubMed2002

Stimulus-specific induction of an Egr-1 transgene in rat brain.

Regulated expression of Egr-1 (Zif268/NGFIA) in a variety of brain networks suggests a diversity of roles in neuronal plasticity. Here, we aimed to determine whether an egr-1 transgene would mediate transcriptional responses to different pharmacological and physiological stimuli in the brain of transgenic rats. Constitutive transgene expression was observed in the cortex, CA1 hippocampal area and pituitary, recapitulating expression of egr-1. Transgene induction was stimulus-specific. Metrazole induced widespread expression in the dentate gyrus, CA2 and CA3 areas, amygdala, and ventromedial nucleus. In contrast, induction following a light stimulus was restricted to the hypothalamic suprachiasmatic and periventricular nuclei. Our studies have provided novel insights into the differential regulation of egr-1, and facilitated approaches to the genetic manipulation of Egr-1-regulated neuronal systems.

Animals↗
PubMed2001

Genetic engineering of neural function in transgenic rodents: towards a comprehensive strategy?

As mammalian genome projects move towards completion, the attention of molecular neuroscientists is currently moving away from gene identification towards both cell-specific gene expression patterns (neuronal transcriptions) and protein expression/interactions (neuronal proteomics). In the long term, attention will increasingly be directed towards experimental interventions which are able to question neuronal function in a sophisticated manner that is cognisant of both transcriptomic and proteomic organization. Central to this effort will be the application of a new generation of transgenic approaches which are now evolving towards an appropriate level of molecular, temporal and spatial resolution. In this review, we summarize recent developments in transgenesis, and show how they have been applied in the principal model species for neuroscience, namely rats and mice. Current concepts of transgene design are also considered together with an overview of new genetically-encoded tools including both cellular indicators such as fluorescent activity reporters, and cellular regulators such as dominant negative signalling factors. Application of these tools in a whole animal context can be used to question both basic concepts of brain function, and also current concepts of underlying dysfuction in neurological diseases.

Animals↗
PubMed2001

Skeletal growth acceleration with growth hormone secretagogues in transgenic growth retarded rats: pattern-dependent effects and mechanisms of desensitization.

The transgenic growth retarded (Tgr) rat is the first genetic model of growth hormone (GH) deficiency whose growth can be accelerated with exogenous GH secretagogues (GHSs). In this study, we have demonstrated that GHS-receptor (GHS-R) mRNA expression in the arcuate nucleus of Tgr rats was not significantly different to that in wild-type littermates. We have confirmed that GHS-induced elevation in body weight gain was accompanied by acceleration of skeletal growth, and that the effects of the GHS, GHRP-6, were both dose- and pattern-dependent. The growth response with continuous infusion of GHRP-6 was transient, accompanied by suppression of GH and corticosterone responses to bolus injection of GHRP-6. This desensitization occurred without downregulation of arcuate GHS-R mRNA expression, but was accompanied by elevated periventricular somatostatin mRNA expression. In contrast, pulsatile (3-hourly) infusion of GHRP-6 produced sustained growth and GH responses, which were accompanied by suppression of corticosterone responses and elevated arcuate GH-releasing factor (GRF) mRNA expression. Skeletal growth was further accelerated by coinfusion of GRF, but significant depletion of pituitary GH stores suggested that this growth rate may not be sustainable. These experiments confirm the importance of the Tgr rat for investigating the growth promoting potential of the GHSs in the context of GH-deficient dwarfism, and suggest that elevated somatostatin expression may mediate the suppression of the GRF-GH and hypothalamo-pituitary-adrenal axes following continuous GHRP-6 treatment.

Animals↗
PubMed2001

Congenital abdominal aortic aneurysm in the infant: case report and review of the literature.

Congenital abdominal aortic aneurysms are a distinct entity from acquired aortic aneurysms. The authors present the case of a 6-week-old boy with a 6-cm aneurysm involving the abdominal aorta and common iliac arteries. Three other cases of congenital aortic aneurysms are reviewed, and an approach to these rare patients is discussed. J Pediatr Surg 36:657-658.

Abnormalities, Multiple↗
PubMed2001

Single nucleotide polymorphism markers for genetic mapping in Drosophila melanogaster.

For nearly a century, genetic analysis in Drosophila melanogaster has been a powerful tool for analyzing gene function, yet Drosophila lacks the molecular genetic mapping tools that recently have revolutionized human, mouse, and plant genetics. Here, we describe the systematic characterization of a dense set of molecular markers in Drosophila by using a sequence tagged site-based physical map of the genome. We identify 474 biallelic markers in standard laboratory strains of Drosophila that span the genome. Most of these markers are single nucleotide polymorphisms and sequences for these variants are provided in an accessible format. The average density of the new markers is one per 225 kb on the autosomes and one per megabase on the X chromosome. We include in this survey a set of P-element strains that provide additional use for high-resolution mapping. We show one application of the new markers in a simple set of crosses to map a mutation in the hedgehog gene to an interval of <1 Mb. This new map resource significantly increases the efficiency and resolution of recombination mapping and will be of immediate value to the Drosophila research community.

Animals↗
PubMed2001

Tissue-specific transgenic knockdown of Fos-related antigen 2 (Fra-2) expression mediated by dominant negative Fra-2.

Fos-related antigen 2 (Fra-2) is a member of the Fos family of immediate-early genes, most of which are rapidly induced by second messengers. All members of this family act by binding to AP-1 sites as heterodimeric complexes with other proteins. However, each appears to have a distinct role. The role and biology of Fra-2 are less well understood than those of its relatives c-Fos, Fra-1, and FosB; moreover, Fra-2 target genes remain largely unknown, as does the basis of its selective effects on transcriptional activity. To pursue these issues, we created a transgenic rat line (NATDNF2) in which a dominant negative fra-2 (DNF2) gene is strongly expressed in the pineal gland; tissue selectivity was achieved by putting the DNF2 gene under the control of the rat arylalkylamine N-acetyltransferase (AANAT) regulatory region, which targets gene expression to a very restricted set of tissues (pineal gland >> retina). Expression of AANAT is normally turned on after the onset of darkness in the rat; as a result, pineal DNF2 expression occurs only at night. This was associated with marked suppression of the nocturnal increase in fra-2 mRNA and protein levels, indicating that DNF2 expression inhibits downstream effects of Fra-2, including the maintenance of high levels of fra-2 gene expression. Analysis of 1,190 genes in the NATDNF2 pineal gland, including the AANAT gene, identified two whose expression is strongly linked to fra-2 expression: the genes encoding type II iodothyronine deiodinase and nectadrin (CD24).

3T3 Cells↗
PubMed2001

The pharmacokinetics of enalapril in children and infants with hypertension.

Forty children with hypertension between the age of 2 months and 15 years received 0.07 to 0.14 mg/kg of enalapril as a single daily dose. Enalapril was administered orally as a novel extemporaneous suspension in children younger than 6 years of age and as tablets in older children. First-dose and steady-state pharmacokinetics were estimated in children ages 1 to 24 months, 25 months to < 6 years, 6 to < 12 years, and 12 to < 16 years. Maximum serum concentrations for enalapril occurred approximately 1 hour after administration. Serum concentrations of enalaprilat, the active metabolite of enalapril, peaked between 4 and 6 hours after the first dose and 3 and 4 hours after multiple doses. The area under the concentration versus time curve (AUC), adjusted for body surface area, did not differ between age groups. Based on comparison of first-dose and steady-state AUCs, the accumulation of enalaprilat in children ranged from 1.13- to 1.45-fold. For children ages 2 to 15 years, mean urinary recovery of total enalaprilat ranged from 58.3% in children ages 6 to < 12 years to 71.4% in children ages 12 to < 16 years. Urinary recovery for children ages 2 to < 6 years was 66.8%. The mean percentage conversion of enalapril to enalaprilat ranged from 64.7% for children ages 1 to 24 months to 74.6% for children ages 6 to < 12 years. The median effective half-life for accumulation ranged from 14.6 hours in children ages 12 to < 16 years to 16.3 hours in children ages 6 to < 12 years. There were two serious adverse events, neither of which was attributed to enalapril or resulted in discontinuation of the study drug. The extemporaneous suspension used in this study was tolerated well. The pharmacokinetics of enalapril and enalaprilat in hypertensive children ages 2 months to 15 years with normal renal function appears to be similar to that previously observed in healthy adults.

Adolescent↗
PubMed2000

Anti-arrhythmic effects of levcromakalim in the ischaemic rat heart: a dual mechanism of action?

The action of pharmacological openers of K(ATP) channels depends on the availability and levels of various intracellular nucleotides. Since these are subject to change during myocardial ischaemia, K(ATP) channel openers may affect ischaemic and non-ischaemic tissue differentially. Using a recently developed dual coronary perfusion method, we investigated the effects on arrhythmias of the prototypical K(ATP) channel opener levcromakalim when applied selectively to ischaemic and/or non-ischaemic tissue. A novel perfusion cannula was used to independently perfuse the left and right coronary beds of hearts isolated from rats. Selective infusion of levcromakalim (3, 10 or 30 microM) into the left coronary bed in the absence of ischaemia did not induce ventricular arrhythmias. Regional zero-flow ischaemia was induced by cessation of flow to the left coronary bed and hearts received levcromakalim selectively into either the left, right, or both coronary beds. When applied selectively to the ischaemic left coronary bed, levcromakalim (3, 10 or 30 microM; n=10/group) delayed the onset of ventricular tachycardia in a dose-dependent manner (by 21*, 43* and 112%* at 3, 10 and 30 microM; *P<0.05 vs. control). When applied only to the non-ischaemic right coronary bed, levcromakalim reduced the incidence of ventricular tachycardia during later phases of ischaemia (from 100% in controls to 30%*). When present in both coronary beds, levcromakalim had a striking anti-arrhythmic effect--the overall incidence of ventricular tachycardia being reduced from 100% in controls to 20%*. We conclude that levcromakalim may have an anti-arrhythmic effect when applied either to ischaemic or non-ischaemic tissue but that the mechanisms may differ depending on the metabolic state of the heart.

ATP-Binding Cassette Transporters↗