Biomedical subjects
Publications and source records attributed to J S Barton.
We describe what is to our knowledge the first use of fiber Bragg gratings written into three separate cores of a multicore fiber for two-axis curvature measurement. The gratings act as independent, but isothermal, fiber strain gauges for which local curvature determines the difference in strain between cores, permitting temperature-independent bend measurement.
Tubulin is an unstable protein when stored in solution and loses its ability to form microtubules rapidly. We have found that D2O stabilizes the protein against inactivation at both 4 and 37 degrees C. In H2O-based buffer, tubulin was completely inactivated after 40 h at 4 degrees C, but in buffer prepared in D2O, no activity was lost after 54 h. Tubulin was completely inactivated at 37 degrees C in 8 h in H2O buffer, but only 20% of the activity was lost in D2O buffer. Tubulin also lost its colchicine binding activity at a slower rate in D2O. The deuterated solvent retarded an aggregation process that occurs during incubation at both temperatures. Inactivation in H2O buffer was partially reversed by transferring the protein to D2O buffer; however, aggregation was not reversed. The level of binding of BisANS, a probe of exposed hydrophobic sites in proteins, increases during the inactivation of tubulin. In D2O, the rate of this increase is slowed somewhat. We propose that D2O has its stabilizing effect on a conformational step or steps that involve the disruption of hydrophobic forces. The conformational change is followed by an aggregation process that cannot be reversed by D2O. As reported previously [Ito, T., and Sato, H. (1984) Biochim. Biophys. Acta 800, 21-27], we found that D2O stimulates the formation of microtubules from tubulin. We also observed that the products of assembly in D2O/8% DMSO consisted of a high percentage of ribbon structures and incompletely folded microtubules. When these polymers were disassembled and reassembled in H2O/8% DMSO, the products were microtubules. We suggest that the combination of D2O and DMSO, both stimulators of tubulin assembly, leads to the rapid production of nuclei that lead to the formation of ribbon structures rather than microtubules.
Serum insulin-like growth factor 1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), and a range of growth and nutritional variables were investigated in 62 infants with congenital heart disease and healthy controls. Infants with congenital heart disease were small, underweight, and had a reduced energy intake. Serum IGF-1 and IGFBP-3 concentrations were significantly reduced. Decreased IGF-1 and IGFBP-3 levels are observed in nutritional deficiency; similar findings in congenital heart disease suggest that undernutrition contributes to the poor growth of these infants. Serial measurements of serum IGF-1 and IGFBP-3 may be helpful in monitoring the effect of nutritional treatment in congenital heart disease.
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OBJECTIVE: It is possible that high dose GH treatment may have beneficial effects on growth but important adverse effects on cardiac function. We have therefore investigated the efficacy and cardiovascular effects of high dose biosynthetic human GH (r-hGH) treatment in children with idiopathic short stature and a normal pretreatment height velocity. STUDY DESIGN: Randomized controlled study. PATIENTS: Twenty-nine short (height SDS < 1.5), normally growing (height velocity SDS > -1.5), prepubertal children referred to two specialist growth clinics. INTERVENTIONS: Children were randomly assigned to an observation group or to receive 'standard' (20 IU/m2/week) or 'high' (40 IU/m2/week) dose r-hGH by daily subcutaneous injection. At the end of 1 year the observation group were randomly assigned to 'standard' or 'high' dose r-hGH therapy for the second year of the study. Regular growth, biochemical and echocardiographic monitoring were performed throughout the study period. MAIN OUTCOME MEASURES: Changes in height velocity, HtSDS for bone age (HtSDSBA), left ventricular mass index (LVMI) and left ventricular function (fractional shortening) during 2 years treatment. RESULTS: Twenty-seven children completed the study. Ht velocity SDS increased with r-hGH therapy in a dose dependent fashion. First-year height velocity SDS was +5.7 in the high dose r-hGH group compared with +2.7 in the standard dose r-hGH group and -0.5 in the observation group (P < 0.001). In those children treated for 2 years HtSDSBA was -0.5 in the high dose group but had not changed significantly in the standard dose group (-1.7) (P = 0.01). After one year r-hGH treatment LVMI was 71 g/m2 (observation group), 73 g/m2 (20 IU/m2/week group) and 74 g/m2 (40 IU/m2/week group) (P = 0.77). LVMI increased significantly from baseline to 76 g/m2 after 2 years therapy with 40 IU/m2/week r-hGH (P = 0.04) but nevertheless remained within the normal range. Fractional shortening did not change significantly over 2 years of r-hGH therapy. CONCLUSIONS: High dose (40 IU/m2/week) r-hGH treatment of children with idiopathic short stature resulted in a greater short-term acceleration in growth rate than 'standard' dose therapy without an excessive advance in skeletal maturity and probably represents the optimal growth promoting dose for short, normally growing children. Whether continued high dose r-hGH therapy increases final height requires further study. Left ventricular morphology and function remained within the normal range during r-hGH therapy but regular monitoring of cardiovascular status should continue in non-GHD children receiving r-hGH in high doses over a longer time period.
We report an 18 month old girl with developmental delay, dysmorphic features, and a karyotype 46,XX,del (1) (p32.1p32.3). To our knowledge the clinical features associated with this deletion have not been reported previously.
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Growth failure is a well recognised consequence of severe congenital heart disease. Total daily energy expenditure (TDEE) was investigated in eight infants with severe congenital heart disease to determine whether an increase in this parameter is an important factor in their failure to thrive, and to estimate the energy intake that would be required to allow normal growth. The infants were studied over a seven day period before surgery using the doubly labelled water method. Growth failure was evident; their mean age standardised body mass index was 80% of the expected value. Mean TDEE was 425 kJ/kg, significantly greater than in healthy infants (mean TDEE/kg SD score = +1.4; 95% confidence interval +0.27 to +2.57). In contrast, their energy intake was only 82% of the estimated average requirements. It was estimated that in early infancy a gross energy intake of 600 kJ/kg/day is required for normal growth in patients with congenital heart disease. This is unlikely to be achieved by energy supplements alone and early recourse to nasogastric feeding should be considered.
OBJECTIVE: We investigated the effect of growth hormone (GH) treatment on salt and water metabolism and the renin-angiotensin-aldosterone system in children with short stature. DESIGN: Randomized, controlled study. PATIENTS: Twenty-nine short, pre-pubertal children referred to two specialist growth clinics for further assessment. MEASUREMENTS: Serial measurements of blood pressure, body weight, plasma renin activity (PRA), aldosterone, electrolytes, insulin and insulin-like growth factor I (IGF-I) have been made following the initiation of GH treatment. RESULTS: A small and transient increase in systolic blood pressure was observed during the first week of GH treatment. The increase in blood pressure over baseline was -1.1 mmHg in controls compared to +11.5 and +3.0 mmHg in children receiving standard (20 units/m2/week) and high dose (40 units/m2/week) GH respectively (P = 0.004). Over the same time interval body weight also tended to increase with GH compared with controls. These changes were greater in those children receiving the lower dose of GH and were not significantly related to age or prior GH status. PRA did not change with GH treatment. Although plasma aldosterone concentration tended to increase with GH, maximal values did not differ from controls and all remained within our normal range. Plasma IgF-I levels were increased by a similar amount in both treatment groups (1.5 and 1.12 U/ml compared to 0.44 U/ml in controls at 4 months). No difference in plasma insulin concentration was noted after 7 days of GH. CONCLUSIONS: In contrast to adult subjects, treatment with high dose GH in childhood is not associated with activation of the renin-angiotensin-aldosterone system. Clinical signs consistent with transient salt and water retention are observed with GH therapy, however, suggesting either a direct effect of GH or of IGF-I on renal tubular function. Blood pressure, plasma renin activity and plasma aldosterone levels were not increased after more prolonged GH therapy. These data suggest that high dose GH therapy in childhood is unlikely to be associated with the increased risk of hypertension seen in adults with GH hypersecretion.
Growth hormone (GH) hypersecretion is associated with an increased incidence of hypertension and cardiac hypertrophy, resulting in excess cardiovascular morbidity and mortality. Abnormalities in the renin-angiotensin-aldosterone (RAA) system have been reported in acromegaly and in normal adults treated with recombinant human GH. The RAA system was investigated in prepubertal children with idiopathic short stature during treatment with recombinant human GH in doses up to 40 IU/m2/week. In addition, left ventricular size and function were assessed by serial echocardiography over an initial 12-month period. Modest and transient increases in blood pressure and body weight were observed during the first 7 days of GH treatment, but this was not accompanied by activation of the RAA system. Echocardiographic parameters of left ventricular size and function remained within the normal range for age and body size. Short-term GH treatment of idiopathic short stature was thus not associated with an increase in risk factors known to be associated with later cardiovascular morbidity. Longer follow-up studies will be required to confirm the safety of high-dose GH in this respect.
The question of whether nonhydrolyzable nucleotide analogues and other nucleoside triphosphates support tubulin assembly was addressed. Tubulin which contained residual GTP at the exchangeable site polymerized in the absence of added GTP in the presence of DMSO or glycerol. After maximum absorbance was reached, disassembly occurred at a slow rate. When 0.5 mM GMPPCP, GMPPNP, or ATP was included in the assembly reaction, disassembly did not occur, and about 0.1 mol of these nucleotides per mole of tubulin was incorporated into the protein. When 5 mM nucleotide was used or alkaline phosphatase was included in the case of the nonhydrolyzable analogues, a greater amount of assembly occurred and about 0.7-0.8 mol of analogue was incorporated. The products of the assembly reaction were cold-labile microtubules and protofilament ribbons. After cold-depolymerization of the microtubules and ribbons, a second cycle of assembly produced some microtubules, but cold-stable amorphous polymers were the major product. In addition, when GTP at the exchangeable site was first removed by a cycle of assembly, followed by depolymerization, assembly in the presence of GMPPCP, GMPPNP, or ATP produced a mixture of microtubules and cold-stable polymers, both of which contained bound analogue. Incorporation of GMPPCP, GMPPNP, or ATP into polymerized tubulin always occurred at the expense of GDP at the exchangeable site, the content of which decreased correspondingly. Incubation of tubulin with 5 mM GMPPCP, GMPPNP, or ATP under nonassembly conditions also displaced GDP.(ABSTRACT TRUNCATED AT 250 WORDS)
We recently demonstrated that the nonhydrolyzable analogues of GTP (GMPPCP and GMPPNP) and ATP support the elongation phase of tubulin assembly and are incorporated into the E-site of polymerized tubulin. In this report we studied the stability of microtubules containing GTP analogues by examining length redistributions after shearing at polymer steady state. The mean length of a population of microtubules containing GMPPCP increased only by 37% over a 150 min time period after shearing. Microtubules which contained 70% ATP and 30% GDP at the E-site increased in length by 88%. In contrast, the mean length of microtubules assembled in the presence of GTP increased by 410% in the same time period. These results suggest that microtubules containing GMPPCP or ATP at their ends are stabilized from depolymerization.
The assembly kinetics of microtubule protein are altered by ionic strength, temperature and Mg2+, but not by pH. High ionic strength (I0.2), low temperature (T less than 30 degrees C) and elevated Mg2+ (greater than or equal to 1.2 mM) induce a transition from biphasic to monophasic kinetics. Comparison of the activation energy obtained for the fast biphasic step at low ionic strength (I0.069) shows excellent agreement with the values obtained at high ionic strength, low temperature and elevated Mg2+. From this observation it can be implied that the tubulin-containing reactant of the fast biphasic event is also the species that elongates microtubules during monophasic assembly. Second-order rate constants for biphasic assembly are 3.82(+/- 0.72) x 10(7) M-1.s-1 and 5.19(+/- 1.25) x 10(6) M-1.s-1, and for monophasic assembly the rate constant is 2.12(+/- 0.56) x 10(7) M-1.s-1. The microtubule number concentration is constant during elongation of microtubules for biphasic and monophasic assembly.
Patients with atypical facial pain (AFP) are subject to ineffective dental and surgical procedures for their pain complaints. Twenty-one of fifty-eight patients (36.2 percent) with AFP had sixty-five dental and surgical treatments, with only one patient showing less pain as a result of the treatment. While the majority of patients (69 percent) with AFP suffered from a psychiatric illness, fourteen (24 percent) of the patients referred for AFP had a specific medical or dental disorder that was causal in their pain complaints. There is a trend for the AFP patient with a psychiatric diagnosis to receive more ineffective treatments than those AFP patients for whom a specific medical or dental diagnosis was made. Patients with AFP should receive conservative dental and medical treatment and a psychiatric assessment before dental and surgical procedures are contemplated.
Chromatography of microtubule protein through 8% agarose at 4 and 31 degrees C demonstrated that tubulin oligomer was not dissociated to tubulin dimer and microtubule associated proteins by assembly temperatures. During chromatography, formation of microtubules was prevented by using 10 microM podophyllotoxin and/or 25 microM GTP. In the presence of 25 microM GTP, tubulin oligomer at 31 degrees C and microtubule protein retained the ability to polymerize. Evidence against dimer formation from tubulin oligomer was also obtained via a turbidity study of the initial events (the first 90 s) of microtubule assembly.
For microtubule assembly, the data reported here support an initial nucleation phase followed by a growth or elongation phase. The nucleation phase was not detected kinetically. Evidence for this step was given by the existence of the critical concentration and the dependence of the number of microtubules on oligomer concentration. Kinetic evidence indicated the existence of two consecutive steps in the growth phase of microtubules. The fast process increased and the slow one decreased with the concentration of microtubule protein. Similar kinetics were found upon recombination of tubulin oligomer and dimer which had been resolved by agarose chromatography. The fast process increased with oligomer and decreased with dimer concentration while the slow one depended positively on dimer concentration. Microtubules were formed when the oligomeric fraction only was employed. In contrast, under identical conditions, no microtubule formation was detected turbidimetrically or by electron microscopy from dimer alone. When dimer caused elongation of seed tubules, there was only one growth step with a rate constant of the same order of magnitude as the slow process for the other experiments.
When stored frozen in 1 M sucrose and 1 mM GTP, tubulin loses polymerizing ability exponentially. Since addition of diethiothreitol does not change the decay half-life, this decrease in activity can not be attributed to disulfide bond formation. When tubulin is stored frozen in dithiothreitol and GTP only, the decay half-life increases by a factor of four, indicating that sucrose destabilizes polymerizing ability. Frozen storage in sucrose has the opposite effect on colchicine binding, which remains at 100% for 40 days. This temporal divergence indicates that colchine binding and polymerization are two independent properties of tubulin.
Bacteroides amylophilus has growth requirements for Na(+), PO(4) (3-), K(+), and small quantities of Mg(2+). No requirement could be shown for Ca(2+) in media previously found growth-yield-limiting for Bacteroides succinogenes. Deletion of Co(2+), Mn(2+), Cl(-), or SO(4) (2-) did not affect growth. Quantitative studies indicate that Na(+), K(+), and PO(4) (3-) have differing effects on the growth of B. amylophilus. A concentration of sodium and potassium ions affects both growth rate and growth yield, whereas a phosphate concentration markedly affects growth yield, but affects growth rate only slightly, if at all. The sodium requirement of B. amylophilus is absolute. It cannot be replaced by K(+), Li(+), Rb(+), or Cs(+). The latter three monovalent cations are toxic to B. amylophilus if supplied to the organism at Na(+)-replacing concentrations. K(+) is inactive at similar concentrations. The K(+) requirement of B. amylophilus may be satisfied by Rb(+). The concentration of Na(+) required by B. amylophilus for abundant growth suggests that B. amylophilus should be considered a slightly halophilic organism. The results suggest that Na(+) may be a more frequent requirement among terrestial bacteria obtained from relatively low-salt environments than has been previously believed.