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  • Author or Editor: B. Ravindran x
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Abstract

The physiology of baroreceptors and chemoreceptors present in large blood vessels of the heart is well known in the regulation of cardiorespiratory functions. Since large blood vessels and peripheral blood vessels are of the same mesodermal origin, therefore, involvement of the latter in the regulation of cardiorespiratory system is expected. The role of perivascular nerves in mediating cardiorespiratory alterations produced after intra-arterial injection of a nociceptive agent (bradykinin) was examined in urethane-anesthetized male rats. Respiratory frequency, blood pressure, and heart rate were recorded for 30 min after the retrograde injection of bradykinin/saline into the femoral artery. In addition, paw edema was determined and water content was expressed as percentage of wet weight. Injection of bradykinin produced immediate tachypneic, hypotensive and bradycardiac responses of shorter latency (5–8 s) favoring the neural mechanisms involved in it. Injection of equi-volume of saline did not produce any responses and served as time-matched control. Paw edema was observed in the ipsilateral hind limb. Pretreatment with diclofenac sodium significantly attenuated the bradykinin-induced responses and also blocked the paw edema. Ipsilateral femoral and sciatic nerve sectioning attenuated bradykinin-induced responses significantly, indicating the origin of responses from the local vascular bed. Administration of bradykinin in the segment of an artery produced reflex cardiorespiratory changes by stimulating the perivascular nociceptors involving prostaglandins. This is a novel study exhibiting the role of peripheral blood vessels in the regulation of the cardiorespiratory system.

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Abstract  

Precursor powders for yttrium aluminum garnet (YAG) were synthesized by solution combustion reactions (nitrate–glycine reaction with stoichiometric and sub-stoichiometric amount of fuel) and simple decomposition of nitrate solution. The TG-DTA, FTIR and XRD analyses of the precursors and the typical heat-treated samples were carried out to understand the processes occurring at various stages during heating to obtain phase pure YAG. Precursors from all the reactions exhibited dehydration of adsorbed moisture in the temperature range of 30 to 300°C. The precursor from nitrate–glycine reaction with stoichiometric amount of fuel (precursor- A) contained entrapped oxides of carbon (CO and CO2) and a carbonaceous contaminant. It exhibited burning away of the carbonaceous contaminant and crystallization to pure YAG accompanied by loss of oxides of carbon in the temperature ranges of 400 to 600 and 880 to 1050°C. The precursor from simple decomposition of nitrates (precursor-B) exhibited denitration cum dehydroxylation and crystallization in the temperature ranges of 300 to 600 and 850 to 1050°C. The precursor from nitrate–glycine reaction with sub-stoichiometric amount of fuel (precursor-C) contained entrapped carbon dioxide and exhibited its release during crystallization in the temperature range of 850 to 1050°C. This study established that, in case of metal nitrate–glycine combustion reactions, crystalline YAG formation occurs from an amorphous compound with entrapped oxides of carbon. In case of simple decomposition of metal nitrates, formation of crystalline YAG occurs from an amorphous oxide intermediate.

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