Clonidine after renal ischemia to lessen acute renal failure and microvascular damage

Anesthesia and the renal sympathetic nervous system in perioperative AKI

Approximately 7% of patients undergoing non-cardiac surgery with general anesthesia develop postoperative acute kidney injury (AKI). It is well-known that general anesthesia may have an impact on renal function and water balance regulation, but the mechanisms and potential differences between anesthetics are not yet completely clear. Recently published large animal studies have demonstrated that volatile (gas) anesthesia stimulates the renal sympathetic nervous system more than intravenous propofol anesthesia, resulting in decreased water and sodium excretion and reduced renal perfusion and oxygenation. Whether this is the case also in humans remains to be clarified. Increased renal sympathetic nerve activity may impair renal excretory function and oxygenation and induce structural injury in ischemic AKI models and could therefore be a contributing factor to AKI in the perioperative setting. This review summarizes anesthetic agents' effects on the renal sympathetic nervous system that may be important in the pathogenesis of perioperative AKI.

Role of α- and β-adrenergic signaling in phenotypic targeting: significance in benign and malignant urologic disease

The urinary tract is highly innervated by autonomic nerves which are essential in urinary tract development, the production of growth factors, and the control of homeostasis. These neural signals may become dysregulated in several genitourinary (GU) disease states, both benign and malignant. Accordingly, the autonomic nervous system is a therapeutic target for several genitourinary pathologies including cancer, voiding dysfunction, and obstructing nephrolithiasis. Adrenergic receptors (adrenoceptors) are G-Protein coupled-receptors that are distributed throughout the body. The major function of α1-adrenoceptors is signaling smooth muscle contractions through GPCR and intracellular calcium influx. Pharmacologic intervention of α-and β-adrenoceptors is routinely and successfully implemented in the treatment of benign urologic illnesses, through the use of α-adrenoceptor antagonists. Furthermore, cell-based evidence recently established the antitumor effect of α1-adrenoceptor antagonists in prostate, bladder and renal tumors by reducing neovascularity and impairing growth within the tumor microenvironment via regulation of the phenotypic epithelial-mesenchymal transition (EMT). There has been a significant focus on repurposing the routinely used, Food and Drug Administration-approved α1-adrenoceptor antagonists to inhibit GU tumor growth and angiogenesis in patients with advanced prostate, bladder, and renal cancer. In this review we discuss the current evidence on (a) the signaling events of the autonomic nervous system mediated by its cognate α- and β-adrenoceptors in regulating the phenotypic landscape (EMT) of genitourinary organs; and (b) the therapeutic significance of targeting this signaling pathway in benign and malignant urologic disease. Video abstract.

Renal Sympathetic Nerve-Derived Signaling in Acute and Chronic kidney Diseases

The kidney is innervated by afferent sensory and efferent sympathetic nerve fibers. Norepinephrine (NE) is the primary neurotransmitter for post-ganglionic sympathetic adrenergic nerves, and its signaling, regulated through adrenergic receptors (AR), modulates renal function and pathophysiology under disease conditions. Renal sympathetic overactivity and increased NE level are commonly seen in chronic kidney disease (CKD) and are critical factors in the progression of renal disease. Blockade of sympathetic nerve-derived signaling by renal denervation or AR blockade in clinical and experimental studies demonstrates that renal nerves and its downstream signaling contribute to progression of acute kidney injury (AKI) to CKD and fibrogenesis. This review summarizes our current knowledge of the role of renal sympathetic nerve and adrenergic receptors in AKI, AKI to CKD transition and CKDand provides new insights into the therapeutic potential of intervening in its signaling pathways.

The sympathetic nervous system in acute kidney injury

Acute kidney injury (AKI) is frequently accompanied by activation of the sympathetic nervous system (SNS). This may result from pre-exisiting chronic diseases associated with sympathetic activation prior to AKI or it may be induced by stressors that ultimately lead to AKI such as endotoxins and arterial hypotension in circulatory shock. Conversely, sympathetic activation may also result from acute renal injury. Focusing on studies in experimental renal ischaemia and reperfusion (IR), this review summarizes the current knowledge on how the SNS is activated in IR-induced AKI and on the consequences of sympathetic activation for the development of acute renal damage. Experimental studies show beneficial effects of sympathoinhibitory interventions on renal structure and function in response to IR. However, few clinical trials obtained in scenarios that correspond to experimental IR, namely major elective surgery, showed that peri-operative treatment with centrally acting sympatholytics reduced the incidence of AKI. Apparently, discrepant findings on how sympathetic activation influences renal responses to acute IR-induced injury are discussed and future areas of research in this field are identified.

Renal sympathetic nerve activation via α2-adrenergic receptors in chronic kidney disease progression

Chronic kidney disease (CKD) is increasing worldwide without an effective therapeutic strategy. Sympathetic nerve activation is implicated in CKD progression, as well as cardiovascular dysfunction. Renal denervation is beneficial for controlling blood pressure (BP) and improving renal function through reduction of sympathetic nerve activity in patients with resistant hypertension and CKD. Sympathetic neurotransmitter norepinephrine (NE) via adrenergic receptor (AR) signaling has been implicated in tissue homeostasis and various disease progressions, including CKD. Increased plasma NE level is a predictor of survival and the incidence of cardiovascular events in patients with end-stage renal disease, as well as future renal injury in subjects with normal BP and renal function. Our recent data demonstrate that NE derived from renal nerves causes renal inflammation and fibrosis progression through alpha-2 adrenergic receptors (α₂-AR) in renal fibrosis models independent of BP. Sympathetic nerve activation-associated molecular mechanisms and signals seem to be critical for the development and progression of CKD, but the exact role of sympathetic nerve activation in CKD progression remains undefined. This review explores the current knowledge of NE-α₂-AR signaling in renal diseases and offers prospective views on developing therapeutic strategies targeting NE-AR signaling in CKD progression.

Effects of dexmedetomidine on renal tissue after lower limb ischemia reperfusion injury in streptozotocin induced diabetic rats

AIM

The aim of this study was to investigate whether dexmedetomidine - administered before ischemia - has protective effects against lower extremity ischemia reperfusion injury that induced by clamping and subsequent declamping of infra-renal abdominal aorta in streptozotocin-induced diabetic rats.

MATERIAL AND METHODS

After obtaining ethical committee approval, four study groups each containing six rats were created (Control (Group C), diabetes-control (Group DM-C), diabetes I/R (Group DM-I/R), and diabetes-I/R-dexmedetomidine (Group DM-I/R-D). In diabetes groups, single-dose (55 mg/kg) streptozotocin was administered intraperitoneally. Rats with a blood glucose level above 250 mg/dl at the 72nd hour were accepted as diabetic. At the end of four weeks, laparotomy was performed in all rats. Nothing else was done in Group C and DM-C. In Group DM-I/R, ischemia reperfusion was produced via two-hour periods of clamping and subsequent declamping of infra-renal abdominal aorta. In Group DM-I/R-D, 100 μg/kg dexmedetomidine was administered intraperitoneally 30 minutes before ischemia period. At the end of reperfusion, period biochemical and histopathological evaluation of renal tissue specimen were performed.

RESULTS

Thiobarbituric acid reactive substance (TBARS), Superoxide dismutase (SOD), Nitric oxide synthase (NOS), Catalase (CAT) and Glutathion S transferase (GST) levels were found significantly higher in Group DM-I/R when compared with Group C and Group DM-C. In the dexmedetomidine-treated group, TBARS, NOS, CAT, and GST levels were significantly lower than those measured in the Group D-I/R. In histopathological evaluation, glomerular vacuolization (GV), tubular dilatation (TD), vascular vacuolization and hypertrophy (VVH), tubular cell degeneration and necrosis (TCDN), tubular hyaline cylinder (THC), leucocyte infiltration (LI), and tubular cell spillage (TCS) in Group DM-I/R were significantly increased when compared with the control group. Also, GV, VVH, and THC levels in the dexmedetomidine-treated group (Group DM-I/R-D) were found significantly decreased when compared with the Group DM-I/R.

CONCLUSION

We found that dexmedetomidine - 100 μg/kg intraperitoneally - administered 30 minutes before ischemia in diabetic rats ameliorates lipid peroxidation, oxidative stress, and I-R-related renal injury. We suggest that dexmedetomidine administration in diabetic rats before I/R has renoprotective effects.

Postischemic microvasculopathy and endothelial progenitor cell-based therapy in ischemic AKI: update and perspectives

Acute kidney injury (AKI) dramatically increases mortality of hospitalized patients. Incidences have been increased in recent years. The most frequent cause is transient renal hypoperfusion or ischemia which induces significant tubular cell dysfunction/damage. In addition, two further events take place: interstitial inflammation and microvasculopathy (MV). The latter evolves within minutes to hours postischemia and may result in permanent deterioration of the peritubular capillary network, ultimately increasing the risk for chronic kidney disease (CKD) in the long term. In recent years, our understanding of the molecular/cellular processes responsible for acute and sustained microvasculopathy has increasingly been expanded. The methodical approaches for visualizing impaired peritubular blood flow and increased vascular permeability have been optimized, even allowing the depiction of tissue abnormalities in a three-dimensional manner. In addition, endothelial dysfunction, a hallmark of MV, has increasingly been recognized as an inductor of both vascular malfunction and interstitial inflammation. In this regard, so-called regulated necrosis of the endothelium could potentially play a role in postischemic inflammation. Endothelial progenitor cells (EPCs), represented by at least two major subpopulations, have been shown to promote vascular repair in experimental AKI, not only in the short but also in the long term. The discussion about the true biology of the cells continues. It has been proposed that early EPCs are most likely myelomonocytic in nature, and thus they may simply be termed proangiogenic cells (PACs). Nevertheless, they reliably protect certain types of tissues/organs from ischemia-induced damage, mostly by modulating the perivascular microenvironment in an indirect manner. The aim of the present review is to summarize the current knowledge on postischemic MV and EPC-mediated renal repair.

Renal denervation prevents long-term sequelae of ischemic renal injury

Signals that drive interstitial fibrogenesis after renal ischemia reperfusion injury remain undefined. Sympathetic activation is manifest even in the early clinical stages of chronic kidney disease and is directly related to disease severity. A role for renal nerves in renal interstitial fibrogenesis in the setting of ischemia reperfusion injury has not been studied. In male 129S1/SvImJ mice, ischemia reperfusion injury induced tubulointerstitial fibrosis as indicated by collagen deposition and profibrotic protein expression 4 to 16 days after the injury.. Leukocyte influx, proinflammatory protein expression, oxidative stress, apoptosis, and cell cycle arrest at G2/M phase were enhanced after ischemia reperfusion injury. Renal denervation at the time of injury or up to 1 day post-injury improved histology, decreased proinflammatory/profibrotic responses and apoptosis, and prevented G2/M cell cycle arrest in the kidney. Treatment with afferent nerve-derived calcitonin gene-related peptide (CGRP) or efferent nerve-derived norepinephrine in denervated and ischemia reperfusion injury-induced kidneys mimicked innervation, restored inflammation and fibrosis, induced G2/M arrest, and enhanced TGF-β1 activation. Blocking norepinephrine or CGRP function using respective receptor blockers prevented these effects. Consistent with the in vivo study, treatment with either norepinephrine or CGRP induced G2/M cell cycle arrest in HK-2 proximal tubule cells, whereas antagonists against their respective receptors prevented G2/M arrest. Thus, renal nerve stimulation is a primary mechanism and renal nerve-derived factors drive epithelial cell cycle arrest and the inflammatory cascade causing interstitial fibrogenesis after ischemia reperfusion injury.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Dexmedetomidine provides renoprotection against ischemia-reperfusion injury in mice

INTRODUCTION

Acute kidney injury following surgery incurs significant mortality with no proven preventative therapy. We investigated whether the α2 adrenoceptor agonist dexmedetomidine (Dex) provides protection against ischemia-reperfusion induced kidney injury in vitro and in vivo.

METHODS

In vitro, a stabilised cell line of human kidney proximal tubular cells (HK2) was exposed to culture medium deprived of oxygen and glucose. Dex decreased HK2 cell death in a dose-dependent manner, an effect attenuated by the α2 adrenoceptor antagonist atipamezole, and likely transduced by phosphatidylinositol 3-kinase (PI3K-Akt) signaling. In vivo C57BL/6J mice received Dex (25 μg/kg, intraperitoneal (i.p.)) 30 minutes before or after either bilateral renal pedicle clamping for 25 minutes or right renal pedicle clamping for 40 minutes and left nephrectomy.

RESULTS

Pre- or post-treatment with Dex provided cytoprotection, improved tubular architecture and function following renal ischemia. Consistent with this cytoprotection, dexmedetomidine reduced plasma high-mobility group protein B1 (HMGB-1) elevation when given prior to or after kidney ischemia-reperfusion; pretreatment also decreased toll-like receptor 4 (TLR4) expression in tubular cells. Dex treatment provided long-term functional renoprotection, and even increased survival following nephrectomy.

CONCLUSIONS

Our data suggest that Dex likely activates cell survival signal pAKT via α2 adrenoceptors to reduce cell death and HMGB1 release and subsequently inhibits TLR4 signaling to provide reno-protection.

Moxonidine prevents ischemia/reperfusion-induced renal injury in rats

Enhancement of renal sympathetic nerve activity during renal ischemia and its consequent effect on norepinephrine overflow from nerve endings after reperfusion play important roles in the development of ischemic acute kidney injury. In the present study, we evaluated whether moxonidine, an alpha(2)-adrenaline/I(1)-imidazoline receptor agonist which is known to elicit sympathoinhibitory action, would prevent the post-ischemic renal injury. Ischemic acute kidney injury was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Intravenous (i.v.) injection of moxonidine at a dose of 360 nmol/kg to ischemic acute kidney injury rats suppressed the enhanced renal sympathetic nerve activity during the ischemic period, to a degree similar to findings with intracerebroventricular (i.c.v.) injection of moxonidine at a dose of 36 nmol/kg. On the other hand, suppressive effects of the i.v. treatment on renal venous norepinephrine overflow, renal dysfunction and tissue injury in the post-ischemic kidney were significantly greater than those elicited by the i.c.v. treatment. These results suggest that renoprotective effects of moxonidine on ischemic acute kidney injury probably result from its suppressive action on the ischemia-enhanced renal sympathetic nerve activity followed by norepinephrine spillover from the nerve endings of the post-ischemic kidney.

Preventive mechanisms of agmatine against ischemic acute kidney injury in rats

The excitation of renal sympathetic nervous system plays an important role in the development of ischemic acute kidney injury in rats. Recently, we found that agmatine, an adrenaline alpha(2)/imidazoline I(1)-receptor agonist, has preventive effects on ischemic acute kidney injury by suppressing the enhanced renal sympathetic nerve activity during renal ischemia and by decreasing the renal venous norepinephrine overflow after reperfusion. In the present study, we investigated preventive mechanisms of agmatine against ischemic acute kidney injury in rats. Ischemic acute kidney injury was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after the contralateral nephrectomy. Pretreatment with efaroxan (30 mumol/kg, i.v.), an alpha(2)/I(1)-receptor antagonist, abolished the suppressive effects of agmatine on the enhanced renal sympathetic nerve activity during renal ischemia and on the elevated norepinephrine overflow after reperfusion, and eliminated the preventing effects of agmatine on the ischemia/reperfusion-induced renal dysfunction and histological damage. On the other hand, pretreatment with yohimbine (6 mumol/kg, i.v.), an alpha(2)-receptor antagonist, eliminated the preventing effects of agmatine on the ischemia/reperfusion-induced renal injury and norepinephrine overflow, without affecting the lowering effect of agmatine on renal sympathetic nerve activity. These results indicate that agmatine prevents the ischemic renal injury by sympathoinhibitory effect probably via I(1) receptors in central nervous system and by suppressing the norepinephrine overflow through alpha(2) or I(1) receptors on sympathetic nerve endings.

Selective antagonism of the postsynaptic alpha(1)-adrenoceptor is protective against ischemic acute renal failure in rats

We investigated the effects of prazosin, an alpha(1)-adrenoceptor antagonist, on the pathogenesis of ischemic acute renal failure in rats. Ischemic acute renal failure was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. An in vivo microdialysis study revealed that renal interstitial norepinephrine levels were increased with the ischemia/reperfusion (n=3). Renal function in vehicle-treated acute renal failure rats markedly decreased 1 day after reperfusion (n=6), compared with those in sham-operated control animals (n=6). Pre-ischemic treatment with prazosin (100 microg/kg, i.v.) markedly and significantly attenuated the ischemia/reperfusion-induced renal dysfunction (n=6). Histopathological examination of the kidney of vehicle-treated acute renal failure rats revealed severe renal damage, which was also significantly suppressed by pre-ischemic treatment with 100 microg/kg prazosin. The same dose of prazosin given after reperfusion failed to improve the ischemia/reperfusion-induced renal dysfunction (n=6), in contrast to cases of the pre-ischemic treatment with this agent. The administration of prazosin before ischemia did not influence the elevation of renal venous plasma norepinephrine levels (n=6), which were observed both immediately and 1 day after reperfusion. From these findings, we suggest that norepinephrine released excessively from the post-ischemic kidney is involved in the pathogenesis of ischemic acute renal failure, probably acting at the postsynaptic alpha(1)-adrenoceptors.

Evidence-based renal protection in cardiac surgery

Acute renal dysfunction is a common serious complication of cardiac surgery. Although a diversity of mechanisms exist by which the kidney can be damaged during cardiac surgery, atheroembolism, ischemia-reperfusion, and inflammation are believed to be primary contributors to perioperative renal insult. In addition, the high metabolic demands of active tubular reabsorption and the oxygen diffusion shunt characteristic of renal circulation make the kidney particularly vulnerable to ischemic injury. Remote effects of acute renal injury likely contribute to the strong association of this condition with other major postoperative morbidities and mortality and justify the search for renoprotective agents, even when dialysis is never required. Nonpharmacologic preventive strategies include procedure planning that is based on risk stratification, avoidance of nephrotoxins, and meticulous perioperative clinical care, including optimizing intravascular volume and attention to modifiable risk factors such as minimizing hemodilution. Although numerous pharmacologic interventions to prevent or treat acute renal injury have shown promise in animal models, randomized placebo-controlled clinical trials that have looked at measures of significant adverse outcomes such as death and dialysis have not confirmed a benefit.

The role of renal sympathetic nervous system in the pathogenesis of ischemic acute renal failure

We investigated the role of renal sympathetic nervous system in the progression of ischemia/reperfusion-induced acute renal failure in rats. Acute renal failure was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after the contralateral nephrectomy. Renal venous plasma norepinephrine concentrations markedly and significantly increased immediately after reperfusion, thereafter, the increased level declined but remained higher even at 24 h after reperfusion. Renal sympathetic nerve activity was significantly augmented during the renal ischemia. Renal denervation or the administration of pentolinium, a ganglion blocking agent, (5 mg/kg i.v.) at 5 min before ischemia attenuated the ischemia/reperfusion-induced renal dysfunction and histological damage, such as proteinaceous casts in tubuli and tubular necrosis. The elevation of renal venous norepinephrine levels after reperfusion was suppressed by renal denervation or pentolinium treatment. Thus, a surgical or pharmacological blockade of renal sympathetic nerve prevents the progression of ischemia/reperfusion-induced acute renal failure, thereby suggesting that renal sympathetic nervous system plays an important role in the development of the ischemic acute renal failure.

Preventive effect of L-carnosine on ischemia/reperfusion-induced acute renal failure in rats

We investigated the effect of L-carnosine (beta-alanyl-L-histidine) on ischemic acute renal failure in rats. Ischemic acute renal failure was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function in untreated acute renal failure rats markedly decreased at 1 day after reperfusion. Pre-ischemic treatment with L-carnosine dose-dependently (1, 10 microg/kg, i.v.) attenuated the ischemia/reperfusion-induced renal dysfunction. Histopathological examination of the kidney of untreated acute renal failure rats revealed severe renal damage, which was significantly suppressed by pre-treatment with L-carnosine, at each dose given. In untreated acute renal failure rats, norepinephrine concentrations in renal venous plasma remarkably increased within 2 min after reperfusion and thereafter rapidly decreased. Pre-ischemic treatment with L-carnosine at a dose of 10 microg/kg significantly depressed the elevated norepinephrine level. On the other hand, although the higher dose of L-carnosine given 5 min after reperfusion tended to ameliorate the renal dysfunction after reperfusion, the improvement was moderate compared with those seen in pre-ischemic treatment. These results indicate that L-carnosine prevents the development of ischemia/reperfusion-induced renal injury, and the effect is accompanied by suppression of the enhanced norepinephrine release in the kidney immediately after reperfusion. Thus, the preventing effect of L-carnosine on ischemic acute renal failure is probably through the suppression of enhanced renal sympathetic nerve activity induced by ischemia/reperfusion.

Role of L-arginine-derived NO in ischemic acute renal failure in the rat

Nitric oxide (NO) is involved in the regulation of renal perfusion and glomerular hemodynamics under basal conditions. We examined the hypothesis that L-arginine-derived NO modifies ischemic acute renal failure (ARF) in the rat. After a basal period ischemia was induced by clamping of both renal arteries (40 min). Thereafter, in the reperfusion period, we intravenously infused L-arginine (Arg, 300 mg/kg/60 min), or L-monomethylarginine (MeArg, 30 mg/kg/60 min), or Arg + MeArg (300 mg/kg/60 min, 30 mg/kg/60 min, resp.). Besides monitoring of urinary flow rate and arterial blood pressure, and determination of sodium excretion, glomerular filtration rate (GFR, mL/min/100 g) was estimated at the end of the infusion period and again after another 30 and 120 min by inulin clearance (fluorescence-marked inulin). In the basal period GFR showed no differences between the groups (Arg: 0.86 +/- 0.07, MeArg: 0.92 +/- 0.06, Arg + MeArg: 0.89 +/- 0.08, control: 0.84 +/- 0.07). At 180 min after the beginning of the reperfusion period, GFR was 0.13-0.02 in the control group. After administration of Arg, a remarkable and persistent increase in GFR was observed (0.28 +/- 0.03), whereas infusion of MeArg showed no significant effects (0.13 +/- 0.04). Combined administration of Arg + MeArg revealed a moderate increase of GFR (0.19 +/- 0.05), ranging between the Arg and the control group. Also, 60 and 90 min after the beginning of the reperfusion period, the highest values for GFR were obtained in the Arg group. We conclude that in this model of ischemic ARF in the rat, L-arginine-derived NO is capable of improving renal function. These data underline the regulatory role of the L-Arg-NO pathway for renal function, not only under normal conditions, but also in ARF.

The protective effect of thromboxane synthetase inhibition on renal function in systemic sepsis

To study the role of thromboxane in systemic sepsis and renal failure, peritonitis was induced surgically in 22 sheep, leading to local and systemic sepsis. A selective thromboxane synthetase inhibitor, U63,557A (Upjohn Co, Kalamazoo, MI) was given before surgery in five animals and 30 minutes after surgery in five animals. A typical picture of volume-loaded, normotensive, vasodilated septic shock developed in all animals. Twenty four hours after induction of sepsis, the control group showed a marked reduction in glomerular filtration rate (GFR), urine volume, and urinary sodium excretion. Pretreated animals showed no change in GFR and a smaller reduction in urine volume and sodium excretion. The posttreatment group showed no change in any parameters of renal function. Plasma renin activity, urinary TXB2 excretion, and urinary 6-keto PGF1 alpha excretion increased after 24 hours only in the control group. Urinary TXB2 excretion was reduced by 80% in animals given U63,557A before surgery. The results indicate a significant protective effect of U63,557A on renal function during septic shock, probably related to reduced thromboxane synthesis, with no apparent deleterious systemic effects. The results support a role for thromboxane in the pathogenesis of acute renal failure in systemic sepsis.

Vasoactive hormones in the renal response to systemic sepsis

The pathophysiology of renal dysfunction in generalized sepsis remains unknown. In this study, 24 hours after surgical induction of peritonitis in 20 volume-loaded sheep, three patterns of renal function were seen. In group 1 (n = 8), glomerular filtration rate (GFR) decreased by 70%, urine volume by 85%, absolute sodium excretion by 95%, and fractional sodium excretion by 83%. Group 2 (n = 4) exhibited similar sodium retention but GFR did not fall. Group 3 (n = 8) showed no change in GFR or urine volume and only minimally reduced sodium excretion. Mean arterial pressure fell 17% in group 1 only; central venous pressure, pulmonary capillary wedge pressure, and plasma volume were maintained at or above presepsis values in all groups. Cardiac index was either increased or unchanged, and renal plasma flow was maintained in all groups; there was thus no hemodynamic evidence to suggest volume contraction. Histologic examination showed only minor changes with no consistent pattern. Renal functional changes correlated with other manifestations of severe sepsis--GFR and sodium retention correlated significantly with increased cardiac index, decreased systemic vascular resistance, pulmonary arterial hypertension, leukopenia, hypoproteinemia, and hypoglycemia. All of these changes were most marked in group 1. In groups 1 and 2, plasma renin activity (PRA) increased and urinary kallikrein excretion decreased. PRA correlated inversely with GFR, urine volume, and sodium excretion; urinary kallikrein excretion correlated positively with urine volume and sodium excretion. Urinary excretion of 6-keto-PGF1 alpha was increased in groups 1 and 2 and correlated inversely with mean arterial pressure in group 1 animals. During sepsis, urinary thromboxane B2 excretion continued at presepsis values in all groups. The results suggest that unusual reciprocal changes in activity of the renin-angiotensin and renal kallikrein-kinin systems may play a role in the renal response to sepsis. PGI2 synthesis is increased and may affect systemic hemodynamics and renal function; the role of thromboxane A2 in this context is unknown.

The renal response produced by nonhypotensive sepsis in a large animal model

We describe an animal model of generalized sepsis, induced in the sheep by cecal perforation, which reproduces the high systemic flow and peripheral vasodilation seen in early human sepsis. Despite volume loading, animals demonstrate a fall in glomerular filtration rate, oliguria, low fractional sodium excretion, maintained urine osmolarity, and increased plasma renin activity. Histologically, kidneys show no consistent abnormality; overall the findings suggest volume contraction or hypoperfusion. This is contradicted, however, by maintained blood pressure and pulmonary capillary wedge pressure, increased cardiac output, and reduced peripheral resistance. Increased Fc lysozyme and low molecular weight proteinuria suggest tubular damage. These paradoxical observations are currently unexplained.

Functional characterization of the alpha adrenergic receptor modulating the hydroosmotic effect of vasopressin on the rabbit cortical collecting tubule

To characterize the type of alpha adrenergic receptor, the effects of specific alpha adrenergic agonists and antagonists on antidiuretic hormone [( Arg8]-vasopressin [AVP])-induced water absorption were evaluated in cortical collecting tubules isolated from the rabbit kidney and perfused in vitro. In the presence of AVP (100 microU/ml), net fluid volume absorption (Jv, nanoliters per minute per millimeter) was 1.39 +/- 0.09 and osmotic water permeability coefficient (Pf, X 10(-4) centimeters per second) was 150.2 +/- 15.0. The addition of 10(-6) M phenylephrine (PE), an alpha adrenergic agonist, resulted in a significant decrease in Jv and Pf to 0.72 +/- 0.11 (P less than 0.005) and 69.9 +/- 10.9 (P less than 0.005). The addition of 10(-4) M prazosin (PZ), an alpha adrenergic antagonist, did not cause any significant change in Jv and Pf, which were 0.71 +/- 0.09 (P = NS vs. AVP + PE) and 67.8 +/- 9.5 (P = NS vs. AVP + PE), respectively. In a separate group of tubules, in the presence of AVP (100 microU/ml) and PE (10(-6) M), Jv and Pf were 0.78 +/- 0.17 and 76.1 +/- 18.0, respectively. The addition of 10(-6) M yohimbine (Y), an alpha 2 adrenergic antagonist, resulted in a significant increase in Jv to 1.46 +/- 0.14 (P less than 0.01) and Pf to 157.5 +/- 22.3 (P less than 0.005). Y (10(-4) M) or PZ (10(-4) M) alone did not significantly affect Jv and Pf in the presence of AVP )100 microU/ml). The effect of the natural endogenous catecholamine norepinephrine (NE) on Jv and Pf in the presence of AVP and propranolol (PR) was next examined. Jv and Pf were 1.53 +/- 0.07 and 176.3 +/- 5.2, respectively, in the presence of AVP (100 microU/ml) and PR (10(-4) M). The addition of NE (10(-8) M) resulted in a significant decrease in Jv to 1.19 +/- 0.11 (P less than 0.05) and Pf to 127.0 +/- 11.3 (P less than 0.02). Increasing the concentration of NE to 10(-6) M resulted in a further decrease in Jv and Pf to 0.70 +/- 0.10 (P less than 0.01 vs. NE 10(-8) M) and 68.5 +/- 10.6 (P less than 0.01 vs. NE 10(-8) M), respectively. The inhibitory effect of NE on AVP-induced water absorption was blocked by Y, but not by PZ. The effect of the alpha 2 adrenergic agonist clonidine (CD) on Jv and Pf was also examined. In the presence of AVP (10 microU/ml) Jv and Pf were 1.65 +/- 0.04 and 175.1 +/- 13.1, respectively. The addition of CD (10(-6) M) resulted in a significant decrease in Jv to 1.08 +/- 0.12 (P < 0.01) and Pf to 108.1 +/- 15.4 (P < 0.01). Increasing the concentration of CD to 10(-4) M resulted in a further significant decrease in Jv and Pf to 0.57 +/- 0.13 (P < 0.02 vs. CD 10(-6) M) and 54.7 +/- 13.8 (P < 0.01 vs. CD 10(-6) M), respectively. Similar results were obtained in the presence of AVP (100 microU/ml). The inhibitory effect of CD on AVP-induced water absorption was blocked by Y. CD did not significantly affect Jv and Pf in the presence of 8-bromo adenosine 3',5'-cyclic monophosphate. These studies indicate that alpha adrenergic agonists directly inhibit AVP-mediated water absorption at the level of renal tubule, an effect that can be blocked by specific alpha2 adrenergic antagonists, but not by specific alpha1 adrenergic antagonists. Alpha2 adrenergic stimulation directly inhibits AVP-mediate water absorption at the level of the tubule, an effect that can be blocked by a specific alpha2 adrenergic antagonist. This effect appears to be exerted at the level of activation of adenylate cyclase, since it is absent in the present of cyclic AMP.

Disparity between surface and deep nephron function early after renal ischemia

Experiments were performed using a variety of methods to assess the functional status of different nephron populations following 45 min of renal ischemia in the rat. Micropuncture techniques revealed that SNGFR and reabsorption in the surface nephrons are only modestly reduced after ischemia, whereas kidney GFR and reabsorption are more severely affected. Determinations of bolus velocity with the Hanssen technique or of glomerular blood flow with the microsphere method confirmed that both were highest in the surface nephrons, lower in the middle nephrons and lowest of all in the juxtamedullary nephrons after ischemia. It is concluded that surface nephron function is well-maintained following ischemia and that it is the functional deficiency of the deeper nephrons that is predominantly responsible for the impairment in whole kidney function. Although the pathogenic mechanism is not yet clear, neither tubular obstruction nor tubular leakage in the deeper nephrons seems to be involved. The present findings suggest that micropuncture of the surface nephrons is a technique of questionable validity for studying this type of acute renal failure, they explain the inability of the kidney to concentrate the final urine, and they predict a more pronounced deficiency in medullary than in outer cortical blood flow.

Nervous disorders of renal function

Renal nerves contribute to the genesis of at least four disease processes. 1. Excess renal nerve activity contributes significantly to salt and water retention by patients with congestive circulatory failure. 2. Circumstantial evidence suggests that dopamine production may be deficient in a group of patients with idiopathic edema. Aldosterone secretion is high in this group and it has been shown that dopamine exerts a tonic inhibitory effect on angiotensin-stimulated aldosterone secretion. 3. Excess renal nerve activity probably plays a crucial role in the transition from hypotension and pre-renal failure to ischemic acute tubular necrosis. 4. Without doubt hyperactivity of renal nerves causes systemic hypertension in a variety of animal disease models. There is also good reason to believe that this occurs in some forms of human hypertension. The effects of the sympathetic nervous system on renal vascular resistance, renin release, tubular electrolyte reabsorption and aldosterone secretion are discussed in the context of these four diseases.

Renal functional and metabolic studies on the role of preventive measures in experimental acute ischemic renal failure

In the present study 1 h of total occlusion of the left renal artery in conscious rats was chosen as experimental model of ischemic acute renal failure (ARF), while the contralateral kidney was left intact. Chronic high dietary sodium intake, acute isotonic saline infusion, or administration of saralasin did not protect from ARF. Furosemide, mannitol, and verapamil converted oliguric into non-oliguric ARF in 100%, 75%, and 60% of the animals, resp. Protection from oliguria and preservation of GFR inversely correlated with the depression of cortical ATP-concentration (control: 1.32 +/- 0.07 mumoles/g wet weight) 6 h after ischemia by 16%, 41%, and 58% in mannitol- and verapamil- treated rats and in untreated rats, resp. At this time, Na-K-ATPase enzyme activities in renal cortex and papilla were unaffected, while enzyme activity in outer medulla was suppressed from 15.4 +/- 1.4 to 9.4 +/- 1.0 mumoles Pi/mg protein h in all groups of animals. The results suggest that in this model of ARF renal ischemia not only affects cellular energy supply in renal cortex but also causes severe structural and functional impairment in the outer medulla, probably leading to tubular obstruction and depression of glomerular function. Pharmacological protection from ischemic oliguric ARF cannot be achieved by prior induction of high urine flow rates alone but depends on the degree of metabolic and functional reserve of the injured tubular epithelium.

Acute renal failure. 2. Pathophysiology, prevention, management, and prognosis

During the past five years, much has been learned about the complex pathophysiology of acute renal failure. A number of mechanisms appear to be involved, including cell swelling, inhibition of prostaglandin synthesis, tubular obstruction, and disruption of the basement membrane of the proximal tubule. For patients at high risk of acute tubular necrosis, prophylaxis with mannitol or furosemide (Lasix) should be considered under certain circumstances. If this syndrome does occur, management should focus on maintenance of proper fluid and electrolyte levels and nutrition, which is facilitated by dialysis. The prognosis of acute tubular necrosis has changed little in the past ten years, and mortality remains high.