Hepatorenal syndrome: emerging perspectives of pathophysiology and therapy

Progressive oliguric renal failure (designated "hepatorenal syndrome") commonly complicates the course of patients with advanced hepatic disease. Despite the severe derangement of renal function and ominous prognosis when renal failure develops, minimal and inconsistent pathologic abnormalities of the kidneys are found at autopsy. Furthermore, the kidneys, if transplanted, are capable of normal function, which supports the concept that the renal failure is functional and potentially reversible. In contrast to patients with classical acute failure (ATN), hepatorenal syndrome patients manifest characteristic alterations of renal function including (1) relatively hyperosmolar urine; (2) high creatinine urine:plasma ratio, and (3) a very low urine sodium concentration (< 10 mEq/L). The past several years have witnessed newer insights into both the pathophysiology and the therapeutics of this syndrome. The application of newer methodology such as tracer kinetics has more rigorously delineated the role of a number of pathogenic mechanisms including activation of the sympathetic nervous system. The characterization of endothelin and the nitric oxide-arginine pathway and their roles in biology and medicine has provided additional new insights with regard to the pathogenesis of hepatorenal syndrome. For example, nitric oxide has been proposed to constitute a mediator of both the hyperdynamic circulation and renal failure. Finally, recently initiated therapeutic approaches lend a note of optimism to the future management of a syndrome that is so often incompatible with recovery. These include the acceptance of orthotopic liver transplantation as definitive treatment for patients with end-stage liver disease and attempts to improve renal function by countervailing the decreases in systemic vascular resistance while minimizing concomitant increments in renal vascular resistance. Hopefully, ongoing and future clinical trials will establish the precise contribution of each of these treatment modalities and their respective roles in the therapeutic armamentarium.

Hypertension as a risk factor for progression of chronic renal disease

The declining mortality due to coronary artery disease and stroke has been attributed in part to improved effectiveness and application of antihypertensive therapy, and successful identification and treatment of the population at risk. In striking contrast, end-stage renal disease (ESRD) attributed to hypertension has increased annually for the last decade and will probably worsen through the year 2000. Taken together, patients with diabetic nephropathy and those with hypertensive renal disease account for the majority of new cases annually. The reasons for the striking dissociation between the success with coronary artery disease and stroke on the one hand and the inability to lessen the incidence of ESRD remain to be clarified. Evidence reveals that all levels of untreated hypertension are associated with potentially declining renal function. Data from the Hypertension Detection and Follow-up Program and other studies suggest that antihypertensive treatment can prevent or retard development of progressive renal failure. No data are readily available on repeated measurement of glomerular filtration rate during prolonged treatment of mild hypertension in patients with normal or near-normal renal function. Although the importance of blood pressure control is implicit, a theoretical framework based on data derived from experimental animals suggests that angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists may exert specific renoprotective effects beyond those achieved by blood pressure reduction per se. The results of two recent long-term prospective studies support such a formulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrinsic and extrinsic characteristics of human tumors relevant to radiosurgery: comparative cellular radiosensitivity and hypoxic percentages

We have collected the in vitro x-ray radiation survival characteristics of 181 lines from 12 different classes of exponentially growing human tumor cells (sarcomas, lung cancers, colo-rectal cancers, medulloblastomas, melanoma, breast cancers, prostate cancers, renal cell cancers, grades III and IV brain tumors, ovarian, and head and neck cancers). This information was used to intercompare survival after single high doses of 20-40 Gy for each tumor line. Radiosensitivities could roughly be divided into two groups. The more radiosensitive group included: sarcoma, small-cell lung cancer, non-small cell lung cancer, colorectal cancer, medulloblastoma and melanoma. The more radioresistant group included breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers. Using a model of a 3 cm diameter brain lesion containing about 1.4 x 10(9) oxic cells, the single doses calculated to reduce survival to 1 cell were: sarcoma and small cell lung cancers-22-23 Gy; melanoma-25 Gy; non-small cell lung and colorectal cancer-26 Gy; medullo-blastoma-28 Gy; breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers-30-36 Gy. If, however, tumors contained on average 20 percent hypoxic cells, the dose needed for equivalent cell killing increased by about a factor of 2.6-2.8. Also, there was no correlation between the ranking of relative radiosensitivities of the various classes of tumor cells at high doses (as in radiosurgery) to the sensitivity at low doses (as in conventional fractionated radiotherapy).

CONCLUSION

available information on the intrinsic radiosensitivity of human tumor cells indicates that meaningful differences exist among different histological classes of neoplasm that are relevant to the single high doses used in radioneurosurgery, and which could constitute a basis for "tailoring" the administered dose to the particular neoplasm. However, if intracerebral lesions contain a large number of hypoxic cells (e.g., 20%), this may constitute a significant problem.

Interactions between 4-HPR and diet in NMU-induced mammary tumorigenesis

The present study was designed to determine whether the chemopreventive effect of the synthetic retinoid N(4-hydroxyphenyl)retinamide (4-HPR) on mammary tumorigenesis was influenced by diet. Three diets were used: the closed-formula grain-based Wayne Lab Blox, the open-formula grain-based NIH-07, and the casein-based semipurified AIN-76A. Groups of 25 virgin female F-344 rats were fed the experimental diets beginning one week before a single injection of N-methyl-N-nitrosourea (NMU, 45 mg/kg body wt i.v.) at 50 days of age. The experimental design was as follows: Group 1, unsupplemented AIN-76A; Group 2, AIN-76A supplemented with 4-HPR starting seven days before NMU until termination (-7); Group 3, AIN-76A supplemented with 4-HPR seven days after NMU until termination (+7); Group 4, Wayne (no 4-HPR); Group 5, Wayne (4-HPR, -7); Group 6, Wayne (4-HPR, +7); Group 7, NIH-07; Group 8, NIH-07 (4-HPR, -7). 4-HPR [782 mg/kg diet (2 mM)] was given to all supplemented groups. Termination was 25 weeks post-NMU. Analysis of tumor incidence, multiplicity, and latency indicated that 1) control rats fed the AIN-76A diet exhibited significantly higher mammary tumor yields than rats fed unsupplemented natural-ingredient diets (Wayne and NIH-07) and 2) 4-HPR inhibited mammary tumor development in the two grain-based diets but enhanced tumor development in the AIN-76A diet. Animals fed the AIN-76A diet gained weight to a greater extent than those fed the Wayne or NIH-07 diets and exhibited lower levels of circulating 4-HPR.

A quantitative assessment of renal blood flow autoregulation in experimental diabetes

Several approaches have been utilized to describe renal blood flow (RBF) autoregulation in normal and pathological conditions. When describing the relation between RBF and stepwise decrements in renal perfusion pressure (RPP), these methods have several limitations, including: the necessity for predetermining a pressure 'break-point', and establishing constraints on changes in flow. To circumvent these limitations, we successfully utilized a third order polynomial, the cubical parabola, to characterize the autoregulatory responses in untreated streptozotocin (STZ) diabetic and control rats. The nonlinear relationship occurring between RBF and RPP was estimated from individual observations using the equation RBF = a + b x 10(-6) (RPP-c)3. Variables a and c represent RBF and RPP at the inflection point of the curve, respectively; variable b represents the rate of fall of RBF as RPP decreases (shape factor). Variable c was significantly lower in the diabetic group than in the control group whereas variable b was greater in the diabetic group. RBF (a) did not differ between the two groups. In conclusion, we determined that the range of RBF autoregulation in untreated diabetic rats is reset to a lower RPP. Furthermore, the curve below the inflection point declines more rapidly in diabetic rats than in controls. We propose that the equation described herein constitutes a promising and reproducible method for describing RBF autoregulation in vivo.

Successful delivery following myocardial ischemia during the second trimester of pregnancy

Acute myocardial infarction during pregnancy is considered to be associated with approximately 50% mortality of both mother and fetus. However, there are not enough data regarding the role of acute myocardial ischemia. We present a 36-year-old, pregnant, white female who was admitted twice at 18 and 20 weeks of gestation with acute myocardial ischemia. Cardiac catheterization revealed 70-80% stenosis of the mid left anterior descending artery (LAD) with normal antegrade flow and very good retrograde filling of the LAD from distal collaterals of the right coronary artery. Therefore, due to angiographic suggestion of protected LAD territory, we recommended medical therapy and scheduled a vaginal delivery that was successfully completed without cardiovascular complications. A stress thallium test performed 6 months later was normal, supporting our clinical judgment. In conclusion, every case of a pregnant woman with coronary insufficiency should be treated according to individual coronary anatomy and blood supply to the territory of the diseased artery, and should not be based on the old data in the literature. The decision for revascularization prior to delivery versus medical therapy, or Caesarean section versus natural delivery, should be made by a team of a cardiologist and an obstetrician.

Protein kinase C and calcium channel activation as determinants of renal vasoconstriction by angiotensin II and endothelin

The mechanisms mediating renal microvascular constriction induced by angiotensin II (Ang II) and endothelin (ET) have not been fully established. In the present study, we have determined the effects of isradipine, a dihydropyridine calcium antagonist, on Ang II- or ET-induced constriction of afferent arterioles (AAs) and efferent arterioles (EAs) using the isolated perfused hydronephrotic kidney. Ang II (0.3 nmol/L) and ET (0.3 nmol/L) constricted AAs by 36 +/- 2% and 29 +/- 3%, respectively. Isradipine reversed AA constriction induced by both peptides. However, Ang II-induced AA constriction was more sensitive to isradipine than ET-induced constriction (half-maximal inhibitory concentration [IC50], 1.2 +/- 0.2 nmol/L [n = 12] versus 170 +/- 65 nmol/L [n = 19]; P < .01). The sensitivity of Ang II-induced AA constriction to isradipine was identical to that of KCI-induced AA constriction (IC50, 4.2 +/- 0.9 nmol/L; n = 12). Pretreatment with staurosporine (50 nmol/L), a protein kinase C inhibitor, enhanced the sensitivity of ET-induced AA constriction to isradipine (4.3 +/- 1.7 nmol/L, n = 14), rendering it identical to that of KCl-induced AA constriction. Ang II and ET decreased EA diameter by 26 +/- 2% (n = 12) and 12 +/- 2% (n = 8), respectively. In contrast to AA constriction, EA constriction induced by both peptides was relatively refractory to isradipine.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-converting enzyme inhibitors and progression of nondiabetic chronic renal disease

In recent years, considerable attention has focused on the possibility that some classes of antihypertensive agents may confer a greater renoprotective effect in retarding the progression of chronic renal insufficiency. Experimental studies in rats have demonstrated that the sustained increase in glomerular capillary pressure evoked in response to loss of renal mass produces a destructive sclerosing reaction. Administration of angiotensin-converting enzyme inhibitors decreases glomerular capillary pressure with a resultant reduction of glomerular sclerosis, suggesting that angiotensin-converting enzyme inhibitor therapy may protect the injured kidney from hemodynamically mediated glomerular damage. On the basis of these experimental observations, many studies have attempted to investigate whether angiotensin-converting enzyme inhibitors can slow the progression of chronic renal disease in humans. We surveyed the literature critically and concluded that, the data from animals notwithstanding, the majority of studies in humans have been nonrandomized, of too short duration, or confounded by investigative difficulties. Therefore, we cannot yet conclude that angiotensin-converting enzyme inhibitors modify the rate at which renal disease progresses in nondiabetic patients.

Calcium antagonists and the kidney. Implications for renal protection

During the past decade, attention has focused on the effects of calcium antagonists on renal function. When administered in vitro to the isolated perfused kidney, calcium antagonists exhibit consistent actions permitting characterization of their renal effects. Calcium antagonists do not affect the vasodilated isolated perfused kidney, but they alter dramatically the response of this preparation to vasoconstrictor agents. Our recent studies using the isolated perfused hydronephrotic rat kidney model, which permits direct visualization of afferent and efferent arterioles, demonstrated that the preferential augmentation of glomerular filtration rate observed in the isolated perfused kidney is attributable to preferential vasodilation of preglomerular vessels. Although the clinical implications of such observations have not been fully delineated, the results of recent studies indicate that calcium antagonists exert salutary effects on renal function in clinical settings characterized by impaired renal hemodynamics. Such disorders include radiocontrast-induced nephrotoxicity and transplant-associated acute renal insufficiency. It is apparent, however, that the renal hemodynamic effects of calcium antagonists commend their use in the management of essential hypertension.

Calcium antagonists and the kidney: future therapeutic perspectives

During the past decade, attention has focused on the effects of calcium antagonists on renal function. Recent studies using diverse videomicroscopic techniques including the isolated perfused hydronephrotic rat kidney model, which permits direct visualization of afferent and efferent arterioles, have demonstrated that calcium antagonists acutely antagonize preglomerular vasoconstriction. In contrast, most studies suggest that the efferent arteriole appears to be refractory to the vasodilatory effects of these agents. Although the clinical implications of such observations have not been fully delineated, the results of recent studies indicate that calcium antagonists exert salutary effects on renal function in clinical settings characterized by impaired renal hemodynamics, including transplant-associated acute renal insufficiency and, possibly, cyclosporine nephrotoxicity. Evidence has accrued to suggest that calcium antagonists also may be protective against acute radiocontrast-induced nephrotoxicity. Finally, the renal hemodynamic and natriuretic effects of calcium antagonists commend their use as antihypertensive agents in the management of essential hypertension and transplant-associated hypertension.

Characterization of the renal microvascular actions of a new dopaminergic (DA1) agonist, YM435

The renal vasculature is known to possess receptors for dopamine. The effects of dopamine and its mimetics on renal hemodynamics, however, have not been fully determined. In the present study, we have characterized the actions of the dopaminergic (DA1) agonist, YM435, on renal microvascular constriction induced by two dissimilar peptide vasoconstrictors, angiotensin II (AII) and endothelin (ET), in the isolated perfused hydronephrotic rat kidney. AII (0.3 nM) constricted afferent (AA) and efferent arterioles (EA) by 30 +/- 2% and 28 +/- 4%, respectively. ET (0.3 nM) preferentially constricted AA (37 +/- 2%) more than EA (18 +/- 2%). The subsequent administration of YM435 reversed the constrictor effects of AII or ET on both AA and EA in a dose-dependent manner. Although YM435 reversed AA and EA vasoconstriction induced by each peptide, the half-maximal inhibitory concentration for YM435 of ET-induced constriction exceeded that of AII (P < .001). Our findings constitute the first demonstration that YM435 is a potent vasodilator in the setting of either AII- or ET-induced AA and EA constriction. These results indicate that DA1 agonists reverse renal microvascular constriction mediated by AII and/or ET, and suggest that both AA and EA constitute the renal microvascular sites of action for DA1 agonists.

Atrial natriuretic factor and liver disease

A working formulation for the role of ANF in the sodium retention of cirrhosis is summarized in Figure 4. Sodium retention is initiated early in cirrhosis, either as a result of hepatic venous outflow block or of primary vasodilation. The consequent intravascular volume expansion causes increases in ANF levels. At this stage of disease, the rise in ANF level is sufficient to counterbalance the antinatriuretic influences. However, this occurs at the expense of an expanded intravascular volume with the potential for overflow ascites. With progression of disease, disruption of intrasinusoidal Starling forces and loss of volume from the vascular compartment into the peritoneal compartment occur. This underfilling of the circulation may attenuate further increases in plasma ANF and promotes the activation of antinatriuretic factors. At this later stage of disease, elevated levels of ANF are insufficient to counterbalance antinatriuretic influences. Thus the role of ANF in cirrhosis is primarily beneficial in that it successfully attenuates the antinatriuretic forces in the compensated stage. Raised ANF levels have two potential deleterious effects. First, ANF may exacerbate arterial vasodilation, leading to further sodium retention. The primacy of vasodilatation has been proposed as an alternate formulation to the overflow and underfill hypotheses. Second, Epstein et al. found higher basal ANF levels in cirrhotic patients with edema than in those patients without edema. ANF is known to reduce plasma volume in anephric animals and to increase the ultrafiltration coefficients of isolated capillaries. Therefore it is conceivable that in the clinical setting in which antinatriuretic factors limit the renal responsiveness to ANF but in which ANF levels are elevated (i.e., cirrhosis, congestive heart failure, primary kidney disease), ANF itself may contribute to edema formation at the level of the peripheral microcirculation. In general, ANF likely has no primary role in the sodium retention in cirrhosis. In early compensated cirrhosis, ANF may maintain sodium homeostasis despite the presence of mild antinatriuretic factors. In late ascitic cirrhosis renal resistance to ANF develops, rendering it ineffective.(ABSTRACT TRUNCATED AT 400 WORDS)

Diagnosing sphingolipidoses in murine and human embryos

The aim of this study was to diagnose lipid storage diseases in embryos at the preimplantation stage. Two parallel approaches were employed. Firstly, activities of several sphingolipid hydrolases were determined in extracts of murine embryos and also human oocytes and polyspermic embryos. Sensitive fluorescent or fluorogenic procedures provided indications that Tay-Sachs, Gaucher and Krabbe diseases might be diagnosed in one human blastomere, while for Niemann-Pick disease two might be required. Secondly, pyrene lipids were administered into murine embryos and their fluorescence was quantified by computerized imaging microscopy. As a model of Gaucher disease, the fluorescent substrate pyrene glucosylceramide was administered into murine embryos in the presence or absence of an inhibitor of the enzyme beta-glucosidase. Because of decreased degradation of the substrate in enzyme-inhibited cells, the fluorescence per blastomere was considerably greater relative to those which received no inhibitor. The results indicated that lipid storage diseases might be diagnosed in single human blastomeres at the preimplantation stage, obviating the need for pre-natal diagnosis and abortion of affected foetuses.