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  • 1
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Atlantic salmon embryos and alevins Salmo salar that had been exposed to isosorbide dinitrate (ISDN) for 4 weeks, on transfer to fresh water, showed an increase in heart rate. Unexposed embryos and alevins showed a decrease in heart rate following transfer to 100 μmol l−1 ISDN for 4 h. This is in contrast to adult rainbow trout and higher vertebrates where tachycardia occurred in response to nitric oxide (NO) donors. The decreased heart rate in response to ISDN was inhibited by 2 mg 1−1 methylene blue, indicating that NO activates cardiovascular events via guanylyl cyclase and cyclic guanidine monophosphate. Heart rate of rainbow trout alevins Oncorhynchus mykiss exposed to 100 μmol l−1 aminoguanidine responded with a slowly developed but significant bradycardia over 10 min as did those reared in aminoguanidine for 4 weeks then transferred to fresh water. A potentiated increase in heart rate on exposure to the NO donor sodium nitroprusside (SNP), occurred within 1 min in salmon alevins reared in l-nitro-arginine methyl ester (l-NAME) for 4 weeks, indicating up-regulation of NO receptors. The evidence for down-regulation of SNP-reared alevins exposed to l-NAME was less well defined. The results suggest that both salmonid embryos and alevins have a functional l-arginine-NO pathway and that NO has a physiological role in control of cardiovascular events.
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  • 2
    ISSN: 1573-5168
    Keywords: Fish ; NO ; ISDN ; cardiovascular responses ; development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rainbow trout (Oncorhynchus mykiss) eggs and alevins were exposed for up to 4 weeks to the nitricoxide (NO) donor isosorbide dinitrate (ISDN) at concentrations up to 100 μmol l−1. Hatching success was over 95%, but increasing concentrations of ISDN significantly delayed hatching, without significant affects on survival. Alevins exposed to ISDN concentrations of 50 or 100 μmol l−1 showed significant cardiovascular and developmental changes compared to unexposed alevins. These included lowered heart rate and ventilation rate, doubling of cardiac output, dilation of the vitelline vein and increased in alevin weight. The results indicate a vasodilatory role of NO in trout alevins, and their cardiovascular responses to NO, with reference to the role of the vitelline vein, are discussed.
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  • 3
    ISSN: 1573-269X
    Keywords: Unbalanced shaft ; nonlinear vibrations ; limited power supply ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Rotation of an elastically mounted unbalanced shaft may be in general affected by its lateral vibration, due to a “vibrational torque”. This interaction is nonlinear, and can be neglected only in case of an unlimited power supply. Whenever the available power of the drive is comparable with power consumption due to vibration, various nonlinear phenomena may be observed, the most well-known of these being the so called Sommerfeld effect – slowing down or complete capture of the shaft at resonance. The corresponding steady-state motions and their stability can be studied by asymptotic methods, as applied to the governing nonlinear set of two second-order equations. However, study of transient motions in general requires numerical solution. This numerical solution is obtained here, and extensive parametric studies are performed of the Sommerfeld effect. In particular, the influence is evaluated of damping ratio and slope of the torque-speed curve of the drive on a passage/capture threshold. The results of numerical simulation, as well as experiments with a physical model, also demonstrate the effect of smooth passage through resonance with a limited power supply, based on using a “switch” of suspension stiffness from a certain artificially increased value to the design one. A brief description is presented also of time-variant components of the resonant amplitude and rotational frequency responses in the case of capture, as observed both in numerical simulation studies and in experiments. Whilst these components are small compared with the corresponding constant ones, i.e. steady-state vibration amplitude and rotational frequency, the above observations indicate the possibility for periodic or chaotic nonstationarity in the system's response.
    Type of Medium: Electronic Resource
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