Clinical Chemistry of Newly-found Esterase for Endogenous Digitalis-like Factor

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Endogenous digitalis-like factor (EDLF) act as important modulator for water and salt metabolism. From recent studies endogenous digitalis-like factor is consisted of cardenolides and bufadienolides. Recently we found marinobufotoxin (MBT) as the new member of EDLF. The structure of this compound was confirmed by tandem mass spectrometric signals of liquid chromatography-mass spectrometry and nuclear magnetic resonance (NMR) analysis. Interestingly this compound consists of cardiotonic steroid with C6-chain and amino acids, argentine. And the esterase for this side chain was searched. The reaction of this esterase mimicked by the tissue kallikrein and other esterases such as cholesterol esterase were relatively slow and the physiological meanings are still ambiguous. But we found the contribution of rennin-angiotensin system (RAS) and MBT on hypertension with use of SHR rats. In the angiotensin-receptor blocker (ARB), telmisartan group, the plasma level of MBT was lower than that in the control group. The urine MBT excretion increase after 2 and 4 weeks but the MBT excretion modified by the ARB did not increase and the blood pressure did not increase. These results suggested that MBT contributed the control mechanism in SHR with RAS. And this analytic system was also applied to clinical toxicology area.