Evolving microbial patterns of acute mastoiditis in pediatric patients undergoing mastoidectomy

OBJECTIVE

To investigate the microbial patterns and clinical outcomes of pediatric patients undergoing mastoidectomy for acute coalescent mastoiditis and to identify factors associated with poor outcomes and/or prolonged treatment.

STUDY DESIGN

Monocentric retrospective cohort study.

SETTING

Tertiary referral pediatric hospital in Indiana.

METHODS

By cross-referencing database data from the Pediatric Health Information System (PHIS) querying for all inpatient stays (patients younger than eighteen) with a diagnostic code of mastoiditis between January 1st, 2010 and August 31, 2019, and the electronic health record (Cerner) for Riley Hospital for Children, 46 patients with mastoidectomy were included. A two-tailed T-test was used to evaluate continuous parametric data. Statistical significance was determined as P < 0.05. For continuous variables, data was analyzed using continuous logistic regression. A criteria of p > 0.1 was used for inclusion in the multivariate regression.

RESULTS

Inclusion criteria was met by 46 patients. From 2010 to 2019, S. pyogenes and S. pneumoniae were the most common bacteria, each isolated in 11 of 42 bacterial isolates (26.2%). There was no growth in 35.4% (17/48) of intra-operative wound cultures. On univariate analysis, patients with negative cultures had longer length of hospital stay (LOS) (7.7 days [6.5] vs. 4.3 [2.8]; p = 0.018) as well as higher rates of PICC (peripherally inserted central catheter) placement (53.3% vs. 19.4%; p = 0.021). There was a statistically significant difference in terms of gender (p = 0.021), with 15 males and 16 females in the positive culture cohort and 13 males and 2 females in the negative culture cohort. On multivariate analysis, which included gender, PICC placement, both intracranial and extracranial complications, duration of antibiotics, and LOS, female gender was the only significant predictor of positive culture status (p = 0.039).

CONCLUSION

S. pyogenes and S. pneumoniae were the predominant etiologic agents in acute coalescent mastoiditis between 2010 and 2019, and negative wound cultures were associated with worse clinical outcomes.

TMPRSS3 expression is limited in spiral ganglion neurons: implication for successful cochlear implantation

BACKGROUND

It is well established that biallelic mutations in transmembrane protease, serine 3 (TMPRSS3) cause hearing loss. Currently, there is controversy regarding the audiological outcomes after cochlear implantation (CI) for TMPRSS3-associated hearing loss. This controversy creates confusion among healthcare providers regarding the best treatment options for individuals with TMPRSS3-related hearing loss.

METHODS

A literature review was performed to identify all published cases of patients with TMPRSS3-associated hearing loss who received a CI. CI outcomes of this cohort were compared with published adult CI cohorts using postoperative consonant-nucleus-consonant (CNC) word performance. TMPRSS3 expression in mouse cochlea and human auditory nerves (HAN) was determined by using hybridisation chain reaction and single-cell RNA-sequencing analysis.

RESULTS

In aggregate, 27 patients (30 total CI ears) with TMPRSS3-associated hearing loss treated with CI, and 85% of patients reported favourable outcomes. Postoperative CNC word scores in patients with TMPRSS3-associated hearing loss were not significantly different than those seen in adult CI cohorts (8 studies). Robust Tmprss3 expression occurs throughout the mouse organ of Corti, the spindle and root cells of the lateral wall and faint staining within <5% of the HAN, representing type II spiral ganglion neurons. Adult HAN express negligible levels of TMPRSS3.

CONCLUSION

The clinical features after CI and physiological expression of TMPRSS3 suggest against a major role of TMPRSS3 in auditory neurons.

Calvarium Thinning in Patients with Spontaneous Cerebrospinal Fluid Leaks of the Anterior Skull Base

OBJECTIVES/HYPOTHESIS

Patients with spontaneous cerebrospinal fluid leaks (sCSF-L) of the temporal bone have isolated calvarial and skull base thinning that is independent of obesity. This study determines if anterior skull base (ASB) sCSF-L patients also have calvarial thinning.

STUDY DESIGN

Retrospective Cohort Study.

METHODS

This was a retrospective cohort study of ASB sCSF-L patients compared to nonobese (body mass index [BMI] < 30 kg/m² ) and obese (BMI ≥ 30) control groups. Twenty-one patients in the ASB sCSF-L group and 25 patients in each control group were included. Calvarium and extracranial zygoma thicknesses were measured bilaterally with blinded, standardized, volumetric analysis.

RESULTS

ASB sCSF-L patients had a mean (SD) age of 50.43 (10.19) years, an average (SD) BMI of 38.81 (8.92) kg/m² , and most were female (85.71%). The calvarium in patients with ASB sCSF-L was significantly thinner than the nonobese (2.55 mm [0.77] vs. 2.97 [0.67] mm; P = .006; 95% confidence intervals [CI], 0.12-0.30; Cohen d, 0.58) and obese control groups (2.55 [0.77] vs. 2.92 [0.76] mm; P = .02; 95% CI, 0.05-0.34; Cohen d, 0.66). The calvarium thickness of the nonobese patients was not significantly different from the obese patient controls (2.97 [0.67] vs. 2.92 [0.76] mm, P = .9). The extracranial zygoma was not significantly different among the groups (analysis of variance, P = .33).

CONCLUSIONS

ASB sCSF-L patients have isolated calvarial thinning that is independent of obesity. Like lateral skull base sCSF-L patients, these data suggest that the additional obesity-associated intracranial process contributes to skull thinning.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:1271-1276, 2021.

Metastatic Disease of the Temporal Bone: A Contemporary Review

OBJECTIVES

To identify the frequency and primary site of metastatic pathologies to the temporal bone and characterize the associated symptomatology.

METHODS

The MEDLINE, Embase, and Web of Science databases were systematically reviewed according to the PRISMA guidelines to identify all cases of pathologically confirmed distant temporal bone metastases published with English translation until October 2019. Descriptive statistics were performed.

RESULTS

Out of 576 full-length articles included for review, 109 met final criteria for data extraction providing 255 individual cases of distant temporal bone metastases. There was a male predominance (54.9%) with median age of 59.0 years (range 2-90). The most common locations of primary malignancy included the breasts (19.6%), lungs (16.1%), and prostate (8.6%). Most tumors were carcinomas of epithelial origin (75.3%) and predominantly adenocarcinoma (49.4%). The commonest metastatic sites encountered within the temporal bone were the petrous (72.0%) and mastoid (49.0%) portions. Bilateral temporal bone metastases occurred in 39.8% of patients. Patients were asymptomatic in 32.0% of cases. Symptomatic patients primarily reported hearing loss (44.3%), facial palsy (31.2%), and otalgia (16.6%) for a median duration of 1 month. Petrous lesions were associated with asymptomatic cases (P = .001) while mastoid lesions more often exhibited facial palsy (P = .026), otalgia (P < .001), and otorrhea (P < .001). Non-carcinomatous tumors were associated with petrosal metastasis (P = .025) and asymptomatic cases (P = .109). Carcinomatous metastases more often presented with otalgia (P = .003).

CONCLUSIONS

Temporal bone metastasis is uncommon but should be considered in patients with subacute otologic symptoms or facial palsy and history of distant malignancy. Laryngoscope, 131:1101-1109, 2021.

Vector competence of Aedes vexans (Diptera: Culicidae) for West Nile virus and potential as an enzootic vector

Vector competence of Aedes vexans (Meigen) and Culex pipiens pipiens L. (Diptera: Culicidae) for West Nile virus (family Flaviviridae, genus Flavivirus, WNV) was compared. Infection rates of both species were similar 14 d after feeding on chickens, with WNV titers ranging from 10(4.2) to 10(8.7) plaque-forming units (PFU)/ml. Median infectious doses and 95% confidence intervals (CI) were 10(6.0(5.8, 63)) and 10(5.7(5.4, 5.9)) PFU for Ae. vexans and Cx. p. pipiens, respectively. WNV transmission was not observed in Ae. vexans that fed on chickens with WNV titers < 10(5.0) PFU/ml, in contrast to a mean (95% CI) transmission rate of 7(2,18)% for Cx. p. pipiens. Mean WNV transmission rates for Ae. vexans and Cx. p. pipiens were 13(7,21)% and 10(5,19)%, respectively, after feeding on chickens with WNV titers of 10(5.3 +/- 0.1) and 10(5.7 +/- 0.1) PFU/ml, and 31(25,37)% and 41(30,53)% after feeding on chickens with WNV titers > or = 10(6.1 +/- 0.1) PFU/ml. Time postinfection (p.i.) significantly influenced WNV transmission by Ae. vexans as indicated by a nearly 10-fold increase in transmission rate between days 7 and 14 p.i. Mean WNV load expectorated with saliva ofAe. vexans was 10(2.4(2.1, 2.7)) PFU, and it was not significantly affected by the titer of chickens on which they originally fed or time p.i. These data indicate that vector competence of the primarily mammalophilic Ae. vexans, which also feeds on birds, approaches that of Cx. p. pipiens for WNV. Because peridomestic mammals, such as cottontail rabbits, squirrels, and chipmunks, develop WNV titers infective for Ae. vexans, this species may play a significant role in WNV enzootic cycles.

The potential of Aedes triseriatus (Diptera: Culicidae) as an enzootic vector of West Nile virus

The susceptibility of Aedes triseriatus (Say) (Diptera: Culicidae) to low levels of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) was determined and compared with that of Culex pipiens L. to assess the likelihood of its participation in an enzootic cycle involving mammals. Ae. triseriatus and Cx. pipiens were exposed to WNV by feeding on baby chickens with WNV serum titers ranging from 10(4.1 +/- 0.1) to 10(8.6 +/- 0.1) plaque-forming units (PFU)/ml and from 10(4.1 +/- 0.1) to 10(7.0) PFU/ml, respectively. Infection rates and 95% confidence intervals (CIs) of 8% (4, 14) and 25% (15, 38) occurred in Ae. triseriatus and Cx. pipiens after feeding on chickens with WNV titers of 10(4.1 +/- 0.1) PFU/ml and increased to 65% (49, 79) and 100% (72, 100) in Ae. triseriatus and Cx. pipiens after feeding on chickens with titers of 10(7.1 +/- 0.1) PFU/ml. The mean infection rate of Ae. triseriatus ranged from 97% (84, 100) to 100% (79, 100) after feeding on chickens with WNV titers of > or = 10(8.2) PFU/ml. The infectious dose (ID)50 values for Ae. triseriatus and Cx. pipiens were 10(6.5) (6.4, 6.7) and 10(4.9) (4.6, 5.1) PFU/ml, respectively. The combined estimated transmission rate of Ae. triseriatus at 14 and 18 d after feeding on chickens with a mean WNV titer of 10(8.6 +/- 0.1) PFU/ml was 55%. Although Ae. triseriatus is significantly less susceptible to WNV than Cx. pipiens, the susceptibility of Ae. triseriatus to WNV titers < 10(5.0) PFU/ml and its ability to transmit WNV suggest that Ae. triseriatus has the potential to be an enzootic vector among mammalian populations.

Effects of 30 day simulated microgravity and recovery on fluid homeostasis and renal function in the rat

Transition from a normal gravitational environment to that of microgravity eventually results in decreased plasma and blood volumes, increasing with duration of exposure to microgravity. This loss of vascular fluid is presumably due to negative fluid and electrolyte balance and most likely contributes to the orthostatic intolerance associated with the return to gravity. The decrease in plasma volume is presumed to be a reflection of a concurrent decrease in extracellular fluid volume with maintenance of normal plasma-interstitial fluid balance. In addition, the specific alterations in renal function contributing to these changes in fluid and electrolyte homeostasis are potentially responding to neuro-humoral signals that are not consistent with systemic fluid volume status. We have previously demonstrated an early increase in both glomerular filtration rate and extracellular fluid volume and that this decreases towards control values by 7 days of simulated microgravity. However, longer duration studies relating these changes to plasma volume alterations and the response to return to orthostasis have not been fully addressed. Male Wistar rats were chronically cannulated, submitted to 30 days head-down tilt (HDT) and followed for 7 days after return to orthostasis from HDT. Measurements of renal function and extracellular and blood volumes were performed in the awake rat.

Alterations in glomerular and tubular dynamics at 1 and 14 days simulated microgravity and after acute return to orthostasis

Head-down tilt (HDT) is utilized to simulate microgravity and produces a cephalad fluid shift, which results in alterations in fluid and electrolyte balance. These changes in volume homeostasis are due, in part, to alterations in multiple volume control mechanisms in which renal function is a major participant. We have previously demonstrated that glomerular filtration rate increases early in HDT and eventually returns to values not different from non-tilt measurements. This early increase in glomerular filtration rate was also demonstrated during days 2 and 8 of the SLS-1 mission. However, urine flow and electrolyte excretion does not parallel the alterations in glomerular filtration rate and the site of this change in nephron fluid reabsorption pattern has not been previously examined. Through determination of the location of alterations in tubular fluid reabsorption within the nephron, a more detailed hypothesis can be forwarded as to which specific neuro-humoral agents participating in control of renal function in microgravity conditions. The importance of this type of examination is that measurements in circulating neuro-humoral agents and urinary excretion patterns alone are not accurate predictors of how renal functional response may alter to head-down tilt or other models of simulated weightlessness. To examine this issue, renal micropuncture techniques were utilized in Munich-Wistar rats submitted 24 hours and 14 day head-down tilt, measuring all the determinants of glomerular ultrafiltration and obtaining data regarding segmental tubular fluid reabsorption. Following these measurements, the rats were returned to an orthostatic position and after 60 min, the measurements were repeated.

Renal response to blood pressure elevation in normal and glomerulonephritic rats

Concurrent renal disease appears to augment greatly the adverse effects of systemic hypertension on renal function and the development of glomerulosclerosis. This study examined the effects of systemic hypertension and treatment of hypertension in groups of normal non-nephritic rats and rats submitted to 16 wk of glomerulonephritis induced by the administration of anti-glomerular basement membrane antibody. Hypertension was produced by application of a clip to the right renal artery and blood pressure was treated with an angiotensin-converting enzyme (ACE) inhibitor, quinapril. Glomerulosclerosis of two types developed: a diffuse type that is characteristic of anti-glomerular basement membrane glomerulonephritis, and a focal segmental glomerulosclerosis that is characteristic of systemic hypertension. Glomerulonephritis significantly reduced the capacity of ACE inhibitors to decrease systolic blood pressure in awake animals. In addition, glomerulonephritis produced significant effects on plasma angiotensin II concentrations, whereby ACE inhibition no longer lowered plasma angiotensin II levels and in fact produced an increase. Glomerular capillary hydrostatic pressure and hydrostatic pressure gradient correlated with systolic blood pressure and with the incidence of focal glomerulosclerosis in non-nephritic rats. However, in glomerulonephritis, systolic blood pressure no longer correlated with glomerular capillary pressure, and glomerular capillary pressure no longer correlated with the development of glomerulosclerosis, although systolic blood pressure did correlate with the degree of focal segmental glomerulosclerosis. Concurrent glomerulonephritis strongly conditions the effects of superimposed hypertension by altering the relationship between systemic blood pressure and glomerular capillary hydrostatic pressure and by decreasing the response of hypertension to therapy.

Glomerular filtration and tubular reabsorption of albumin in preproteinuric and proteinuric diabetic rats

Microalbuminuria (26-250 mg/d) is considered to be an indicator of incipient diabetic nephropathy in humans in insulin-dependent diabetes (IDD). However, before microalbuminuria is observed, glomerular alterations, such as glycosylation of the glomerular basement membrane and glomerular hyperfiltration, in IDD may result in increased filtration of albumin before any observed increase in albumin excretion. Glomerular and tubular albumin kinetics were examined in streptozotocin (65 mg/kg body wt, i.v.) diabetic, Munich-Wistar rats at 7-10 (untreated) and 50-70 d (poorly controlled with small doses of insulin) after the onset of diabetes and compared with nondiabetic controls. Additional rats in each condition received acute lysine treatment to prevent tubular protein reabsorption. Urinary albumin excretion and nonvascular albumin distribution volumes were measured in the renal cortex and compared with morphometric measurements of interstitial space and the proximal tubule to assess intracellular uptake of albumin in the proximal tubule. Urinary albumin excretion under anesthesia was not different in 7-10-d IDD versus controls (19 +/- 3 vs. 20 +/- 3 micrograms/min) but increased in the 50-70-d IDD (118 +/- 13 micrograms/min, P < 0.05). Lysine treatment resulted in increased albumin excretion compared with respective nontreatment in 7-10-d IDD (67 +/- 10 micrograms/min, P < 0.05) but not in controls (30 +/- 6 micrograms/min) or in 50-70-d IDD (126 +/- 11 micrograms/min). Glomerular filtration rate was increased both in 7-10-d IDD (2.7 +/- 0.1 ml/min, P < 0.05) and in 50-70-d IDD (2.6 +/- 0.1 ml/min, P < 0.05) compared with control (2.2 +/- 0.1 ml/min). Calculated urinary space albumin concentrations increased early in IDD with 2.5 +/- 0.4 mg% in 7-10-d IDD and 4.9 +/- 0.6 mg% in 50-70-d IDD compared with control (1.4 +/- 0.3 mg%). The increase in filtration of albumin is in excess of that attributable to hyperfiltration before increased albumin excretion early in diabetes. In 50-70-d IDD, absolute tubular reabsorption of albumin is decreased, correlating to the decrease in brush border height of the proximal tubule.

Contrasting effects of acute insulin infusion on renal function in awake nondiabetic and diabetic rats

Glomerular hyperfiltration in established, moderately hyperglycemic, insulin-dependent diabetes has been hypothesized to be the result of mild volume expansion. Because glomerular hyperfiltration in diabetics is normalized by insulin treatment, then insulin treatment should also reduce extracellular fluid or plasma volume. Previous studies have demonstrated that acute insulin treatment in nondiabetic kidneys results in vasodilation and increased GFR. It is possible that stimuli to the diabetic kidney, as a result of insulin-induced fluid shifts that reduce extracellular fluid volume (ECF) via glucose transport, result in reduction in GFR, opposing the direct renal vasodilatory action of insulin. Awake, chronically cannulated Wistar rats were used in both nondiabetic and established, moderately hyperglycemic, streptozotocin diabetic conditions. After the initial measurements of GFR, RPF, and ECF were obtained, insulin R (5 U) was administered acutely, both groups of rats were glucose clamped at euglycemic levels, and the measurements were repeated. In nondiabetic rats, GFR increased from 0.90 +/- 0.04 to 1.12 +/- 0.06 mL/min.100 g body wt after insulin treatment (P < 0.05), whereas in diabetic rats, GFR, which was greater than in the nondiabetic rats (P < 0.05), decreased from 1.37 +/- 0.03 to 1.13 +/- 0.05 mL/min.100 g body wt (P < 0.05) after acute insulin treatment. The alterations in GFR paralleled the changes in RPF, and the GFR alterations are most likely mediated by the changes in RPF. ECF was not different between nondiabetic and diabetic rats (28 +/- 2 versus 26 +/- 2% of body wt, respectively) and was not significantly altered by acute insulin infusion. Therefore, the contrasting effects of insulin infusion on GFR and RPF in nondiabetic versus diabetic rats cannot be attributed to alterations in ECF. In addition, the data demonstrate that ECF expansion is not required to sustain glomerular hyperfiltration.

Direct measurement of capillary blood pressure in the human lip

In this study, we developed and tested a new procedure for measuring microcirculatory blood pressures above heart level in humans. Capillary and postcapillary venule blood pressures were measured directly in 13 human subjects by use of the servo-nulling micropressure technique adapted for micropuncture of lip capillaries. Pressure waveforms were recorded in 40 separate capillary vessels and 14 separate postcapillary venules over periods ranging from 5 to 64 s. Localization and determination of capillary and postcapillary vessels were ascertained anatomically before pressure measurements. Capillary pressure was 33.2 +/- 1.5 (SE) mmHg in lips of subjects seated upright. Repeated micropunctures of the same vessel gave an average coefficient of variation of 0.072. Postcapillary venule pressure was 18.9 +/- 1.6 mmHg. This procedure produces a direct and reproducible means of measuring microvascular blood pressures in a vascular bed above heart level in humans.

Role of mesangial cell in glomerular response to volume and angiotensin II

We have examined the physiological role of the mesangial cell in the regulation of glomerular hemodynamics utilizing mesangial cell lysis by the administration of antithymocyte antibody serum (ATS) 24 h before micropuncture evaluation. Plasma volume expansion (PVE) in normal NaCl-depleted rats increased single-nephron glomerular filtration rate (SNGFR) by 30% because of increases in single-nephron plasma flow (SNPF), whereas glomerular capillary hydrostatic pressure (PG) remained constant. SNGFR did not increase with PVE in NaCl-depleted ATS rats despite increases in SNPF, and PG increased significantly (51 +/- 2 to 67 +/- 3 mmHg) because of afferent arteriolar dilation, whereas efferent resistance remained elevated. Angiotensin II (ANG II) infusion in normal rats decreased SNGFR because of reductions in SNPF and the glomerular ultrafiltration coefficient (LpA), whereas the hydrostatic pressure gradient (delta P) increased. In ATS rats ANG II infusion did not change SNGFR, LpA, or delta P. These in vivo studies suggest that the mesangial cell plays an important role in the regulation of LpA, efferent arteriolar resistance, and the regulation of PG, whereas this cell exerts little effect on the afferent arteriole.

Glomerular hemodynamic alterations during acute hyperinsulinemia in normal and diabetic rats

Treatment of insulin dependent diabetes invariably requires exogenous insulin to control blood glucose. Insulin treatment, independent of other factors associated with insulin dependent diabetes, may induce changes that affect glomerular function. Due to exogenous delivery of insulin in insulin dependent diabetes entering systemic circulation prior to the portal vein, plasma levels of insulin are often in excess of that observed in non-diabetics. The specific effects of hyperinsulinemia on glomerular hemodynamics have not been previously examined. Micropuncture studies were performed in control (non-diabetic), untreated diabetic and insulin-treated diabetic rats 7 to 10 days after administration of 65 mg/kg body weight streptozotocin. After the first period micropuncture measurements were obtained, 5 U of regular insulin (Humulin-R) was infused i.v., and glucose clamped at euglycemic values (80 to 120 mg/dl). Blood glucose concentration in non-diabetic controls was 99 +/- 6 mg/dl. In control rats, insulin infusion and glucose clamp increased nephron filtration rate due to decreases in both afferent and efferent arteriolar resistance (afferent greater than efferent) resulting in increased plasma flow and increased glomerular hydrostatic pressure gradient. However, insulin infusion and glucose clamp produced the opposite effect in both untreated and insulin-treated diabetic rats with afferent arteriolar vasoconstriction resulting in decreases in plasma flow, glomerular hydrostatic pressure gradient and nephron filtration rate. Thromboxane A2 (TX) synthetase inhibition partially decreased the vasoconstrictive response due to acute insulin infusion in diabetic rats preventing the decrease in nephron filtration rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between alpha 2-adrenergic and angiotensin II systems in the control of glomerular hemodynamics as assessed by renal micropuncture in the rat

The hypothesis that renal alpha 2 adrenoceptors influence nephron filtration rate (SNGFR) via interaction with angiotensin II (AII) was tested by renal micropuncture. The physical determinants of SNGFR were assessed in adult male Munich Wistar rats 5-7 d after ipsilateral surgical renal denervation (DNX). DNX was performed to isolate inhibitory central and presynaptic alpha 2 adrenoceptors from end-organ receptors within the kidney. Two experimental protocols were employed: one to test whether prior AII receptor blockade with saralasin would alter the glomerular hemodynamic response to alpha 2 adrenoceptor stimulation with the selective agonist B-HT 933 under euvolemic conditions, and the other to test whether B-HT 933 would alter the response to exogenous AII under conditions of plasma volume expansion. In euvolemic rats, B-HT 933 caused SNGFR to decline as the result of a decrease in glomerular ultrafiltration coefficient (LpA), an effect that was blocked by saralasin. After plasma volume expansion, B-HT 933 showed no primary effect on LpA but heightened the response of arterial blood pressure, glomerular transcapillary pressure gradient, and LpA to AII. The parallel results of these converse experiments suggest a complementary interaction between renal alpha 2-adrenergic and AII systems in the control of LpA.

Disassociation between glomerular hyperfiltration and extracellular volume in diabetic rats

The relationship of the development of glomerular hyperfiltration in diabetes to changes in extracellular fluid volume has not been previously examined. To accomplish this task, male Wistar rats were chronically cannulated in the bladder, femoral artery and vein. Control measurements of glomerular filtration rate (GFR), renal plasma flow (RPF), extracellular fluid volume (ECF), and urinary sodium excretion were performed on two separate days prior to infusion of streptozotocin (65 mg/kg body wt i.v.). After infusion of streptozotocin, the IDDM rats were separated into two groups: untreated IDDM group of rats and IDDM rats treated with insulin at doses sufficient to normalize blood glucose (Ultralente, 2 to 8 IU/day). A third group of normal non-diabetic rats served as time controls. Measurements of renal function occurred at 1, 4, 7, 11, and 15 days after infusion of streptozotocin. Blood glucose in the non-diabetic measurement period averaged 137 +/- 30 mg/dl and increased from 412 +/- 55 after 24 hours in the untreated diabetic rats to 533 +/- 33 mg/dl after 15 days of IDDM. The time controls and the insulin-treated diabetic rats did not differ in blood glucose values at the time measurements were performed. Glomerular filtration rate increased from 1.0 +/- 0.1 to 1.7 +/- 0.1 ml/min/100 g body wt by day 15 in the untreated diabetic rats with significant increases in GFR within 24 hours. GFR of both time controls and the insulin-treated IDDM rats did not significantly vary during the time of the study. The increase in GFR in the untreated IDDM group was associated with a concomitant increase in RPF.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of recombinant human insulin-like growth factor I on glomerular dynamics in the rat

This study was undertaken to investigate the mechanisms by which an infusion of recombinant human insulin-like growth factor I (rhIGF-I) increases GFR and renal plasma flow (RPF) in rats. Glomerular micropuncture studies were carried out in 14 nonstarved Munich Wistar rats and in 12 rats deprived of food for 60-72 h. Animals were given an intravenous injection and infusion of either rhIGF-I or vehicle. In both nonstarved and starved animals, the IGF-I injection and infusion increased the serum IGF-I levels, left kidney GFR, single nephron glomerular filtration rate (SNGFR), single nephron blood flow rate (SNBF), and single nephron plasma flow rate (SNPF). The increase in SNPF and SNGFR was in part due to a fall in efferent arteriolar resistance (RE); there was a tendency, not significant, for afferent arteriolar resistance (RA) to fall in comparison to controls. The increase in SNGFR was partly caused by a rise in SNPF but was primarily due to an increase in glomerular ultrafiltration coefficient (LpA) to twice the control values. The increase in LpA resulted in an increase in SNGFR because the rats operated at ultrafiltration pressure disequilibrium. Control starved as compared with nonstarved rats had lower SNGFR, SNBF, and SNPF. This reduction was due to a tendency, not significant, for both RA and RE to be higher. Decreased SNGFR in food-deprived rats resulted from a reduced SNPF, a lower glomerular transcapillary hydrostatic pressure difference (delta P), and possibly a somewhat reduced LpA. These data indicate that IGF-I increases SNGFR, SNPF, and SNBF primarily by increasing LpA and also by decreasing RE without affecting delta P. Short-term starvation lowers SNGFR, SNPF, and SNBF primarily by decreasing delta P and possibly by lowering LpA and increasing RA and RE. IGF-I reverses some of the glomerular hemodynamic effects of short-term food deprivation.

Effects of beta-adrenergic blockade on the glomerular and tubular response to acute renal denervation

Using micropuncture techniques in euvolemic adult male Munich-Wistar rats, we assessed the functional role of renal beta-adrenoceptors in mediating neural control of glomerular filtration and proximal tubular reabsorption. The determinants of nephron filtration and rate of proximal tubular reabsorption were measured in two groups of animals before and after acute surgical renal denervation (DNX). Group A animals (n = 6) were pretreated with the beta-adrenoceptor antagonist propranolol (25 mg/kg body weight per day for 4-6 days). Group B animals (n = 7) served as non-beta-blocked controls. Acute renal DNX resulted in no significant change in nephron filtration rate or any of its determinants in either group. Acute DNX caused similar decrements in the rate of fluid reabsorption from the proximal convoluted tubule of beta-blocked and control rats. Loop of Henle fluid reabsorption did not appear to be affected by DNX in either group. Because the effect of denervation on proximal tubular reabsorption was not conditioned by prior beta-blockade, the beta-adrenoceptors present within the proximal convoluted tubule do not appear to be the primary mediators of the adrenergic influence on fluid transport in that segment of the nephron.

Adrenergic influences and interactions with angiotensin II

Increasing evidence indicates the existence of a complex interplay between the angiotensin and adrenergic nervous systems within the kidney. Since both of these vasoconstrictor systems are integrally involved in the maintenance of systemic blood pressure and fluid and electrolyte homeostasis, it is not surprising that each might influence the other vis-a-vis their mutual capacity to alter the physiologic determinants of glomerular filtration.

Early onset of increased transcapillary albumin escape in awake diabetic rats

Alteration in transcapillary albumin escape rate (TERalb) is an indicator of changes in macromolecular movement at the capillary filtering bed, which can change the balance of Starling forces for fluid movement from the vasculature to the interstitium and has an impact on volume homeostasis. TERalb can be affected by morphological changes in the capillary membrane and/or alterations in the Starling forces driving larger solutes across the capillary membrane via convection. Previous studies have demonstrated an increased TERalb in established insulin-dependent diabetes (IDDM); however, whether increased TERalb is the result of morphological alterations in the microvasculature or contributes to microangiopathies could not be resolved. TERalb was examined in awake Wistar rats with untreated IDDM induced by streptozocin infusion (65 mg/kg body wt i.v.) at 24 h and 7 and 15 days and compared with control and insulin-treated 7-day IDDM rats. Increased TERalb occurred at the 24-h time point and remained elevated at 7 and 15 days of IDDM (P less than 0.05). Blood volume remained unchanged; however, systemic protein concentration increased from 4.9 +/- 0.1 g/dl in controls to 6.4 +/- 0.4 g/dl in 15-day IDDM rats. Blood glucose was significantly increased, and glycosuria was evident at all three time points of IDDM. The observed increase in TERalb within 24 h of IDDM is indicative of a functional change in the Starling forces in the capillaries, because specific morphological capillary damage is not evident at this time point in the model. The early onset of TERalb in IDDM could indicate functional changes, such as capillary hypertension, and may contribute to future vascular complications in established IDDM.

Acute and subacute prostaglandin and ANG II inhibition on glomerulotubular dynamics in rats

Prostaglandins (PG) and angiotensin II (ANG II) contribute to regulation of glomerular microcirculation. Acute vs. chronic physiological alterations of glomerular hemodynamics that result from inhibition of either PG or ANG II, or both, and their interaction were examined. Four groups of Munich-Wistar rats were submitted to the following micropuncture studies in euvolemic conditions for measurements of glomerular hemodynamics and tubular fluid reabsorption: 1) an untreated control group, 2) 4- to 6-day inhibition of both PG and angiotensin-converting enzyme activity with meclofenamate and MK-421 (enalapril), 3) 4- to 6-day treatment with enalapril followed by acute PG inhibition in the second measurement period, 4) 4- to 6-day PG inhibition followed by acute enalapril treatment in the second period. Dual 4- to 6-day treatment decreased single-nephron filtration rate (SNGFR, 24 +/- 2 vs. 33 +/- 2 nl/min in control; P less than 0.05) as a result of decreases in single-nephron plasma flow (SNPF) and glomerular hydrostatic pressure gradient (delta P). Treatment with enalapril alone for 4-6 days did not reduce SNGFR and SNPF; however, delta P decreased. Acute addition of meclofenamate did not alter these factors. SNGFR was decreased with 4- to 6-day treatment of meclofenamate from 33 +/- 2 in control to 25 +/- 1 nl/min (P less than 0.05). Acute treatment with enalapril in the 4- to 6-day meclofenamate-treated rats increased SNGFR to values not different from control. The results demonstrated that glomerular hemodynamic alterations consequent to inhibition of ANG II and PG systems differ between chronic and acute treatments. Therefore, interpretation of the role of individual hormonal systems in the control of glomerular hemodynamics should be approached with caution, since effects may be altered by duration of treatment and involvement of other vasoactive systems.

Glomerular hemodynamic alterations during renal nerve stimulation in rats on high- and low-salt diets

Renal adrenergic nerve activity exerts a major influence on glomerular hemodynamics and tubular fluid reabsorption. Modulation of the functional expression of adrenergic activity in the kidney can be mediated, in part, by the renin-angiotensin system and by prostanoid activity. Alterations in dietary salt intake have been previously shown to modify the activity of various vasoactive systems, including angiotensin and prostaglandin activity and thereby have a potential of modifying the glomerular hemodynamic response to a given renal adrenergic stimulus. Munich-Wistar rats were fed either a high-, low-, or normal salt diet for 2 wk before the day of the study. Measurements of glomerular hemodynamics were performed in both unstimulated with basal renal nerve traffic eliminated and during exogenous renal nerve stimulation (RNS) (3 Hz). RNS decreased glomerular capillary hydrostatic pressure and single-nephron plasma flow to a similar extent in all three dietary conditions via increases in afferent arteriolar resistance. The data demonstrated that dietary preconditioning does not alter the glomerular hemodynamic response to an exogenous, fixed RNS. Glomerular prostaglandin E2 production and plasma renin activity were significantly greater in rats fed a low-salt diet compared with either normal- or high-salt diet. The constancy of glomerular hemodynamic responses to RNS in spite of wide variations in dietary salt intake indicates that functional renal hemodynamic differences observed as a result of NaCl intake must be primarily the consequence of differences in renal nerve traffic and not hormonal alterations.

Glomerular hemodynamics and alpha 2-adrenoreceptor stimulation: the role of renal nerves

We evaluated the effects of alpha 2-adrenoceptor stimulation on the determinants of nephron filtration rate (SNGFR) using micropuncture in Munich-Wistar rats. Micropuncture was performed in animals 5-7 days after sham surgery (group 1) or renal denervation (DNX) (groups 2, 3, and 4). Glomerular hemodynamic measurements were made before and during a systemic infusion of the alpha 2-agonist, B-HT 933 (1.0 mg.kg-1.h-1) (groups 1, 2, and 3). Group 3 rats were pretreated with the alpha 2-antagonist, yohimbine (3 mg.kg-1.h-1). In group 4, hydralazine was substituted for B-HT 933 to dissociate specific alpha 2-effects from nonspecific effects on blood pressure. Arterial pressure declined by similar amounts between experimental periods in groups 1, 2, and 4. In group 1, B-HT 933 caused SNGFR to increase due to an increment in nephron plasma flow. In group 2, B-HT 933 caused SNGFR to decrease due to a decrement in glomerular ultrafiltration coefficient (LpA). In groups 3 and 4, SNGFR was unaffected by B-HT 933 or hydralazine. Ligand-binding studies in glomerular membranes documented the presence of alpha 2-adrenoreceptors (275 +/- 22 fmol/mg protein). Receptor density was not altered by DNX. These observations could be explained by an alpha 2-mediated inhibition of renal nerve activity combined with intrinsic sympathomimetic effects not dependent on renal nerves, with the latter effects unmasked by DNX and manifested by a decrease in LpA.

Effects of beta-adrenergic stimulation with isoproterenol on glomerular hemodynamics

To evaluate the contribution of beta 1-2-adrenergic receptor stimulation to the regulation of single-nephron glomerular filtration rate (SNGFR), we examined by micropuncture techniques the effects of systemic and intrarenal infusion of isoproterenol on glomerular hemodynamics in plasma volume-expanded Munich-Wistar rats. Isoproterenol infused systemically was consistently associated with an elevation in glomerular capillary hydrostatic pressure difference (delta P) from 44.2 +/- 1.2 to 50.1 +/- 1.3 mmHg, P less than 0.01, the consequence of a 5.9-mmHg fall in Bowman's space hydrostatic pressure, P less than 0.005. The potentially beneficial effect of increased delta P on SNGFR was overcome by a 40% reduction in the glomerular ultrafiltration coefficient (LpA) from 0.043 +/- 0.003 to 0.026 +/- 0.003 nl.s-1.mmHg-1.g kidney wt-1, P less than 0.005, with a net effect of a modest 13% decline in SNGFR, P less than 0.01. In contrast, the intrarenal infusion of isoproterenol did not modify glomerular hemodynamics. Suppression of angiotensin II activity eliminated the influences of systemic isoproterenol infusion on LpA and delta P, the latter was the consequence of lower efferent arteriolar resistance. The findings suggest that systemic infusion of a beta 1-2-adrenergic agonist results in a decrease in LpA via angiotensin II effects and exerts a vasodilatory action on postglomerular vessels during angiotensin II inhibition.

Effects of beta 1-adrenergic blockade on glomerular dynamics and angiotensin II response

Adrenergic activity regulates renal function by several mechanisms. Renal nerves not only exert vasoconstrictor functions but also may influence glomerular hemodynamics by beta-adrenergic activity, especially via the effects on renin angiotensin activity. Little is known of the specific glomerular hemodynamic alterations resulting from beta 1-adrenergic blockade. Current studies examined the effects of 4-6 days of treatment with atenolol (50 mg/kg), a beta 1-selective adrenergic antagonist, on glomerular hemodynamics in plasma volume-expanded Munich-Wistar rats. Atenolol treatment reduced blood pressure both in the awake state and during micropuncture. This reduction in blood pressure contributed to a decrease in nephron filtration rate (48 +/- 1 in untreated rats vs. 40 +/- 1 nl.min-1.g kidney wt-1 in the atenolol-treated group, P less than 0.05) by reduction in nephron plasma flow (182 +/- 2 vs. 154 +/- 4 nl.min-1.g kidney wt-1 in the atenolol-treated rats). No other determinant of glomerular ultrafiltration was influenced by atenolol treatment. Since beta 1-adrenergic blockade may influence the generation of angiotensin II, the response to angiotensin II infusion was assessed and found not to differ from control untreated animals. These studies demonstrate that beta 1-receptor blockade reduced nephron filtration rate by decreasing mean arterial blood pressure and nephron plasma flow without significant modifications in vascular resistance and the glomerular hydrostatic pressure gradient.

Functional effects on glomerular hemodynamics of short-term chronic cyclosporine in male rats

We evaluated the effects of chronic cyclosporine (CsA) administration on the determinants of nephron filtration rate (SNGFR) using micropuncture techniques (mp) in male Munich-Wistar rats. Animals received CsA (30 mg/kg SQ) in olive oil daily for 8 d before mp. Controls (PFC) were pair fed. SNGFR, glomerular capillary hydrostatic pressure gradient (delta P), nephron plasma flow (SNPF), plasma protein oncotic pressure (pi A), and glomerular ultrafiltration coefficient (LpA) were quantitated in each experiment. CsA was associated with a lower SNGFR due to decreases in SNPF and a major reduction in delta P but no decrease in LpA. Plasma volume expansion (PVE) caused SNGFR, delta P, and SNPF to increase in both CsA and PFC without eliminating the differences between CsA and PFC. CsA/PVE rats responded normally to angiotensin II (AII) infusion indicating that the low delta P associated with CsA is not due to unresponsiveness to AII. Prior renal denervation caused SNGFR and SNPF to increase in CsA-treated animals but failed to alter the reduction in glomerular capillary pressure after CsA or to eliminate the glomerular hemodynamic differences between treated animals and pair-fed controls. This constellation of glomerular hemodynamic abnormalities suggests that the renal effect of short-term chronic CsA administration is mediated primarily by a reduction in the afferent effective filtration pressure resulting from an imbalance between pre- and postglomerular vascular resistances.

Birth prevalence and recurrence rates of neural tube defects in southern Alberta in 1970-81

Given the observed variation in birth prevalence and recurrence rates of neural tube defects, it is important to obtain such data specific to a given locality for research and genetic counseling purposes. A review of hospital medical charts, the patient lists of the Medical Genetics and Myelomeningocele clinics at Alberta Children's Hospital and data from the Canadian Congenital Anomalies Surveillance System revealed the annual birth prevalence rate of neural tube defects in southern Alberta in 1970-81 to be 1.62/1000 total births. This figure suggests southern Alberta to be a low-frequency area. There was no significant variation in the annual rates of spina bifida, encephalocele or all neural tube defects combined over the study period. A significant linear decline in the frequency of births of anencephalic infants, however, was noted (p = 0.025). Information on the total reproductive history of the mothers revealed that the empiric risk of recurrence of a neural tube defect was 2.2%, and the risk to all siblings was estimated to be 2.3%. In future prevalence studies multiple sources of case ascertainment should be used, including data on pregnancies terminated because of a fetal neural tube defect.

Head-down tilt and restraint on renal function and glomerular dynamics in the rat

A model utilizing 25 degree head-down tilt (HDT) and incorporated with chronic catheterization and renal micropuncture techniques in rats was employed to study alterations in renal function induced by HDT. Renal function and extracellular volume measurements were performed after 24 h, 4 days, and 7 days of HDT in conscious rats and compared with their own control measurements and to nontilted but similarly restrained rats. After 24 h HDT, glomerular filtration rate (GFR) increased 19 +/- 8% and renal plasma flow (RPF) increased 18 +/- 8% with increases in urine flow rate, Na+, and K+ excretion in conscious rats. These increases after 24 h were associated with an increase in extracellular volume of 16 +/- 3% (P less than 0.01). In the nontilted controls, there was a decrease in extracellular volume after 24 h of suspension. After 7 days of HDT, GFR was decreased by 7 +/- 1% (P less than 0.01), but RPF and extracellular fluid volume were not different from control values. However, RPF and GFR increased in the nontilted rats after 7 days. After 7 days of HDT renal micropuncture studies demonstrated that single-nephron filtration rate was also decreased from 43 +/- 2 to 31 +/- 3 nl/min (P less than 0.05) due solely to reductions in the glomerular ultrafiltration coefficient (0.11 +/- 0.01 to 0.07 +/- 0.01 nl.s-1 X mmHg-1, P less than 0.05). There was a dissociation between GFR and water and Na+ excretion at days 4 and 7 of HDT not observed in the nontilt restraint controls.

Adrenergic and angiotensin II influences on renal vascular tone in chronic sodium depletion

To examine the role of adrenergic activity on the reduction in nephron filtration rate during chronic sodium depletion in rats, we have measured all the determinants of glomerular ultrafiltration before and after acute unilateral renal denervation. We also examined whether this adrenergic influence was angiotensin II mediated by performing the same protocol with the addition of systemic infusion of an angiotensin-converting enzyme inhibitor, MK 421. The results indicate that both angiotensin II and adrenergic activity contribute to the maintenance of renal vascular resistance during chronic sodium depletion. Acute renal denervation restored nephron filtration rate in chronic sodium-depleted rats (27 +/- 1 to 32 +/- 2 nl/min, P less than 0.05) to control levels (33 +/- 1 nl/min) via reductions in afferent and efferent arteriolar resistances, which also increased nephron plasma flow (85 +/- 5 to 109 +/- 6 nl/min, P less than 0.05). Infusion of MK 421 also increased plasma flow in chronic sodium-depleted rats (116 +/- 11 nl/min, P less than 0.05) through decreases in both arteriolar resistances. Denervation in MK 421-treated rats further increased nephron plasma flow to 137 +/- 10 nl/min (P less than 0.05) only as a result of decreased afferent resistance. The findings indicate that the glomerular hemodynamic changes that characterize chronic sodium depletion are primarily due to the activity of angiotensin II. However, renal adrenergic activity contributes an independent effect on afferent resistance and an effect on efferent resistance via adrenergic effects on angiotensin II.

Changes in glomerular hemodynamic response to angiotensin II after subacute renal denervation in rats

We examined the changes in glomerular hemodynamics produced by angiotensin II (AII) in both normal Munich-Wistar rats and rats which were unilaterally renal denervated (measured kidney) 4-6 d prior to the measurement periods. Measurements of glomerular dynamics were performed in a control period after plasma volume expansion and during infusion of 11 ng X 100 g body wt-1 X min-1 of AII. The glomerular hydrostatic pressure gradient increased from 38 +/- 1 to 49 +/- 1 mmHg in denervated rats compared with a lesser response in controls (from 39 +/- 1 to 45 +/- 1 mmHg, P less than 0.05). Single nephron plasma flow decreased from 213 +/- 17 to 87 +/- 4 nl X min-1 X g kidney wt (KW)-1 in denervated kidneys versus a more modest decrease in control kidneys (from 161 +/- 9 to 102 +/- 5 nl X min X gKW-1). These changes were due to a greater increase in both afferent and efferent arteriolar resistance after AII infusion in denervated compared with control kidneys. Glomerular AII receptor maximum binding was 1,196 +/- 267 fmol/mg protein in denervated kidneys compared with 612 +/- 89 fmol/mg protein (P less than 0.01) in controls with no change in receptor affinity. We conclude the subacute unilateral renal denervation results in renal vasodilation, denervation magnifies the vasoconstrictive effect of AII infusion on glomerular hemodynamics, and the observed increased response to AII after denervation is associated with increases in glomerular AII receptors.

Can causality be determined from proximal tubular reabsorption and peritubular physical factors?

Many studies in the literature have drawn conclusions regarding the mechanism of change in absolute proximal tubular reabsorption (APR) based on steady-state measurements of proximal reabsorptive rates and the peritubular capillary. The proximal reabsorptive rate, APR, is the product of the effective reabsorptive pressure (ERP) and the peritubular capillary reabsorptive coefficient (LpAR) (APR = ERP . LpAR). The ERP is defined by the net hydrostatic and oncotic pressure gradient acting across the capillary wall from interstitium to peritubular capillary flow. The relationship APR = ERP . LpAR is predefined, and steady-state measurements do not permit determination of causality because primary changes in any variable obligate a proportional change in a second variable. As an example of the difficulties in interpretation of this type of analysis, we have examined the APR and factors contributing to ERP and LpAR before and after the administration of benzolamide, a carbonic anhydrase inhibitor, to saline-expanded Munich-Wistar rats. Alterations in peritubular capillary fluid uptake cannot always be interpreted as casual mechanisms for changes in absolute fluid reabsorption but may result from primary alterations in epithelial transport.

Effect of leukocyte depletion on glomerular dynamics during acute glomerular immune injury

Large doses of anti-glomerular basement membrane antibody (AGBM-Ab) have been shown consistently to decrease both single nephron filtration rate (SNGFR) and the glomerular ultrafiltration coefficient (LpA) within 60 min of administration of the antibody. Both the decrease in SNGFR and LpA may be the result of infiltration of leukocytes blocking capillary loops and/or endothelial cell separation from the glomerular basement membrane through leukocyte dependent activated cytotoxic products or by mechanisms associated with leukocyte activation and infiltration. Administration of 2.5 micrograms/g body wt AGBM-Ab was performed in 10 control Munich-Wistar rats and in six Munich-Wistar rats in which 3 to 5 days prior to micropuncture experiments the rats were splenectomized and then irradiated to produce leukocyte depletion. Micropuncture measurements were performed in a condition of plasma volume expansion both prior to and after AGBM-Ab administration. In the control group, SNGFR decreased from 64 +/- 3 to 48 +/- 2 nl/min X g kidney wt after AGBM-Ab administration due to a decrease in LpA from 0.13 to 0.06 nl X sec-1 X mm Hg-1 X g kidney wt-1. This decrease in either SNGFR or LpA did not occur in the leukocyte depleted group. Linear deposits of IgG and C3 were similar in both groups. Polymorphonuclear leukocytes were significantly decreased in glomerulus from 7.4 +/- 0.7 in control vs. 0.7 +/- 0.3 in leukocyte depletion (P less than 0.01). There was no difference in glomerular dynamics between controls and leukocyte depleted rats prior to AGBM-Ab administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of furosemide administration on glomerular and tubular dynamics in the rat

Furosemide, a potent diuretic, has also been shown (1) to inhibit or reduce tubuloglomerular feedback activity, (2) act as a vasodilatory agent, and (3) exhibit a modest carbonic anhydrase inhibitory effect, which could potentially reduce proximal tubule reabsorption. If furosemide can inhibit tubuloglomerular feedback as well as cause vasodilation, then glomerular filtration rate (GFR) should increase through alterations in the dynamics of glomerular ultrafiltration. The effect of acute furosemide infusion (4 mg/kg of body wt per hour) on glomerular and tubular dynamics was examined in Munich-Wistar rats by two protocols: The first allowed a 3% volume depletion (based on body wt) to occur as a result of furosemide administration (group 1); the second allowed a complete replacement of volume after furosemide administration (group 2). The results demonstrated that when volume status was maintained after furosemide administration, the nephron filtration rate remained constant (35 +/- 3 vs. 33 +/- 2 nl/min, NS) despite a twofold increase in distal flow rate (5 +/- 1 vs. 10 +/- 1 nl/min, P less than 0.01), indicating an inhibition or suppression of the tubuloglomerular feedback system. With either protocol, furosemide administration did not alter total nephron vascular resistance and nephron blood flow (190 +/- 17 vs. 200 +/- 15 ml/min); however, the afferent arteriolar resistance did decrease in rats in which volume status was maintained. Finally, with volume status maintained, we were not able to demonstrate a reduction in absolute proximal fluid reabsorption despite a 7 mm Hg increase in interstitial hydrostatic pressure (4 +/- 1 to 11 +/- 1 mm Hg, P less than 0.01) and no compensatory increase in interstitial oncotic pressure. These data indicate that tubuloglomerular feedback was inhibited but that GFR was not increased. Major changes occurred in interstitial pressures and interstitial volume after furosemide administration, but absolute proximal reabsorption remained constant.

Fluid shifts and muscle function in humans during acute simulated weightlessness

Head-down tilt is considered an effective experimental model to simulate weightlessness. To determine the acute effects of simulated weightlessness on transcapillary fluid balance, tissue fluid shifts, muscle function, and triceps surae reflex time, eight supine subjects were tilted 5 degrees head down for 8 h. A cephalic fluid shift from the legs was indicated by facial edema, nasal congestion, increased urine flow, decreased creatinine excretion, reduced calf girth, and decreased lower leg volume. As measured by wick catheters inserted under local anesthesia, interstitial fluid pressure in the tibialis anterior muscle (4.6 +/- 0.6 mmHg) and subcutaneous tissue (0.6 +/- 0.5 mmHg) of the lower leg fell significantly to -2.8 +/- 0.5 and -3.8 +/- 0.4 mmHg, respectively. Other transcapillary pressures (capillary and interstitial fluid colloid osmotic pressures) were relatively unchanged. Needle-biopsy specimens, obtained just before and after tilt, indicated that total water content of soleus muscle was unchanged during 8 h of head-down tilt. After head-down tilt, isometric strength and isokinetic strength of the plantar flexors were unchanged. Triceps surae reflex time associated with plantar flexion movement slowed slightly after the tilt maneuver. Collectively these results demonstrated a dehydration effect of head-down tilt on muscle and subcutaneous tissues of the lower leg that may affect muscle function.

Mechanism of diuresis following acute modest hyperglycemia in the rat

In paired micropuncture studies in the Munich-Wistar rat we examined the mechanism of diuresis after acute induction of modest hyperglycemia (430-460 mg/dl) in the absence of an increase in total body water. The major reasons for the diuresis were an increase in nephron filtration rate (SNGFR) (from 30.3 +/- 1.8 to 35.3 +/- 1.6 nl/min) and a reduction in absolute proximal reabsorption (APR) (from 14.0 +/- 0.6 to 9.8 +/- 1.2 nl/min). All determinants of SNGFR were measured and a reduction in systemic oncotic pressure was the sole reason for the increase in SNGFR; vascular resistances did not change. Late proximal tubular fluid-to-plasma glucose concentration ratio was 0.96 +/- 0.04; therefore, the osmotic effects of unreabsorbed glucose could not account for the reduction in APR. Directly measured net renal interstitial pressure increased by 5 mmHg and the peritubular capillary effective reabsorptive pressure decreased (from 15.5 to 10.9 mmHg) in direct proportion to the reduction in APR, changes that could contribute to the reduction in APR. Equal elevations in glucose concentration in tubule and plasma may have also eliminated effective osmotic pressure gradients for water movement and influenced APR. As a result of increases in late proximal tubular flow rate, loop of Henle tubular reabsorption and absolute tubular reabsorption beyond the distal tubule both increased with hyperglycemia. The major reduction in APR was secondary to altered "physical factors" and osmotic effects of glucose that are not dependent on creation of unfavorable chemical gradients for Na+ reabsorption.

Mechanism of altered glomerular hemodynamics during chronic sodium depletion

Chronic sodium depletion in the rat is associated with decreased nephron filtration rate (SNGFR), nephron plasma flow (rpf), and a reduction in the glomerular permeability coefficient (LpA). This study was designed to determine whether the reduction in LpA could be acutely reversed with volume repletion and whether administration of angiotensin I converting enzyme inhibitor will restore LpA to normal values in the sodium-depleted rat. Measurements were performed in Munich-Wistar rats employing micropuncture techniques to assess the effects of acute volume repletion, 3-5 days of oral converting enzyme inhibitor (CEI) (30 mg . kg body wt-1 . day-1), and longer term (13-18 days) treatment with CEI begun just before or after initial volume depletion. Volume repletion in chronic sodium-depleted rats restored LpA to normal control values within a 60-min period, and values for glomerular dynamics were not different from a group of normal NaCl-intake rats to which the same treatment was applied. Both short-term and long-term CEI treatment during sodium depletion resulted in restoration of rpf to values not different from those with normal NaCl intake. However, only long-term but not short-term CEI treatment restored LpA to normal values. These studies suggest that intrarenal angiotensin II may mediate this reduction in LpA during chronic sodium depletion, but an effect of adrenergic nerve activity has not been excluded.

Analysis of adrenergic effects of the anesthetics Inactin and alpha-chloralose

Renal and systemic adrenergic system responses were examined and compared under conditions of Inactin, a barbiturate, and alpha-chloralose anesthesia in hydropenic Munich-Wistar rats. Base-line plasma norepinephrine and other catecholamine levels were higher in Inactin-anesthetized rats. Norepinephrine was infused to raise blood pressure 15-20 mmHg above base line and plasma norepinephrine was again significantly higher with Inactin. In another group, angiotensin II was infused into the cerebral lateral ventricle in both Inactin- and alpha-chloralose-anesthetized rats, a method of stimulating centrally activated adrenergic output. After central stimulation, mean arterial pressure increased only in alpha-chloralose-anesthetized rats. Micropuncture studies examining systemic and glomerular hemodynamics were performed in alpha-chloralose- and Inactin-anesthetized rats before and after the infusion of phentolamine, an alpha-adrenergic antagonist. Infusion of phentolamine decreased mean arterial pressure to a significantly greater extent in the Inactin-anesthetized rats, suggesting a greater base-line systemic alpha-adrenergic activity with Inactin anesthesia. However, renal afferent and efferent arteriolar resistances were not significantly different after phentolamine, and any trend for resistances to decrease could be explained by autoregulation. Inactin increases systemic adrenergic activity, but renal vascular resistances are not significantly affected by this increased activity.

Effect of modest hyperglycemia on tubuloglomerular feedback activity

Tubuloglomerular feedback activity was evaluated in hydropenic rats, using "borrowed," glucose-free hydropenic late proximal tubular fluid as microperfusion solution, and in rats with modest hyperglycemia using both hyperglycemic (glucose-containing) and hydropenic (glucose-free) late proximal fluid as test solutions. Changes in nephron filtration rate (SNGFR) in the same nephron were evaluated in all states at zero and 24.6 nl/min late proximal tubule microperfusion rates (the observed hyperglycemic late proximal flow rate) using a Hampel microperfusion pump. In hydropenia, increased microperfusion rate decreased SNGFR, but in hyperglycemic rats, increased perfusion rate with glucose-containing fluid failed to change SNGFR. But when glucose-free, hydropenic fluid was used, SNGFR decreased numerically less than it did in hydropenia. Renal interstitial hydrostatic pressure increased in hydropenia during hyperglycemia, which may account for part of the inhibition of feedback response. Abolition of tubuloglomerular feedback activity during modest hyperglycemia is due to (1) the effects of glucose in the tubular fluid beyond the late proximal tubule and (2) the extraluminal effects of hyperglycemia on the renal interstitial pressure. These findings may explain the elevated GFR in early diabetes mellitus and excessive urinary volume losses during modest hyperglycemia.

Glomerular hemodynamics in moderate Goldblatt hypertension in the rat

Glomerular hemodynamics were studied by micropuncture technique in the unclipped kidney in rats in which modest two kidney Goldblatt hypertension was maintained for 4 weeks and in normotensive controls. Both groups ingested less than 2 mEq Na+/day. In hypertensive rats at micropuncture, mean hydrostatic pressure was elevated both systematically (128 +/- 5 vs 113 +/- 3 mm Hg, p less than 0.05) and within glomerular capillaries (55 +/- 2 vs 48 +/- 1 mm Hg, p less than 0.05), resulting in an increase in the transglomerular hydrostatic pressure gradient (40 +/- 2 vs 33 +/- 1 mm Hg, p less than 0.05). The glomerular capillary permeability coefficient, however, was decreased in the hypertensive rats (0.063 +/- 0.017 vs 0.115 +/- 0.011 nl/s/g kw/mm Hg, p less than 0.05), resulting in no change in nephron filtration rate 38.9 +/- 2.3 vs 39.0 +/- 2.5 nl/min/g kw). Nephron plasma flow also remained unchanged (154 +/- 10 vs 140 +/- 7 ml/min/g kw). In separate studies in this model of hypertension, saralasin infusion demonstrated a peripheral effect of circulating angiotensin II which was increased over controls. Kidney mass and GFR were not different between clipped and unclipped kidneys. No consistent abnormalities were observed by light or electron microscopy either in glomeruli or in vessels in the unclipped kidney. This study demonstrates that glomerular hemodynamics may be altered early in the course of modest hypertension in this model without altering blood flow or filtration rate. The decrease in glomerular capillary area and/or permeability (LpA) in the hypertensive rats could be either a result of the increased effect of circulating angiotensin II or the direct effect of glomerular capillary hypertension.

Glomerular immune injury in the rat: effect of antagonists of histamine activity

The participation of histamine via H1 and H2 receptors, in the alteration of glomerular ultrafiltration consequent to acute glomerular immune injury was evaluated in three groups of Munich-Wistar rats, before and after the administration of large doses of antiglomerular basement membrane antibody (AGBM). Group 1 was the control and was untreated; group 2, rats continuously infused with H1 receptor antagonist diphenhydramine; and group 3, rats receiving continuous infusion of the H2 receptor antagonist cimetidine. In group 1, nephron filtration rate (SNGFR) decreased within 60 min after AGBM from 58 +/- 2 to 32 +/- 5 nl . min-1 . g kidney wt-1 (P less than 0.0005) due to decreases in both nephron plasma flow (RPF) (291 +/- 35 to 119 +/- 23 nl . min-1 . g kidney wt-1) (P less than 0.0005) and the glomerular permeability coefficient (LpA) (0.13 +/- 0.02 to 0.06 +/- 0.01 nl . sec-1 . g kidney wt-1 . mm Hg-1) (P less than 0.01). In group 2, SNGFR decreased similarly with AGBM (59 +/- 2 to 23 +/- 10 nl . mm-1 . g kidney wt-1) (P less than 0.0005) due again to major reductions in RPF and LpA, suggesting no protective effect of H1 receptor blockade. In group 3, control, pre-AGBM values for SNGFR and RPF were lower than they were in groups 1 and 2 due to cimetidine infusion. SNGFR and RPF decreased but to a lesser extent in group 3 (48 +/- 3 to 41 nl . min-1 . g kidney wt-1) (P less than 0.0005). Renal vascular resistance did not change after AGBM in this group but interpretation of this finding is complicated because blood pressure decreased after the antibody administration. LpA decreased in group 3 as in group 1, therefore neither H1 nor H2 receptor antagonist prevented reductions in LpA. The absence of vasoconstriction after AGBM during H2 receptor blockade may have been a nonspecific effect of cimetidine. Histamine plays no major role in AGBM-induced immune injury in the rat and does not prevent a reduction in nephron filtration rate.

Glomerular immune injury in the rat: the influence of angiotensin II and alpha-adrenergic inhibitors

Nephron filtration rate (SNGFR) decreases significantly after the administration of large doses of antiglomerular basement membrane antibody (anti-GBM) as a result of reductions in both nephron (renal) plasma flow (RPF) and the glomerular permeability coefficient (LpA). We have examined the participation of angiotensin II (AII) and alpha-adrenergic activity in this process in paired studies in three groups of Munich-Wistar rats: group 1, control and untreated; group 2, rats receiving continuous infusion of sar1-ala8-AII (1 microgram . kg of body wt-1 . min-1), and AII receptor antagonist; and group 3, rats receiving continuous infusion of phentolamine (27 micrograms . kg body wt-1 . min-1), a dose sufficient to block alpha-adrenergic responses. In group 1, SNGFR decreased from 58 +/- 4 to 35 +/- 6 nl . min-1 . g kidney wt-1 (P less than 0.001) after anti-GMB administration due to reductions in RPF (272 +/- 35 to 170 +/- 52 nl . min-1 . g of kidney wt-1, P less than 0.0001) and LpA (0.13 +/- 0.03 to 0.04 +/- 0.01 nl . sec-1 . g of kidney wt-1 . mm Hg-1, P less than 0.02). In group 2, the sar1-ala8-AII-infused rats. SNGFR decreased to a greater extent than it did in group 1 (P less than 0.01) (55 +/- 2 to 18 +/- 6 nl . min-1 . g of kidney wt-1, P less than 0.005) due to a greater reduction in RPF and a similar decrease in LpA. In group 3, phentolamine infusion prevented the decrease in SNGFR (52 +/- 3 to 52 +/- 4 nl . min-1 . g of kidney wt-1, NS) due primarily to elimination of vasoconstriction and a significantly lesser reduction in LpA (0.10 +/- 0.02 to 0.07 +/- 0.01 nl . sec-1 . g of kidney wt-1 . mm HG-1). There were no morphologic differences after anti-GBM administration that were unique to group 3. Blockade of AII activity does not prevent immune induced vasoconstriction or the reduction in LpA. alpha-Adrenergic blockage (1) prevents acute immune induced vasoconstriction and (2) partially prevents the imune induced reduction in LpA.

Effects of glomerular filtration dynamics on the glomerular permeability coefficient

Studies were performed in Munich-Wistar rats (n = 24) to determine if the glomerular permeability coefficient (LpA) is affected by changes in the systemic oncotic pressure (pi A) as well as other determinants of glomerular filtration [nephron plasma flow (RPF) and glomerular hydrostatic pressure gradient (delta P)] and systemic hematocrit (Hct). Multiple regression analysis was used to separate the respective relationships of pi A, delta P, RPF, and Hct to LpA to ascertain whether the correlation of LpA to these variables was direct or mediated by some concurrently changing factor. Three two-period protocols were used to examine the changes of these determinants of filtration: 1) hydropenia to 10% body wt saline expansion (SE), 2) SE to 1% body wt of concentrated rat plasma protein (25 g/100 ml) solution (HP) with removal of 1.5% body wt whole blood, and 3) SE to 1% body wt HP with 2.5% body wt whole blood removed with reinfusion of the removed erythrocytes. Changes in LpA correlated directly with changes in pi A (P less than 0.01) and inversely with delta P (P less than 0.01). There was no direct correlation of LpA to RPF or consistent correlation of LpA to Hct.

The efferent limb of the tubuloglomerular feedback system

The effector mechanisms which constitute the efferent limb of the tubuloglomerular feedback system were examined after the administration of benzolamide, a carbonic anhydrase inhibitor, which decreased proximal tubule fluid reabsorption by approximately 8 nl/min and transiently increased delivery of fluid out of the proximal tubule. Since benzolamide administration resulted in a decrease in nephron filtration rate (SNGFR) from 29.2 to 21.1 nl/min, late proximal flow rate returned to control values. If the proximal tubule was blocked after benzolamide by insertion of an oil block, the SGNFR returned towards control values. If a proximal tubule oil block was inserted prior to control measurements, SNGFR did not decrease. These data suggest that benzolamide reduces SNGFR by activating tubulo-glomerular feedback mechanisms secondary to increases in the rate of distal delivery. Analysis of the determinants of glomerular ultrafiltration before and after benzolamide administration revealed that the decrease in SNGFR was solely the result of a decrease in nephron plasma flow secondary to increases in afferent and efferent glomerular arteriolar resistance. No change in either the hydrostatic pressure gradient (delta P) or the glomerular permeability coefficient (LpA) was observed. Continuous infusion in saralasin, an angiotensin II antagonist, prevented the reduction in SNGFR and nephron plasma flow after benzolamide. These studies suggest that changes in nephron plasma flow are involved in a mediating the tubuloglomerular feedback response and that angiotensin II may have a role in the effector mechanism.

Glomerular hemodynamics in rats with chronic sodium depletion. Effect of saralasin

In chronic sodium depletion the glomerular filtration rate may be reduced, and alterations in proximal tubular function may contribute to the maintenance of antinatriuresis. Measurements were made by micropuncture technique in superficial nephrons of the Munich-Wistar rat of (a) the determinants of glomerular filtration rate, (b) peritubular capillary hydrostatic and oncotic pressure, and (c) proximal tubular fractional and absolute reabsorption in both a control group (group 1, n = 12) and a group of chronically sodium-depleted rats (group 2, n = 12). Single nephron filtration rate (sngfr) was 37.2+/-1.2 in group 1 and 31.6+/-1.0 nl/min/g kidney wt (P < 0.05) in group 2. Of the factors potentially responsible for the observed reduction in sngfr, there was no change in systemic oncotic pressure or the transglomerular hydrostatic pressure gradient. Sngfr was lower in group 2 because of both a reduced single nephron plasma flow (rpf) (128+/-6 vs. 112+/-5 nl/min per g kidney wt, P < 0.05) and additionally to a decrease in the glomerular permeability coefficient, L(p)A, from a minimum value of 0.105+/-0.012 in group 1 to 0.054+/-0.01 nl/s per g kidney wt per mm Hg (P < 0.01) after chronic sodium depletion. There was no difference in fractional proximal tubular reabsorption between group 1 and group 2. Absolute proximal reabsorption (APR) was reduced from 20.8+/-1.3 in group 1 to 16.3+/-0.9 nl/min per g kidney wt in group 2. The role of angiotensin II (AII) in maintaining glomerular and proximal tubular adaptations to chronic sodium depletion was assessed in subsets of groups 1 and 2 by the infusion of the AII antagonist Saralasin at a rate of 1 mug/kg per min. In group 1 rats, Saralasin had no effect on sngfr, rpf, or L(p)A, because animals remained at filtration pressure equilibrium. In group 2 rats, AII blockade was associated with an increase in sngfr from 31.6+/-1.0 to 37.1+/-1.7 nl/min per g kidney wt (P < 0.01). Rpf increased during Saralasin infusion solely as a result of a decrease in afferent arteriolar resistance from 21.7+/-2.3 to 15.2+/-2.3 10(9) dyn-s-cm(-5) (P < 0.01). Saralasin infusion did not affect the reduced L(p)A in group 2, as L(p)A remained 0.056+/-0.02 nl/s per g kidney wt per mm Hg and rats remained disequilibrated. In spite of the increase in sngfr in group 2, AII antagonism further decreased APR to 13.1+/-1.5 (P < 0.01). Distal delivery therefore, increased from a control value of 15.3+/-1.3 to 24.3+/-1.5 nl/min per g kidney wt (P < 0.01). In conclusion, both a decrease in L(p)A and a reduction in rpf were major factors mediating the decrease in glomerular filtration rate observed in chronic sodium depletion. Saralasin infusion revealed a significant effect of AII on rpf and afferent arteriolar resistance in chronic sodium depletion, but no effect of AII on either efferent arteriolar resistance or the decrease in L(p)A could be demonstrated. Saralasin had no effect in rats that were not chronically sodium depleted. In group 2 rats AII antagonism reduced APR even though sngfr increased, suggesting an influence of AII on proximal reabsorption. The marked changes observed during Saralasin infusion in the chronically sodium-depleted rat reveal important modifying effects of endogenously generated AII on both the glomerulus and proximal tubule.

Studies on the tubulo-glomerular feedback system in the rat. The mechanism of reduction in filtration rate with benzolamide

The specific mechanism whereby superficial nephron glomerular filtration rate (sngfr) is reduced after the administration of benzolamide, a carbonic anhydrase inhibitor with a primary inhibitory effect in the proximal tubule, have been examined by measuring pertinent pressures, flows, and glomerular permeabilities in the hydropenic Munich-Wistar rat, a strain with surface glomeruli. Because benzolamide decreases absolute proximal reabsorptive rate, the rate of delivery of tubular fluid to the distal nephron should be at least transiently increased and may reduce sngfr by activating the tubulo-glomerular feedback system. Sngfr fell from 29.2+/2.0 to 2.1+/3.1 nl/min (P less than 0.01) after benzolamide (group 1), a percentage reduction equal to kidney glomerular filtration rate and similar to sngfr obtained in collections from distal tubules. Separate studies (group 2) revealed that if transient increases in distal nephron delivery were prevented by insertion of a long oil block in proximal tubules before control, the decrease in sngfr was prevented (30.3+/1.0 vs. 30.3+/1.8 nl/min, P greater than 0.9). In paired "unblocked" nephrons in the same rats, sngfr fell in group 2 (33.0+/1.0 vs. 25.2+/2.3 nl/min, P less than 0.01). In "blocked" nephrons in which sngfr reduction was prevented, the rate of fluid leaving the proximal tubule increased from 16.9+/ to 23.1+/1.0 nl/min (P less than 0.01). In group 1 studies in which sngfr fell and transient increases in flow out of the last segment of the proximal tubule (distal delivery) (approximately equal to 8 nl/min) were not prevented, steady-state distal delivery was unchanged by benzolamide (13.9+/1.1 vs. 14.2+/2.2 nl/min). Also, sngfr returned toward control, pre-benzolamide values, when a proximal oil block was placed for 15 min and the rate of distal delivery reduced after benzolamide administration, which suggests that this activation was reversible. These data suggest that activation of tubulo-glomerular feedback by transient increases in distal delivery was responsible for decreases in sngfr. Analysis of all determinants of glomerular ultra-filtration revealed that the efferent mechanism leading to reduced sngfr after benzolamide was decreased nephron plasma flow (101+/13 vs. 66+/13 nl/min, P less than 0.01). Hydrostatic pressure and the glomerular permeability coefficient did not contribute to reductions in sngfr with benzolamide. Because the rate of distal delivery remained constant in spite of large changes in both sngfr and absolute proximal reabsorptive rate, it is suggested that the rate of distal delivery may be the physiologic entity that is regulated by the tubulo-glomerular feedback system via alterations in sngfr.