Time-dependent transition from H(2)O(2)-extracellular signal-regulated kinase- to O(2)-nitric oxide-dependent mechanisms in the stimulatory effect of leptin on renal Na+/K+/-ATPase in the rat

1. Recent studies suggest that leptin, a peptide hormone secreted by white adipose tissue, is involved in the pathogenesis of arterial hypertension, in part by regulating renal sodium handling. Previously, we have demonstrated that in normal rats leptin has a time-dependent effect on renal Na(+)/K(+)-ATPase that drives tubular sodium reabsorption. Short-term leptin infusion results in a transient decrease in Na(+)/K(+)-ATPase activity, whereas prolonged administration stimulates the enzyme. 2. In the present study, we investigated whether these acute effects of leptin are preserved in rats with experimentally induced chronic hyperleptinaemia. 3. Hyperleptinaemia was induced by administration of exogenous leptin (0.25 mg/kg twice daily, s.c., for 7 days). Acute effects of leptin in anaesthetized control (normoleptinaemic) and hyperleptinaemic animals was investigated. Leptin was infused into the abdominal aorta proximally to the renal arteries for 0.5, 1, 2 or 3 h. 4. Leptin (1 microg/min per kg) had a time-dependent effect on renal Na(+)/K(+)-ATPase in both the control and hyperleptinaemic groups. The inhibitory effect observed after 0.5 h infusion was impaired in the hyperleptinaemic group. However, in both groups this effect was abolished by the Janus kinase inhibitor tyrphostin AG490 (100 nmol/min per kg), as well as by the phosphatidylinositol 3-kinase inhibitors wortmannin (10 nmol/min per kg) and LY294002 (1 micromol/min per kg). 5. The stimulatory effect of leptin on Na(+)/K(+)-ATPase activity was observed after 3 h of infusion and was of similar magnitude in control and hyperleptinaemic groups. In the control group, the stimulatory effect of leptin was abolished by the NADPH oxidase inhibitor apocynin (1 micromol/min per kg), the H(2)O(2) scavenger catalase (1 mg/min per kg) and the extracellular signal-regulated kinase (ERK) inhibitor PD98059 (100 nmol/min per kg). In contrast, in the hyperleptinaemic group, the stimulatory effect of leptin was abolished by the cGMP analogue 8-bromo-cGMP (100 nmol/min per kg) and by the superoxide dismutase mimetic tempol (100 micromol/min per kg) but was not affected by catalase or PD98059. 6. Leptin increased urinary H(2)O(2) excretion and ERK phosphorylation in the renal tissue only in the control group. 7. The results suggest that the acute stimulatory effect of leptin on renal Na(+)/K(+)-ATPase is mediated by divergent mechanisms depending on the chronic leptin level (i.e. by H(2)O(2)-dependent stimulation of ERK in normoleptinaemic animals and by superoxide-dependent impairment of the nitric oxide-cGMP pathway in hyperleptinaemic rats).

Asymmetric dimethylarginine (ADMA) as a target for pharmacotherapy

Asymmetric dimethylarginine (ADMA) is synthesized during the methylation of protein arginine residues by protein arginine methyltransferases (PRMT) and is released during proteolysis. ADMA is a competitive inhibitor of nitric oxide synthase and may decrease NO availability. ADMA is eliminated by renal excretion or is metabolized by dimethylarginine dimethylaminohydrolase (DDAH) to citruline and dimethylamine. Two other endogenous methylarginines are also synthesized by PRMT: N-monomethyl-L-arginine (L-NMMA) and symmetric dimethylarginine (SDMA). L-NMMA inhibits NO synthase but its concentrations in circulation are much lower than ADMA whereas SDMA is inactive. Plasma concentration of ADMA is markedly increased in patients with chronic renal failure and moderately increased in patients with many other diseases including hyperlipidemia, diabetes mellitus, arterial hypertension, hyperhomocysteinemia and heart failure. The increased concentration of ADMA is positively correlated with markers of atherosclerosis, such as carotid artery intima-media thickness and has a predictive value for acute cardiovascular events in prospective studies. Angiotensin-converting enzyme inhibitors, angiotensin AT1 receptor antagonists, vitamin E and, according to some studies, estrogens used in hormonal replacement therapy reduce plasma ADMA concentration, which may contribute to their beneficial effect on NO synthesis and endothelial function. However, in some states associated with excess of NO, such as septic shock or excitotoxic neuronal injury ADMA may be protective by limiting toxic effect of high concentrations of NO. This article reviews the effect of pharmacotherapy on ADMA metabolism and its possible clinical implications.

Comparison of fluorine level in the tissues of healthy teeth and teeth with decay process

The aim of the study was to examine quantitative fluorine content in tooth tissues with the decay process, tissues of teeth without decay and tissues with diseases different than those of decay origin. It has been found that in the examined teeth decay process the average fluorine content in hard tissues amounted to 235.6 ppm of fluorine and it was lower than in healthy teeth (304.8 ppm) extracted for orthodontic or periodontological reasons, whereas the highest fluorine content--383.5 ppm--was found in teeth with diseases of non-decay etiology. Analyzing particular teeth groups depending on the age of the patients, it was observed that the fluorine level is higher in the teeth received from younger patients, especially in the group of healthy teeth and teeth with wedge defects. Susceptibility of tooth enamel to dissolution was estimated by the CRT test with the use of discs impregnated with crystal violet (hexamethylene-4 hydrochloride of fuchsin) with the range of colour change from yellow and green to violet and blue at ph 0.1-1.5. The lengthening of the time of reaction in this test testified to lower acid sensitivity of tissues and at the same time to harder demineralization of enamel, e.g. in the process of decay. Longer time of reaction was observed in teeth with higher indicated fluorine content.

Platelet aggregation is not necessary for occurrence of Raynaud's phenomenon: a clinical history and laboratory results

"Raynaud's phenomenon (R.P.) is characterized by a spastic vasoconstriction of hand and/or feet extremities leading to painful ischemic attacks. In the pathogeny of this syndrome the role of a platelet hyperactivation was evidenced. Nevertheless, the responsibility of platelet aggregation remains controversial. We report here the case of a patient presenting with a Glanzmann thrombasthenia defined by the complete lack of platelet aggregation, and showing a typical RP which was confirmed by the measurement of hand temperature and the decrease of digital and hand blood flow. Thus, the description of this case shows that platelet aggregation by itself is not necessary for the occurrence of RP, and encourages for therapeutic purposes the development of vasodilatators rather than platelet antiaggregants agents."