A micropuncture study of the early phase of acute urate nephropathy.

The early pathophysiological changes in acute urate nephropathy were investigated in a rat model using micropuncture, clearance, and morphologic methods. Plasma urate was increased from 1.2 +/- 0.6 to 20.1 +/- 3.1 mg/100 ml (P less than 0.001). Urinary urate rose from 24.3 +/- 5.1 to 142.2 +/- 21.0 mg/100 ml (P less than 0.001). Renal plasma flow and glomerular filtration rate fell to 17 and 14% of control values, respectively, and urine flow rate decreased from 11.3 +/- 4.8 to 4.2 +/- 2.2 mul/min (all P less than 0.005) Superficial nephron filtration rate fell less than that of the whole kidney (70 vs. 86%). Both proximal and distal tubular pressures were increased from 10.6 to 26.1 mm Hg and from 7.2 to 24.7 mm Hg, respectively (P less than 0.005). Efferent arteriolar and peritubular capillary pressures were increased twofold. Vascular resistance beyond the peritubular capillaries increased from 4.8 X 10(9) to 21.6 X 10(9) dynes s/cm5. Extensive deposits of uric acid and urate were found in the tubular system and vasa recti from the corticomedullary junction to the tip of the papilla. It is concluded from these experiments that not only tubular obstruction in the collecting ducts, but also obstruction of the distal renal vasculature, are the primary early pathogenetic events in acute urate nephropathy.

Distal tubular feedback in the autoregulation of single nephron glomerular filtration rate.

Renal clearance and recollection micro-puncture experiments were conducted to evaluate the possible role of a distal tubular feedback mechanism in the phenomenon of renal autoregulation in dogs. Single nephron glomerular filtration rate (SNGFR) was measured from collection sites in both the proximal (proximal SNGFR) and distal tubules (distal SNGFR). Single nephron autoregulatory behavior was assessed by evaluating the response of SNGFR to a reduction in renal arterial pressure imposed by means of an aortic constrictor. Whole kidney function was evaluated by parallel measurements of renal blood flow and inulin clearance. Whole kidney autoregulation was observed when renal arterial pressure was decreased from 141 +/- 3 (SE) mm Hg to 101 +/- 2 mm Hg; renal blood flow and GFR were not significantly altered from control values of 3.76 +/- 0.2 ml/min.g and 0.69 +/- 0.04 ml/min.g kidney weight, respectively. In 11 autoregulating preparations, proximal transit time was likewise unchanged from the control value of 26 +/- 2 s, indirectly suggesting that the superficial nephrons also participated in the autoregulatory response. However, proximal SNGFR decreased significantly from 88 +/- 7 nl/min to 66 +/- 6 nl/min, a reduction which was proportional to the decrease in arterial pressure. In 14 dogs in which both proximal SNGFR and distal SNGFR were measured at control blood pressure (136 +/- 5 mm Hg), distal SNGFR was 47 +/- 4 nl/min, a value significantly lower than that for proximal SNGFR (79 +/- 6 nl/min). In contrast to the results based upon proximal collections, distal SNGFR was not significantly altered following aortic constriction (44 +/- 5 nl/min vs. 47 +/- 5 nl/min) therefore exhibiting autoregulation in association with that observed for the whole kidney. These experiments indicate that though superficial nephrons do possess autoregulatory capability, interruption of distal delivery due to complete collection from the proximal tubule interferes with that nephron's ability to manifest an autoregulatory response. They support the concept that a feedback mechanism, related to some function of distal delivery, is of significance in the intrinsic regulation of SNGFR. The data further suggest that quantitative estimates of SNGFR based on complete proximal collections may not be representative of those throughout the superficial cortex of the dog, at least in certain experimental circumstances.

Evidence for role of cytosolic free calcium in hypoxia-induced proximal tubule injury.

The role of cytosolic free Ca2+ ([Ca2+]i) in hypoxic injury was investigated in rat proximal tubules. [Ca2+]i was measured using fura-2 and cell injury was estimated with propidium iodide (PI) in individual tubules using video imaging fluorescence microscopy. [Ca2+]i increased from approximately 170 to approximately 390 nM during 5 min of hypoxia. This increase preceded detectable cell injury as assessed by PI and was reversible with reoxygenation. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA; 100 microM) reduced [Ca2+]i under basal conditions (approximately 80 nM) and during hypoxia (approximately 120 nM) and significantly attenuated hypoxic injury. When [Ca2+]i and hypoxic cell injury were studied concurrently in the same individual tubules, the 10 min [Ca2+]i rise correlated significantly with subsequent cell damage observed at 20 min. 2 mM glycine did not block the rise in [Ca2+]i, yet protected the tubules from hypoxic injury. These results indicate that in rat proximal tubules, hypoxia induces an increase of [Ca2+]i which occurs before cell damage. The protective effect of BAPTA supports a role for [Ca2+]i in the initiation of hypoxic proximal tubule injury. The glycine results, however, implicate calcium-independent mechanisms of injury and/or blockade of calcium-mediated processes of injury such as activation of phospholipases or proteases.

Protective effect of intrarenal calcium membrane blockers before or after renal ischemia. Functional, morphological, and mitochondrial studies.

The present study examined whether a pre- or postischemic infusion of verapamil (V) or a postischemic infusion of nifedipine (N), drugs which block calcium (Ca++) influx across plasma membranes, provides protection against ischemic acute renal failure (ARF) in dogs. Renal hemodynamics and excretory function were examined 1 h (initiation phase) and 24 h (maintenance phase) after a 40-min intrarenal infusion of norepinephrine (NE). In each case, the uninfused contralateral kidney served as control. Four groups were studied: (a) dogs receiving NE alone; (b) dogs receiving an intrarenal infusion of V for 30 min before NE (V + NE); (c) dogs in which intrarenal V was infused for 2 h, beginning immediately after completion of NE infusion (NE + V); and (d) dogs in which intrarenal N was infused for 2 h, beginning immediately after completion of NE infusion (NE + N). Glomerular filtration rate (GFR) in the NE kidneys, as assessed by inulin clearance, at 1 and 24 h averaged 2.4 +/- 1.1 and 5.0 +/- 2.0 ml/min, respectively, as compared with control kidney GFRs of 28.0 +/- 3.5 and 43.8 +/- 5.0 ml/min, respectively (both at least P less than 0.01). In the V + NE group, GFR at 1 and 24 h averaged 15.0 +/- 5.5 and 31.0 +/- 4.5 ml/min, respectively, both at least P less than 0.05 as compared with values from NE kidneys. GFRs in the NE + V group averaged 15.0 +/- 2.4 and 16.3 +/- 3.6 ml/min at 1 and 24 h, both at least P less than 0.02 as compared with values from NE kidneys. GFR in the NE + N group averaged 18.6 +/- 6.0 ml/min at 24 h (P less than 0.05 as compared with GFRs in the NE kidneys). In addition, function of cortical mitochondria (Mito) was examined at the end of the 40-min NE infusion and after 1 and 24 h of reperfusion in the NE alone and NE + V groups. Mito respiration, assessed by acceptor control ratios, was reduced at each period in the NE alone kidneys. After 24 h, these Mito had accumulated Ca++ and exhibited reduced Ca++ uptake and increased Ca++ release rates. Mito from NE + V kidneys respired normally, did not accumulate Ca++, and exhibited no alterations in Ca++ uptake or release. Light and electron microscopy also demonstrated morphological protection of V against tubular necrosis and cell injury. Mito from the NE + N kidneys also respired normally and did not accumulate significant amounts of Ca++. The results of the present studies therefore demonstrated that chemically dissimilar calcium entry blockers exert substantial functional, cellular, and morphological protection against experimental ischemic ARF. These findings are compatible with the hypothesis that increased cytosolic Ca++ is critically important in the maintenance of renal vasoconstriction and the development of cellular necrosis with subsequent tubular obstruction in NE-induced ischemic ARF. V or N may provide protection against renal injury by retarding any increase in cytosolic Ca++ in renal vasculature and epithelium.

Development and application of fluorescence polarization assays in drug discovery.

Fluorescence polarization technology has been used in basic research and commercial diagnostic assays for many decades, but has begun to be widely used in drug discovery only in the past six years. Originally, FP assays for drug discovery were developed for single-tube analytical instruments, but the technology was rapidly converted to high-throughput screening assays when commercial plate readers with equivalent sensitivity became available. This review will discuss fluorescence polarization assays in current use in drug discovery research as well as those in development that will likely be used in the near future. These assays include targets such as kinases, phosphatases, proteases, G-protein coupled receptors, and nuclear receptors.

cGMP and cAMP cause pulmonary vasoconstriction in the presence of hemolysate.

We recently reported that addition of a small amount of hemolysate to the salt solution that perfused isolated rat lungs hypersensitized the vasculature to subsequent additions of ANG II or exposure to hypoxia, and addition of NO gas (. NO) to the perfusate that contained hemolysate caused a strong vasoconstrictor rather than a vasodilator response. In the present study, we demonstrate that CO and the secondary messengers cGMP and cAMP (usually associated with vasodilation) exert similar effects in hemolysate-perfused lungs. Analogs of the cyclic nucleotides cGMP or cAMP (8-bromo-cGMP and dibutyryl-cAMP, respectively) caused profound vasoconstriction in the isolated rat lung perfused with a salt solution that contained hemolysate. The cGMP- or cAMP-analog-induced vasoconstriction was inhibited by chemically dissimilar Ca2+ antagonists, by the protein phosphatase inhibitor okadaic acid, and, to a lesser degree, by protein kinase inhibitor H-7. Antiphosphothreonine immunoblotting demonstrated that lungs perfused with hemolysate exhibit increased phosphorylation of several proteins. These data indicate that, in the presence of hemolysate, pulmonary vasculature responds to nominally vasodilatory stimuli, including analogs of cGMP and cAMP, with vasoconstriction rather than vasodilation. The importance of our finding is the paradoxical nature of the response to (analogs of) cyclic nucleotides because, to our knowledge, cyclic nucleotide-induced vasoconstriction has not been previously reported.

Role of a macula densa feedback mechanism as a mediator of renal autoregulation.

The phenomenon of renal autoregulation demonstrates the presence of a sensitive intrarenal mechanism capable of maintaining GFR stable even during extrinsic disturbances that would be expected to alter renal hemodynamics. Substantial evidence has accumulated indicating that autoregulatory capability is dependent on the integrity of normal distal tubule flow dynamics and an intact distal tubuloglomerular feedback mechanism. Several whole-kidney and micropuncture studies have shown that interruption of volume delivery to the distal nephron interferes with autoregulation of renal blood flow (RBF) and GFR. The autoregulatory adjustments are probably localized at the afferent arterioles because the pressure in the larger arterioles does not exhibit autoregulation in response to decreases in renal perfusion pressure. It remains uncertain if the distal tubuloglomerular feedback mechanism is entirely responsible for autoregulatory responses. Data obtained in dog experiments indicate that under conditions of interrupted delivery to the distal nephron, SNGFR responses to decreases in arterial pressure are approximately those expected of a passive system where proximal tubule pressure is allowed to adjust to new steady-state levels with regard to the rapidity with which signals are transmitted to the distal nephron. Whole-kidney experiments indicate that, under conditions of a mild osmotic diuresis, the changes in urine flow following an increase in arterial pressure occur within 1 sec of the initiation of autoregulatory adjustments in vascular resistance. These experiments are consistent with the view that the major fraction of renal autoregulatory adjustments in resistance is mediated by the distal tubuloglomerular feedback mechanism that responds to some component of distal tubular flow and transmits signals to the afferent arteriolar segment of the same nephron.

Effect of indapamide on volume-dependent hypertension, renal haemodynamics, solute excretion and proximal nephron fractional reabsorption in the dog.

Indapamide, a newly developed antihypertensive agent with modest diuretic properties, reduced mean arterial pressure toward normal in dogs made hypertensive with salt and DOCA, while low-dose furosemide (0.1 mg per day) and hydrochlorothiazide (1 and 50 mg per day) did not result in similar degrees of blood pressure control. Indapamide, low-dose furosemide and hydrochlorothiazide treatment all resulted in similar decreases in body weight suggesting that the antihypertensive effect of indapamide occurs through a mechanism independent of contraction of extracellular fluid volume. Intravenous indapamide at doses of 0.3, 1.0 and 3.0 mg/kg caused progressive increases in sodium, potassium and chloride excretion when urine losses were replaced by isotonic saline to prevent extracellular fluid volume contraction. Only at 3.0 mg/kg did plasma potassium decrease significantly (2.92 +/- 0.03 to 2.69 +/- 0.05 mmol/l; p less than 0.05). Neither glomerular filtration rate (GFR) nor renal blood flow (flowmeter) decreased in a dose-related manner; however, effective renal plasma flow assessed by para-aminohippurate clearance did decrease about 15% at the highest dose (p less than 0.05). Proximal re-collection micropuncture studies demonstrated decreased proximal reabsorption. Cortical diluting segment reabsorption was decreased, but CNa + CH2O/GFR increased from 7% to 11% (p less than 0.05). These results indicate that, at doses up to 3.0 mg/kg, indapamide causes a natriuresis which is modest and similar to that seen with thiazides. No decrease in GFR or renal blood flow was observed. This drug apparently exerts a natriuretic effect through an inhibition of solute reabsorption in both the proximal nephron and the cortical diluting segment.

Small for gestational age: a new insight?

Acidosis reduces the ability of nitric oxide synthase to generate nitric oxide (NO) from L-arginine (L-arg), even if dietary intake or circulating plasma levels of L-arg are normal. During systemic acidemia, therefore, vascular perfusion in one or more organs may be compromised. Arginine is also a powerful anabolic amino acid. If dietary sources of L-arg are lower than normal, or if the production of NO is reduced even without frank acidemia, then vascular perfusion, and growth, and tissue repair are likely to be compromised. Two conditions in which acidemia is reported to occur, namely slow fetal growth in utero (acidemia is severe) and loss of bone and muscle in microgravity (acidemia is modest), are compared with respect to the accompanying alteration in the balance between acidemia and NO production.

A 280-day tolerance-efficacy study with mibolerone for suppression of estrus in the cat.

Mibolerone, a synthetic anabolic steroid, prevented estrus in domesticated cats when orally given a daily dose of 50 microng over a 180-day period. Doses of 20 microng daily and 50 microng given once a week failed to prevent estrus. Treatment with the 50-microng dose each day for 6 months had no apparent effects on subsequent estrus, mating, queening, or litter size. Kittens born to queens which had been treated did not have obvious developmental defects. Systemic metabolic changes produced by treatment were detected only in thyroid function, as revealed in dose- and time-related changes in serum cholesterol concentrations, thyroid gland weights, and thyroid histology. Clinical evidence of thyroid dysfunction was not apparent during the 6 months of treatment. Clinical and microscopic evidence of slight masculinization was apparent in cats after 3 months of treatment with 20 or 50 microng per day. Masculinizing changes consisted of thickening of the cervical dermis and clitoral hypertrophy. Behavioral changes were not observed. The apparent mechanism of action of mibolerone in the cat is the suppression of the release of pituitary luteinizing hormone.

Detection of canine antisperm antibodies by indirect immunofluorescence and gelatin agglutination.

Canine infertility has diverse and multiple causes. Immunologic infertility due to antisperm antibody is recognized and quantitated in other species, but this entity appears not to have been described in the dog. Before this time, there has been no practicable and reliable method to measure canine antisperm antibodies. This study was directed at inducing the production of such antibodies by immunizing dogs with sperm antigens and measuring the resulting antibodies, using the recognized techniques of indirect fluorescent antibody testing and sperm agglutination testing. Measurable antibody responses were observed.

Uterine motility during the estrous cycle: studies in healthy bitches.

Natural and drug-induced uterine motilities (UM) were recorded via uterine-implanted catheter-tip pressure transducers in 5 bitches during proestrus and estrus and in 6 bitches during early (30 days) and late (60 days) diestrus. The UM was monitored in unanesthetized bitches for 2 days after the estrous-cycle stage had been determined by vaginal cytologic findings. Natural UM, expressed as Alexandria units (pressure X frequency X duration of contractions), was greatest during estrus, moderate during proestrus, and appreciably decreased or lacking during early and late diestrus. During proestrus and estrus, prostaglandin F2 alpha (5 micrograms/kg of body weight, IV) induced intrauterine pressures of 107 and 115 mm of Hg, respectively, and oxytocin (0.05 USP units/kg, IV) induced pressures of 106 and 116 mm of Hg, respectively. In contrast, the intrauterine pressure values induced by prostaglandin F2 alpha given IV during early and late diestrus were 61 and 58 mm of Hg, respectively, and for oxytocin, were 61 and 51 mm of Hg, respectively. Prostaglandin F2 alpha given IM (50 micrograms/kg) also induced a greater intrauterine pressure during proestrus and estrus than during diestrus. We concluded that in the bitch, natural and drug-induced UM are decreased during early and late diestrus.

Megestrol acetate for estrus postponement in the bitch.

Megestrol acetate was given orally to 389 bitches in early proestrus, at a dosage of 2.2 mg/kg (1 mg/lb) per day for 8 days. Estrus was suppressed in 357 (92%) of the bitches. Additionally, 119 bitches in anestrus were given the drug at the rate of 0.55 mg/kg (0.25 mg/lb) per day for 32 days. Estrus was suppressed in 115 (98%) of these bitches. Adverse effects were minimal. Pyometra developed in 3 (0.8%) of the 389 bitches treated in early proestrus. The drug also was given to 19 bitches at the rate of 0.55 mg/kg/day for 32 days, regardless of the stage ofting at the 1st posttreatment estrus and 4 after mating at the 2nd posttreatment estrus. Litter size, success in rearing pups, and sex ratios were not significantly different from these factors in 53 litters from untreated bitches.

PIP: The postponement of estrus by megestrol acetate (MA) was evaluated in 389 female dogs. MA was administered for 8 days in a daily dose of 2.2 mg/kg body weight, beginning in early proestrus. Estrus was suppressed in 357 of these animals (92%). An additional 119 bitches in anestrus received MA in a daily dose of .55 mg/kg body weight for 32 days. Estrus was suppressed in 115 of these animals (97%). Pyometra was observed in 3 of 389 animals (.8%); other adverse affects were minimal. 19 animals received MA in a daily dose of .55 mg/kg body weight for 32 days, regardless of the stage of the estrous cycle. 15 of these bitches whelped normal litters after the 1st posttreatment estrus, and 4 after mating at the 2nd posttreatment estrus. Litter characteristics were similar to those observed in controls.

Nonenteric Escherichia coli isolates from dogs: 674 cases (1990-1998).

OBJECTIVE: To determine nonenteric sites associated with Escherichia coli isolates in dogs and the antimicrobial susceptibilities of the isolates. DESIGN: Retrospective study. SAMPLE POPULATION: 17,000 canine specimens. PROCEDURE: Medical records of 17,000 canine specimens submitted for bacteriologic culture were examined and the number of isolations of E coli was determined. For these cases, records were further examined with respect to body system involvement, sex, concurrent infection with other species of bacteria, and antimicrobial susceptibility. RESULTS: 674 E coli isolates (424 from urine, 62 from the skin, 52 from the respiratory tract, 45 from the ear, 43 from the female reproductive tract, 25 from the male reproductive tract, and 23 from other organ systems) were identified. There was a significantly higher proportion of isolates from urine specimens from spayed females than from sexually intact females or males. Escherichia coli was isolated in pure culture from 65.9% of the specimens. Most E coli isolates were susceptible to norfloxacin (90%), enrofloxacin (87.5%), gentamicin (90.7%), and amikacin (85.9%). CONCLUSIONS AND CLINICAL RELEVANCE: Most nonenteric E coli infections in dogs involve the urinary tract. Amikacin, gentamicin, norfloxacin, and enrofloxacin have the highest efficacy against canine E coli isolates. For E coli isolates from dogs, in vitro susceptibility to commonly used antimicrobial agents has remained fairly stable during the past decade.

Estimate of requirements for detection and treatment of hypercholesterolemia in U.S. Army aviators.

In May 1988, the Army Surgeon General issued guidelines and a preliminary plan for evaluation and treatment of hypercholesterolemia, based on the recommendations of the National Cholesterol Education Program Expert Panel. Implementation of this plan in the aviation population would require an unknown number of aviators to undergo testing and possibly therapy for hypercholesterolemia. This study uses a mathematical model and information from the Aviation Epidemiology Data Register to estimate the number of aviators who would require detailed lipoprotein analysis and at least dietary therapy, based on evaluation of their total serum cholesterol and other coronary artery disease (CAD) risk factors, as described in the expert panel report. The model predicts that at least 27% of all aviators would require LDL screening, and 24.6% of all aviators would require dietary or drug therapy.