A study of the effects of the neurokinin peptides on respiratory function in sheep

The respiratory responses, including changes in pulmonary resistance (RL) and dynamic compliance (Cdyn), to the neurokinin peptides substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) were assessed in anaesthetised normal Suffolk-cross and conscious Texel-cross asthmatic sheepIn normal sheep (n=l 1) intravenous SP was a more potent bronchoconstrictor than NKA (n=9) and this was similar to findings in sheep with a naturally acquired airway allergy to Ascaris suum antigen (asthmatic) (n=5) where peptides were administered by inhalation. NKB (n=4) was assessed only in normal sheep and caused insignificant changes in bronchomotor tone. Intravenous SP and NKA, in normal anaesthetised sheep, caused a dose-dependent reduction in respiratory rate and this was similar for both peptides.The bronchomotor response to SP in normal sheep demonstrated age-related changes. In sheep under 6 months of age there was a pronounced bronchoconstriction, with a subsequent reduction in the response as animals approach maturity. In old sheep, aged approximately four years, there was minimal bronchomotor response, however, there was dose-dependent apnoea.The bronchomotor response to SP in anaesthetised normal sheep was significantly antagonised after pre-treatment with atropine (lmg/kg; n=6), hexamethonium (20mg/Kg; n=3) and the NK-1 antagonist CP 96,345 (0.1 and 0.5mg/Kg; n=5), but not by the HI receptor antagonist chlorpheniramine (2mg/Kg; n=5) or the neurokinin antagonist spantide (lOug/kg/min; n=3). The anti-asthma drug nedocromil sodium (0.1 and l.Omg/kg; n=4) had a variable effect on the response. In the isolated sheep trachealis muscle preparation the contractile effect of SP was inhibited by atropine (n=4) and the Ml receptor antagonist pirenzepine (n=8), with IC₅₀ values of 5.6xl0⁻⁸ and 5xl0⁻¹⁰ M respectively, while spantide (n=7) and the NK-2 receptor antagonist L-659,874 (n=6) were ineffective.In several normal sheep (n=10) intravenous SP consistently caused augmented breaths. Bilateral vagotomy (n=7) abolished, and cooling of the right cervical vagus (n=7), after section of the left vagus, to temperatures below 7° C significantly attenuated the bronchomotor response to SP in normal sheep.The conclusion of this study is that the order of potency for the bronchomotor effects of the neurokinins is similar to rabbits and pigs but different from that reported for most other species, including man. The mechanism of action of SP is largely indirect, involving activation of vagal reflex mechanisms and/or modulation of ganglionic neurotransmission and acetylcholine release from cholinergic nerve endings

A Sea Change in Eta Carinae

Major stellar-wind emission features in the spectrum of Eta Car have recently decreased by factors of order 2 relative to the continuum. This is unprecedented in the modern observational record. The simplest, but unproven, explanation is a rapid decrease in the wind density.Comment: 11 pages, 3 figures, accepted for publication in ApJ

Spiralling out of control: 3D hydrodynamical modelling of the colliding winds in η \eta\thinspaceCarinae

Three dimensional (3D) adaptive-mesh refinement (AMR) hydrodynamical simulations of the wind-wind collision between the enigmatic super-massive star \etacar and its mysterious companion star are presented which include radiative driving of the stellar winds, gravity, optically-thin radiative cooling, and orbital motion. Simulations with static stars with a periastron passage separation reveal that the preshock companion star's wind speed is sufficiently reduced that radiative cooling in the postshock gas becomes important, permitting the runaway growth of non-linear thin shell (NTSI) instabilities which massively distort the WCR. However, large-scale simulations which include the orbital motion of the stars, show that orbital motion reduces the impact of radiative inhibition, and thus increases the acquired preshock velocities. As such, the postshock gas temperature and cooling time see a commensurate increase, and sufficient gas pressure is preserved to stabilize the WCR against catastrophic instability growth. We then compute synthetic X-ray spectra and lightcurves and find that, compared to previous models, the X-ray spectra agree much better with {\it XMM-Newton} observations just prior to periastron. The narrow width of the 2009 X-ray minimum can also be reproduced. However, the models fail to reproduce the extended X-ray mimimum from previous cycles. We conclude that the key to explaining the extended X-ray minimum is the rate of cooling of the companion star's postshock wind. If cooling is rapid then powerful NTSIs will heavily disrupt the WCR. Radiative inhibition of the companion star's preshock wind, albeit with a stronger radiation-wind coupling than explored in this work, could be an effective trigger.Comment: 25 pages, 20 figures, accepted for publication in Ap

Precession and Nutation in the eta Carinae binary system: Evidences from the X-ray light curve

It is believed that eta Carinae is actually a massive binary system, with the wind-wind interaction responsible for the strong X-ray emission. Although the overall shape of the X-ray light curve can be explained by the high eccentricity of the binary orbit, other features like the asymmetry near periastron passage and the short quasi-periodic oscillations seen at those epochs, have not yet been accounted for. In this paper we explain these features assuming that the rotation axis of eta Carinae is not perpendicular to the orbital plane of the binary system. As a consequence, the companion star will face eta Carinae on the orbital plane at different latitudes for different orbital phases and, since both the mass loss rate and the wind velocity are latitude dependent, they would produce the observed asymmetries in the X-ray flux. We were able to reproduce the main features of the X-ray light curve assuming that the rotation axis of eta Carinae forms an angle of 29 degrees with the axis of the binary orbit. We also explained the short quasi-periodic oscillations by assuming nutation of the rotation axis, with amplitude of about 5 degrees and period of about 22 days. The nutation parameters, as well as the precession of the apsis, with a period of about 274 years, are consistent with what is expected from the torques induced by the companion star.Comment: 9 pages, 8 figures, MNRAS accepte