Phytoremediation of landfill leachate.

Leachate emissions from landfill sites are of concern, primarily due to their toxic impact when released unchecked into the environment, and the potential for landfill sites to generate leachate for many hundreds of years following closure. Consequently, economically and environmentally sustainable disposal options are a priority in waste management. One potential option is the use of soil-plant based remediation schemes. In many cases, using either trees (including short rotation coppice) or grassland, phytoremediation of leachate has been successful. However, there are a significant number of examples where phytoremediation has failed. Typically, this failure can be ascribed to excessive leachate application and poor management due to a fundamental lack of understanding of the plant-soil system. On balance, with careful management, phytoremediation can be viewed as a sustainable, cost effective and environmentally sound option which is capable of treating 250m(3)ha(-1)yr(-1). However, these schemes have a requirement for large land areas and must be capable of responding to changes in leachate quality and quantity, problems of scheme establishment and maintenance, continual environmental monitoring and seasonal patterns of plant growth. Although the fundamental underpinning science is well understood, further work is required to create long-term predictive remediation models, full environmental impact assessments, a complete life-cycle analysis and economic analyses for a wide range of landfill scenarios.

In vivo demonstration of alpha-adrenoceptor-mediated positive inotropy in pithed rats: evidence that noradrenaline does not stimulate myocardial alpha-adrenoceptors.

1. This study examines whether positive inotropy via alpha-adrenoceptors could be observed in vivo in pithed rats. Cardiac contractility was measured as the maximum rate of rise of left ventricular pressure (dP/dt(max)). Heart rate and aortic blood pressure were also recorded. 2. The selective alpha1-adrenoceptor agonists, methoxamine, cirazoline, amidephrine and phenylephrine caused dose-related increases in dP/dt(max). This response was progressively reduced by increasing doses of the alpha1-adrenoceptor antagonist prazosin. However, since the concomitant increase in diastolic blood pressure (DBP) was also blocked, the changes in dP/dt(max) may have been a consequence of increased after load. 3. Adrenaline and noradrenaline also increased dP/dt(max), accompanied by pressor responses. Propranolol (1 mg kg(-1)) antagonized the increase in dP/dt(max) in response to noradrenaline, suggesting beta-adrenoceptor involvement, but not that to adrenaline. The additional presence of prazosin (1 mg kg(-1)) further shifted the dose-response curves for both noradrenaline and adrenaline to the right. 4. Analysis of the increases in dP/dt(max) at predetermined increases in DBP by each agonist revealed three groups of regression lines. Adrenaline in the presence of propranolol and the four selective alpha1-adrenoceptor agonists occupied a common central position. Above this group were adrenaline and noradrenaline in the absence of antagonists; their additional effects on contractility were beta-adrenoceptor-mediated since the regression lines were lowered by propranolol. Clearly below the main group of agonists was noradrenaline in the presence of propranolol. 5. Thus, for a given increase in DBP, adrenaline (in the presence of beta-blockade) and the alpha1-adrenoceptor agonists exert an additional inotropic effect to noradrenaline (also in the presence of beta-blockade). This is concluded to be an alpha-adrenoceptor-mediated increase in cardiac contractility which is not shared by noradrenaline.

Autoerotic asphyxia in adolescents.

The death of a child or young adult is always tragic, regardless of the cause. Cases of autoerotic asphyxia are often labeled as suicide, or are underreported because of embarrassment of relatives or misidentification of the initial clinical manifestations. It may be that autoerotic asphyxial death is far more common than realized. Many emergency nurses and physicians lack adequate knowledge about this phenomenon to make an accurate diagnosis. Family members are often reluctant or unwilling to provide enough data surrounding the circumstances in which the patient was found, and the cause of death is mislabeled as suicide. Autoerotic asphyxia is frequently labeled as a sexual aberrancy and an act that society would rather not acknowledge. But there are a number of implications for emergency nurses, such as prevention and sensitive support of family in the emergency department, that demand our attention.

Whether phenylephrine exerts inotropic effects through alpha- or beta-adrenoceptors depends upon the relative receptor populations.

Phenylephrine produced concentration-related positive inotropic responses in isolated left atria and papillary muscles of guinea-pigs and rats. In rat tissues, these responses were unaffected by propranolol but antagonized by prazosin and therefore mediated via alpha 1-adrenoceptors. The alpha 1-adrenoceptor agonist methoxamine also exerted positive inotropic effects in these rat tissues. The maximum alpha-adrenoceptor-mediated effect of methoxamine (relative to the isoprenaline maximum) was greater than that of phenylephrine in left atria (in the presence of propranolol), whereas in papillary muscles phenylephrine exerted the greater maximum. In guinea-pig papillary muscles, the response to phenylephrine was unaffected by prazosin but was antagonized by propranolol and therefore caused by stimulation of beta-adrenoceptors. Methoxamine had no effect in guinea-pig papillary muscles. Guinea-pig left atria produced biphasic concentration-response curves for phenylephrine, the lower portion being antagonized by phentolamine and was therefore alpha-adrenoceptor-mediated, while the upper portion was antagonized by propranolol and therefore beta-adrenoceptor-mediated. Methoxamine exerted a small inotropic response, the maximum of which was similar to that of the first component of the phenylephrine response. Phenylephrine was a partial agonist for the cardiac beta-adrenoceptor. The density of rat ventricular alpha-adrenoceptors was 4 times greater than beta-adrenoceptor density, as measured by [3H]-prazosin and [3H]-dihydroalprenolol binding. This explains why the responses of rat papillary muscles were alpha-adrenoceptor-mediated. In contrast, the density of beta-adrenoceptor binding sites in guinea-pig ventricles was 6 times greater than the alpha-adrenoceptor density. This explains why the phenylephrine responses were beta-adrenoceptor-mediated in guinea-pig papillary muscles. In the left atria of guinea-pigs, which displayed both alpha- and beta-adrenoceptor-mediated responses, the densities of alpha- and beta-adrenoceptor binding sites were similar. Thus, phenylephrine exerts positive inotropic effects through alpha- or beta-adrenoceptors depending upon their relative densities.

Do both adrenaline and noradrenaline stimulate cardiac alpha-adrenoceptors to induce positive inotropy of rat atria?

1. The positive inotropic responses of rat paced left atria to adrenaline and noradrenaline were recorded. Desmethylimipramine (DMI, 1 microM) and metanephrine (10 microM) were initially present throughout. 2. The positive chronotropic responses of spontaneously beating right atria to adrenaline were used as a reference. In these, pindolol, in increasing concentrations, caused progressive shift of the concentration-response curves to the right, which yielded a pA2 value (8.15) compatible with antagonism of beta-adrenoceptors. 3. The left atrial tension responses to adrenaline showed an initial progressive displacement by pindolol (up to 3 microM) which gave an unexpectedly low pA2 value (6.48). However, with further increases in pindolol concentration there was no additional shift of the curve. In the presence of pindolol (3 microM), prazosin (0.1 microM) displaced the curve to the right but the pA2 value derived from this shift (7.75) was less than expected for alpha 1-adrenoceptor antagonism. 4. When the experiments in the presence of pindolol (3 microM) were repeated in the absence of DMI, prazosin displaced the concentration-response curves for adrenaline-induced left atrial tension to a greater extent and the pA2 value (8.76) was now compatible with adrenaline stimulating typical alpha 1-adrenoceptors. 5. The concentration-response curves for noradrenaline-induced left atrial tension were also progressively displaced to the right by pindolol (0.1, 0.3 and 1.0 microM). These concentrations yielded a Schild plot of unity slope and a pA2 value of 7.94 +/- 0.04. This was not significantly different from the pA2 value of 8.02 +/- 0.07 determined for pindolol against isoprenaline in the left atria, which indicates a normal interaction of noradrenaline with beta-adrenoceptors in the absence and presence of low concentrations of pindolol. 6. A further increase in the concentration of pindolol to 3 microM failed to induce an additional shift of the noradrenaline curves, whether a 'before and after' antagonist or a 'naïve tissue' design was adopted. Similarly, the rightwards shift of the concentration-response curves by timolol reached a limit as the concentration was increased. In all cases the limit of shift occurred at a noradrenaline EC50 value of 5-10 microM. 7. At the limit of beta-adrenoceptor antagonism, prazosin and dibenamine did not displace the noradrenaline curves further. The residual inotropic response to noradrenaline therefore appeared to be mediated via neither alpha- nor beta-adrenoceptors. 8. DMI, in the absence of beta-blockade, produced the potentiation of adrenaline and noradrenaline expected of a neuronal uptake inhibitor. However, in the presence of pindolol, there was no potentiation of the right atrial rate response to adrenaline while its left atrial tension responses were antagonized. This suggested that DMI was acting as an alpha-adrenoceptor antagonist. It also explained the less-than-expected shift by prazosin of the adrenaline responses in the presence of both pindolol and DMI, the latter drug already exerting some alpha-blocking activity. In contrast, the left atrial tension responses to noradrenaline in the presence of pindolol (1 microM) were neither potentiated nor antagonized by DMI. 9. When the effects of prazosin upon left atrial tension responses to noradrenaline in the presence of pindolol (10 microM) were examined in the presence of a lower concentration of DMI (O.1 microM) or cocaine (1O microM), again there was no further shift of the curve. However, when the effect of prazosin) The Macmillan Press Ltd 1989 598 K.L. WILLIAMSON & K.J. BROADLEY was examined in the absence of DMI, but in the presence of pindolol (1 and 1O microM) or timolol (3 microM), there was a small shift of the curves by prazosin (0.1 microM). This yielded pA2 values of 7.19, 7.34 +/- 0.1 and 7.66 +/- 0.09, which were at least one order of magnitude less than literature values and that obtained with adrenaline (8.76 +/- 0.18), and are not consistent with noradrenaline stimulating an alpha 1-adrenoreceptor in the presence of beta-adrenoceptor blockade, the increase in left atrial tension by noradrenaline does not appear to be mediated by beta l- or typical alpha-adrenoceptors. This is in contrast to adrenaline which in these conditions stimulates typical alpha 1-adrenoceptors.

Characterization of the alpha-adrenoceptors mediating positive inotropy of rat left atria by use of selective agonists and antagonists.

Positive inotropic responses to selective alpha-adrenoceptor agonists of isolated paced left atria and chronotropic responses of isolated spontaneously beating right atria of rats were examined. After establishing a cumulative concentration-response curve to isoprenaline, and washout, a concentration-response curve for phenylephrine, methoxamine, cirazoline, amidephrine or UK 14,304 was constructed in the presence of beta-adrenoceptor blockade by propranolol. The 4 alpha 1-selective agonists produced positive inotropic responses, the order of maximum effectiveness being methoxamine greater than phenylephrine greater than cirazoline greater than amidephrine. In terms of EC50 values, methoxamine was the least potent, the other 3 agonists having approximately equivalent potencies. The alpha 2-selective agonist UK 14,304 had no inotropic activity. Weak positive chronotropic activity occurred with phenylephrine, methoxamine and amidephrine; cirazoline exerted only negative chronotropy and UK 14,304 was without effect. Phenylephrine was examined in the absence or presence of prazosin (3 nM) or propranolol (1 microM). Propranolol failed to affect the concentration-response curve for left atrial tension, but prazosin displaced the curve to the right. This indicates that the inotropic responses obtained in the absence of antagonists were mediated solely via alpha-adrenoceptors. After displacement by prazosin there was a further shift by propranolol, suggesting the presence of a beta-adrenoceptor-mediated component at higher concentrations of phenylephrine. The right atrial rate responses to phenylephrine were unaffected by prazosin, but abolished by propranolol; beta-adrenoceptors only are therefore involved in this response. The pA2 values for antagonism of methoxamine-induced increases in left atrial tension by the alpha 1- and alpha 2-selective antagonists prazosin (9.05 +/- 0.06) and idazoxan (6.37 +/- 0.05), respectively, were consistent with the responses being mediated via alpha-adrenoceptors of the alpha 1-subtype. The pA2 value for prazosin was similar to that obtained for antagonism of methoxamine-induced contractions of rat aortic spirals (8.83 +/- 0.13).

Proton NMR studies of denatured lysozyme.

Evidence is presented from 1H NMR studies for non-random conformational behaviour in denatured lysozyme in aqueous solution. A method is presented which permits the assignment of resonances in the 1H NMR spectrum of the denatured protein by observing magnetisation transfer from resonances of the native state. The use of these experiments in characterising the denatured state and the significance of these studies for the investigation of protein folding are discussed.

Xenon NMR: chemical shifts of a general anesthetic in common solvents, proteins, and membranes.

The rare gas xenon contains two NMR-sensitive isotopes in high natural abundance. The nuclide 129Xe has a spin of 1/2: 131Xe is quadrupolar with a spin of 3/2. The complementary NMR characteristics of these nuclei provide a unique opportunity for probing their environment. The method is widely applicable because xenon interacts with a useful range of condensed phases including pure liquids, protein solutions, and suspensions of lipid and biological membranes. Although xenon is chemically inert, it does interact with living systems; it is an effective general anesthetic. We have found that the range of chemical shifts of 129Xe dissolved in common solvents is ca. 200 ppm, which is 30 times larger than that found for 13C in methane dissolved in various solvents. Resonances were also observed for 131Xe in some systems; they were broader and exhibited much greater relaxation rates than did 129Xe. The use of 129Xe NMR as a probe of biological systems was investigated. Spectra were obtained from solutions of myoglobin, from suspensions of various lipid bilayers, and from suspensions of the membranes of erythrocytes and of the acetylcholine receptor-rich membranes of Torpedo californica. These systems exhibited a smaller range of chemical shifts. In most cases there was evidence of a fast exchange of xenon between the aqueous and organic environments, but the exchange was slow in suspensions of dimyristoyl lecithin vesicles.

Conformational analysis by nuclear magnetic resonance: insulin.

High-resolution 270-MHz proton nuclear magnetic resonance (NMR) spectra of the native two-zinc insulin hexamer at pH 9 have been obtained, and assignments of key resonances have been made. Spectra of zinc-free insulin titrated with Zn2+ are unchanged after the addition of 1 equiv of zinc per insulin hexamer, indicating that the conformation of the hexamer is fixed at this point and that the second zinc ion does not significantly change the conformation. Titration of the two-zinc insulin hexamer with anions high on the Hofmeister series such as SCN- causes marked changes in the NMR spectra which are interpreted as the result of major conformational changes to a new hexameric form of insulin having a twofold axis perpendicular to the threefold axis. Analysis of difference spectra indicates that this new hexamer (which should be capable of binding six zinc ions) binds 2 equiv of SCN- at two sites which are assumed to be identical and independent (K1 = 10(3), K2 = 2.5 X 10(2) M-1).

Variation in cardiac glycoside content of monarch butterflies from natural populations in eastern North America.

A new spectrophotometric assay has been used to determine the gross concentration of cardiac glycoside in individual monarch butterflies. Adults sampled during the fall migration in four areas of eastern North America exhibited a wide variation in cardiac glycoside concentration. The correlation between spectrophotometrically measured concentrations and emetic dose determinations supports the existence of a broad palatability spectrum in wild monarch butterflies. The cardiac gylcoside concentration is greater in females than in males and is independent of the dry weight of the butterflies; contrary to prediction, both the concentration mean and variance decrease southward. The defensive advantage of incorporating cardiac glycosides may be balanced by detrimental effects on individual viability.