Regulation of the renal circulation

Angiotensin II inhibition increases diuresis during acute sympathetic activation in intact and denervated kidneys in rats with chronic myocardial infarction

We examined urine excretion during primary acute sympathetic activation (PASA) in Wistar-Kyoto rats with myocardial infarction (MI). The rats underwent unilateral renal denervation (RDN) 7 weeks after coronary artery ligation. 4-10 days later, an acute experiment was performed under anesthetized conditions (n = 8 rats). Isolated carotid sinus pressure was changed stepwise from 60 to 180 mmHg, and the relationship between the arterial pressure (AP) and the normalized urine flow (nUF, urine flow normalized by the body weight) was examined. After obtaining the control data, an angiotensin II type 1 receptor blocker telmisartan (2.5 mg/kg) was intravenously administered. The effects of RDN, telmisartan, and heart weight (biventricular weight) on the relationship between AP and nUF were examined using multiple regression analyses. Regarding the slope of nUF versus AP (nUF_slope), the constant term of the regression was positive (0.315 ± 0.069 μL·min^-1·kg^-1·mmHg^-1), indicating that nUF increased with AP. The heart weight had a negative effect on nUF_slope (P < 0.05), suggesting that the severity of MI was associated with the impairment of urine excretion. Telmisartan increased nUF_slope by 0.358 ± 0.080 μL·min^-1·kg^-1·mmHg^-1 (P < 0.001), whereas RDN had no significant effect on this parameter. The results indicate that unilateral RDN was unable to abolish the effect of the renin-angiotensin system on urine excretion during PASA. Circulating or locally produced angiotensin II, rather than ongoing renal sympathetic nerve activity, played a dominant role in the impairment of urine excretion during PASA in rats with chronic MI.

Cardiovascular disease and hypertension risk in living kidney donors: an analysis of health administrative data in Ontario, Canada

BACKGROUND

Knowledge of any harm associated with living kidney donation guides informed consent and living donor follow-up. Risk estimates in the literature are variable, and most studies did not use a healthy control group to assess outcomes attributable to donation.

METHODS

We observed a retrospective cohort using health administrative data for donations which occurred in Ontario, Canada between the years 1993 and 2005. There were a total of 1278 living donors and 6359 healthy adults who acted as a control group. Individuals were followed for a mean of 6.2 years (range, 1-13 years) after donation. The primary outcome was a composite of time to death or first cardiovascular event (myocardial infarction, stroke, angioplasty, and bypass surgery). The secondary outcome was time to a diagnosis of hypertension.

RESULTS

There was no significant difference in death or cardiovascular events between donors and controls (1.3% vs. 1.7%; hazard ratio 0.7, 95% confidence interval 0.4-1.2). Donors were more frequently diagnosed with hypertension than controls (16.3% vs. 11.9%, hazard ratio 1.4, 95% confidence interval 1.2-1.7) but were also seen more often by their primary care physicians (median [interquartile range] 3.6 [1.9-6.1] vs. 2.6 [1.4-4.3] visits per person year, P<0.001).

CONCLUSIONS

Based on administrative data, the risk of cardiovascular disease was unchanged in the first decade after kidney donation. The observed increase in diagnosed hypertension may be due to nephrectomy or more blood pressure measurements received by donors in follow-up and requires prospective study.

Relationship between activation of the sympathetic nervous system and renal blood flow autoregulation in cirrhosis

BACKGROUND & AIMS

It has been proposed that activation of the sympathetic nervous system causes a rightward shift in the renal autoregulatory curve such that renal blood flow is critically dependent on renal perfusion pressure and that this contributes to the development of the hepatorenal syndrome. The aims of the study were to determine the relationship of renal blood flow and renal perfusion pressure in patients with liver cirrhosis and the effect on renal hemodynamics following insertion of a transjugular intrahepatic portosystemic shunt (TIPS).

METHODS

Fifty-six patients were recruited into groups (1) with no ascites, (2) with diuretic-responsive ascites, (3) with intractable ascites, (4) with type II hepatorenal syndrome, and (5) requiring a TIPSs for refractory ascites. We measured cardiac hemodynamics, renal blood flow, renal perfusion pressure, and portal pressure and norepinephrine levels and mathematically modeled the renal autoregulatory curve.

RESULTS

Renal blood flow correlated with renal perfusion pressure (r(2) = 0.78; P < .001) and inversely with the hepatic venous pressure gradient (r(2) = 0.61; P < .0001) and plasma norepinephrine levels (r(2) = 0.78; P < .0001). Norepinephrine levels increased with increasing disease severity, and this was associated with a rightward and downward shift of the renal blood flow/renal perfusion pressure autoregulatory curve. TIPS insertion reduced portal pressure and plasma norepinephrine levels (P < .001), and the renal blood flow/renal perfusion pressure curve was shifted upward.

CONCLUSIONS

The relationship between renal blood flow and renal perfusion pressure involves a critical interplay between the sympathetic nervous system and the kidney. TIPS insertion decreases sympathetic activation and improves renal function through positive effects on renal blood flow autoregulation.

Developmental changes in cyclo-oxygenase mRNA induction by hypoxia in rat kidney

BACKGROUND

Prostaglandins, synthesized by cyclo-oxygenase (COX), regulate renal hemodynamics and also epithelial water and solute transport. Developmental changes occur in COX-2 mRNA expression and its response to lipopolysaccharide stimulation in rats. We examined age-related changes in COX mRNA expression induced by hypoxia in the renal cortex and medulla of developing rats.

METHODS

Total RNA was extracted from 1- and 4-week-old male Wistar rats exposed to one or 4 h of hypoxia (8% O2). Cyclo-oxygenase mRNA was quantitatively analyzed using a real-time polymerase chain reaction with dual-labeled fluorogenic probes.

RESULTS

Expression of COX-1 mRNA did not change in response to hypoxia in the cortex or medulla in either infantile or adult rats. In infantile rats, COX-2 mRNA expression was not induced by one or 4 h of hypoxia. In adults, 1- and 4-h exposures to hypoxia induced COX-2 mRNA in the renal cortex, and 1-h of exposure induced COX-2 mRNA in the medulla.

CONCLUSIONS

Response of expression of COX-2 mRNA in rats exposed to acute hypoxia show age-related variability treated by acute hypoxia. Cyclo-oxygenase-2 might not play a major role in the hypoxic infantile rat kidney.

Functional assessment of the circulation of the single kidney

Functional alterations in the renal circulation that can contribute to abnormal renal perfusion have been demonstrated in various models of renal injury. To detect impairments in renal vascular function, renal flow reserve can be determined by repeated measurements of renal blood flow (RBF) during pharmacological challenge with short-acting vasodilators that should increase RBF in kidneys that are not severely damaged structurally. Among the invasive techniques for such measurements, the most readily available is probably the intravascular Doppler, which can be employed during renal angiography for rapid evaluation of changes in RBF during intrarenal injections of vasoactive substances. High-resolution tomographic imaging techniques, like electron-beam x-ray computed tomography, further offer the potential for noninvasive measurements of renal parenchymal perfusion and function, in association with either intrarenal or systemic injections of vasoactive substances. Acetylcholine is a potent short-acting renal vasodilator that can be useful to assess the response of the renal microcirculation, define renal flow reserve, and examine the endothelium-dependent responses of RBF. Such assessments of the function of the renal circulation can assist in evaluation of patients with systemic or renal disease for early detection and monitoring of renovascular injury.

Differential regulation of COX-2 expression in the kidney by lipopolysaccharide: role of CD14

Induction of the inducible cyclooxygenase isoform COX-2 is likely to be an important mechanism for increased prostaglandin production in renal inflammation. We examined the effect of lipopolysaccharide (LPS) on regional renal COX-2 expression in the rat. In the inner medulla, LPS injection (4 mg/kg ip) induced a twofold and 2.5-fold increase in the levels of COX-2 mRNA and COX-2 protein, respectively. In contrast, COX-2 expression in the renal cortex was not significantly altered. COX-2 promoter transgenic mice were created using the 2.7-kb flanking region of the rat COX-2 gene. In these animals, LPS injection induced reporter gene expression predominately in the inner medulla. The LPS receptor CD14, usually regarded as a monocyte/macrophage-specific marker, was found to be abundantly expressed in the inner medulla and in dissected inner medullary collecting duct (IMCD) cells, suggesting that it may mediate medullary COX-2 induction. CD14 was present only at low levels in cortex and cortical segments, including glomeruli. In cultured cells, it was abundant in mouse IMCD (mIMCD-K2) cells and renal medullary interstitial cells, but largely undetectable in mesangial cells and M1 cells, a cell line derived from mouse cortical collecting ducts. In the mIMCD-K2 cell line, LPS significantly induced COX-2 mRNA expression, with concomitant induction of CD14. LPS-stimulated COX-2 expression was reduced by the addition of an anti-CD14 monoclonal antibody to the culture medium. These results demonstrate that LPS selectively stimulates COX-2 expression in the renal inner medulla through a CD14-dependent mechanism.

Effects of long-term caffeine consumption on renal function in spontaneously hypertensive heart failure prone rats

Our previous studies supported the hypothesis that prolonged administration of caffeine to animals with high-renin hypertension causes progressive deterioration of renal function. However, thus far this hypothesis has been tested with only a few animal models of hypertension. The aim of this study was to test this hypothesis further by investigating the effects of long-term caffeine consumption on renal function in adult spontaneously hypertensive heart failure (SHHF/Mcc-fa(cp)) rats, another model of high-renin hypertension. Lean, male, 9-month-old SHHF/Mcc-fa(cp) rats were randomized to receive either normal drinking water (control group) or drinking water containing 0.1% caffeine (caffeine group) for 20 weeks. No changes in body weight, food and fluid intake, urine volume, and sodium and potassium excretion were found in conscious SHHF/Mcc-fa(cp) rats after 10 or 20 weeks of caffeine treatment. However, caffeine treatment accelerated the time-related decline in renal function and augmented urinary protein excretion. Ten weeks into the protocol, creatinine clearance was 3.6+/-0.4 and 5.7+/-0.9 L/kg/day in the caffeine group and control group, respectively (p<0.02), whereas 20 weeks into the study, creatinine clearance was similarly diminished in both groups. Proteinuria was greater in the caffeine group compared with the control group at both 10 (928+/-131 vs. 439+/-21 mg/kg/day, respectively; p<0.02) and 20 weeks (1,202+/-196 vs. 603+/-30 mg/kg/day, respectively; p<0.01) into the protocol. After 20 weeks, all animals were anesthetized and instrumented. Caffeine treatment for 20 weeks had no effects on blood pressure, heart rate, or vascular resistance in four examined vascular beds (abdominal aorta and renal, carotid, and mesenteric arteries). No changes in renal hemodynamics and electrolyte excretion were found, whereas significantly lower glomerular filtration rate (GFR; inulin clearance) and creatinine clearance (p<0.05) were observed in caffeine-treated animals. These data support our hypothesis that prolonged consumption of caffeine has adverse effects on renal function, in high-renin hypertension.

Influence of the renal endothelin A system on the autoregulation of renal hemodynamics in SHRs and WKY rats

In this study, we investigated the influence of a short-term blockade of the renal endothelin A system on the autoregulation of total renal blood flow, cortical renal blood flow, and pressure-dependent plasma renin activity in spontaneously hypertensive rats (SHRs) and normotensive controls [Wistar-Kyoto (WKY) rats]. In anesthetized rats, renal blood flow was measured by a transit-time flow probe and cortical blood flow by a laser flow probe. Blood samples were taken for measurement of plasma renin activity. Renal perfusion pressure was reduced in 5-mm Hg steps by means of a servocontrolled electropneumatic device by an inflatable suprarenal cuff. During the experiments, the rats (n = 6, each group) received an intrarenal infusion of either the selective endothelin A-receptor antagonist BQ123 (3 mg/kg/h) or vehicle. We observed an improvement of total and cortical blood flow autoregulation as indicated by a shift of lower limits of autoregulation to lower threshold pressures [103 +/- 2 vs. 132 +/- 4 mm Hg compared with 98 +/- 3 vs. 120 +/- 4 mm Hg (mean +/- SEM); p < 0.01 resp. p < 0.05] in BQ123-treated SHRs, whereas BQ123 had no influence on breakpoints of autoregulation in WKY rats (p > 0.05). Pressure-dependent plasma renin activity in SHRs was not influenced by BQ123. Renal blood flow autoregulation is improved in SHRs after short-term blockade of the renal endothelin A system. This effect is independent of the renin-angiotensin system. The endothelin A system does not seem to play an important role in the autoregulation of renal blood flow in normotensive WKY rats.

Renal haemodynamic characteristics in patients with lupus nephritis

OBJECTIVE

To clarify the characteristics of renal haemodynamics in patients with lupus nephritis (LN).

METHODS

The glomerular filtration rate (GFR) and renal plasma flow (RPF) of 37 patients with active LN were studied longitudinally over an interval of 8 to 144 weeks during treatment with corticosteroids or cytotoxic drugs, or both. All patients had clinical renal disorders and underwent renal biopsies.

RESULTS

Analysis of renal biopsy specimens showed that 31 patients had class IV LN. Class II, III, and VLN were present in two patients each. The average GFR increased significantly from 65.4 (SD 33.0) in the pretreatment stage to 86.6 (31.6) ml/min in the post-treatment stage, accompanied by an improvement in urinary or immunological abnormalities, or both. On the other hand, RPF decreased significantly from 625.2 (243.0) to 519.8 (179.0) ml/min. Therefore, the filtration fraction (FF) increased significantly from 10.7 (4.3)% to 16.8 (3.7)%. Low FF was recognised predominantly in patients with class IV LN, but was also observed in patients with other classes. The FF returned towards normal irrespective of the degree of GFR recovery. No significant changes were observed in the levels of blood pressure.

CONCLUSION

A reduction in GFR out of proportion to the reduction in RPF as demonstrated by the low FF values was related to the severity of LN or disease activity, or both. Therefore, relative evaluation of GFR and RPF, namely the determination of FF, may be a useful clinical parameter to determine the status of LN.

Comparison of systemic and renal hemodynamics measured by Doppler ultrasonography in canine experimental hypovolemia

The aim of this study was to examine renal hemodynamics at the hypovolemic and recovery phases in two different hypovolemic shock models using Doppler ultrasonography, and to compare this with systemic hemodynamics. In experiment 1, the hypovolemic phase was induced in 6 mongrel dogs by removing arterial blood at 30 ml/kg for 60 min. In the recovery phase, this blood was reinfused at 30 ml/kg over 60 min. In experiment 2, hypovolemia was induced in 12 beagle dogs by rapid blood removal until blood pressure decreased to 40 mmHg and was maintained at this pressure for 30 min. Six of the dogs were then infused with 20 ml/kg hydroxyethyl starch over 5 min, and the other 6 were infused with 60 ml/kg lactated Ringer's solution also over 5 min. Parameters for systemic and renal hemodynamics were measured by using a polygraph and the Doppler method, respectively. The decrease of diastolic blood flow, resulted in an increase of vessel resistance, and was detected in the hypovolemic kidney by the Doppler method. The rapid and large volume infusion of resuscitation fluids was effective for the recovery of both systemic circulation and renal blood flow, however this induced an increase of kidney vessel resistance, a result of the autoregulation mechanism of the kidney. The changes in these parameters at the main renal artery and interlobar artery were similar.

The hepatorenal syndrome

Hepatorenal syndrome may occur in any form of severe liver disease. It appears less common in children than adults, but still carries a poor prognosis. There are several factors involved in its aetiology, including a decreased renal perfusion pressure, activation of the renal sympathetic nervous system and increased synthesis of several vasoactive mediators, which may modulate glomerular filtration by acting as both renal vasoconstrictors and dynamic regulators of the glomerular capillary ultrafiltration coefficient, through their action on mesangial cells. This review will discuss the pathophysiology of the hepatorenal syndrome and some of the principles of management of patients with renal failure and severe liver disease. The role of renal support and liver transplantation will also be covered.

Color Doppler ultrasonography for the assessment of renal blood flow in heart failure

To validate color Doppler ultrasonography of renal arteries for the assessment of renal blood flow (RBF), we compared left and right RBF estimates and their sum (total RBF) by echo-Doppler with data obtained by iodine 123-123I-p-aminohippuric acid (PAH) scintigraphy in 19 patients with heart failure and 7 normal control subjects. Single-side and total RBF estimates by echo-Doppler ranged, respectively, between 179 and 428 mL/min/m2 and from 378 to 835 mL/min/m2 in patients with heart failure and between 265 and 601 mL/min/m2 and from 564 to 1,182 mL/min/m2 in normal control subjects. Single-side and total RBF estimates by echo-Doppler correlated well with measurements obtained by scintigraphy (r = 0.74 and 0.76, respectively, in patients with heart failure; both: p < 0.001). At Bland and Altman's analysis of correspondence between the 2 techniques, there were 17 disagreements (33.7%) for single-side RBF and 8 disagreements (31.8%) for total RBF. However, the two techniques disagreed markedly in only two single-side and one total RBF estimates. Thus, in patients with heart failure, RBF assessed noninvasively by color Doppler ultrasonography has a good correlation with 123I-PAH renal scintigraphy data over a wide range of blood flow.

Short-term effects of intra-aortic balloon pumping on renal blood flow and renal oxygen consumption in cardiogenic shock

Intra-aortic balloon pumping is frequently used in patients with cardiogenic shock when oliguria persists despite maximal pharmacologic support. The objective of this study was to measure the effect of intra-aortic balloon pumping on renal blood flow, renal oxygen delivery, and renal oxygen consumption in such patients. Central hemodynamics, renal blood flow, and oxygen transport were measured in 10 patients in low cardiac output states. Measurements were made with and without intra-aortic balloon counterpulsation. Renal blood flow was measured by continuous renal vein thermodilution. Small improvements were observed in cardiac output (3.1 +/- 0.8 vs 3.5 +/- 0.8 L/min, P < .01) and pulmonary capillary wedge pressure (22 +/- 5.6 vs 19 +/- 5.3 mmHg, P < .05), but mean arterial blood pressure was unchanged (69 +/- 11 vs 69 +/- 5 mmHg, not significant). Baseline renal blood flow was reduced to approximately 37%, renal oxygen delivery to 31%, and renal oxygen consumption to 60% of normal values. No significant improvement was seen in single-kidney renal blood flow (184 +/- 108 vs 193 +/- 107 mL/min), renal oxygen delivery (28 +/- 16 vs 30 +/- 16 mL/min), or renal oxygen consumption (4.9 +/- 2.0 vs 4.7 +/- 2.5 mL/min) in response to 1:1 counterpulsation. In comparison with measurements made during short-term suspension of counterpulsation, 1:1 aortic balloon pumping failed to result in an increase in renal blood flow, oxygen delivery, or oxygen consumption from the low levels observed in these patients.

Amelioration of glycerol-induced acute renal failure in rats by an adenosine A1 receptor antagonist (FR-113453)

A potent adenosine A1 receptor antagonist, FR-113453, was tested for its preventive effect on glycerol-induced acute renal failure in rats. First, the optimum timing of FR-113453 administration was studied. Oral FR-113453 (100 mg/kg) given 1 h before or 5-10 min after glycerol injection produced a significant reduction of the serum creatinine at 24 h (4.3 +/- 0.8 mg/dL [vehicle] vs. 1.4 +/- 0.4 mg/dL [FR-113453], and 4.7 +/- 1.1 mg/dL vs. 1.3 +/- 0.6 mg/dL, respectively, p < 0.001). However, when FR-113453 was given 2 h after glycerol injection, the serum creatinine did not improve. Creatinine clearance at 24 h after the induction of acute renal failure was significantly better in rats given FR-113453 (100 mg/kg) 1 h before glycerol than in rats given vehicle alone (0.08 +/- 0.08 mL/min vs. 0.01 +/- 0.02 mL/min), (p < 0.01). The kidney weight was lower and less severe histologic changes were observed at 24 h in the FR-113453-treated group. Renal blood flow (measured using 85Sr microspheres) did not change at 24 h after glycerol injection (3.0 +/- 0.9 mL/min/g [vehicle] vs. 3.6 +/- 0.9 mL/min/g [FR-113453]), but renal vascular resistance was significantly reduced by FR-113453 (47.9 +/- 37.9 vs. 26.4 +/- 5.2 mm Hg/mL/min/g, p < 0.05). Beta-ATP levels (measured by 31P-magnetic resonance spectroscopy) were reduced in glycerol-induced acute renal failure, with no difference between the vehicle and FR-113453-treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dipyridamole on kidney function in cirrhosis

Adenosine is a potent endogenous renal vasoconstrictor. To investigate the sensitivity of the renal circulation to adenosine in cirrhosis, we evaluated kidney function and vasoactive hormones in 20 patients with cirrhosis before and after administration of dipyridamole (0.4 mg/kg, intravenously), a drug that increases extracellular levels of adenosine. In patients with ascites and increased plasma renin activity (6.9 +/- 4.0 ng/ml.hr [mean +/- S.D.]) (n = 7), dipyridamole induced marked reductions in renal plasma flow (from 623 +/- 294 to 374 +/- 188 ml/min, p = 0.03), glomerular filtration rate (from 89 +/- 22 to 48 +/- 16 ml/min, p = 0.009), urine volume (from 7.1 +/- 2.1 to 1.5 +/- 1.1 ml/min, p = 0.0001), free water clearance (from 4.0 +/- 1.7 to 0.4 +/- 0.6 ml/min, p = 0.001) and sodium excretion (from 28 +/- 36 to 7 +/- 15 mu Eq/min, p = 0.05) in the absence of changes in arterial pressure, plasma renin activity and levels of aldosterone, norepinephrine and antidiuretic hormone. In patients without ascites (n = 5) and in patients with ascites and normal plasma renin activity (0.9 +/- 0.5 ng/ml.hr) (n = 8), renal plasma flow and glomerular filtration rate did not change significantly after dipyridamole administration, whereas excretion of sodium and free water was reduced. These results indicate that in cirrhotic patients with ascites and overactivity of the renin-angiotensin system, dipyridamole induces renal vasoconstriction in the absence of changes in systemic hemodynamics, suggesting that these patients are particularly sensitive to the renal vasoconstrictor effect of endogenous adenosine.

Angiotensin dependence of endothelium-mediated renal hemodynamics

Endothelium-derived relaxing factor has been shown to regulate renal blood flow, and inhibition of its synthesis increases blood pressure and renal vascular resistance and decreases renal blood flow. Using the substrate antagonist NW-nitro-L-arginine methyl ester (L-NAME), we tested whether renal vasoconstriction induced by endothelium-derived relaxing factor synthesis inhibition could be mediated in part by angiotensin II. In 14 control rats, 10 mg/kg body wt L-NAME increased blood pressure from 106 +/- 6 to 126 +/- 6 mm Hg (p < 0.001), increased renal vascular resistance by 74% (from 19.3 +/- 2.6 to 33.6 +/- 2.9 resistance units), and decreased renal blood flow by 34% (from 5.9 +/- 0.5 to 3.9 +/- 0.3 ml.min-1.g kidney wt-1, p < 0.005). When six rats were treated with 10 mg/kg body wt of the angiotensin receptor antagonist DuP 753, L-NAME increased blood pressure from 84 +/- 4 to 106 +/- 4 mm Hg (p < 0.001); however, renal vascular resistance increased by only 27% (from 13 +/- 2 to 17 +/- 3 resistance units, p < 0.01; p < 0.05 different from control value) and renal blood flow was unchanged. Likewise, after pretreatment of six rats with 32 micrograms/100 g body wt of the angiotensin converting enzyme inhibitor enalaprilat, L-NAME increased blood pressure from 88 +/- 5 to 124 +/- 6 mm Hg (p < 0.001) and renal vascular resistance by 54% (from 12 +/- 1 to 18 +/- 3 resistance units, p < 0.01; p < 0.05 different from control value) but renal blood flow was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal function in patients with untreated acute myocardial infarction

This study provides data on plasma volume (PV), extracellular volume (ECV) and renal function in 8 untreated patients with acute myocardial infarction (AMI). At day 2 and day 10 after AMI, glomerular filtration rate (GFR), urinary excretion rate of water (Vu), sodium clearance (CNa) and lithium clearance (CLi) were used for assessing reabsorption rates of sodium and water in proximal and distal nephron segments. PV and blood pressure at day 2 were not significantly different from values at day 10. Heart rate (HR), weight and ECV at day 2 were significantly increased when compared with values at day 10 (78 vs. 62 pr. min and 17.0 vs. 16.2 1, respectively). Plasma norepinephrine values were slightly elevated at day 2 and day 10. GFR was initially high and decreased from day 2 to day 10 (118 vs. 104 ml min-1) together with CLi and Ck. However, Vu, CNa and fractional excretion rate of sodium increased markedly from day 2 to day 10. The results suggest that sodium and water retention in the initial phase of AMI without left ventricular failure is due to an increase in tubular reabsorption in distal nephron segments mediated by mechanisms other than the sympathetic nervous system.

Adenosine infusion for the reversal of pulmonary vasoconstriction in biventricular failure. A good test but a poor therapy

BACKGROUND

Elevation of pulmonary vascular resistance is an important determinant of right ventricular function in patients with end-stage biventricular heart failure. Vasodilator drug therapy directed at the pulmonary vasculature is used in the hemodynamic assessment of patients for orthotopic heart transplantation, and therapy aimed at decreasing pulmonary vascular resistance and transpulmonary pressure gradient has been advocated in patients awaiting heart transplantation. Adenosine infusion has been shown to cause selective pulmonary vasodilatation in normal subjects and in patients with primary pulmonary hypertension but has not been assessed in patients with biventricular heart failure.

METHODS AND RESULTS

Using two infusion doses, we studied the pulmonary and renal hemodynamic effects of adenosine on patients referred for heart transplantation (n = 21) and compared it with sodium nitroprusside (n = 18). Patients received 30% oxygen via face mask throughout the study. Adenosine at 100 micrograms/kg min achieved the same percentage fall in pulmonary vascular resistance as nitroprusside (41 +/- 6% versus 42 +/- 4%) and a greater and more consistent fall in transpulmonary pressure gradient (35 +/- 6% versus 9 +/- 30%, p less than 0.02). The mean arterial blood pressure fell by 16 mm Hg with nitroprusside but was unchanged by adenosine, indicating that in contrast to nitroprusside, adenosine acted as a selective pulmonary vasodilator. Despite this, cardiac index showed only a modest increase with adenosine (1.73 +/- 0.09 to 1.89 +/- 0.16 l.m-2, p less than 0.05), and there was a rise in pulmonary capillary wedge pressure from baseline at the higher dose (29.7 +/- 2.5 to 33.4 +/- 3.4 mm Hg, p less than 0.05). Renal blood flow was unchanged during adenosine infusion.

CONCLUSIONS

Adenosine is a potent selective pulmonary vasodilator in patients with biventricular heart failure and is preferable to sodium nitroprusside as a test for the reversibility of pulmonary vasoconstriction. However, its deleterious effects on left atrial pressure make it unsuitable as a therapeutic agent in patients awaiting heart transplantation.

Morphometric investigations on intrarenal vessels of streptozotocin-diabetic rats

We have investigated 975 different grazing sections of vessels in kidney preparations of 20 rats of the Wistar strain. Half of these genetically identical animals had an insulin-deficiency diabetes induced by injection of streptozocin. The kidneys were removed for investigation after 2 and 12 weeks duration of diabetes. The vessel cross-section, wall, lumen and endothelial surface area were determined in renal arteries, arterioles and preglomerular afferent arterioles in a blind experiment. Statistically detecteable changes were found in the diabetic vessels in the early stage of the diabetes. Preglomerular afferent arterioles showed a highly significant and increasing lumen dilatation commencing after 2 weeks. Diabetic arteries and arterioles developed narrower lumina. A significant thickening of the endothelium took place at the same time in both vessel types. All three vessel regions became smaller and had thinner walls than healthy vessels as the diabetes progressed. The findings on the afferent vessels indicate that haemodynamic effects on the glomerulus are to be expected. Familial diabetic gloermulopathy begins with a reversible hyperfiltration. However, the mechanism has not been clarified in the context of the diabetic metabolic disorder, and this change is probably the haemodynamic consequence of the substantial dilatation of the preglomerular afferent arterioles. With their renin-positive segment, these arterioles are the centre of intrarenal regulation. The increase of the capillary glomerular pressure associated with the dilatation of the preglomerular afferent arterioles is a crucial factor in the development of diabetic glomerulopathy.