Effects of hyperinsulinemia on the regulation of regional blood flow and blood pressure in anesthetized dogs: hemodynamic role of nitric oxide

The purpose of this study was to investigate whether acute hyperinsulinemia induces selective hemodynamic effects in the mesenteric, renal, and iliac vascular beds, and to determine whether nitric oxide (NO) plays a role in the regulation of blood flow and mean arterial pressure (MAP) during acute hyperinsulinism. In eight anesthetized dogs (Group A), the response to a hyperinsulinemic test was determined before and after NO inhibition, with L-nitro-arginine methyl esther (L-NAME), during the last 45 min of the experiment. In seven dogs (Group B), NO inhibition was induced before and maintained throughout hyperinsulinemia. In Group A, the hyperinsulinemic test did not alter MAP, but induced a significant reduction in both renal and mesenteric blood flow without a significant change in iliac blood flow. In contrast, the administration of L-NAME in Group B was followed by a significant decrease in mesenteric, renal, and iliac blood flow, but mean arterial pressure remained unchanged. In this group, hyperinsulinemia instituted after the blockade of NO was followed by a significant elevation in blood pressure levels, concomitant with reductions in blood flow to the three vascular beds. In summary, acute hyperinsulinemia induced a redistribution of blood supply, which preserves skeletal muscle irrigation while reducing blood flow to the kidney. Nitric oxide participates in this redistribution because L-NAME infusion abolishes the compensatory influence on skeletal muscle blood flow.

Systemic inhibition of nitric oxide and prostaglandins in volume-induced natriuresis and hypertension

Nitric oxide (NO) synthesis inhibition with NG-nitro-L-arginine methyl ester (L-NAME) (10 micrograms.kg-1.min-1 i.v.), cyclooxygenase inhibition with meclofenamate (Meclo; 5 mg/kg i.v. bolus), and combination of drugs (L-NAME + Meclo) were used to investigate the roles of NO and prostaglandins (PG) in the hemodynamic and natriuretic responses to isotonic saline volume expansion (VE; 5% body wt over 60 min) in anesthetized dogs. Before VE, L-NAME (n = 6), Meclo (n = 6), and L-NAME + Meclo (n = 6) produced significant increments in mean arterial pressure (MAP) of 12 +/- 2, 15 +/- 3, and 17 +/- 3 mmHg, respectively. VE did not change MAP in Meclo-treated dogs, but produced a significant elevation in the control dogs (14 +/- 6 mmHg), in L-NAME-treated dogs (17 +/- 6 mmHg), and in dogs pretreated with L-NAME + Meclo (12 +/- 5 mmHg). VE alone induced marked natriuretic responses in the control (38 +/- 9 to 562 +/- 86 mumol/min), L-NAME (31 +/- 9 to 664 +/- 65 mumol/min), and Meclo groups (41 +/- 10 to 699 +/- 51 mumol/min). However, this natriuretic response was attenuated in dogs pretreated with L-NAME + Meclo (12 +/- 4 to 185 +/- 52 mumol/ min). These results indicate that 1) blockade of both NO and PGs has significant diminishing effects on volume-induced natriuresis, 2) NO blockade alone impairs volume-induced natriuresis in a manner that requires further increases in MAP to restore the natriuresis, and 3) PG blockade alone does not curtail volume-induced natriuresis.

Three-dimensional microcomputed tomography of renal vasculature in rats

Current microscopic methods to view renal microvasculature reveal only a very limited portion of the total renal volume. Identification of connectivity for postglomerular vessels in the cortex and the medulla during functional states related to changes in sodium excretion will help better to understand the coupling of renal vasculature to tubular function. The purpose of this study was to investigate the possibility of visualizing the continuity of pre- and postglomerular vasculature using three-dimensional micro-computed tomography (micro-CT). Kidneys from normal rats were perfusion fixed in situ at physiological pressure, filled with latex microfil containing lead chromate, and embedded in plastic. The micro-CT scans of the intact kidneys were carried out on a rotating stage illuminated either by a synchrotron x-ray source or a conventional x-ray spectroscopy tube. Images were reconstructed by a filtered backprojection algorithm and volume-rendering techniques were utilized to display the vasculature. The reconstructed images clearly showed the large distribution vessels and the venous drainage of the kidneys, while pre- and postglomerular vessels and their vascular connections throughout the kidney were displayed in great detail. Efferent arterioles showed the characteristics of their peritubular capillary beds in the cortical and medullary regions. The vascular volume of the cortex was 27%, the outer stripe of the outer medulla 18%, the inner stripe of the outer medulla 30%, and the inner medulla 18%. In conclusion, micro-CT is a promising method to evaluate renal vascular architecture relative to physiological and pathological alterations.

Perfusion pressure dependency of in vivo renal tubular dynamics

To examine whether changes in renal perfusion pressure (RPP) within the range of autoregulation induce detectable changes in tubular dynamics in an entire nephron population of the intact kidney, we measured, using electron beam computed tomography (EBCT), transit times (TT, s) and intratubular concentration (%) of filterable contrast media in various nephron segments simultaneously with renal regional perfusion. In seven dogs (group A) this was performed at the upper and lower limits of autoregulation (RPP = 130 and 95 mmHg, respectively) while group B (n = 5) served as control. In group A alone, a decrease in RPP led to an increase in TT by 40%, 68%, and 32% in the proximal tubules, ascending limb of Henle's loop, and distal tubules, respectively, in association with an increase in intratubular concentration (+ 50%, 80%, and 42%, respectively). Papillary perfusion decreased, whereas perfusion of the adjacent, outlying inner medulla increased. The decrease in papillary perfusion correlated positively with the concurrent change in sodium excretion (R = 0.81). This study demonstrates that changes in RPP within the autoregulatory range elicit changes of tubular sodium reabsorption mainly in proximal, distal, and ascending tubules, in which most of the nephrons participate. These tubular changes are associated with an alteration of perfusion circumscribed to two areas of the inner renal medulla.

Comparative effect of PGE2 and PGI2 on renal function

Rapid degradation of prostacyclin (PGI2) inherent to its molecular structure has long been a major limitation in assessing the natriuretic effect of this prostaglandin. The recent availability of the stable PGI2 analogue iloprost now allows for a comparative study with prostaglandin E2 (PGE2). In the present study conducted in six anesthetized dogs, the intrarenal effects of two consecutive doses (1 and 4 ng x kg(-1) x min(-1)) of PGE2 on renal blood flow, glomerular filtration rate, and urinary sodium excretion were compared with the effects of two identical doses of iloprost. The selected doses of PGE2 were those producing a maximal natriuretic and vasodilator response without affecting mean arterial pressure. A washout period was allowed between administration of PGE2 and iloprost. PGE2 infusion significantly increased fractional sodium excretion from 0.69+/-0.1 to 2.79+/-1.1% and 4.27+/-1.2%% (P<.05), respectively. These changes in fractional sodium excretion induced by PGE2 were associated with significant increases in renal blood flow from 151.1+/-62 to 185+/-64.3 and 185.6+/-64.3 mL/min (P<.05), respectively; however, no significant alterations were seen in glomerular filtration rate, from 29.5+/-9.4 to 35.2+/-12.2 and 32.7+/-7.8 mL/min (NS), and mean arterial pressure, from 117.6+/-26 to 113.9+/-24.1 and 112.3+/-24.1 mm Hg (NS) during control and PGE2 infusion. At identical doses, sequential infusion of PGI2 had no effect on renal blood floww and glomerular filtration rate, producing natriuresis only at the highest dose, a fractional sodium excretion from 0.69+/-0.1 to 0.8+/-0.28 mm Hg (NS) and 1.05+/-0.34% (P<.05), respectively. In conclusion, the present study confirms that PGE2 exerts a natriuretic effect during increases in renal blood flow. In contrast, PGI2 had no hemodynamic effect, and the natriuresis was markedly blunted.

[Bladder neoplasms in patients under 40 years of age]

The incidence, presentation and clinical evolution of vesical tumours diagnosed in our Centre over the last 10 years (1986-1995) in patients under forty are examined. This retrospective study included 19 of the 643 neoplasias treated during that period; 7 of these in patients under 30 and 12 in patients over 31. Haematuria was the most frequent reason for visiting the Centre. At the time of diagnosis, all cases were surface tumours and none progressed to the infiltrant stage. Tumours in patients over 30 are characterised by a higher histological grade and greater relapse rate versus those in patients under 30. Therefore, age may be a favourable prognostic factor in patients under 30 versus the older group who follow a course more similar to the remainder of usual patients. Diagnosis and treatment of these neoplasias should be just the same as for tumours in older patients.

Hemodynamic and renal effects of cross-linked hemoglobin infusion

It is well known that hemoglobin binds nitric oxide (NO) and produces a pronounced vasoconstriction in isolated arteries. However, it is debatable whether such an effect takes place in whole animals, because hemoglobin also catalyzes the formation of prostaglandins from arachidonic acid. Short-term studies were performed to evaluate the effects induced by intravenous infusion of cross-linked hemoglobin (XL-Hb) on blood pressure (BP) and renal, iliac, and mesenteric flows, and on renal function in six anesthetized dogs. A similar volume-matched expansion with 6% dextran was used as a control (n = 6). Glomerular filtration rate (GFR), urinary flow, and total and fractional sodium excretion were measured before and after XL-Hb or dextran infusion to evaluate possible renal function changes. XL-Hb administration resulted in a 29% elevation in BP and a significant decrease of blood flow (30-37%) to the three vascular beds. XL-Hb did not alter GFR or sodium excretion, despite the increase in BP. In contrast, the administration of dextran did not significantly alter BP but induced a significant increase (6-13%) of blood flow in the three vascular beds. These changes were accompanied by threefold increases in urinary flow and sodium excretion without alterations in GFR. The binding effect of XL-Hb on NO was studied in isolated renal arteries in organ chambers. These in vitro studies showed that XL-Hb blunted the endothelium-mediated vasodilator response to calcium ionophore A-23187 and to acetylcholine. Our results demonstrate that XL-Hb administration is followed by hypertension, vasoconstriction, and blunted natriuresis. All these effects are compatible with the scavenging effect on NO attributed to XL-Hb.

New insights into the pathophysiology of renovascular hypertension

In recent years, the pathophysiology of renovascular hypertension has been reviewed, and the classic concept that activation of the renin-angiotensin system is solely responsible for the development and maintenance of renovascular hypertension has been challenged. In fact, experimental evidence indicates that other systems, such as the lipoxygenase pathway, may have a more critical role in the long-term maintenance of high blood pressure after renal artery stenosis. Herein we discuss the intrarenal mechanisms that control pressure-induced natriuresis under physiologic conditions and the role of the kidney in the pathophysiology of renovascular hypertension.

Chronic effects of nitric oxide and prostaglandin inhibition on pressure diuresis and natriuresis in rats

The long-term interaction between nitric oxide (NO) and prostaglandins (PGs) in the pressure diuresis and natriuresis response has been studied. Experiments were performed in rats with chronic (8 weeks) inhibition of NO (NG-nitro L-arginine methyl Ester, L-NAME, 40 mg/kg/day) with or without simultaneous PGs synthesis blockade (indomethacin, 1 mg/kg/day). A time control group with no treatment was studied in parallel. At the end of this period, the animals were anesthetized and renal hemodynamics and excretion were studied at three levels of renal perfusion pressure (RPP; 100, 125 and 150 mm Hg). Renal blood flow, glomerular filtration rate, diuresis and natriuresis were lower at the three RPP levels in both L-NAME-treated groups than in the control or indomethacin-treated animals. Simultaneous administration of indomethacin plus L-NAME did not further modify the hemodynamic or excretory responses observed in the L-NAME-treated animals. These results show that chronic NO inhibition impairs the renal excretory response to changes in renal perfusion pressure, and simultaneous NO and prostaglandin synthesis inhibition does not reduce those responses further. It is concluded that, on a long-term basis, a preserved NO production, but not prostaglandin production, is critical for a normal pressure diuretic and natriuretic mechanism.

Computed tomography-derived intrarenal blood flow in renovascular and essential hypertension

The effect of renal artery stenosis on intrarenal perfusion and volume in renovascular hypertensive patients is unclear. Alterations in these attributes may ultimately be involved in deterioration of renal function. We measured whole kidney, cortical, and medullary perfusion and volume with electron beam computed tomography (EBCT) in 33 hypertensive patients, with well-preserved renal function, scheduled for renal angiography. EBCT-derived whole kidney perfusion was lower in patients with atherosclerotic renal artery stenosis (RAS; N = 20) than in fibromuscular dysplasia (FMD; N = 10) or essential hypertension (N = 28; P < 0.05), as was cortical perfusion (2.44 +/- 0.16 vs. 3.26 +/- 0.17 and 3.07 +/- 0.09 ml/min/cc tissue, respectively, P < 0.005), but medullary perfusion was similar. Whole kidney, cortical, and medullary perfusion correlated inversely with degree of stenosis in FMD, but not in atherosclerotic RAS. Renal volumes were similar. These results demonstrate that, in contrast to patients with FMD, in patients with atherosclerotic RAS the decrease in cortical perfusion is not directly related to the degree of stenosis in the main renal artery. Factors other than the stenosis itself may play a role in the pathophysiology of atherosclerotic RAS and associated renal failure.

Synchronous signet ring cell carcinoma and squamous cell carcinoma arising in an augmented ileocystoplasty. Case report and review of the literature

We report a case of synchronous squamous cell carcinoma and signet ring cell carcinoma in an augmented bladder 22 years after ileocystoplasty. The clinical features, predisposing factors and pertinent literature are reviewed.

High-fructose feeding elicits insulin resistance without hypertension in normal mongrel dogs

This study was undertaken to characterize blood pressure (by continuous blood pressure recording), renal hemodynamics, and excretory function in high-fructose-fed insulin-resistant dogs. We fed 10 mongrel dogs for 28 days with a normal sodium diet containing 60% of the calories either as fructose (n = 6) or dextrose (n = 4). Fructose-fed dogs developed insulin resistance by the 21st day of the experimental diet, as estimated by the mean glucose concentrations (in arbitrary units, AU) during the final hour of the insulin suppression test (640.3 +/- 57 AU fructose-fed dogs upsilon 397.5 +/- 24.7 AU dextrose fed dogs; P < .05). Neither of the groups showed any change in body weight, or in fasting plasma levels of glucose or insulin. There was no difference in mean arterial pressure between the groups before or during either diet, nor did we find any important alterations in renal function in these animals. We conclude that insulin resistance can be induced by a high-fructose diet in the dog. However, it is not accompanied by either hypertension or alteration in renal function. These findings emphasize the importance of continuously recording blood pressure under resting conditions and suggests that in the fructose-fed dog, insulin resistance does not appear to lead directly to hypertension.

Urinary endothelin and renal vasoconstriction with cyclosporine or FK506 after liver transplantation

Transplant immunosuppression using either cyclosporine (CsA) or FK506 leads to renal vasoconstriction. To examine the role of endothelin (ET) in this process, we measured plasma and urinary ET before and at intervals for two years after liver transplantation. Urinary prostacyclin (as 6-keto-PG-F1 alpha), thromboxane, glomerular filtration rate and renal plasma flow were also measured. Forty-four patients were treated with CsA-based regimens and 31 patients with FK506-based regimens. Prednisone doses after one year were lower with FK506 (5.5 +/- 0.5 vs. 10.5 +/- 0.5 mg/day) by study design. Circulating plasma ET remained above normal, but not different from pre-transplant levels. Urinary ET was elevated before transplant (24.6 +/- 3.4 ng/day vs. normal 16 +/- 1.5 ng/day, P < 0.05) and rose further after transplantation (48.5 +/- 13 ng/day, P < 0.05), remaining elevated for two years. 6-keto-PG-F1 alpha fell from 2567 +/- 338 ng/day to subnormal levels and remained suppressed (1158 +/- 128 ng/day, P < 0.01). Over the same period GFR fell (84 +/- 3 ml/min to 60 +/- 3 ml/min, P < 0.01) and renal vascular resistance index rose (11,119 +/- 561 to 23,279 +/- 1692 d.s.cm-5.m-2, P < 0.01). Similar changes were observed both with CsA and FK506-based immunosuppression. No changes in ET were attributable to dihydropyridine calcium channel blockers. These results demonstrate that urinary ET changes independently from plasma ET after transplantation. Elevated ET and suppression of endothelium-derived prostacyclin persist with intense renal vasoconstriction for at least two years after transplant.

Pressure dependency of canine intrarenal blood flow within the range of autoregulation

The mechanism of pressure-induced natriuresis remains controversial. To assess whether intracortical or medullary renal blood flows (RBF) change with changes in renal perfusion pressure (RPP), global and regional RBFs were measured using the dynamic spatial reconstructor, a fast computed tomography scanner, in eight anesthetized dogs (group B) within the range of RBF autoregulation (RPP of 153.5 and 114.4 mmHg). Similar measurements were obtained in seven control dogs (group A) in which RPP was not manipulated. In group B, only inner medullary perfusion decreased (from 0.84 to 0.51 ml/min per cm3 of tissue, P = 0.03) with reduction of RPP, whereas global renal, intracortical, and outer medullary perfusions remained unaltered. In group A there was no change in global or regional renal perfusion. The change in inner medullary perfusion in group B (-34.7%) was significantly different (P = 0.021) from that in group A (+27.4%). Global, cortical, and total medullary RBFs (ml/min) and volumes did not change in either group. These results suggest that with changes in RPP, the only detectable change in intrarenal perfusion occurs in the inner medulla.

Renal effects of nitric oxide synthesis inhibition in cirrhotic rats

In the present study, we have characterized the renal response to inhibition of endogenous nitric oxide (NO) synthesis [intravenous NG-nitro-L-arginine methyl ester (L-NAME) for 3 h] in anesthetized cirrhotic rats, with (ASC) and without (CIR) ascites, at doses that do not change blood pressure (BP). Administration of L-NAME induced opposite effects on water (UV) and sodium (UNaV) excretion in cirrhotic and control animals. Infusion of 1 microgram.kg-1.min-1 of L-NAME in CIR (n = 5) decreased renal plasma flow (RPF) at the end of the 3-h period, whereas UV, UNaV, and glomerular filtration rate (GFR) were unaltered. In contrast, infusion of L-NAME at 10 micrograms.kg-1.min-1 in six more CIR increased UV and UNaV significantly by the 1st h, without changes in BP or GFR, and these parameters remained elevated throughout the experiment. Infusion of 1 microgram.kg-1.min-1 in ASC (n = 6) did not change BP or GFR but significantly enhanced UV and UNaV after the 1st h. These effects were prevented by pretreatment with L-arginine (0.1 mg.kg-1.min-1) in another group of ASC infused with 1 microgram.kg-1.min-1 of L-NAME. These results indicate that, in ASC and CIR cirrhotic rats, inhibition of NO synthesis at nonpressor does improves renal excretion of sodium and water via a decrease in tubular reabsorption. NO is an important mediator of the renal excretory and hemodynamic alterations of experimental liver cirrhosis.

Cyclosporine-induced hypertension after transplantation

OBJECTIVE

To describe the features and mechanisms of posttransplantation hypertension and suggest appropriate management of the disorder.

DESIGN

We review our own experience and reports from the literature on hypertension in cyclosporine A (CSA)-treated transplant recipients.

RESULTS

Soon after immunosuppression with CSA and corticosteroids, hypertension develops in most patients who undergo transplantation. The blood pressure increases, which are usually moderate, occur universally because of increased peripheral vascular resistance. Disturbances in circadian patterns of blood pressure lead to loss of the normal nocturnal decline, a feature that magnifies hypertensive target effects. Changes in blood pressure sometimes are severe and associated with rapidly developing target injury, including intracranial hemorrhage, left ventricular hypertrophy, and microangiopathic hemolysis. The complex mechanisms that underlie this disorder include alterations in vascular reactivity that cause widespread vasoconstriction. Vascular effects in the kidney lead to reduced glomerular filtration and impaired sodium excretion. Many of these changes affect local regulation of vascular tone, including stimulation of endothelin and suppression of vasodilating prostaglandins. Effective therapy includes use of vasodilating agents, often calcium channel blocking drugs. Caution must be exercised to avoid interfering with the disposition of CSA or aggravating adverse effects relative to kidney and electrolyte homeostasis.

CONCLUSION

Recognition and treatment of CSA-induced hypertension and vascular injury are important elements in managing the transplant recipient.

Hormonal, renal, and metabolic alterations during hypertension induced by chronic inhibition of NO in rats

The evolution of renal excretory function and circulating vasoactive systems was studied during progressive increases in blood pressure (BP) induced in rats by oral administration of NG-nitro-L-arginine methyl ester (L-NAME; 5-30 mg/100 ml) for 5 wk. L-NAME induced a stepped elevation (P < 0.05) in BP levels without changing creatinine clearance, urine flow, or sodium excretion rate along the study. Reductions (P < 0.05) in plasma renin activity and plasma aldosterone concentration were found only during treatment with 30 mg/100 ml of L-NAME. Plasma norepinephrine and epinephrine concentrations were elevated (P < 0.05) in the last week of the study. Plasma concentrations of endothelin-1 and urinary excretion of prostaglandin E2, 6-ketoprostaglandin F1 alpha, and thromboxane B2 were not significantly affected by L-NAME. Similarly, no changes in plasma concentrations of glucose, insulin, total cholesterol, or triglycerides were observed. In summary, during long-term administration of L-NAME, progressive increases in BP levels were observed without changes in either sodium excretion or enhanced circulating vasoconstrictor activity. Thus, it is likely that inhibition of synthesis of nitric oxide (NO) in the vasculature leads to an imbalance between the tonic relaxing action of NO and the influences of vasoconstrictor agents even when the latter remain at normal levels.

Resolution of posttransplant hypertension after liver transplantation despite impaired glomerular filtration

Hypertension developing after transplantation is characterized by widespread vasoconstriction including the kidney. Late resolution (mean, 29 +/- 4 months) of posttransplant hypertension has been observed in 15 (Group I) of 278 subjects monitored after liver transplantation. These studies were undertaken to define the systemic and renal changes associated with resolution, as compared with a group matched for age, sex, and time after transplant who remained hypertensive (Group II; N = 15) or a group who never developed hypertension (Group III; N = 23). Blood pressure during resolution paralleled changes in the systemic resistance index, which fell from 3,052 +/- 548 to 1,872 +/- 205 dyne/s.cm5/m2 (P < 0.01). GFR and RBF remained low, despite the resolution of hypertension, and renal vascular resistance did not change. Circulating endothelin levels remained above normal in all transplant recipients (Group I, 11.9 +/- 3.0 versus normal subjects, 7.0 +/- 1.1 pg/mL; P < 0.05), and urinary prostacyclin excretion was suppressed (880 +/- 120 versus 2,247 +/- 187 ng/day; P < 0.01). No hormonal differences were apparent between transplant groups. These results demonstrate the capacity for systemic vasodilation to occur after transplantation, independent of vascular tone in the kidney. They further suggest that renal vasoconstriction and impaired GFR alone are not sufficient to explain de novo hypertension after transplantation.

Chronic alcoholic myopathy and nutritional status

To investigate the prevalence of alcoholic myopathy and its relationship to the nutritional status, we performed a muscle biopsy on the vastum lateralis of 60 consecutive hospitalized alcoholic patients using a Tru-Cut needle, processing it for light microscope and ultrastructural analysis. The nutritional status was assessed by anthropometric measurements such as midarm circumference, triceps skinfold and midarm muscle area, and serum albumin. The hallmark of chronic alcoholic myopathy, fiber muscle atrophy, was present in 33% of the patients, necrosis scarcely being observed (1.5%). Ultrastructural alterations as lipid and glycogen accumulation or mitochondrial and myofibrillar alterations were nonspecific and observed in nearly all the cases where atrophy was present. Malnutrition was frequent in our patients: 39% and 34% showed a triceps skinfold and a midarm muscle area, respectively, under the fifth populational percentile. Patients with muscle fiber atrophy or ultrastructural changes showed a worse nutritional status, not only regarding muscle protein (assessed by midarm muscle area or creatininuria and explained by fiber atrophy), but also regarding fat stores assessed by triceps skinfold. Toxic effect of ethanol and malnutrition may act synergistically leading to chronic alcoholic myopathy.

Quantification of global and regional renal blood flow with electron beam computed tomography

Alterations in renal blood flow distribution may occur in a variety of pathophysiologic situations; however, quantification of global and regional renal blood flows has been limited because of the lack of reliable, noninvasive techniques. To determine the feasibility of flow measurements with electron-beam computed tomography (EBCT), six anesthetized dogs were scanned by EBCT during basal conditions, after renal vasodilation, and at recovery. Flow (mL/min/cm3 tissue) was calculated from EBCT-derived time-density curves using three different algorithms and compared with simultaneously obtained electromagnetic flow (EMF) probe measurements after indexing to EBCT-derived renal volume. EBCT-determined flow correlated well with EMF measurements regardless of the algorithm used. An algorithm using the area under the time-density curve was concluded to be the most suitable for calculation of renal blood flow; it correlated with EMF as EBCT flow = 44.5 + 1.05 EMF (r = 0.885, SEE = 31.2 mL/min, P < .0001). Consistent overestimation of flow by EBCT resulted probably from retention of contrast media in the renal parenchyma. EMF showed an increase of 20 +/- 10% in renal blood flow after vasodilation. EBCT-derived global, cortical, and medullary flows increased by 33.8 +/- 10.3%, 24.8 +/- 17.8%, and 99.0 +/- 73.8%, respectively. In conclusion, EBCT was found feasible for credible quantitation of renal blood flow in the physiologic range studied.

Increased endothelium-dependent renal vasodilation in cirrhotic rats

We have evaluated the renal blood flow (RBF) response of cirrhotic rats to endothelium-dependent [acetylcholine (ACh)] and -independent [sodium nitroprusside (NP)] vasodilators. In anesthetized rats, ACh dose dependently increased RBF, but the response of the cirrhotic rats (n = 6) was significantly higher than that of the controls (n = 6). NP also increased RBF in a dose-dependent manner, but there were no differences between both groups. NG-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg i.v.) significantly reduced the responses to ACh in both groups, but those of the cirrhotic rats were still higher than those of the controls. In experiments performed in isolated perfused kidneys, preconstricted with phenylephrine, dose-response curves for ACh and NP were obtained in the presence of indomethacin. Both ACh and NP decreased renal perfusion pressure dose dependently, but only the response of the cirrhotic rats (n = 5) to ACh was significantly higher than that of the controls (n = 5). L-NAME (100 microM) significantly reduced the responses to ACh and increased those of NP and abolished the differences between groups, except at the high dose of ACh. These results demonstrate an elevated endothelium-dependent vasodilator response in the cirrhotic kidney, which is eliminated by combined prostaglandin and nitric oxide (NO) synthesis inhibition and suggest that increased intrarenal activity of NO may be contributing to the renal alterations of liver cirrhosis.

Direct measurement of renal medullary blood flow in the dog

We studied the responses of total renal blood flow (RBF) and renal medullary blood flow (RMBF) to changes in renal perfusion pressure (RPP) within and below the range of renal autoregulation in the anesthetized dog (n = 7). To measure RMBF, we developed a technique in which the medulla is exposed by excising a section of infarcted cortex and a multiple optical fiber flow probe, connected to a laser-Doppler flowmeter, is placed on the medulla. At the baseline RPP of 120 +/- 1 mmHg, RBF was 2.58 +/- 0.33 ml.min-1.g perfused kidney wt-1, and RMBF was 222 +/- 45 perfusion units. RPP was then decreased in consecutive 20-mmHg steps to 39 +/- 1 mmHg. At 80 +/- 1 mmHg, RBF remained at 89 +/- 4% of the baseline value; however, RMBF had decreased significantly (P < 0.05) to 73 +/- 4% of its baseline value. The efficiency of autoregulation of RBF and of RMBF within the RPP range of 120 to 80 mmHg was determined by calculating an autoregulatory index (AI) for each parameter using the formula AI = (%delta blood flow)/(%delta RPP). An AI of 0 indicates perfect autoregulation, and an index of 1 indicates a system with a fixed resistance. The AI for RBF averaged 0.33 +/- 0.12 over this pressure range and showed a significantly greater (P < 0.05) autoregulatory ability than did the RMBF (0.82 +/- 0.13). Decreasing perfusion pressure < 80 mmHg produced significant decreases in both RBF and RMBF.(ABSTRACT TRUNCATED AT 250 WORDS)