Myocardial capillaries in the fetal and the neonatal rat: a morphometric analysis of the maturing myocardial capillary bed

Developing myocardial capillaries from 16-day-gestation fetus to adult undergo several morphological changes including a thinning of the lateral extensions of the capillary endothelial cells, the formation of a basal lamina, and an increase in the number of plasmalemmal vesicles. A decrease in the extracellular space, an increase in the number of capillaries, and a decrease in the capillary diameter were also observed during the developmental period. In view of these ultrastructural changes, a morphometric analysis was made on the developing myocardial wall to demonstrate specific quantitative changes. The volumes which were occupied by capillary endothelial cells, capillary lumina, extracellular space, and myocardial myocytes within a reference volume of myocardium were measured; and we found that 8% of the reference myocardial volume was occupied by capillary endothelial cells, 85% was occupied by myocardial myocytes, 4% was occupied by capillary lumina, and, except for a significant change in extracellular space at 16 days gestation, 3% was occupied by extracellular space. Each volume ratio was found to be nearly constant throughout the studied period. In contrast to this constancy in the volume ratios, other parameters which were measured demonstrated significant changes during the developmental period studied. These overall changes include a 135% increase in capillary density, a 63% increase in luminal surface area of capillary endothelial cells, a 24% decrease in capillary diameter, a 12% decrease in diffusion distance, and a 35% decrease in the diameter of the erythrocyte population.(ABSTRACT TRUNCATED AT 250 WORDS)

Maturation of myocardial capillaries in the fetal and neonatal rat: an ultrastructural study with a morphometric analysis of the vesicle populations

The ultrastructural morphology of the cellular and extracellular components of the developing myocardial capillary wall--from the 16-day-gestation fetus of the rat to the 21-day neonate--was examined. A morphometric analysis of plasmalemmal vesicles and of coated vesicles and pits of capillary endothelial cells was performed during the same developmental period. As the lateral extensions of the capillary endothelial cells change from irregular to regular in their thickness during development, there is an increase in the number of plasmalemmal vesicles and a progression from clusters of plasmalemmal vesicles to a uniform distribution in the endothelial cell. The ratio of vesicles which are open to the luminal front, which are "free" in the cytoplasm, or which are open to the abluminal front of the endothelial cell was consistent throughout development. The numerical density of plasmalemmal vesicles demonstrates a gradual and significant increase. In contrast, the numbers of coated vesicles and pits are variable within a very narrow range, and no pattern of increase or decrease is discernible during development. Similarly, there is no change in interendothelial cell junctions, which consist of occluding and primitive adhesive junctional types, during development. The lamina densa of the basal lamina gradually develops from discontinuous, patchy densities along the abluminal surface of the endothelial cells to a continuous and distinct layer by 21 days gestation. The presence of the proteoglycan species in the developing basal lamina was assessed with the cationic dye ruthenium red (RR), and the appearance of RR-marked proteoglycans was found to parallel the appearance of lamina densa material. found to parallel the appearance of lamina densa material. The RR sites appear discontinuously in patches; and later, the RR sites appear in a continuous and regular planar lattice in the lamina rara interna and externa at 21 days gestation. A complete array of RR-stainable anionic sites outside a continuous lamina densa near birth indicates that the basal laminae of developing capillaries in the heart are morphologically, and in part biochemically, mature by the end of the first neonatal week. Our results show that the endothelial cells and the subtending basal lamina of myocardial capillaries gradually mature morphologically during the final days of gestation and the first neonatal week.(ABSTRACT TRUNCATED AT 400 WORDS)

Assimilate Unloading from Maize (Zea mays L.) Pedicel Tissues : I. Evidence for Regulation of Unloading by Cell Turgor

Sugar and (14)C-assimilate release from the pedicel tissue of attached maize (Zea mays L.) kernels was studied following treatment with solute concentrations of up to 800 millimolal. Exposure and collection times ranged from 3 to 6 hours. Sugar and (14)C-assimilate unloading and collection in agar traps was reduced by 25 and 43%, respectively, following exposure to 800 millimolal mannitol. Inhibition of unloading was not specific to mannitol, since similar concentrations of glucose, fructose, or equimolar glucose plus fructose resulted in comparable inhibition. Ethylene glycol, a rapidly permeating solute which should not greatly influence cell turgor, did not inhibit (14)C-assimilate unloading. Based on these results, we suggest that inhibition of unloading by high concentrations of sugar or mannitol was due to reduced pedicel cell turgor. Changes in pedicel cell turgor may play a role in the regulation of assimilate transfer within the maize kernel.

Modification of experimental gentamicin nephrotoxicity by selective parathyroidectomy

Dietary calcium loading reduces gentamicin nephrotoxicity in rats. Since parathyroid hormone increases renal brush border membrane anionic phospholipids, the putative gentamicin receptors, the effects of selective parathyroidectomy on gentamicin nephrotoxicity were examined. Male Fisher 344 rats underwent parathyroidectomy or sham surgery. All animals were fed a diet containing 0.5% calcium for 2 wk prior to gentamicin, 20 mg/kg twice daily for 6 and 10 days. Other parathyroidectomized rats were fed a 4% calcium diet for 2 wk and treated similarly with gentamicin On day 6, serum creatinine (mg/100 ml) was 2.0 +/- 0.9 in the sham-operated animals, 1.7 +/- 1.6 in the parathyroidectomized animals on the 0.5% diet, and 0.8 +/- 0.1 in the parathyroidectomized animals on the 4% diet. By 10 days, the sham-operated animals had creatinine values of 6.3 +/- 1.6 (mg/100 ml) compared with 1.7 +/- .9 in the parathyroidectomized animals on the same diet and 0.8 +/- 0.2 in the 4% diet animals. More severe tubular necrosis was present in the sham-operated compared with the parathyroidectomized animals. High calcium diet in the parathyroidectomized animals produced structural and functional protection from gentamicin nephrotoxicity. Human parathyroid hormone (1-34) 20 IU twice daily given subcutaneously to a separate group of parathyroidectomized rats, eliminated the protective effect of parathyroidectomy on renal structure and function. Parathyroidectomy modifies experimental gentamicin nephrotoxicity. The additional protective effect of dietary calcium loading may be independent of parathyroid ablation.

Sugar Efflux from Maize (Zea mays L.) Pedicel Tissue

Sugar release from the pedicel tissue of maize (Zea mays L.) kernels was studied by removing the distal portion of the kernel and the lower endosperm, followed by replacement of the endosperm with an agar solute trap. Sugars were unloaded into the apoplast of the pedicel and accumulated in the agar trap while the ear remained attached to the maize plant. The kinetics of (14)C-assimilate movement into treated versus intact kernels were comparable. The rate of unloading declined with time, but sugar efflux from the pedicel continued for at least 6 hours and in most experiments the unloading rates approximated those necessary to support normal kernel growth rates. The unloading process was challenged with a variety of buffers, inhibitors, and solutes in order to characterize sugar unloading from this tissue.Unloading was not affected by apoplastic pH or a variety of metabolic inhibitors. Although p-chloromercuribenzene sulfonic acid (PCMBS), a nonpenetrating sulfhydryl group reagent, did not affect sugar unloading, it effectively inhibited extracellular acid invertase. When the pedicel cups were pretreated with PCMBS, at least 60% of sugars unloaded from the pedicel could be identified as sucrose. Unloading was inhibited up to 70% by 10 millimolar CaCl(2). Unloading was stimulated by 15 millimolar ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid which partially reversed the inhibitory effects of Ca(2+). Based on these results, we suggest that passive efflux of sucrose occurs from the maize pedicel symplast followed by extracellular hydrolysis to hexoses.

Effect of amiloride on experimental gentamicin nephrotoxicity

Potassium and magnesium deficiency have been reported as risk factors for experimental gentamicin nephrotoxicity. Amiloride, a potassium-sparing diuretic, also leads to increased renal magnesium reabsorption. Amiloride, 2 mg/kg/day, was given to groups of 8-12 Fischer 344 rats receiving gentamicin, 20 mg/kg b.i.d., for 3, 7, 10 and 14 days. Control animals received the vehicle for gentamicin, amiloride alone or gentamicin alone. The degree of renal failure and weight loss were similar in gentamicin and gentamicin + amiloride groups at all time points despite increases in serum potassium and magnesium in the amiloride-treated animals. Tubular dysfunction as assessed by depression of renal cortical slice uptake of p-aminohippurate and N-methylnicotinamide was not improved by the addition of amiloride. In addition, a comparable degree of tubular necrosis and regeneration was observed in all gentamicin-treated groups. Maximum gentamicin concentrations in the renal cortex did not differ. Thus, despite reduction of urinary losses of potassium and magnesium with resultant increased serum values, amiloride did not protect against experimental gentamicin nephrotoxicity. The tubular electrolyte wasting noted clinically is likely to be a result, rather than a cause of proximal tubular cell damage.

Gentamicin-induced stimulation of DNA synthesis in rat kidney. Comparison between in vivo and in vitro models

We have performed combined in vivo and in vitro measurements of thymidine uptake into kidney cortex DNA of animals treated with gentamicin for 7 days at 10 or 20 mg/kg daily (BID). Labelled thymidine is taken up by cortex fragments in vitro (90 min incubation) and incorporated into DNA; treatment of the animals with gentamicin results in a significant dose-dependent enhancement of this in vitro thymidine incorporation; labelled cells are found primarily in the proximal tubules and interstitium; there is an excellent correlation (r : 0.983, n = 15) between the changes of incorporation measured in vivo and in vitro as demonstrated by the sequential use of [3H]thymidine (in vivo) and [14C]thymidine (in vitro) within the same animals.

Chronology of the sodium hypothesis and hypertension

The observations that have provided the foundation of the sodium hypothesis of human hypertension are reviewed. Clinical observations made over 125 years ago initiated an investigative effort that has encompassed epidemiologic data, development of salt-related experimental models, and elucidation of theoretical mechanisms that interface Na+ balance with abnormal regulation of peripheral vascular resistance. In spite of the data available, a consensus is lacking on the relevance of applying the link between sodium intake and increased blood pressure in certain hypertensive patients to all persons.

Effect of basis amino acids and aminoglycosides on 3H-gentamicin uptake in cortical slices of rat and human kidney

The uptake of 3H-gentamicin was assessed in renal cortical slices of Fischer 344 male rats and four human cadaver kidneys not utilized for renal transplantation. In both species the uptake was maximal at 90 min and maintained a steady state thereafter. The characteristics of the energy-dependent component of 3H-gentamicin uptake were not altered by various basic amino acids, but competitive inhibition was induced by other aminoglycosides in a dose-dependent fashion. Thus aminoglycosides appear to share a transport process that is distinct from those of organic bases or other cationic substances. In addition, under the experimental conditions employed, the basolateral membrane of the tubular cell is capable of energy-dependent uptake of gentamicin. The role of this route of cellular uptake of aminoglycoside in clinical nephrotoxicity is speculative.

Nephrotoxic acute renal failure due to common drugs

Antibiotics are the most common drugs implicated in clinical reports of drug-induced nephrotoxicity. The experimental basis for proposed mechanisms of acute renal failure in association with three groups of antibiotics--aminoglycoside, cephalosporin, and amphotericin B--are reviewed in detail. Proposed mechanisms of antibiotic-induced acute renal tubular necrosis involve either altering plasma membrane permeability or interference with cellular energy derived from mitochondria, For either aminoglycoside or cephalosporin antibiotics, cellular accumulation followed by interruption of mitochondrial respiration is the concept that has greatest support, although the possibility of an induced phospholipidosis involving intracellular lysosomes cannot be excluded. Altered renal tubular cell permeability due to the incorporation of amphotericin B into the pore structure of the plasma membrane is consistent with in vivo observation in either clinical or experimental examples of nephrotoxicity with this agent. The metal cis-platinum, used in treatment of neoplastic disease, has a clearly defined incidence of clinical nephrotoxicity with little insight as to cellular mechanisms. A possible mediation involving cis-platinum reducing the protein-bound sulfhydryl group of renal tissue has been proposed. With the ever increasing potency of modern pharmacologic agents come a rising risk of serious toxic side effects.

Amikacin nephrotoxicity in the rat

When amikacin was administered to Fischer rats at a dose of 120 mg/kg/day for up to 14 days, renal proximal tubule cells became vacuolated, but BUN and creatinine remained normal. Renal cortical drug levels rose steadily throughout the treatment period. When, in a second trial of the same duration, the drug dose was tripled, focal proximal tubular necrosis, then regeneration, occurred and the animals became azotemic. Tissue drug concentrations peaked and began to decline during the treatment period, having reached levels more than three times higher than achieved at the lower dose. Ultrastructural changes were similar to those observed with other aminoglycosides. The results indicate that amikacin is less nephrotoxic than gentamicin and more toxin than tobramycin and netilmicin in the Fischer rat.

Pathogenesis of renal failure due to aminoglycosides and contrast media used in roentgenography

The etiology of acute renal failure has changed in recent years due to the recognition of drug nephrotoxicity as a more common cause. In this communication we emphasize recent information concerning the pathophysiology of nephrotoxic acute renal failure produced by aminoglycoside antibiotics and the contrast media used in roentgenography. The aminoglycosides are excreted primarily by glomerular filtration; however, net tubular reabsorption and renal parenchymal accumulation do occur. The exact mechanism of uptake is not clear, but the luminal membrane seems primarily involved. The pathogenesis of nephrotoxicity, although probably linked to cortical accumulation, is complex since experimental animals recover from gentamicin-induced renal failure despite continued administration of the drug. Knowledge of the precise cellular mechanisms of injury awaits further studies. Histologic damage is usually limited to proximal tubular necrosis and, clinically, the renal failure is nonoliguric. Although reports of the contrast media used in roentgenography producing acute renal failure have increased, the pathogenesis is unclear. Evidence supporting various theories is reviewed.

Comparative nephrotoxicities of high-dose netilmicin and tobramycin in rats

The nephrotoxic potentials of netilmicin and tobramycin given in doses of 180 mg/kg per day for up to 14 days were compared in Fischer rats. At this dosage, tobramycin produced mortality and significant changes in renal structure and function; netilmicin evoked minimal nephrotoxicity.

Effect of sodium bicarbonate and ammonium chloride ingestion in experimental gentamicin nephrotoxicity in rats

To examine the possibility that gentamicin binding to renal tubular epithelium is electrostatic, the effect of sodium bicarbonate-induced alkaline diuresis and ammonium chloride administration on the course of gentamicin nephrotoxicity in male Fischer 344 rats was examined. After 14 days of gentamicin, sodium bicarbonate drinking animals did not differ significantly from tap water drinking controls in the degree of nephrotoxicity as determined by serum creatinine, in vitro para-aminohippurate and N-methylnicotinamide uptake, histology and renal cortical gentamicin concentrations. However, 7/10 sodium bicarbonate drinking animals had extensive intratubular renal calcifications as compared to 0/29 tap water drinkers. Ammonium chloride drinking animals had more severe toxicity than tap water drinking controls. We conclude that in our model, sodium bicarbonate administration does not reduce experimental gentamicin toxicity and is associated with intratubular calcification. Ammonium chloride potentiates gentamicin nephrotoxicity.

The influence of dosage regimen on experimental gentamicin nephrotoxicity: dissociation of peak serum levels from renal failure

Peak serum levels of gentamicin were varied in rats by administering a standard nephrotoxic dosage of 40 mg/kg per day in one (QD), two, or three (TID) daily doses. The QD animals had the highest peak serum levels but showed no appreciable increase of serum creatinine concentrations over a 10-day treatment period. The TID rats had the lowest peak serum levels, but, after 10 days of drug administration, the serum creatinine concentration (2.8 +/- 0.2 mg/100 ml, mean +/- SE) was significantly higher than in control rats (0.6 +/- 0.01 mg/100 ml) (P less than 0.001). After two days of gentamicin treatment, the renal concentration of gentamicin was 269 +/- 77 micrograms/g in the QD rats and 820 +/- 29 micrograms/g in the TID rats (P less than 0.001). In this rat model, the frequency of doses was a more important factor in the development of nephrotoxicity than the peak serum concentration of gentamicin. The results suggest that dose frequency should be considered when data from different laboratories are compared.

Effect of milk constituents on hepatic cholesterol-genesis

Two preparations active in reducing hepatic cholesterol biosynthesis were isolated from bovine skim milk. One of the inhibitors was in the dialysate and was identified as orotic acid (OA). The other inhibitor, present in the retentate, was not identified. Orotic acid appears to act by inhibiting cholesterol biosynthesis before the formation of mevalonate, whereas the retentate inhibitor exerts its effect beyond the formation of mevalonate in the biosynthetic pathway. Human milk also inhibited the incorporation of both labeled acetate and mevalonate into cholesterol by rat liver. Orotic acid was not detectable in human milk samples employed in this study. Administration of [6-14C]orotate to rats revealed its conversion to uracil in the liver. Subsequent work demonstrated that uracil had inhibitory activity on hepatic cholesterol biosynthesis similar to that of orotate when incubated with rat liver slices.

Influence of progestin upon hemodynamics in castrated male pygmy goats

Effects of progestin administration for 5 to 6 weeks upon hemodynamics were studied in two separate experiments, using trained, adult castrated male Pygmy goats. Measurements of cardiac output, blood pressure, plasma volume, and oxygen content of arterial and mixed venous blood were made before, during, and after treatment. In experiment 1, four animals were used. Progesterone was implanted subcutaneously in silicone envelopes which released an average of 44 mg of progesterone/day/goat. A 20% decrease in cardiac output occurred by the 5th week of treatment. Blood pressure was maintained by an increased peripheral vascular resistance. The five animals in experiment 2 were given (IM) 6 mg of 17-alpha-hydroxyprogesterone/kg of body weight/day. Cardiac output decreased 17% in the 2nd and 3rd weeks of hormone treatment. 17-alpha-Hydroxyprogesterone caused a transient natriuresis followed by sodium retention. Urinary aldosterone excretion increased after 9 days of treatment, but returned to normal by the 15th day.

Adrenocorticotropin-cortisol axis abnormalities in hemodialysis patients

The ACTH-cortisol axis was studied in 15 hemodialysis patients. Basal plasma cortisol concentrations were found to be elevated and ACTH to be in the high normal range. Cortisol responded normally to exogenous ACTH, but neither cortisol nor ACTH were suppressed in response to oral dexamethasone. 11-Deoxycortisol and ACTH concentrations did not rise normally in response to either oral or iv metyrapone. We conclude that standard testing of the ACTH-cortisol axis in dialysis patients yields results suggesting Cushing's syndrome.

Natural history of asymptomatic coronary arteriographic lesions in diabetic patients with end-stage renal disease

Arteriosclerotic heart disease is a major cause of death in insulin-requiring juvenile diabetic patients treated for end-stage renal disease. Eleven consecutive diabetic patients without clinical evidence of coronary artery disease underwent complete cardiac evaluations, including coronary arteriography, as part of transplant recipient work-ups. Seven were women and four were men; their mean age was 32 (21 to 50 years). Angiographically, every patient had multifocal atherosclerotic coronary disease. Four of seven patients tested had positive-stress electrocardiograms. In this group of patients followed for a mean of 19.8 months, eight died. Of these deaths, six were due to coronary heart disease and another due to a stroke. In two patients who became clinically symptomatic, serial angiograms revealed progressive disease of the coronary circulation; in one case, despite normal renal allograft function and serum lipid levels. The mode of end-stage renal disease treatment, serum lipids or blood pressure control could not be linked to mortality. It is concluded that arteriosclerotic heart disease is common in diabetic patients with end-stage renal disease even when angina is absent. The natural history in this high risk population is an important consideration in the selection of patients for end-stage renal disease treatment.

Myeloid bodies in the renal tubules of humans: relationship to gentamicin therapy

Ultrastructural changes in renal proximal tubule lysosomes, including the formation of myeloid bodies, occur reliably with gentamicin administration in experimental animals. The present study reviewed the electron microscopic tubular morphology of renal biopsies and nephrectomies performed in our institution over a 2-year period. The frequency of myeloid bodies and their relation to drug therapy and selected clinical features were determined. Myeloid bodies were found in the proximal tubules of 19 of 109 cases that were judged adequate for study. On review of the drug histories of these 19 patients, 15 had received gentamicin within 6 weeks of biopsy or nephrectomy. None of the 90 patients without myeloid bodies had received the drug within 6 weeks of tissue examination. Of 4 patients with myeloid bodies who had not received gentamicin, 1 had received chloroquin and 3 had received drugs with no known or suspected capacity to induce myeloid bodies. The presence of myeloid bodies in proximal tubules did not appear to be related to the total dose of gentamicin, duration of therapy, or serum drug concentration. Clinical evidence of gentamicin nephrotoxicity was present in only 1 case.

Gentamicin binding to serum and plasma proteins

Gentamicin binding to serum proteins was studied by equilibrium dialysis at 37 degrees C and pH 7.4 in the presence of both physiologic and adjusted concentrations of ionized calcium and magnesium. The percentage of bound drug was inversely related to the concentration of these two divalent cations, raning from 27% bound with no calcium and magnesium present to 17% bound in the presence of four times physiologic concentrations. No significant difference in the extent of drug-protein binding was noted in a comparison of sera from healthy and uremic subjects. Heparin also was found to affect gentamicin binding. Increasing heparin concentration in serum increased apparent gentamicin-protein binding to 34% in the presence of physiologic amounts of calcium and magnesium. Buffered heparin solutions without plasma proteins bound up to 65% of total drug concentration. Gentamicin-protein binding may have implications regarding pharmacokinetics and renal cortical uptake.

Drug-related syndromes in clinical nephrology

The major clinical presentations of disease to a nephrologist can be grouped into six general areas: acute renal failure, chronic renal failure, nephrotic syndrome, fluid-electrolyte disorders, acid-base disturbances, and the uremic symptom-complex. Each of these major clinical syndromes can be caused by, or related to, drugs or environmental toxins. Prototype drugs can be used to highlight the features of each drug-related syndrome. Although it is preventable, drug-related disease may present opportunities to learn about general pathophysiologic mechanisms in clinical nephrology.

Do diuretics have antihypertensive properties independent of natriuresis?

To ascertain whether diuretics have an antihypertensive effect independent of natriuresis, 12 stable patients on maintenance hemodialysis underwent a crossover evaluation with hydrochlorothiazide, 50 mg daily, metolazone, 5 mg daily, or placebo in 4-wk treatment periods for 6 mo. Compliance was assured by pill counts and serum drug concentrations. All patients had daily urine less than 100 ml. Pre- and postdialysis blood pressure, body weight, plasma volume, and plasma renin activity were monitored. Over the 6-mo study period there were no statistically significant changes in any parameter related to diuretic therapy. It is concluded that a functioning kidney with the ability to respond to diuretics with a natriuresis is necessary for the antihypertensive action of diuretics. Direct vascular effects of diuretics to lower peripheral resistance could not be demonstrated in this unique patient population.

Gentamicin nephrotoxicity--morphologic and pharmacologic features

Images

Long-term minoxidil therapy in patients with refractory hypertension and renal disease

Minoxidil, an orally effective vasodilator, was successful in lowering blood pressure in 22 patients, followed up for up to 3 yrs, with hypertension refractory to medical management, including both antihypertensive drug combinations and ultrafiltration. In nondialysis patients renal function was preserved and in dialysis patients bilateral nephrectomy was avoided. Although sodium retention and reflex tachycardia were common, they were managed by beta-adrenergic blockade with propranolol and diuresis with furosemide.

Ultrasound monitoring of fetal movements. A method for assessing fetal development?

Human fetal movements in utero have been analysed by conventional compound B-scan ultrasound techniques. With practice, movements of specific parts of the fetus can be readily recognised, and even as early as the 6th week after conception gross movements of the whole embryo are visible. Monitoring of fetal movements as an indication of normal or abnormal fetal development appears to have been neglected, and future studies in this important area of antenatal paediatrics are suggested.

Effect of sodium intake on gentamicin nephrotoxicity in the rat

Gentamicin nephrotoxicity was examined in rats on normal, high, and low sodium diets. Low sodium diet markedly potentiated nephrotoxic effects of the drug as evidenced by animal mortality, renal failure, pathological changes, and increased renal cortical concentration of the drug. High sodium intake reduced the cortical concentration of gentamicin but renal function and ultrastructure were similar to normally fed rats given in the same dose.

The natriuretic effect of p-aminohippurate in man

The effects of p-aminohippurate (PAH) on electrolyte clearances were measured in 8 human volunteers. At plasma PAH levels used to measure renal plasm flow, the only significant increase was in sodium clearance, while with PAH levels used to measure maximum tubular secretion, the clearances of sodium, potassium and phosphorus were all significantly increased. The antriuresis combined with a depression of free water clearance and the absence of a chloruresis led to the conclusion that PAH- changed the anion composition of the filtrate delivered to the ascending limb, thus interfering with coupled Na+ reabsorption. This finding must be taken into account when electrolyte excretion is being measured during PAH infusion. A similar mechanism may operate in patients with chronic uremia whose endogenous hippurate level is increased.

Abnormalities of renal perfusion and the renal pressor system in dogs with chronic aortic coarctation

To clarify the role of the renin-angiotensin system in coarctation hypertension, 2-year-old inbred dogs with chronic neonatally induced thoracic aortic coarctation were subjected to 6 days of rigorous salt restriction. The following parameters were then measured: glomerular filtration rate, renal plasma flow, plasma renin activity, plasma renin concentration, renin reactivity, and renin substrate concentration. Glomerular filtration rate and renal plasma flow were significantly lower in salt-restricted coarcted dogs: 3.0 +/- 0.2 and 9.0 +/- 1.5 ml/min kg-1, respectively, compared with values of 4.0 +/- 0.2 (P less than 0.005) and 13.2 +/- 0.6 (P less than 0.025) ml/min kg-1 in salt-restricted controls. Plasma renin activity was abnormally high in experimental dogs: 13.5 +/- 2.5 vs. 4.5 +/- 1.5 ng angiotensin I/ml hour-1 in controls (P less than 0.005). In addition, a significant elevation of renin reactivity (indicating a relative increase in circulating accelerators or a relative decrease in inhibitors of the renin reaction) was apparent in the plasma of coarcted dogs. Plasma renin concentration was elevated but to an insignificant degree in coarcted dogs, and renin substrate concentration was comparable with that of controls. The impaired renal perfusion and abnormal elevation of plasma renin activity during salt restriction is analogous to clinical and experimental observations in hypertensive states associated with total renal underperfusion and supports a major role for the renal pressor system in the pathogenesis of coarctation hypertension. The insignificant elevation of plasma renin concentration is not incompatible with this view. The demonstration of increased renin reactivity in coarctation hypertension provides additional evidence that acceleration of the renin reaction is common to all hypertensive states.

Response to dopamine hydrochloride in the hepatorenal syndrome

Functional renal failure accompanying advanced cirrhosis of the liver carries a grave prognosis. Seven patients with the hepatorenal syndrome and five patients with decompensated cirrhosis of the liver without renal failure were studied by the xenon Xe 133 washout technique. Mean renal blood flow and its cortical component were decreased in both groups compared to normal transplant donors, but to a significantly greater degree in hepatorenal syndrome. In hepatorenal patients, intra-arterial infusion of subpresor doses of dopamine hydrochloride improved the angiographic appearance of the renal cortical vasculatrue and the cortical blood flow rate. Urine flow rate and glomerular filtration rate did not consistently improve with 12- to 24-hour intravenous infusions, although two patients survived, temporally related to the study. These patients had shown signs of liver function recovery.

Morphine and phenytoin binding to plasma proteins in renal and hepatic failure

The binding of morphine and phenytoin to plasma proteins was examined in healthy subjects and in patients with renal and hepatic failure. In the uremic patients without hepatic failure, morphine binding was dependent on the concentration of total serum proteins and albumin, but not the severity of renal failure as measured by creatinine clearance. Binding of phenytoin, however, was dependent on the degree of renal failure and albumin concentration, but not on total serum protein concentration. Renal transplant in 1 patient restored the binding of both drugs to a value within the normal range. The combination of hypoalbuminemia and hyperbilirubinemia resulted in the greatest impairment to binding for both drugs. It is concluded that patients with uremia, jaundice, hypoalbuminemia, particularly in combination, are sensitive to usual clinical doses of morphine, at least in part, because of decreased binding to plasma proteins.

Renal consequences of valvular heart disease

Three aspects of potential renal involvement in patients with valvular heart disease are discussed. These include (1) disturbances in renal salt and water handling and their implications with respect to diuretic management; (2) the hemodynamic effects of angiographic contrast agents with identification of potentially dangerous effects on the kidneys; and (3) the histologic patterns of bacterial endocarditis in the kidney and their similarity to those of immunologically mediated disease.