Inverse regulation of alpha-2 and beta-2 adrenoceptors in salt-sensitive hypertension: an hypothesis

A high salt diet leads to up-regulation of alpha-2 adrenoceptors and down-regulation of beta-2 adrenoceptors in normotensive subjects. Although the increase in blood pressure with a high salt diet is not related to the magnitude of the alpha-2 or beta-2 adrenoceptor changes alone, it is related to the increase in the ratio of the receptor changes (operative alpha/beta adrenoceptor ratio). An increase in the operative alpha/beta adrenoceptor ratio with a high salt intake results in vasoconstriction and reduced vasodilatation at resistance vessels, as well as increased renal proximal tubular sodium reabsorption. An influence of heredity on this relationship is supported by four lines of evidence: 1) salt-sensitivity of blood pressure occurs predominantly in subjects with a family history of hypertension; 2) studies in twin children document the influence of genetic variance on salt-sensitivity of blood pressure; 3) subjects with a family history of hypertension have a significantly lower salivary sodium concentration and an altered urinary sodium excretion after salt loading compared to subjects with no such history; 4) salt-sensitivity of blood pressure may be associated with specific genetic markers. On the basis of these observations, we propose the hypothesis that enhanced inverse alpha-beta-adrenoceptor regulation in response to a high salt intake may be responsible for salt sensitivity in the normal population, and may contribute to the development of essential hypertension in susceptible individuals. This alteration is likely to be genetically mediated.

Quantitative morphologic changes in nephron structures and urinary enzyme activity pattern in sodium-maleate-induced renal injury

The morphologic changes in sodium-maleate-induced acute renal injury in the rat were quantified by a stereologic analysis. The major changes were confined to an increase in endocytic vacuoles and a decrease in mitochondrial inner membrane surface area. These results were found to be linked to significantly increased urinary activities of the cytosolic of the cytosolic enzymes fructose-1,6-bisphosphatase (FBP) and lactate dehydrogenase, the lysosomal enzyme N-acetyl-beta-glucosaminidase (NAG) and the NAD-dependent mitochondrial isocitrate dehydrogenase (ICDH). The highest increase was found for NAG, followed by FBP and ICDH.

Noninvasive diagnosis of renal allograft rejections--application of an information-theoretical model

This paper describes an information-theoretical model developed for detection of renal allograft rejection on the basis of various laboratory data. In this report the mathematical background of the model is described in detail and the rationale of its use is discussed. An example is given for the practical application of the model in kidney grafted patients. In the 30 patients of the test collective, seven rejection episodes were diagnosed by the clinicians and verified histologically. All seven rejection episodes were detected by the model, in the mean 2.4 days (median; 3 days) before the clinical diagnosis.

Adrenergic receptors and sodium reabsorption in normotensive subjects as related to salt sensitivity

We have studied proximal tubular sodium reabsorption as measured by lithium clearance, alpha-2 and beta-2 adrenergic receptors on circulating platelets and lymphocytes, respectively, and urinary aldosterone after variations of sodium intake in 24 normotensive volunteers. Fractional lithium clearance was 14.8% +/- 2.64 under a high salt diet of 200 mmol per day. After a low salt diet of 50 mmol/d for two weeks fractional lithium clearance did not change significantly (13.3% +/- 3.35). There were no correlations between alpha-2 adrenergic receptors, beta-2 adrenergic receptors or the alpha-2/beta-2 ratio and fractional lithium clearance, irrespective of the high or low salt diet. In contrast, a significant correlation was found between urinary aldosterone excretion and alpha-2 receptor densities under low salt diet (r = -0.55, n = 17, p less than 0.02). There were no correlations between beta-2 adrenoceptor density, alpha-2/beta-2 ratio and urinary aldosterone during high or low salt diet. Whereas our results are inconclusive about the value of lithium clearance determinations as a measure of proximal tubular sodium reabsorption during variations of sodium intake, we conclude, that alpha-adrenoceptor density, as measured on circulating blood cells, may possibly be representative for alpha-adrenergic equipment of the kidney. The inverse correlation between urinary aldosterone excretion in subjects equilibrated on a low salt diet of 50 mmol/d and alpha-2 adrenoceptor densities could be interpreted as an indirect evidence, that those subjects with a high alpha-2 adrenoceptor equipment show a high proximal tubular sodium reabsorption and thus can afford a low rate of aldosterone mediated distal tubular sodium reabsorption to maintain sodium balance. Our results are thus in accord with our previous hypothesis, that different receptor equipment of individual subjects may cause marked differences in sodium handling by the kidney. These differences may be responsible, at least in part, for the degree of salt sensitivity in individual subjects.

Up-regulation of alpha 2 adrenoceptors and down-regulation of beta 2 adrenoceptors by high-salt diet in normotensive men: enhanced up-regulation of operative (alpha 2:beta 2) adrenoceptor ratio predicts salt sensitivity

In 24 normotensive male volunteers (age 20-25 years) reduction of sodium intake from 200 to 50 mmol/day over 2 weeks resulted in a 14% fall of alpha 2-adrenoceptors of platelets from 209.5 to 179.4 fmol/mg (P less than 0.01) and in a 16% rise of beta 2-adrenoceptors of lymphocytes from 13.3 to 16.2 fmol/mg (P less than 0.05) which was reversible by 2 weeks of high sodium intake. In contrast to the comparatively minor changes of alpha 2- and beta 2-adrenoceptor density, the functionally probably more relevant 'operative (alpha 2:beta 2) adrenoceptor ratio' decreased by 53% from 22.9 to 14.9 (P less than 0.01) during the low-salt diet. Although neither the individual changes of alpha 2- and of beta 2-adrenoceptor densities correlated with individual blood pressure changes induced by variations in sodium intake, there was a highly significant positive correlation (r = 0.55, n = 33; P less than 0.01) between the rises of the 'operative adrenoceptor ratio' and the rises of blood pressure induced by high salt intake. We conclude that the 'operative adrenoceptor ratio', although only determined on alpha 2- and beta 2- and not on alpha 1- and beta 1-adrenoceptors, and only on circulating blood cells, may be representative for sympathetic resistance vessel tone, at least as a function of variations of salt intake. Enhanced up-regulation of the 'operative adrenoceptor ratio' in the salt-sensitive part of the population may be one important early step in the development of essential hypertension.

Urinary enzyme analysis in renal allograft transplantation

The urinary excretion of four enzymes (fructose-1,6-bisphosphatase, glutathione S-transferase, N-acetyl-beta-D-glucosaminidase and pyruvate kinase) was assayed daily in 59 patients following renal cadaveric allografting. 51 patients were given cyclosporin A (CyA group) as an immunosuppressive, 8 patients were treated conventionally with azathioprine and prednisolone (CON-group). Urinary enzyme output was evaluated by two different mathematical models. Model A follows single enzyme excretion, whereas model B also analyzes enzyme patterns. The best results were obtained by a combined analysis of all four enzymes with model B. In the CON-group the sensitivity was 1.00, the specificity 0.85, the predictive values of positive test 0.45 and all 12 graft rejections were diagnosed correctly. In the CyA group the sensitivity was 0.40, the specificity 0.99, the predictive value of positive test 0.33, and 6 out of 9 rejections were recognized. The evaluation of the single enzymes did not produce similarly good results with either model.

Biochemical characterization of renal epithelial cell cultures (LLC-PK1 and MDCK)

The expression of enzymes in LLC-PK1 and MDCK cells was used to study the retention of differentiated properties of the renal epithelial cell lines by a biochemical approach. Activities of marker enzymes, for which intracellular and intranephron localization is known, were determined from crude cell homogenates of LLC-PK1 and MDCK monolayer cultures. The activity patterns of the particular enzymes found were then compared with the in vivo distribution of the enzymes along the rat nephron. LLC-PK1 cells exhibit high activities of apical membrane enzymes when compared with MDCK cells, whereas in the latter high activity of Na-K-ATPase could be detected. The activities of lysosomal enzymes, mitochondrial enzymes, and transaminases were higher in LLC-PK1 than in MDCK cells. Glycolytic enzymes, however, displayed identical activity levels in both the LLC-PK1 and MDCK cells, which may be due to the fact that these are continuous cell lines and to the culture conditions used, since glucose is a major energy source in the culture media.

Interrelation between oxygen consumption and Na-K-ATPase activity in rat renal proximal tubule suspension

The portion of Na-K-ATPase activity on oxygen consumption was determined in suspensions of rat proximal tubules by monitoring oxygen consumption (QO2) under different metabolic states: in the presence or absence of succinate or lactate (10 mmol/l) and increasing concentrations of ouabain (0.4; 0.8; 1.2 and 1.6 mmol/l). In the metabolic states tested, the ouabain induced decrease of QO2 was identical, which implies a fixed rate between Na-K-ATPase activity and QO2. On the basis of these results, Ki and maximal inhibition rate were determined by Lineweaver-Burk and Eadie-Hofstee plots Ki was 0.67 mmol/l ouabain and the maximal inhibition of QO2 was 77%. This corresponds to an absolute decrease of QO2 of 1,630 mumol O2 . h-1 . g-1 protein. Since this value represents the real portion of Na-K-ATPase on QO2, the activity of Na-K-ATPase can be calculated, yielding an activity of 163 mumol ATP . min-1 . g-1 tubule protein.

Compartmentation of ATP within renal proximal tubular cells

Studies on the relations between active solute transport and cell metabolism require not only knowledge of the total cellular ATP, but also of the separate mitochondrial and cytosolic ATP levels. For this purpose, mitochondrial and cytosolic fractions were separated from isolated proximal tubular suspensions by the digitonin technique and the amount of ATP analyzed separately for each compartment. In a parallel series of experiments, the absolute volumes of mitochondrial and extramitochondrial spaces were determined in rat renal cortical tubular suspension utilizing electron microscopic morphometry. When referring ATP measurements to the morphometrically determined absolute volumes, the ATP concentrations were calculated to be 4.33 mmol/l for the cytosolic and 2.62 mmol/l for the mitochondrial space. The cytosolic and mitochondrial ATP, thus, represent 70 and 30% of the total cellular ATP, respectively.

[Urinary enzymes in the non-invasive diagnosis of kidney epithelial lesions in acute kidney failure]

The present investigation describes the urinary output of four different enzymes localized within nephron cells in two models of experimental acute renal failure. The activities of fructose-1,6-diphosphatase (FDP), glutathione-S-transferase (GST), N-acetyl-beta-D-glucosaminidase (NAG) and pyruvate kinase (PK) were determined in the urine of rats after maleate or HgCl2 intoxication. 2 hours after maleate intoxication the urinary output of FDP, GST and NAG was significantly increased above control values. 6 hours after HgCl2 poisoning FDP, GST and NAG showed increased urinary enzyme activities. The urinary activity of each enzyme was significantly increased 24 hours after intoxication. These results are in good accordance with the damage observed on light and electron microscopic investigations carried out with both experimental models. Furthermore, general problems of urinary enzyme measurements are discussed in this paper.

Immunocytochemical localization of gamma-glutamyl-transferase on isolated renal cortical tubular fragments

The localization of gamma-Glutamyltransferase (gamma-GT, E.C.2.3.2.2) was studied on isolated tubular fragments from rat kidney cortex immunocytochemically. Monospecific antibodies raised in the goat against rat kidney gamma-GT were used. Antigoat immunoglobulin from the rabbit conjugated with ferritin was used for visualisation of the antibody binding sites. The enzyme was found to be localized at the brush border membrane of proximal tubules, the luminal membrane of distal tubules and collecting duct segments. The enzyme could further be localized on the antiluminal or basolateral cell membranes of proximal and distal tubular fragments, whereas no such localization was verified for collecting duct segments. The role of this basolateral gamma-GT localization in context with the kidney's ability to extract over 83% of the renal arterial glutathione (GSH) input during a single passage is discussed.

Glutathione depletion and in vitro lipid peroxidation in mercury or maleate induced acute renal failure

Nephrotoxic acute renal failure was experimentally induced in male rats by s.c. application of mercuric chloride and i.p. administration of maleate, respectively. Mercuric chloride and maleate are known to enhance the formation of free radicals and peroxides, which presumably overload the cell's natural elimination mechanisms for these highly reactive intermediates. In addition, a reduction in activities of superoxide dismutase, catalase and glutathione-peroxidase, enzymes responsible for the protection of cells against peroxidative action of superoxide anions and hyperperoxides was found. In both models of acute renal failure, enhanced lipid peroxidation in kidney homogenates in vitro, monitored as malondialdehyde production, was observed. Furthermore, HgCl2 and maleate may react with free SH-groups and thus lead to a depletion of glutathione in tubular cells. Indeed, renal cortical contents of reduced and oxidized glutathione were drastically diminished. These results suggest that alterations in membrane integrity, possibly caused by peroxidative processes, can be considered the cause underlying the well-known disturbances in renal function commonly observed during the initiation phase of HgCl2 and maleate induced acute renal failure.