Epinephrine enhances neurogenic vasoconstriction in the rat perfused kidney

Epinephrine has been implicated in the genesis of some forms of hypertension. We have investigated the effects of epinephrine on vasoconstrictor responses evoked by adrenergic stimuli in the isolated perfused rat kidney. Low concentrations of epinephrine (2.5 - 5 X 10(-9) M) increased the amplitude of vasoconstrictor responses evoked by electrical stimulation of the renal adrenergic nerves. These concentrations of epinephrine had no effect on the basal perfusion pressure of the kidney or on the amplitude of vasoconstrictor responses evoked by exogenous norepinephrine. The potentiating effect of epinephrine persisted after infusion of the amine had ceased. Kidneys that had been perfused with 3H-epinephrine accumulated radioactivity, which could then be released by renal nerve stimulation. Cocaine (3 X 10(-5) M) reduced the renal accumulation of 3H-epinephrine and abolished both the persistent potentiating effect of the amine and the release of radioactivity evoked by subsequent nerve stimulation. The potentiating effect of epinephrine infusion was abolished by the beta 2-selective adrenergic receptor antagonist ICI 118,551 (3 X 10(-8) M), but not by the beta 1-selective adrenergic receptor antagonist atenolol (10(-6) M). These results indicate that concentrations of epinephrine that can be achieved during acute stress can enhance the amplitude of neurogenic vasoconstrictor responses. This effect appears to be mediated via a prejunctional beta 2-adrenergic receptor. The persistent nature of this effect may be due to the neuronal accumulation and subsequent release of epinephrine.     

Effects of atrial natriuretic peptide on renal function and renin release in the isolated perfused rat kidney

The effects of synthetic atrial natriuretic peptide (ANP) on the renal hemodynamics, glomerular filtration rate (GFR), fluid and electrolyte excretion and renin release were studied in the isolated perfused rat kidney (IPK). When 10(-9) mol of ANP was administered in 75 ml of perfusate, the renal vascular resistance (RVR) was transiently decreased for 3 to 5 min, thereafter increased for 30 min and then tended to return to the control level. ANP increased the GFR (0.55 +/- 0.08 to 0.71 +/- 0.07 ml/min), urine flow (UV) (0.018 +/- 0.002 to 0.194 +/- 0.028 ml/min), absolute Na excretion (UNaV) (1.83 +/- 0.03 to 17.93 +/- 2.71 microEq/min) and absolute K excretion (UKV) (0.67 +/- 0.13 to 2.33 +/- 0.18 microEq/min). The addition of indomethacin or mefenamic acid to the perfusate before the administration of ANP exerted no influence on any of the effects of ANP. Renin release was inhibited by approximately 50% compared to the ANP-free control group. With the administration of ANP, UV and UNaV reached a peak 15-20 min after the GFR reached a peak and remained elevated after the GFR fell below the control level. These findings suggest that 10(-9) mol of ANP causes natriuresis and renin suppression in the IPK, and that the natriuresis is prostaglandin-independent and cannot be explained only by an increase in GFR.     

Disposition of bumetanide in the isolated perfused rat kidney: Effects of probenecid and dose response

The isolated perfused rat kidney was used to study the pharmacokinetic-pharmacodynamic relation of bumetanide and furosemide. Diuresis, as indicated by the concomitant increase in urine volume and fractional excretion of sodium, was produced with both drugs. The action of furosemide was dependent on a high clearance resulting from combined glomerular filtration and tubular secretion. The site of furosemide action was the luminal side of the nephron and a large amount of drug was required in the tubular lumen to produce diuresis. A bidirectional transport of bumetanide was indicated. Although tubular secretion of bumetanide was demonstrated, the action of bumetanide was not dependent on secretion and the highest response was achieved when bumetanide was filtered and partially reabsorbed. The lack of dependency on secretion to produce a response may be indicative of bumetanide reaching its site of action from the luminal as well as the vascular side of the nephron. In the isolated perfused rat kidney, although both drugs had the same pharmacodynamic endpoint, each drug had a different pharmacokinetic profile that characterized its response.     

Effects of perfusate leucine concentration on the metabolism of valine by the isolated rat hindquarter

Rates of oxidation of valine and release of alpha-ketoisovaleric acid by hindquarters from rats fed a 9% casein diet were measured at intervals over 90 minutes. The hindquarters were perfused with medium containing between 0.03 and 10 mmol/L L-leucine; concentrations of valine and isoleucine were kept constant at 0.2 and 0.1 mmol/L, respectively. The rate of oxidation of [1-14C]valine increased two to threefold when the perfusate contained 0.8 or 1.0 mmol/L leucine but was depressed by 50% when the leucine concentration was 10 mmol/L. The rate of release of alpha-ketoisovaleric acid from the hindquarter was affected little by perfusate leucine concentrations up to 1.0 mmol/L, but release was depressed when perfusate leucine concentration was increased to 10 mmol/L. The rate of release of alpha-ketoisocaproic acid increased with increasing perfusate leucine concentration, as did intracellular alpha-ketoisocaproic acid and leucine concentrations. These results indicate that valine oxidation by the isolated perfused hindquarter is stimulated by a high perfusate leucine concentration (1.0 mmol/L), suggesting that this response contributes to the depressed plasma and tissue valine pools of rats fed a high-leucine diet. An excessively high concentration of leucine (10 mmol/L) suppresses valine oxidation, presumably by competing with valine for transmination or transport.     

Effects of particle size and perfusate composition on the uptake of colloidal gold by the rabbit thoracic aorta perfused in situ

The influence has been investigated of particle size on the uptake of radioactive gold colloid by the rabbit thoracic aorta perfused in situ. Particles ranging in diameter from 14 nm to 40 nm were suspended in 0.9% NaCl and infused either at a pressure of 15 mm Hg for times of between 2 1/2 and 60 min or at pressure of between 15 and 160 mm Hg for 5 min. Uptake by the whole intima-media increased with perfusion time and hydrostatic pressure but did not depend on particle size. Radioactive assay of serial sections across the aortic wall also showed that particle size did not influence the distribution of tracer. An effect of perfusate composition on uptake was demonstrated in further experiments in which particles either 14 or 40 nm in diameter were suspended in pooled rabbit serum and infused at pressures of between 15 and 140 mm Hg for 5 min. Uptake and transmural distribution were again independent of particle size, but uptake was 4-5-fold less than when the particles were perfused in saline. Under all perfusion conditions radioactivity fell steeply across the intima and then rose gradually across the media and adventitia. Radioactivity in the outer media and adventitia increased with perfusion time but little change could be detected in intimal activity. In transmission electron micrographs, particles in the intima were not seen to penetrate the internal elastic lamella and in the outer media particles remained extracellular and did not enter collagen bundles. Autoradiographs showed that particles in the intima were uniformly distributed around the circumference of the vessel but in the outer media and adventitia particles usually clustered close to the vasa vasorum.     

Effects of rat pancreatic polypeptide on islet-cell secretion in the perfused rat pancreas.

Pancreatic polypeptide (PP) secretory cells are abundant in the islets of Langerhans. Results concerning the effects of exogenous PP on islet-cell secretion are controversial. This might be due in part to species specificity, given that most reports refer to studies performed using PP of bovine, porcine, or human origin in a heterologous animal model. Thus, we have investigated the influence of synthetic rat PP (80 nmol/L) on unstimulated insulin, glucagon, and somatostatin release, and on the responses of these hormones to glucose (11 mmol/L) and to arginine (3.5 mmol/L) in a homologous animal model, the perfused rat pancreas. Infusion of rat PP (rPP) reduced unstimulated insulin release by 35% (P = .03), and the insulin responses to glucose by 65% (P = .029) and to arginine by 50% (P = .026), without modifying glucagon output. rPP did not affect somatostatin secretion, either in unstimulated conditions or in the presence of 11 mmol/L glucose. However, it induced a clear-cut increase in somatostatin release during 3.5 mmol/L arginine infusion. Our observation that rPP inhibited insulin secretion without affecting glucagon and somatostatin output points to a direct effect of PP on B-cell function. However, during aminogenic priming of the D cell, the inhibition of insulin output induced by rPP was accompanied by an increase in somatostatin release. Thus, in this circumstance, it might be considered that the blocking effect of PP on B-cell secretion could be, at least in part, mediated by a D-cell paracrine effect.     

Direct nephrotoxicity of Russell's viper venom demonstrated in the isolated perfused rat kidney

Envenoming by Russell's Viper (Vipera russelli) is an important cause of acute renal failure. The mechanism of renal damage is unresolved. It is difficult to obtain evidence of a direct nephrotoxic action because of the coincidental disturbance to the systemic circulation. We studied the action of Russell's Viper venom on the function of the isolated perfused rat kidney. Direct nephrotoxic action was indicated by a dose dependent decrease in inulin clearance and an increase in fractional excretion of sodium seen at venom concentrations down to 50 ng/ml, a concentration likely to be achieved in the human circulation after envenoming. The isolated perfused kidney was also used to assess the efficiency of antivenom and for a comparison with snake venoms from the Thai cobra (Naja kauothia) and the Nigerian Saw-Scaled Viper (Echis ocellatus).     

Inhibition by diltiazem of pressure-induced afferent vasoconstriction in the isolated perfused rat kidney

The renal hemodynamic response to calcium entry blockade depends on the neural, hormonal and physiologic determinants influencing basal renal vascular tone. The effects of perfusion pressure per se on the renal vascular response of the rat kidney to diltiazem were evaluated using normal kidneys and hydronephrotic kidneys perfused extracorporally. In isolated perfused normal kidneys, diltiazem did not alter perfusate flow or glomerular filtration rate (GFR) when administered at a perfusion pressure of 100 mm Hg. In contrast, when diltiazem was administered at a perfusion pressure of 150 mm Hg, the calcium antagonists caused a striking increase in GFR, which was accompanied by an increase in renal perfusate flow. In the isolated perfused hydronephrotic rat kidney, elevation of perfusion pressure was associated with an increase in renal vascular resistance and a reduction in afferent arteriolar diameter. Diltiazem abolished the pressure-induced constriction of afferent arterioles and caused an increase in renal perfusate flow in hydronephrotic kidneys perfused at pressures above 100 mm Hg. These findings suggest that in the setting of increased renal perfusion pressure, diltiazem's effects on GFR are mediated in part by an inhibition of pressure-induced constriction of the afferent arteriole.     

Effects of angiotensin I converting enzyme inhibitors on the renal excretory function, hemodynamics and renin release in isolated perfused rat kidney

Direct renal effects of angiotensin I converting enzyme inhibitors (CEIs), captopril, SA446 and MK421, were examined in isolated rat kidneys perfused with a renin-substrate-free medium. Among three CEIs, only captopril induced a significant natriuresis, whereas SA446 and MK421 did not. UKV, renal vascular resistance and creatinine clearance were not affected by any of these CEIs. Renin release from perfused rat kidneys were not influenced by CEIs under the present experimental conditions. These results suggest that among three different types of CEIs, only captopril possesses natriuretic action in the isolated perfused rat kidney and that this action may be independent of its inhibitory action on angiotensin converting enzyme. It is also suggested that these three CEIs themselves do not have a direct effect on the renal vascular bed.     

Effects and assay of urotensin I on the perfused hind limb of the rat

Urotensin I, the long-acting mammalian hypotensive principle obtainable from fish urophyses, elicited a marked, dose-dependent decrease in perfusion pressure in the isolated rat hind limb. The sensitivity of the preparation to urotensin I was increased by 2 orders of magnitude by including noradrenaline (5 × 10^?7-1.5 × 10^?6 g/ml) in the perfusion fluid and perfusing at 1.3–2.5 ml/min at 22–24°. Threshold doses of urotensin I were in the range of fractions of mU (<1 μg acetone dried urophysial powder). The effect of urotensin I was not modified by atropine, mecamylamine, propranolol or diphenhydramine nor by acetylcholine or histamine, or both, when present in urotensin samples. Response to urotensin II could not be detected on the hind limb preparation.Use of the hind limb preparation for assays of urotensin I showed a good dose-response resationship and a high degree of precision.     

Effect of TSH on conversion of T4 to T3 in perfused rat kidney

This study was undertaken to elucidate the effect of thyrotropin (TSH) on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat kidney. The kidney was perfused with a synthetic medium containing 20 micrograms/dL T4 and the effect of constant infusion of bovine TSH (125 or 250 microU/mL) on the conversion of T4 to T3 was investigated. T4 uptake in the perfused kidney was not changed by the addition of TSH. However, the release of T3 (89 +/- 11 ng/g/30 min, mean +/- SD), tissue T3 (190 +/- 23 ng/g/30 min), net T3 production (227 +/- 37 ng/g/30 min), and the conversion rate of T4 to T3 (9.5 +/- 1.6%) in the kidney perfused with 250 microU/mL TSH were significantly (P less than 0.005) greater than those in controls (63 +/- 9, 143 +/- 15, 152 +/- 36 ng/g/30 min, and 6.3 +/- 1.9%), respectively. Degradation rate of T3 in perfused rat kidney was not changed by the addition of 250 microU/mL TSH. These results suggest that TSH may directly affect renal iodothyronine-monodeiodinating activity in rats in vitro.     

Influence of calcium on the metabolism of intact parathyroid hormone by isolated perfused rat kidney and liver

The metabolism of synthetic human PTH [PTH-(1-84)] 10(-9) M was studied in isolated rat kidneys and livers, perfused at a calcium concentration of 1 mM or 4 mM. Clearances were measured by an assay specific for intact PTH, and by assays specific for NH2-terminal, mid-molecule, and COOH-terminal immunoreactive PTH (iPTH). Production of PTH fragments was analyzed by HPLC. The kidneys cleared PTH mainly by filtration. The glomerular filtration rate was not lower at 4 mM calcium than at 1 mM calcium, and no significant differences were found between the clearance of PTH at 4 mM and at 1 mM calcium. At 1 mM calcium the kidneys cleared intact PTH without release of detectable fragments. At 4 mM calcium there was significant (P less than 0.05) accumulation of mid-molecule and COOH-terminal iPTH in the perfusate. Both at low and at high calcium the livers cleared NH2-terminal iPTH at the same rate as intact PTH, whereas mid-molecule and COOH-terminal iPTH was cleared significantly (P less than 0.005) slower. In the livers, metabolic clearance of PTH was 60% faster at 4 mM calcium than at 1 mM calcium (P less than 0.001). Assuming that the hepatic metabolism of PTH represents degradation of the biologically active hormone and hormone fragments, rather than activation of the hormone, the present results suggest a homeostatic control of PTH degradation in the liver to enhance inactivation of the hormone at high serum levels of calcium.     

Effects of meconium aspiration in isolated perfused rat lungs

Our objective was to study meconium-induced lung injury in isolated perfused rat lungs exposed to anoxia. Our working hypothesis was that meconium-induced lung injury is independent of preexisting hypoxia, and that hypoxia will increase severity of lung injury observed after meconium aspiration. We compared five different groups of animals (n = 5) for pulmonary arterial pressure (PAP), weight lung changes, and TNFalpha expression. Group I had lungs instilled with 4 ml of normal saline. Group II had lungs exposed to 5 min of anoxia. Group III had lungs instilled with 4 ml of 30% filtered human meconium. Group IV had lungs exposed to 5 min of anoxia and then instilled with 4 ml of 30% filtered human meconium. Group V had lungs instilled with 4 ml of 30% unfiltered human meconium. Our subjects were adult Sprague-Dawley rats. The isolated rat lung model was prepared according to Levey and Gast (J Appl Physiol 1966;21:313-316). Lungs were ventilated with room air. Anoxia was caused by the use of N(2). The pulmonary artery was cannulated, and pulmonary arterial pressure and lung weight were measured. Lung weight and pulmonary arterial pressure were monitored for 120 min, and TNFalpha levels were measured in effluent at 15, 30, 60, and 120 min. Experiments were done at the Michael Reese Hospital (Chicago, IL). At the end of the experiment, PAP reached its highest values in group V (10.0 +/- 1.7 mmHg). Final PAPs in groups I-IV were: 4.85 +/- 0.3, 4.99 +/- 0.4, 5.93 +/- 0.3, and 7.25 +/- 0.51 mmHg, respectively). Lung wet weight increased significantly only in groups IV and V vs. group I; at 120 min, they were: 0.96 +/- 0.3 g, P < 0.01, and 1.5 g +/- 0.2 g, P < 0.01, respectively. TNFalpha levels did not change significantly over time in group I. TNFalpha is a marker as well as proprietor of pulmonary inflammatory response. TNFalpha reached its highest levels in groups IV and V: 595 and 753 pg/ml at 120 min, respectively. In conclusion, a short episode of anoxia prior to meconium aspiration may increase lung sensitivity to meconium-induced lung injury. This effect may be moderated by the TNFalpha present in the pulmonary circulation.     

An inhibitory effect of dietary polyunsaturated fatty acids on renin secretion in the isolated perfused rat kidney

The influence of dietary modification of polyunsaturated fatty acids (PUFA) on renin secretion, renal vascular tone and prostanoid excretion was studied in isolated perfused rat kidneys under basal conditions and in response to angiotensin II. After a four-week regimen of diets enriched with safflower oil, linseed oil or saturated fat, providing 20% of total energy intake (20 energy %), the animals which were fed linseed oil showed a significant fall in the proportion of arachidonic acid in renal phospholipids and a reduction in urinary prostaglandin excretion. In comparison with the other dietary groups, linseed oil feeding also resulted in a consistently lower renal vascular tone with increasing doses of angiotensin II. Under basal conditions both the PUFA-fed groups had significantly lower renal venous renin secretion rates relative to the saturated fat-fed control group. Infusion of angiotensin II (10 ng/min) suppressed renin secretion and abolished significant differences between the groups. As both the control group and the safflower oil group excreted similar levels of urinary prostaglandins, these results suggest that dietary enrichment with 20 energy % PUFA alters renin secretion by a prostaglandin-independent mechanism and that this may contribute to the lower blood pressures observed in these animals compared with the saturated fat-fed control group.     

肿瘤坏死因子-α增强内皮素肾血管收缩作用的研究

目的 探讨肿瘤坏死因子-α(TNF-α)及肝素对内皮素-1(ET-1)收缩肾脏血管作用的影响,研究TN F-α在肝肾综合征发病机制中的作用。方法 应用离体灌注肾技术,恒量灌流正常大鼠的离体肾脏,在多导生理记录仪上连续记录肾脏灌注压力的改变,观察经TNF-α,肝素灌流90 min后,在ET-1刺激下,肾脏灌注压的改变。 结果 对照组,应用2 nmol/L ET-1刺激,可使灌注压上升(47±9)mm Hg;TNF-α(1 μg/L)处理组,基线压力无改变,应用2 nmol/L ET-1刺激,可使灌注压上升(97±36)mm Hg,与对照组比较差异有非常显著性,t=3.811,P<0.01;肝素(10 mg/L)处理组,基线压力无改变,应用2 nmol/L ET-1刺激,可使灌注压上升(11±6)mm Hg,与无肝素预灌流组[高出基础灌注压(30 ±6)mm Hg)]比较其灌注压升高幅度明显下降(t=9.41 4,P<0.01)。肾组织HE染色,3组均未见病理改变。 结论 TN F-α可能是通过增强三磷酸肌醇受体表达促进肾血管收缩,在肝肾综合征的发病机制中发挥重要作用。     

Effects of adrenaline on a compartment of slowly-exchangeable calcium in the perfused rat heart

The effects of adrenaline on kinetically-distinct compartments of exchangeable calcium in the spontaneously-beating perfused rat heart were investigated under steady-state conditions using a 45Ca2+ outflow technique together with a nonlinear least-squares curve fitting procedure and 51Cr-EDTA to monitor the loss of freely-diffusible Ca2+ from the extracellular space. In addition to Ca2+ distributed in the vascular (compartment 1) and interstitial (compartment 2) spaces, the minimum number of kinetically-distinct compartments of cellular exchangeable Ca2+ (which include Ca2+ bound to extracellular sites on the sarcolemma) required to fit the data (compartments 3, 4 and 5) was three. A system in which cellular compartment 3 is linked to the vascular space and compartments 4 and 5 are linked to the interstitial space was consistent with the data. For hearts perfused under control conditions, the fractional transfer rates for Ca2+ outflow from cellular compartments 3, 4 and 5 were 0.70, 0.11 and 0.017 min-1, respectively. Adrenaline increased the quantity of exchangeable Ca2+ in compartment 5 and decreased that present in the compartment 4. Evidence that compartment 5 includes mitochondrial exchangeable Ca2+ is discussed. It is concluded that one of the actions of adrenaline on the heart is to increase the quantity of exchangeable Ca2+ in the mitochondria.