PubMed · 237235
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F H Sterling. 1975-08-07. Letter: Thyroxine pathways--hypothesis.. https://doi.org/10.1056/nejm197508072930628
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We report a reliable fluorimetric assay for the simultaneous determination of norepinephrine, epinephrine, dopamine and dobutamine in human plasma and urine, based on liquid-liquid extraction and derivatization with the fluorogenic agent 1,2-diphenylethylenediamine prior to chromatography. The method is sensitive (detection limit 0.3-0.8 pg injected) and reproducible (coefficients of variation 1-10%), and shows good accuracy (93-98%). The method should also be used when one only wants to measure the concentrations of the natural catecholamines, in order to avoid interference by metabolites of dobutamine and by the late-eluting dobutamine itself.
This hypothesis is that permanent cardiac injury could develop in some endurance athletes despite the absence of coronary atherosclerosis and ventricular hypertrophy. The proposed mechanism by which this injury could arise involves two physiological "vicious cycles". The first vicious cycle would occur between severe ischaemia and high catecholamines, the second would be between coronary vasospasm (induced by high catecholamines) and endothelial injury. The likelihood of the injury becoming permanent might increase if there is insufficient time between bouts of endurance exercise for regression of ischaemia and endothelial repair. Furthermore, magnesium ion deficiency, which can be induced by exercise, could exacerbate these vicious cycles and also contribute to catecholamine-induced thrombogenesis. In addition to ischaemia, there are several mechanisms, including the effect of free fatty acids liberated by the lipolytic effect of high catecholamines, that could cause direct myocardial injury.
It was found that the yield of thiobarbituric acid reactive substances in UV-irradiated liposome membranes was significantly suppressed in the presence of catecholamine-melanins, indicating their ability to inhibit lipid peroxidation. The extent of inhibition depended on the type and concentration of melanin polymers. Melanin-copper complexes inhibited lecithin photooxidation less effectively than copper-free melanins derived from the same precursor. The antioxidant efficiency of melanins appears to be related to the levels of intrinsic and photo-induced free radical centers in the melanin polymer, as well as to accessibility of these centers for active species formed during irradiation of liposomes.