Vasoconstrictor and vasodilator effects of adenosine in the mouse kidney due to preferential activation of A1 or A2 adenosine receptors

The present experiments in mice were performed to determine the steady-state effects of exogenous adenosine on the vascular resistance of the whole kidney, of superficial blood vessels, and of afferent arterioles. The steady-state effect of an intravenous infusion of adenosine (5, 10, and 20 microg/min) in wild-type mice was vasodilatation as evidenced by significant reductions of renal and superficial vascular resistance. Resistance decreases were augmented in adenosine 1 receptor (A1AR) -/- mice. Renal vasodilatation by the A2aAR agonist CGS 21680A [2-p-(2-carboxyethyl)phenethyl-amino-5'-N-ethylcarboxamido-adenosine hydrochloride] (0.25, 0.5, and 1 microg/kg/min) and inhibition of adenosine-induced relaxation by the A2aAR antagonist ZM-241385 [4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol] (20 mg/kg) suggests that the reduction of renovascular resistance was largely mediated by A2aAR. After treatment with Nomega-nitro-L-arginine methyl ester (L-NAME) adenosine was unable to alter superficial blood flow and resistance significantly indicating that adenosine-induced dilatation is NO-dependent. Absence of a dilatory effect in endothelial nitric-oxide synthase (NOS) -/- mice suggests endothelial NOS as the source of NO. When infused into the subcapsular interstitium, adenosine reduced superficial blood flow through A1AR activation. Adenosine (10(-7) M) constricted isolated perfused afferent arterioles when added to the bath but not when added to the luminal perfusate. Luminal adenosine caused vasoconstriction in the presence of L-NAME or the A2AR antagonist 3,7-dimethyl-1-(2-propynyl)xanthine. Our data show that global elevation of renal adenosine causes steady-state vasorelaxation resulting from adenosine 2 receptor (A2AR)-mediated generation of NO. In contrast, selective augmentation of adenosine around afferent arterioles causes persistent vasoconstriction, indicating A1AR dominance. Thus, adenosine is a renal constrictor only when it can interact with afferent arteriolar A1AR without affecting the bulk of renal A2AR at the same time.

Effect of ramipril vs amlodipine on renal outcomes in hypertensive nephrosclerosis: a randomized controlled trial

CONTEXT

Incidence of end-stage renal disease due to hypertension has increased in recent decades, but the optimal strategy for treatment of hypertension to prevent renal failure is unknown, especially among African Americans.

OBJECTIVE

To compare the effects of an angiotensin-converting enzyme (ACE) inhibitor (ramipril), a dihydropyridine calcium channel blocker (amlodipine), and a beta-blocker (metoprolol) on hypertensive renal disease progression.

DESIGN, SETTING, AND PARTICIPANTS

Interim analysis of a randomized, double-blind, 3 x 2 factorial trial conducted in 1094 African Americans aged 18 to 70 years with hypertensive renal disease (glomerular filtration rate [GFR] of 20-65 mL/min per 1.73 m(2)) enrolled between February 1995 and September 1998. This report compares the ramipril and amlodipine groups following discontinuation of the amlodipine intervention in September 2000.

INTERVENTIONS

Participants were randomly assigned to receive amlodipine, 5 to 10 mg/d (n = 217), ramipril, 2.5 to 10 mg/d (n = 436), or metoprolol, 50 to 200 mg/d (n = 441), with other agents added to achieve 1 of 2 blood pressure goals.

MAIN OUTCOME MEASURES

The primary outcome measure was the rate of change in GFR; the main secondary outcome was a composite index of the clinical end points of reduction in GFR of more than 50% or 25 mL/min per 1.73 m(2), end-stage renal disease, or death.

RESULTS

Among participants with a urinary protein to creatinine ratio of >0.22 (corresponding approximately to proteinuria of more than 300 mg/d), the ramipril group had a 36% (2.02 [SE, 0.74] mL/min per 1.73 m(2)/y) slower mean decline in GFR over 3 years (P =.006) and a 48% reduced risk of the clinical end points vs the amlodipine group (95% confidence interval [CI], 20%-66%). In the entire cohort, there was no significant difference in mean GFR decline from baseline to 3 years between treatment groups (P =.38). However, compared with the amlodipine group, after adjustment for baseline covariates the ramipril group had a 38% reduced risk of clinical end points (95% CI, 13%-56%), a 36% slower mean decline in GFR after 3 months (P =.002), and less proteinuria (P<.001).

CONCLUSION

Ramipril, compared with amlodipine, retards renal disease progression in patients with hypertensive renal disease and proteinuria and may offer benefit to patients without proteinuria.

Low chloride stimulation of prostaglandin E2 release and cyclooxygenase-2 expression in a mouse macula densa cell line

Reducing luminal NaCl concentration in the macula densa region of the nephron stimulates renin secretion, and this response is blocked by a specific inhibitor of cyclooxygenase-2 (COX-2) (Traynor, T. R., Smart, A., Briggs, J. P., and Schnermann, J. (1999) Am. J. Physiol. Renal Physiol. 277, F706-710). To study whether low NaCl activates COX-2 activity or expression we clonally derived a macula densa cell line (MMDD1 cells) from SV-40 transgenic mice using fluorescence-activated cell sorting of renal tubular cells labeled with segment-specific fluorescent lectins. MMDD1 cells express COX-2, bNOS, NKCC2, and ROMK, but not Tamm-Horsfall protein, and showed rapid (86)Rb(+) uptake that was inhibited by a reduction in NaCl concentration and by bumetanide or furosemide. Isosmotic exposure of MMDD1 cells to low NaCl (60 mm) caused a prompt and time-dependent stimulation of prostaglandin E(2) (PGE(2)) release that was prevented by the COX-2 specific inhibitor NS-398 (10 microm). Reducing NaCl to 60 and 6 mm for 16 h increased COX-2 expression in a chloride-dependent fashion. Low NaCl phosphorylated p38 kinase within 30 min and ERK1/2 kinases within 15 min without changing total MAP kinase levels. Low NaCl-stimulated PGE(2) release and COX-2 expression was inhibited by SB 203580 and PD 98059 (10 microm), inhibitors of p38 and ERK kinase pathways. We conclude that low chloride stimulates PGE(2) release and COX-2 expression in MMDD1 cells through activation of MAP kinases.

Renin expression in COX-2-knockout mice on normal or low-salt diets

Experiments were performed in mice to investigate whether cyclooxygenase-2 (COX-2) in epithelial cells near the tubulovascular contact point (macula densa and TAL cells) may regulate renin gene expression in juxtaglomerular granular cells. Renin activity, afferent arteriolar granularity, and renin mRNA were determined in wild-type mice and in COX-2-knockout mice on control and low-NaCl diets. Renin activity in microdissected glomeruli assessed as angiotensin I formation in the presence of excess substrate and afferent arteriolar granularity determined by direct visualization and immunostaining were significantly reduced in COX-2 -/- compared with wild-type animals. Similarly, renal cortical mRNA levels were lower in COX-2 -/- than in wild-type mice. Maintaining mice on a low-salt diet for 14 days induced an increase in renin mRNA, afferent arteriolar granularity, and renin activity in wild-type mice. In contrast, renin mRNA and renin granularity did not significantly increase in low-salt-treated COX-2 -/- mice, whereas the increase in juxtaglomerular renin enzyme activity was markedly attenuated, but not fully blocked. In additional experiments we found that COX-2 mRNA was increased in angiotensin type 1A receptor-knockout mice compared with wild-type mice. We conclude that COX-2 in the tubulovascular contact region is a critical determinant of renin synthesis in granular cells under resting conditions and that it participates in the stimulation of renin expression caused by a low-NaCl intake.

MAPK mediation of hypertonicity-stimulated cyclooxygenase-2 expression in renal medullary collecting duct cells

We have previously shown that hypertonicity stimulates cyclooxygenase-2 (COX-2) expression in cultured medullary epithelial cells. The aims of the present study were (i) to examine the role of cytoplasmic signaling through MAPK pathways in tonicity regulation of COX-2 expression in collecting duct cells and (ii) to assess the possible contribution of COX-2 to the survival of inner medullary collecting duct (IMCD) cells under hypertonic conditions. In mIMCD-K2 cells, a cell line derived from mouse IMCDs, hypertonicity induced a marked increase in COX-2 protein expression. The stimulation was reduced significantly by inhibition of MEK1 (PD-98059, 5-50 microm) and p38 (SB-203580, 5-100 microm) and was almost abolished by the combination of the two compounds. To study the role of JNK in tonicity-stimulated COX-2 expression, IMCD-3 cell lines stably transfected with dominant-negative mutants of three JNKs (JNK-1, -2, and -3) were used. Hypertonicity-stimulated COX-2 protein expression was significantly reduced in dominant-negative JNK-2-expressing cells and was unchanged in dominant-negative JNK-1- and JNK-3-expressing cells compared with controls. The reduction of COX-2 expression was associated with greatly reduced viability of dominant-negative JNK-2-expressing cells during hypertonicity treatment. 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) (2-8 microm), an inhibitor of Src kinases, reduced the tonicity-stimulated COX-2 expression in a dose-dependent manner, whereas PP3, an inactive analog of PP2, had no effect. Inhibition of COX-2 activity by NS-398 (30-90 microm) and SC-58236 (10-20 microm) significantly reduced viability of mIMCD-K2 cells subjected to prolonged hypertonic treatment. We conclude that 1) all three members of the MAPK family (ERK, JNK-2, and p38) as well as Src kinases are required for tonicity-stimulated COX-2 expression in mouse collecting duct cells and that 2) COX-2 may play a role in cell survival of medullary cells under hypertonic conditions.

Metanephric rat-mouse chimeras to study cell lineage of the nephron

The nephron is derived from the ureteric bud and metanephric mesenchyme and develops into a complex epithelial structure with a wide variety of phenotypes along its length. This segmental variation in expression of molecules provides an approach to understand the lineage of unique segments. The present study evaluated the expression of four relatively well-localized molecules--renin, Tamm-Horsfall protein (THP), oxytocin receptor (OTR), and the vasopressin type 2 receptor (V2R)--in cultured mouse-rat chimeric metanephric kidneys using reverse transcription-polymerase chain reaction (RT-PCR). Chimeric kidneys were formed by 1) separating the ureteric bud (U) from the metanephric mesenchyme (M) of mouse (m) at E11 and rat (r) at E13 days of gestation and 2) recombining the ureteric bud of one species with the metanephric mesenchyme of the other species (i.e., UrMm and UmM(r), followed by filter culture until differentiated. Species-specific restriction enzymes for all four genes were chosen to digest the PCR product from either rat or mouse. RT-PCR was performed for each mRNA species and the products digested. The V2R product from the UrMm chimera was cleaved by a restriction enzyme known to digest only rat product, suggesting the PCR product was produced predominantly by cells derived from the ureteric bud. The renin, OTR, and THP products from both chimeras were cleaved equally well by species-specific restriction enzymes, suggesting the products were made by cells originating from both the ureteric bud and the metanephric mesenchyme. These studies demonstrate that the cultured chimeric metanephric model is useful to study segment lineage. The results suggest that the lineage of at least certain portions of the nephron is heterogenous.

Vasoconstrictor responses in thromboxane receptor knockout mice: tubuloglomerular feedback and ureteral obstruction

The role of thromboxane (TP) in the vasoconstriction induced by tubuloglomerular feedback or 18-h ureteral obstruction was studied in wild type mice (TP +/+), and in heterozygous (TP +/-) and homozygous TP receptor knockout mice (TPR -/-). TGF function was assessed from the response of stop flow pressure (PSF) to a maximum increase in loop of Henle flow rate (0-30 nL min-1). PSF fell by 6.4 +/- 0.4 mmHg in wild-type mice, by 6.1 +/- 0.6 mmHg in TP +/-, and by 7.9 +/- 0.7 mmHg in TP -/- mice. In the presence of the TP receptor agonist U46,619 (10-5 M) the PSF reduction increased to 10. 4 +/- 0.8 mmHg in TP +/+, and to 10.6 +/- 2.8 mmHg in TP +/-, but was unchanged at 7.7 +/- 0.7 mmHg in TP -/-. Mean arterial blood pressures were comparable between groups (103 +/- 3 mmHg in TP +/+, 113 +/- 4.6 in TP +/- and 113 +/- 2.4 mmHg in TP -/- mice). Intratubular pressure following unilateral ureteral obstruction was significantly higher in TP -/- than in TP +/+ mice both in the early phase (0-3 h) and late phase (18 h) of obstruction. These results indicate that chronic TP receptor deficiency does not significantly alter maximum TGF responses in mice, and that it is accompanied by exaggerated vasodilatation during short-term unilateral ureteral obstruction and attenuated vasoconstriction during longer lasting obstruction. We conclude that thromboxane is primarily a regulator of renal vascular tone under pathophysiological conditions.

Expression of peroxisomal proliferator-activated receptors and retinoid X receptors in the kidney

The discovery that 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) is a ligand for the gamma-isoform of peroxisome proliferator-activated receptor (PPAR) suggests nuclear signaling by prostaglandins. Studies were undertaken to determine the nephron localization of PPAR isoforms and their heterodimer partners, retinoid X receptors (RXR), and to evaluate the function of this system in the kidney. PPARalpha mRNA, determined by RT-PCR, was found predominately in cortex and further localized to proximal convoluted tubule (PCT); PPARgamma was abundant in renal inner medulla, localized to inner medullary collecting duct (IMCD) and renal medullary interstitial cells (RMIC); PPARbeta, the ubiquitous form of PPAR, was abundant in all nephron segments examined. RXRalpha was localized to PCT and IMCD, whereas RXRbeta was expressed in almost all nephron segments examined. mRNA expression of acyl-CoA synthase (ACS), a known PPAR target gene, was stimulated in renal cortex of rats fed with fenofibrate, but the expression was not significantly altered in either cortex or inner medulla of rats fed with troglitazone. In cultured RMIC cells, both troglitazone and 15d-PGJ2 significantly inhibited cell proliferation and dramatically altered cell shape by induction of cell process formation. We conclude that PPAR and RXR isoforms are expressed in a nephron segment-specific manner, suggesting distinct functions, with PPARalpha being involved in energy metabolism through regulating ACS in PCT and with PPARgamma being involved in modulating RMIC growth and differentiation.

The impact of surgical-site infections in the 1990s: attributable mortality, excess length of hospitalization, and extra costs

OBJECTIVE

To determine mortality, morbidity, and costs attributable to surgical-site infections (SSIs) in the 1990s.

DESIGN

A matched follow-up study of a cohort of patients with SSI, matched one-to-one with patients without SSI.

SETTING

A 415-bed community hospital.

STUDY POPULATION

255 pairs of patients with and without SSI were matched on age, procedure, National Nosocomial Infection Surveillance System risk index, date of surgery, and surgeon.

OUTCOME MEASURES

Mortality, excess length of hospitalization, and extra direct costs attributable to SSI; relative risk for intensive care unit (ICU) admission and for readmission to the hospital.

RESULTS

Of the 255 pairs, 20 infected patients (7.8%) and 9 uninfected patients (3.5%) died during the postoperative hospitalization (relative risk [RR], 2.2; 95% confidence interval [CI95], 1.1-4.5). Seventy-four infected patients (29%) and 46 uninfected patients (18%) required ICU admission (RR, 1.6; CI95, 1.3-2.0). The median length of hospitalization was 11 days for infected patients and 6 days for uninfected patients. The extra hospital stay attributable to SSI was 6.5 days (CI95, 5-8 days). The median direct costs of hospitalization were $7,531 for infected patients and $3,844 for uninfected patients. The excess direct costs attributable to SSI were $3,089 (CI95, $2,139-$4,163). Among the 229 pairs who survived the initial hospitalization, 94 infected patients (41%) and 17 uninfected patients (7%) required readmission to the hospital within 30 days of discharge (RR, 5.5; CI95, 4.0-7.7). When the second hospitalization was included, the total excess hospitalization and direct costs attributable to SSI were 12 days and $5,038, respectively.

CONCLUSIONS

In the 1990s, patients who develop SSI have longer and costlier hospitalizations than patients who do not develop such infections. They are twice as likely to die, 60% more likely to spend time in an ICU, and more than five times more likely to be readmitted to the hospital. Programs that reduce the incidence of SSI can substantially decrease morbidity and mortality and reduce the economic burden for patients and hospitals.

Inhibition of macula densa-stimulated renin secretion by pharmacological blockade of cyclooxygenase-2

Previous results from our laboratory have shown that in the isolated perfused juxtaglomerular apparatus, nonselective inhibitors of cyclooxygenase (COX) activity prevent the stimulation of renin secretion by a reduction in luminal NaCl concentration at the macula densa. The present studies were performed to examine which COX isoform is involved in NaCl-dependent renin secretion. In the absence of COX inhibitors, a reduction in luminal NaCl (from Na 141/Cl 120 mM to Na 26/Cl 7 mM) caused an increase in renin secretion rate from 4.5 +/- 1.8 to 26.1 +/- 7.4 nGU/min (P < 0.01, n = 19). The presence of the COX-1 inhibitor valerylsalicylate (500 microM) in lumen and bath did not affect the stimulation of renin secretion by a reduction in luminal NaCl concentration (5 +/- 1.8 nGU/min at high NaCl, and 30.5 +/- 9.4 nGU/min at low NaCl; P < 0.01, n = 8). In contrast, the specific COX-2 inhibitor NS-398 (50 microM) in lumen and bath abolished the stimulating effect of low luminal NaCl (12.8 +/- 3.9 nGU/min at high NaCl, and 10.7 +/- 3.1 nGU/min at low NaCl; NS, n = 15). The finding that COX-2 is critically involved in macula densa control of renin secretion indicates that the COX-2-expressing epithelial cells in the tubuloglomerular contact area are a likely source of prostaglandins participating in the signaling pathway between the macula densa and renin-producing granular cells.

Differential regulation of COX-2 expression in the kidney by lipopolysaccharide: role of CD14

Induction of the inducible cyclooxygenase isoform COX-2 is likely to be an important mechanism for increased prostaglandin production in renal inflammation. We examined the effect of lipopolysaccharide (LPS) on regional renal COX-2 expression in the rat. In the inner medulla, LPS injection (4 mg/kg ip) induced a twofold and 2.5-fold increase in the levels of COX-2 mRNA and COX-2 protein, respectively. In contrast, COX-2 expression in the renal cortex was not significantly altered. COX-2 promoter transgenic mice were created using the 2.7-kb flanking region of the rat COX-2 gene. In these animals, LPS injection induced reporter gene expression predominately in the inner medulla. The LPS receptor CD14, usually regarded as a monocyte/macrophage-specific marker, was found to be abundantly expressed in the inner medulla and in dissected inner medullary collecting duct (IMCD) cells, suggesting that it may mediate medullary COX-2 induction. CD14 was present only at low levels in cortex and cortical segments, including glomeruli. In cultured cells, it was abundant in mouse IMCD (mIMCD-K2) cells and renal medullary interstitial cells, but largely undetectable in mesangial cells and M1 cells, a cell line derived from mouse cortical collecting ducts. In the mIMCD-K2 cell line, LPS significantly induced COX-2 mRNA expression, with concomitant induction of CD14. LPS-stimulated COX-2 expression was reduced by the addition of an anti-CD14 monoclonal antibody to the culture medium. These results demonstrate that LPS selectively stimulates COX-2 expression in the renal inner medulla through a CD14-dependent mechanism.

Regulation of cyclooxygenase-2 expression in renal medulla by tonicity in vivo and in vitro

Renal medullary prostaglandins are believed to exert an important functional role in antagonizing vasopressin effects in dehydration. Studies were undertaken to determine the effect of hyperosmolality on cyclooxygenase (COX) isoform expression in the renal medulla. COX-1 and COX-2 mRNA and protein levels were determined by RT-PCR or Western blotting in Sprague-Dawley rats on varying water intakes, in Brattleboro rats and in Long-Evans controls. Over a wide range of urinary tonicity, COX-2 expression correlated closely with urine osmolality levels (R = 0.872). COX-1 levels did not vary. Immunolocalization showed that the stimulation of COX-2 expression by dehydration occurred predominantly in the collecting duct. Hypertonicity caused by addition of NaCl produced a dose- and time-dependent stimulation of COX-2 expression in mIMCD-K2 cells as well as in MDCK cells. COX-1 was unaffected. In the same cell lines, mannitol, sucrose, and raffinose also had a stimulatory effect. The tonicity-stimulated COX-2 expression in mIMCD-K2 cells was almost completely blocked by a tyrosine kinase inhibitor, genistein at 100 microM. In MDCK cells transfected with a 2.7-kb COX-2 promoter and lacZ reporter construct, NaCl induced a twofold increase in beta-galactosidase activity. Using mIMCD-K2 cells, hypertonic NaCl (600 mosmol/kgH(2)O for 24 h) induced a 33-fold increase in PGE(2) release determined by enzyme immunoassay, an effect completely blocked by 3 microM indomethacin or the COX-2-specific blocker N-(2-cyclohexy-4-nitrophenyl)methanesulfonamide (NS-398). We conclude that in inner medulla, COX-2 but not COX-1 is upregulated by hyperosmolality.

Tubuloglomerular feedback in ACE-deficient mice

In these experiments, we used a strain of angiotensin converting enzyme (ACE) germline null mutant mice, generated by J. H. Krege and co-workers (J. H. Krege, S. W. M. John, L. L. Langenbach, J. B. Hodgin, J. R. Hagaman, E. S. Bachman, J. C. Jennette, D. A. O'Brien, and O. Smithies. Nature 375: 146-148, 1995), to examine the effect of chronic ACE deficiency on the magnitude of tubuloglomerular feedback (TGF) responses. The genotype was determined by PCR on DNA extracted from the tail and was verified after each experiment by assessment of the blood pressure response to an injection of ANG I. To assess TGF responsiveness, we determined the change in stop-flow pressure (PSF) caused by increasing NaCl concentration at the macula densa by using micropuncture techniques. When loop of Henle flow rate was increased from 0 to 40 nl/min, PSF fell from a mean of 42.3 +/- 1.95 to 33.6 +/- 2.09 mmHg (n = 6, P = 0.005) in wild-type mice (+/+), fell from 40.6 +/- 2.35 to 38.6 +/- 1.93 mmHg in heterozygous (+/-) mice (n = 7, P = 0.014), and did not change in homozygous ACE (-/-) mice [36.7 +/- 2.02 mmHg vs. 36.4 +/- 2.01 mmHg; n = 4, P = not significant (NS)]. During an infusion of ANG II at a dose that did not significantly elevate blood pressure (70 ng. kg-1. min-1), TGF response magnitude (PSF 0 - PSF 40) increased from 6.5 +/- 1.4 to 9.8 +/- 1.19 mmHg in +/+ (P = 0.006), from 1.14 +/- 0.42 to 4.6 +/- 1.3 mmHg in +/- (P = 0.016), and from 0.42 +/- 0.25 to 4.02 +/- 1.06 in -/- mice (P = 0.05). Absence of TGF responses in ACE null mutant mice and restoration of near-normal responses during an acute infusion of ANG II supports previous conclusions that ANG II is an essential component in the signal transmission pathway that links the macula densa with the glomerular vascular pole.

Gender matters in renal research: a National Institutes of Health perspective

The National Institutes of Health (NIH) currently anticipates a period of growth in budgets, making renal community input into research planning and prioritizing particularly important. In considering which women's health issues should be given high priority for research study, the questions of both public health impact and scientific opportunity should be considered. A series of health topics in which there is some evidence for particular impact on women's health are briefly reviewed, and the process the NIH uses for community input and priority setting are discussed.

Obstruction stimulates COX-2 expression in bladder smooth muscle cells via increased mechanical stretch

Studies were performed to investigate the regulatory mechanism of bladder cyclooxygenase-2 (COX-2) expression after outlet obstruction. In situ hybridization of murine bladder tissues using COX-2-specific riboprobes demonstrated that COX-2 expression was induced predominantly in the bladder smooth muscle cells after outlet obstruction. To study the effect of increased mechanical stretch on COX isoform expression, cultured rat bladder smooth muscle cells were grown on silicone elastomer-bottomed plates coated with collagen type I and were subjected to continuous cycles of stretch/relaxation for variable duration. COX-1 mRNA levels did not change with stretch. COX-2 expression increased in a time-dependent manner after stretch, with maximal mRNA and protein levels occurring after 4 h. PGE2 levels increased more than 40-fold in the culture media after stretch, consistent with increased COX activity, and this was reduced to near completion in the presence of a COX-2 inhibitor, NS-398. Exposure to stretch over a 48-h period induced a 4.7 +/- 0.6-fold increase in tritiated thymidine incorporation rate. This increase in DNA synthesis was markedly suppressed when the cells were stretched in the presence of NS-398. We conclude that in bladder obstruction COX-2 activation occurs predominantly in the smooth muscle cells in response to mechanical stretch. Our findings also suggest that stretch-activated COX-2 expression may participate in bladder smooth muscle cell proliferation and thereby play a role in pathological bladder wall thickening after obstruction.

Inhibition of adenosine-1 receptor-mediated preglomerular vasoconstriction in AT1A receptor-deficient mice

The effect of the adenosine type 1 receptor agonist N6-cyclohexyladenosine (CHA) on glomerular vascular reactivity was studied in male angiotensin II type 1A (AT1A) receptor knockout mice (9). Vascular reactivity was assessed as the response of stop-flow pressure (PSF) to infusion of CHA into loops of Henle using micropuncture techniques. In AT1A +/+ mice at ambient arterial blood pressure (96.7 +/- 2.8 mmHg), the presence of CHA (10 (-5) M) in the perfusate increased PSF responses from 6.8 +/- 0.6 to 14.3 +/- 0.9 mmHg when the loop of Henle of the index nephron was perfused and from 0.7 +/- 0.3 to 12.3 +/- 1.0 mmHg when the loop of an adjacent nephron was perfused. At reduced arterial blood pressure (82.8 +/- 1. 3 mmHg), index nephron perfusion with CHA increased PSF responses from 4.5 +/- 0.3 to 9.4 +/- 0.4 mmHg. In AT1A -/- mice with a mean arterial blood pressure of 80 +/- 1.9 mmHg, CHA increased PSF responses only from 0.1 +/- 0.3 to 3.6 +/- 0.54 mmHg during index nephron perfusion and from 0.25 +/- 0.2 to 2.7 +/- 0.55 mmHg during adjacent nephron perfusion, significantly less than in wild-type animals (P < 0.001). Responses to CHA were intermediate in AT1A +/- mice. Thus AT1A receptor knockout mice show a markedly reduced constrictor response to CHA both in the presence and absence of simultaneous activation of the tubuloglomerular feedback system. These data support the notion of a functional interaction between adenosine and angiotensin II in the regulation of afferent arteriolar tone.

Expression of Grb7 growth factor receptor signaling protein in kidney development and in adult kidney

Grb7, a signaling protein whose physiological function is unknown, binds receptor tyrosine kinases important for normal kidney development. By investigating and correlating Grb7 gene expression with that reported for Grb7-binding receptors, we provide clues to Grb7 function(s). RT-PCR and immunoblot were used to demonstrate Grb7 gene and protein expression in the mature kidney. Additional RT-PCR studies detected gene expression in all microdissected adult nephron segments examined, except glomeruli, and in the mouse metanephric kidney from embryonic day 11 (E11) through to day 17 (E17). In situ hybridization at E14 demonstrated the following cellular pattern of localization: Grb7 mRNA in metanephric epithelia of mesenchymal and ureteric bud origin; no expression in the undifferentiated mesenchyme; and little expression in podocyte-destined cells or primitive glomeruli. Grb7 mRNA was also present in the epithelia of the lung and gut at E14. Thus Grb7 may have a basic function in growth factor signaling in terminally differentiated epithelia along the nephron and in developing epithelia in the kidney, lung, and gut. It is localized in a pattern permissive for a role in Her2 and Ret receptor signaling.

Tubuloglomerular feedback: new concepts and developments

Luminal [NaCl] at the macula densa (MD) has two established effects: regulation of glomerular arteriolar resistance through tubuloglomerular feedback (TGF) and control of renin secretion. TGF acts as a minute-to-minute stabilizer of distal salt delivery, thereby minimizing the impact of random perturbations in filtration and absorption forces on NaCl excretion. During long-lasting perturbations of MD [NaCl], control of renin secretion becomes the dominant function of the MD. The potentially maladaptive effect of TGF under chronic conditions is prevented by TGF adaptations permitting adjustments in glomerular filtration rate to occur. TGF adaptation is mechanistically coupled to the endpoint targeted by chronic deviations in MD [NaCl], the rate of local and systemic angiotensin II generation. Studies of TGF in transgenic mice are expected to provide further insights into the mechanisms mediating between luminal [NaCl] and afferent arterioles. TGF responses are virtually abolished in mice in which either the AT1A gene or the angiotensin converting enzyme gene is rendered nonfunctional by homologous recombination. In contrast, TGF responses are unaltered in nitric oxide synthase I knockout mice. Thus, an intact renin-angiotensin system appears to be critical for the TGF signaling pathway.

Regulation of cyclooxygenase expression in the kidney by dietary salt intake

The present studies were undertaken to determine the effect of dietary salt intake on the renal expression of cyclooxygenase-1 (COX-1) and -2 COX-2). Protein levels were assessed by Western blotting, and mRNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR) on cDNA prepared from kidney regions, dissected nephron segments, and cultured renal cells. Both isoforms were expressed at high levels in inner medulla (IM), with low levels detected in outer medulla and cortex. COX-1 mRNA was present in the glomerulus and all along the collecting duct, whereas COX-2 mRNA was restricted to the macula densa-containing segment (MD), cortical thick ascending limb (CTAL), and, at significantly lower levels, in the inner medullary collecting duct. Both isoforms were highly expressed at high levels in cultured medullary interstitial cells and at lower levels in primary mesangial cells and collecting duct cell lines. Maintaining rats on a low- or high-NaCl diet for 1 wk did not affect expression of COX-1. In IM of rats treated with a high-salt diet, COX-2 mRNA increased 4.5-fold, and protein levels increased 9.5-fold. In contrast, cortical COX-2 mRNA levels decreased 2.9-fold in rats on a high-salt diet and increased 3.3-fold in rats on a low-salt diet. A low-salt diet increased COX-2 mRNA 7.7-fold in MD and 3.3-fold in CTAL. Divergent regulation of COX-2 in cortex and medulla by dietary salt suggests that prostaglandins in different kidney regions serve different functions, with medullary production playing a role in promoting the excretion of salt and water in volume overload, whereas cortical prostaglandins may protect glomerular circulation in volume depletion.

Cyclooxygenase-2 is expressed in bladder during fetal development and stimulated by outlet obstruction

Studies were undertaken to assess expression of inducible cyclooxygenase (COX)-2 in bladder during fetal development and COX-1 and COX-2 expression after outlet obstruction. Bladder tissue or bladder progenitor tissue was harvested from CD-1 murine embryos at embryonic days 11.5 (E11.5), E14.5, E17.5, E20.5 (newborn), and from adult. Bladder obstruction was created in adult female mice by ligating the urethra, and bladders were harvested after 3-24 h of obstruction. Gene expression was assessed by semiquantitative reverse transcription-polymerase chain reaction and Western blotting. COX-2 was highly expressed at the early stages of bladder development and declined progressively throughout gestation. In adult bladder, both COX-1 and COX-2 were detectable at low levels under basal conditions. An approximately 30-fold increase in COX-2 mRNA was seen after 24 h of obstruction. In contrast, COX-1 did not change with obstruction. COX-2 mRNA levels peaked at 6 h of obstruction. In regional bladder-distention models, COX-2 induction was confined to the area of distention. Bladder outlet obstruction stimulates COX-2 expression dramatically, reactivating a gene that is highly expressed during fetal development.

Absence of tubuloglomerular feedback responses in AT1A receptor-deficient mice

Experiments were performed in a recently generated strain of mice with an angiotensin II AT1A-receptor null mutation (M. Ito, M. I. Oliverio, P. J. Mannon, C. F. Best, N. Maeda, O. Smithies, and T. M. coffman. Proc. Natl. Acad. Sci. USA 92: 3521-3525, 1995) to examine the effects of chronic AT1A receptor deficiency on tubuloglomerular feeback (TGF) responses. All animals were genotyped by polymerase chain reaction using primers designed to amplify sequences from the deleted AT1A gene and from the neomycin resistance gene. Normal mice (AT1A +/+) and mice heterozygous (AT1A +/-) and homozygous (AT1A -/-) for the gene disruption were anesthetized, and stop-flow pressures (PSF) were determined during changes in loop perfusion rate with previously established micropuncture methods. In five AT1A +/+ mice (26 tubules) mean PSF at zero loop flow was 37.2 +/- 1.5 mmHg, falling to 28.2 +/- 1.9 mmHg at a flow of 45 nl/min (P < 0.0001). Flow rate causing the half-maximum response (V1/2) was 8.7 +/- 0.4 nl/min. In four AT1A +/- animals (19 tubules) mean PSF at zero flow was 39.9 +/- 2.4 mmHg, falling to 34.8 +/- 2.7 mmHg at 45 nl/min (mean V1/2 8.6 +/- 1.04 nl/min). In five AT1A -/- mice (24 tubules) PSF was not significantly affected by loop flow with PSF averaging 33.9 +/- 1.7 mmHg at zero flow and 33.2 +/- 1.6 mmHg at 45 nl/min (not significant). Mean arterial blood pressures in the anesthetized and laparotomized mice were 91.8 +/- 2.2, 97.1 +/- 3, and 80.7 +/- 3.2 mmHg in the AT1A +/+, AT1A +/-, and AT1A -/- animals, respectively. Blood pressure responses to exogenous angiotensin II were greatly blunted in the AT1A -/- mice. We conclude that AT1A receptor-mediated effects of angiotensin II are in essential component of TGF responsiveness under chronic conditions. Our studies show the feasibility of using complex micropuncture methods in mice, an approach that widens the potential of genetically altered mouse strains as experimental models.

Expression of PTHrP, PTH/PTHrP receptor, and Ca(2+)-sensing receptor mRNAs along the rat nephron

To provide a frame of reference for studies of renal divalent cation and phosphate metabolism, we assessed the cellular localization of kidney calcium receptor (RaKCaR), parathyroid hormone-related protein (PTHrP), and parathyroid hormone/ parathyroid hormone-related protein (PTH/PTHrP) receptor mRNA. The studies used using reverse transcription-polymerase chain reaction (RT-PCR) applied to cDNA prepared from dissected rat nephron segments and from primary cultures of mouse juxtaglomerular granular cells. With species-specific primers, PCR products of expected size were obtained for RaKCaR (967 bp), PTHrP (420 bp), and PTH/PTHrP receptor (817 bp), with product identity being confirmed by restriction digestion. RaKCaR mRNA was found in medullary and cortical thick ascending limbs (MTAL and CTAL, respectively), the macula densa-containing segment, distal convoluted tubules (DCT), and, to a lesser extent, in cortical collecting ducts (CCD). It was not found in glomeruli, proximal convoluted and straight tubules (PCT and PST, respectively), outer and inner medullary collecting ducts (OMCD and IMCD, respectively), or in juxtaglomerular granular cell isolates. PTHrP mRNA was predominantly expressed in glomeruli and at lower levels in PCT and the macula densacontaining segment but was not detectable in CTAL, MTAL, DCT, and CD segments. Presence of PTH/PTHrP receptor mRNA was demonstrated in glomeruli, PCT, PST, CTAL, MTAL, and DCT but not in CD segments. These results suggest that the function of TAL and DCT cells, in addition to being affected by PTH, may be directly altered by extracellular divalent cations through RaKCaR and that PTHrP may act in the glomerulus and proximal tubule as an autocrine or paracrine regulator of hemodynamics and phosphate transport.

Regulation of endothelin production and secretion in cultured collecting duct cells by endogenous transforming growth factor-beta

Confluent cultures of two renal collecting duct cell lines (M-1 and mIMCD-K2 cells derived from cortical and inner medullary collecting ducts, respectively) express endothelin1 (ET1), transforming growth factor-beta (TGF beta; both TGF beta 1 and TGF beta 2), and both types of the TGF beta receptor. Experiments were performed to test whether endogenous TGF beta may be a paracrine modulator of ET1 expression in these cells. Treatment of M-1 and mIMCD-K2 cells with TGF beta 2 antisense oligodeoxynucleotides (ODN) significantly reduced ET1 messenger RNA (mRNA) and ET secretion (as well as TGF beta 2 mRNA) in a concentration-dependent manner, whereas control ODN were without significant effects. To produce ET inhibition, antisense ODN had to be present in the basolateral medium, whereas its sole presence in the apical medium was without effect. In addition, a pan-specific TGF beta antibody caused a significant reduction of ET1 mRNA expression and ET1 secretion. M-1 cells were found to express high levels of the mRNA for plasminogen activator of both tissue and urokinase types. Addition of the nonspecific serine protease inhibitor aprotinin (50 micrograms/ml) to the medium for 24 h significantly reduced the secretion of ET1. These results suggest that secretion of endogenous TGF beta, at least in part activated by the plasminogen/plasmin system, participates in the regulation of ET1 synthesis and secretion by collecting duct cell lines.

Localization of bumetanide- and thiazide-sensitive Na-K-Cl cotransporters along the rat nephron

The present study was undertaken to investigate the mRNA localization of the two major kidney-specific Na-K-Cl transport proteins, the bumetanide-sensitive cotransporter (NKCC2 in rabbit and BSC1 in rat) and the thiazide-sensitive cotransporter (TSC). NKCC2 from rabbit and mouse has been shown to exist in three isoforms (designated A, B, and F) that differ only in a 96-bp region. The divergent region of each of the three NKCC2 isoforms was cloned from rat kidney by a polymerase chain reaction (PCR)-based strategy, and isoform-specific primers were chosen. RNA and cDNA were prepared from renal cortex and medulla and from microdissected nephron segments. Using reverse transcription (RT)-PCR, the B isoform was detected only in cortex and the F isoform only in medulla, whereas the A from was found in both. In dissected nephron segments, the B form was found exclusively in cortical thick ascending limb (CTAL) and macula densa-containing segment (MDCS), the F form only in medullary thick ascending limb (MTAL) and outer medullary collecting duct, and the A form in CTAL, MDCS, and MTAL. An additional isoform including both A and F exons was identified by direct sequencing of a 592-bp product from medulla. The AF product was found only in the medulla and was localized exclusively in MTAL. TSC mRNA was detected exclusively in the distal convoluted tubule. Differential nephron localization of NKCC2 isoforms suggests that Na-K-Cl cotransporters may differ in their transport characteristics to explain regulation of salt transport along the nephron.

Novel mouse embryonic renal marker gene products differentially expressed during kidney development

Investigators approaching the problem of renal organogenesis have been hampered by a paucity of suitable molecular markers that specify distinct developmental phenotypes. To identify such markers, differential display-polymerase chain reaction (DD-PCR) was used to survey the temporal pattern of gene expression in mouse kidney at 11.5, 13.5, 15.5, and 17.5 days after conception and in the adult kidney. Twenty-two differentially expressed amplification products were identified, isolated, and sequenced. Seventeen clones showed no significant similarity with previously reported nucleotide sequences: two were similar to two housekeeping gene products, and three were similar to human or rat expressed sequence tags. To confirm the differential expression patterns observed by DD-PCR, semiquantitative reverse transcription-PCR was performed using sequence-specific oligonucleotide primers. Nineteen of 22 clones were differentially expressed during kidney development [mouse embryonic renal marker (MERM) sequences 1-19]. The value of MERMs as developmental markers was further assessed in mouse metanephric organ culture, where the pattern of MERM transcript expression mimicked that observed in vivo. Therefore, the DD-PCR method permitted development of a panel of marker sequences that can be used to characterize renal developmental processes and that may allow the identification of novel, functionally relevant gene products.

Synthesis and secretion of endothelin in a cortical collecting duct cell line

Previous experiments have shown that epithelial cells in the renal medulla produce endothelin-1 (ET-1) and possess ETB receptors. It has been suggested that medullary ET-1 may affect water and sodium absorption along the collecting ducts in an autocrine fashion. To study possible mechanisms responsible for the regulation of medullary ET-1 production, experiments were performed in M-1 cells and mIMCD-K2 cells, cell lines derived from cortical and inner medullary collecting ducts of SV40 transgenic mice, grown to confluence on collagen-coated filter inserts. Both cell lines were found to express ET-1 mRNA and to secrete ET almost exclusively into the basolateral medium as long as the transepithelial resistance was high. Inhibition of transcription with actinomycin D was followed by a decline in both ET mRNA [halftime (t1/2) = 30 min] and ET secretion (t1/2 = approximately 90 min). The addition of arginine vasopressin (AVP, 10(-8) M; 2- or 4-h exposure) or incubation of M-1 cells in hypertonic media (+50 mM NaCl, 4- or 6-h exposure) did not significantly alter ET secretion or ET-1 mRNA expression. In contrast, simultaneously increasing AVP(10(-8) M in the basolateral medium) and tonicity (+50 mM NaCl) for 4 h increased ET secretion (from 28.9 +/- 3.9 to 41.8 +/- 3.8 pg.h-1.mg protein-1; P = 0.029, n = 10) and ET-1 mRNA (control = 2,138 cpm/microliter, log of 3.33 +/- 0.048, n = 4; AVP + NaCl = 3,548.1 cpm/microliter, log of 3.55 +/- 0.09; P = 0.045, n = 5). Exposure of M-1 cells to hypertonic media (+50 mM NaCl or 100 mM mannitol) for 24 h was associated with a marked reduction of ET secretion (-83.9% with NaCl and -78.4% with mannitol; P < 0.0001). This reduction was attenuated, but not prevented, by the presence of AVP in the basolateral medium (-40%). ET-1 mRNA, in contrast, did not change with 24-h exposure to hypertonic media and increased when AVP was present. Results are compatible with the concept that generation of ET by collecting duct cells may contribute in a complex and time-dependent fashion to the paracrine control of collecting duct cell function.

Gender discrepancies in living related renal transplant donors and recipients

Renal transplantation is the most successful treatment strategy for patients with ESRD to improve survival and quality of life. The study presented here examines the relationship of gender and living related (LR) transplantation donor and recipient rates in the United States. National data from the United States Renal Data System (USRDS) were used for this study. All LR transplants occurring between 1991 and 1993 among blacks and whites were included (N = 6193). Transplantation and donation rates for men and women were calculated. Poisson regression was used to calculate female/male transplantation and donation rate ratios. Overall, women were 10% less likely to receive a LR transplant than men (rate ratio [RR] = 0.90, P < 0.001). This gender difference increased over time from 1991 (Female/Male RR = 0.95, P = not significant [NS]) to 1993 (RR = 0.85, P < 0.001). In contrast, women were significantly more likely to donate a kidney than men (RR = 1.28, P < 0.001 and RR = 1.29, P < 0.001 among whites and blacks, respectively). Analyses by age subgroups revealed that only among ESRD patients aged 20 to 44 yr was the likelihood of receiving a LR kidney transplant equal for men and women. Higher donation rates among women compared with men were observed in all donor age and race subgroups except young blacks (aged 0 to 19 yr). Recipient gender appeared to influence donation rates. The female-to-male relative donation rates were higher when donations were to female, compared with male, recipients. This study of national data suggests an imbalance in LR donation and transplantation between men and women. Women are more likely to donate a kidney but are less likely to receive a LR transplant than men. Several potential explanatory factors are explored. These findings suggest a need for the development of gender-appropriate interventions to encourage donation among men and LR transplantation among women, to ultimately facilitate greater use of this ESRD treatment modality.

Whys and wherefores of juxtaglomerular apparatus function

The juxtaglomerular apparatus is an anatomic structure which links the distal end of the thick ascending limb at the macula densa with the glomerular vascular pole. Specialized interstital cells and renin containing granular cells are located in the vascular hilum at this site. Evidence has accumulated that this connection is critical for local regulation of renin secretion and glomerular vascular tone via the tubuloglomerular feedback mechanism. The tubuloglomerular feedback mechanism maintains a constant chloride concentration at the macula densa at a set point determined by the volume state of the animal, a effect probably important for adjustment of renin secretion to changing salt balance. Evidence supporting these two regulatory roles is reviewed here.

Coordinate regulation of renal expression of nitric oxide synthase, renin, and angiotensinogen mRNA by dietary salt

Experiments were performed to examine the effect of changes in dietary salt intake on the neuronal form of the constitutive nitric oxide synthase (ncNOS, type I NOS), renin, and angiotensinogen mRNA expression in the kidney. Three groups of Sprague-Dawley rats were studied as follows: rats maintained on a 3% Na diet plus 0.45% NaCl in the drinking fluid for 7 days (high salt), rats given a single injection of furosemide (2 mg/kg i.p.) and a 0.03% Na diet for 7 days (low salt), and rats on a diet containing 0.2% Na (control). mRNA expression was assessed with reverse transcription-polymerase chain reaction (RT-PCR) methods using cDNA prepared from samples of renal cortex and microdissected tubular segments. ncNOS PCR products were quantified by comparison with a dilution series of a mutant deletion template. Compared with their respective control, ncNOS mRNA levels in renal cortical tissue were elevated in rats on a low-salt diet and reduced in rats on a high-salt diet. Similar changes were seen in the expression of renin and angiotensinogen mRNA. Dietary salt intake did not alter the mRNA levels for ncNOS from the inner medulla or for endothelial constitutive NOS (ecNOS, type III NOS) and inducible NOS (iNOS, type II NOS) in the renal cortex. ncNOS mRNA was found in glomeruli dissected with the macula densa-containing segment (MDCS), but only at marginal levels in glomeruli without MDCS. Furthermore, a low-salt diet stimulated ncNOS mRNA in glomeruli with MDCS by 6.2-fold compared with a high-salt diet. There was no effect of salt diet on ncNOS mRNA in glomeruli without MDCS or in inner medullary collecting ducts. These results suggest that ncNOS expression in macula densa cells is inversely regulated by salt intake, thus following the known response of the renin-angiotensin system to changes in salt balance.

SA gene expression in the proximal tubule of normotensive and hypertensive rats

Previous studies have shown that the SA gene is expressed at higher levels in the kidney of genetically hypertensive rats than in control strains and that in hybrid crosses of genetically hypertensive rats and normotensive controls, markers in or close to the SA gene cosegregate with blood pressure. The present studies examine the localization of the SA gene product in the kidney by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). cDNA was prepared from microdissected nephron segments from Sprague-Dawley (SD) rats, spontaneously hypertensive rats (SHRs), and Wistar-Kyoto (WKY) rats, and RT-PCR was performed using specific primers. In all three strains, SA gene mRNA was found to be abundantly expressed in proximal tubules. SA PCR product was occasionally detected at approximately 100-fold lower abundance in glomeruli, while no signal was obtained from the collecting duct, thick ascending limb of the loop of Henle, or arcuate artery. Within the proximal tubule of normotensive rats, distribution of SA mRNA was found to be strain dependent: in SD rats it was expressed at high levels in the proximal convoluted tubule, whereas in WKY rats it was restricted to the proximal straight tubule. In SHRs, SA PCR product was detected along the entire proximal tubule. Induction of hypertension by renal artery clamping (two-kidney, one-clamp Goldblatt model) did not alter the pattern of expression observed in the SD rat. These results indicate that an extension of SA gene expression to the full length of the proximal tubule accompanies spontaneous hypertension and that in nonhypertensive animals the pattern of gene product expression is more restricted but shows substantial strain variability.

Regional and segmental localization of AE2 anion exchanger mRNA and protein in rat kidney

Pages F461–F468: F. C. Brosius III, K. Nguyen, A. K. Stuart-Tilley, C. Haller, J. P. Briggs, and S. L. Alper. “Regional and segmental localization of AE2 anion exchanger mRNA and protein in rat kidney.” The last portion of the legend to Fig. 6 (p. F465) should read as follows: “ B: immunoblot of mouse kidney microsomes prepared with high concentrations of protease inhibitors. All lanes were loaded with 25 μg protein from medulla ( lanes 1 and 4), cortex ( lanes 2 and 5), and whole kidney ( lanes 3 and 6). Blots were visualized with ECL.” Also, in the accompanying section of text in the results (p. 465, column 2), at the paragraph beginning “Membranes prepared...”, the second sentence should read as follows: “Maximal levels of 170-kDa AE2 polypeptide were present in medulla (Fig. 6B, lane 1), whereas cortex (Fig. 6B, lane 2) contained lower levels of AE2.”

Regional and segmental localization of AE2 anion exchanger mRNA and protein in rat kidney

Pages F461–F468: F. C. Brosius III, K. Nguyen, A. K. Stuart-Tilley, C. Haller, J. P. Briggs, and S. L. Alper. “Regional and segmental localization of AE2 anion exchanger mRNA and protein in rat kidney.” The last portion of the legend to Fig. 6 (p. F465) should read as follows: “B: immunoblot of mouse kidney microsomes prepared with high concentrations of protease inhibitors. All lanes were loaded with 25 μg protein from medulla ( lanes 1 and 4), cortex ( lanes 2 and 5), and whole kidney ( lanes 3 and 6). Blots were visualized with ECL.” Also, in the accompanying section of text in the results (p. 465, column 2), at the paragraph beginning “Membranes prepared...”, the second sentence should read as follows: “Maximal levels of 170-kDa AE2 polypeptide were present in medulla (Fig. 6B, lane 1), whereas cortex (Fig. 6B, lane 2) contained lower levels of AE2.”

Regional and segmental localization of AE2 anion exchanger mRNA and protein in rat kidney

Chloride/base exchange activity has been detected in every mammalian nephron segment in which it has been sought. However, in contrast to the Cl-/HCO3- exchanger AE1 in type A intercalated cells, localization of AE2 within the kidney has not been reported. We therefore studied AE2 expression in rat kidney. AE2 mRNA was present in cortex, outer medulla, and inner medulla. Semiquantitative polymerase chain reaction of cDNA from microdissected tubules revealed AE2 cDNA levels as follows [copies of cDNA derived per mm tubule (+/- SE)]: proximal convoluted tubule, 688 +/- 161; proximal straight tubule, 652 +/- 189; medullary thick ascending limb, 1,378 +/- 226; cortical thick ascending limb, 741 +/- 24; cortical collecting duct, 909 +/- 71; and outer medullary collecting duct, 579 +/- 132. AE2 cDNA was also amplified in thin limbs and in inner medullary collecting duct. AE2 polypeptide was detected in all kidney regions. AE2 mRNA and protein were also detected in several renal cell lines. The data are compatible with the postulated roles of AE2 in maintenance of intracellular pH and chloride concentration and with its possible participation in transepithelial transport.

Amphotericin B nephrotoxicity: the adverse consequences of altered membrane properties

Amphotericin B (AmB) has been in clinical use for more than 30 yr but has remained the most effective drug for treatment of serious fungal infections. Its use has increased in recent years, as the result of increases in aggressive intensive care support and increased numbers of immunocompromised patients. Nephrotoxic manifestations are common, and this is the major factor limiting the clinical use of the drug. A number of recent studies have contributed to a better understanding of the mechanism by which AmB exerts its nephrotoxic effect. AmB alters cell membrane permeability and probably as a consequence alters tubular and vascular smooth muscle cell function, leading to various tubular transport defects and vasoconstriction. Decreased RBF appears to play a major role in AmB-induced reduction GFR, and recurrent ischemia may be the basis of permanent structural nephrotoxic effects. Salt loading is the only measure proven by controlled prospective study to ameliorate AmB nephrotoxicity in humans. Liposomal AmB and the formulation of an emulsion of AmB in lipid may provide a protective effect based on altering the affinity of AmB for mammalian cell membranes, while preserving high efficacy against fungal cells. However, further studies are needed to evaluate the efficacy and safety of these new AmB formulations.

Effects of furosemide and verapamil on the NaCl dependency of macula densa-mediated renin secretion

The present studies in perfused specimens of the juxtaglomerular apparatus microdissected from rabbit kidneys were performed to quantitatively evaluate the relation between macula densa NaCl concentration and renin secretion and to study the effect of furosemide and verapamil on NaCl dependency of renin release. Renin secretion was found to decrease exponentially when macula densa NaCl concentration was increased from 26/7 mmol/L (Na/Cl) to 46/27, 66/47, and 86/67 mmol/L. Increasing Na/Cl concentrations from 86/67 to 106/87 mmol/L had no further effect on renin secretion. [Cl]1/2, the chloride concentration producing the half-maximal effect, was 30 mmol/L. Addition of 50 mumol/L furosemide to the luminal fluid caused renin secretion to become essentially independent of macula densa NaCl concentration. This effect was due to both an increase of renin secretion at high NaCl concentrations and a decrease of renin release at low NaCl concentrations. Verapamil added to the superfusate at a concentration of 1 mumol/L also abolished NaCl dependency of renin secretion; most of this effect was due to an increase of renin release at high luminal NaCl. These results suggest that Na-2Cl-K cotransport and calcium flux through voltage-gated channels are two mechanisms required for the expression of NaCl-dependent renin release. Identification of the cellular localizations of these two critical membrane proteins in the renin control pathway requires further study.

Ontogeny of NO synthase and renin in juxtaglomerular apparatus of rat kidneys

The presence of NO synthase (NOS) in cells of the macula densa (MD) suggests a role for arginine-derived NO in tubulovascular information transfer. To investigate the postnatal development of the neuronal isoform of NOS and of renin in the kidney, the cellular distribution of these enzymes was examined in perfusion-fixed kidneys of 2-, 6-, and 15-day-old rats at both the protein and mRNA level (n = 4 rats/group). NOS and renin and their mRNAs were localized by immunohistochemical and in situ hybridization methods. In addition, NOS levels were assessed by using NADPH diaphorase (NADPH-d) histochemistry. For quantification, the fraction of NOS- and renin-positive glomeruli as well as the number of NOS-positive MD cells was evaluated at all stages. Presence of NOS in single cells of the developing distal tubule was encountered already in the S-shaped body. Full expression of a NOS signal in MD cells was seen as soon as a glomerular urinary space was developed. Double labeling with NADPH-d and antibody to Tamm-Horsfall protein (THP) indicated mutual exclusiveness of NADPH-d-positive MD cells and neighboring THP-positive distal tubule cells at all levels of development. The relative intensity of renin status was 2 day > 6 day > 15 day, whereas NOS expression was maximal on postnatal day 6. Our data are consistent with an involvement of MD NO synthesis in the early organization of the juxtaglomerular apparatus during nephrogenesis and suggest an interdependent relation with renin-producing cells.

Effect of nitric oxide on renin secretion. I. Studies in isolated juxtaglomerular granular cells

Experiments were performed on juxtaglomerular granular cells (JGC) in short-term primary culture to determine the direct immediate effect of NO on renin secretion and to test whether JGC are able to generate NO. Renin secretion was measured repeatedly over short time intervals in a cell superfusion system. Renin release did not significantly decrease over a 40-min observation period in untreated JGC. Addition of sodium nitroprusside (SNP) caused a reduction in renin release (measured in nano-Goldblatt hog units vs. time, i.e., nGU/min) from 479 +/- 25, 423 +/- 70, and 388 +/- 54 nGU/min to 295 +/- 19 (n = 5), 102 +/- 21 (n = 7), and 71 +/- 9 nGU/min (n = 6) with 10(-5), 10(-4), and 10(-3) M SNP, respectively. In the presence of the guanylate cyclase inhibitor methylene blue at 10(-4) M, SNP at 10(-4) M had no significant effect on renin secretion. 8-Bromoguanosine 3',5'-cyclic monophosphate at 10(-4) M in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (10(-3) M) caused a reduction of renin secretion to 50.1 +/- 3.6% of control. To examine the possibility that renin secretion is affected by NO release from JGC, we assessed the effect of the NO synthase (NOS) substrate L-arginine (10(-3) M) and the NOS blocker N omega-nitro-L-arginine (10(-4) M) on renin secretion. Renin release was not significantly altered by either stimulation or inhibition of NOS activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of nitric oxide on renin secretion. II. Studies in the perfused juxtaglomerular apparatus

To examine the possible role of NO in macula densa control of renin secretion, we examined the effects of varying NO availability on renin release in the isolated perfused rabbit juxtaglomerular apparatus (JGA). Gradual increments of luminal Na/Cl concentration ratio (mM/mM) from 26/7 over 46/27, 66/47, to 86/67 caused a progressive decrease in renin secretion from (as log of nano-Goldblatt hog units vs. time, i.e., log nGU/min) 1.09 +/- 0.34 to 0.46 +/- 0.24 log nGU/min, with the greatest change occurring at the first concentration step. The presence of 0.7 mM N omega-nitro-L-arginine (NNA), an NO synthase inhibitor, in the luminal fluid significantly reduced renin secretion at the lowest Na/Cl concentration ratio to 0.65 +/- 0.32 log nGU/min (P < 0.01 compared with control). Renin secretion at the higher Na/Cl concentration ratios was not significantly affected by NNA compared with control. In contrast to these results, the addition of the NO donor nitroprusside (1 mM) to the bath caused a reduction in renin secretion from 1.0 +/- 0.39 to 0.47 +/- 0.46 log nGU/min (P < 0.05), an effect that was reversed by bath addition of 0.01 mM methylene blue. Similarly, addition of L-arginine (0.7 mM) to the bath reduced renin secretion from 0.99 +/- 0.37 to 0.81 +/- 0.38 log nGU/min (P < 0.01), whereas addition of L-arginine to the luminal fluid increased renin secretion from 0.85 +/- 0.43 to 1.94 +/- 0.46 log nGU/min (P < 0.05). The stimulatory effect of luminal L-arginine was reversed by the luminal addition of NNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered renal expression of the insulin-responsive glucose transporter GLUT4 in experimental diabetes mellitus

Because the insulin-responsive glucose transporter, GLUT4, is expressed in renal vascular and glomerular cells, we determined the effects of experimental diabetes mellitus on GLUT4 expression and glucose uptake by these tissues. Quantitative reverse-transcription polymerase chain reaction studies of microdissected afferent microvessels and renal glomeruli showed that, after 1 wk of diabetes, GLUT4 mRNA was decreased to 26 and 34% of control values, respectively. GLUT4 immunoblots of renal glomerular and microvessel samples showed that GLUT4 polypeptide was decreased to 51% of control values. These results were confirmed by indirect immunofluorescence, which showed decreased GLUT4 expression in glomerular cells and in vascular smooth muscle cells of the afferent microvasculature of diabetic animals. Uptake of the glucose analogue, 2-deoxyglucose, was also depressed in microvessels of diabetic rats to 57% of control values, supporting the conclusion that fewer total glucose transporters were available for glucose uptake into diabetic renal glomerular and microvascular cells. Thus both GLUT4 expression and glucose uptake by glomerular and microvascular cells are decreased in diabetic animals. These results have led us to suggest a mechanism by which decreased renal GLUT4 expression could contribute to glomerular hyperfiltration and hypertension seen in early diabetes.

Renin and renin mRNA in proximal tubules of the rat kidney

The present study was undertaken to assess the presence of renin enzymatic activity and renin mRNA in proximal tubules of rat kidneys, and to determine the effect of converting enzyme inhibition (CEI) on proximal tubule renin gene expression. Proximal convoluted tubules (PCT), proximal straight tubules (PST), outer medullary collecting ducts (OMCD), and glomeruli (Gloms) were isolated by microdissection. Renin activity was measured in sonicated segments by radioimmunoassay. Renin mRNA levels were assessed using a quantitative PCR. Renin activity in PCT averaged 51 +/- 15 microGU/mm compared to 405 +/- 120 microGU/glomerulus. No measurable renin activity was found in PST and OMCD. Renin activity in both glomeruli and tubules had the same pH optimum, between 7.0 and 7.5. Renin mRNA was consistently detectable in cDNA prepared from PCT and PST, although its abundance per mm tubule was about 1/500th that found in one glomerulus. Renin mRNA was not detectable in OMCD. Tubular renin PCR product identity was confirmed by restriction digestion. CEI administration increased glomerular renin activity and renin mRNA, but not proximal tubular renin. The absence of a stimulatory effect of CEI on proximal tubule renin gene expression suggests the operation of different intracellular signals in control of renin synthesis in the proximal tubule than in the vascular compartment.

Synergistic effects of angiotensin and adenosine in the renal microvasculature

Experiments were performed in the in situ kidney of rats and in isolated afferent arterioles of the rabbit to study the interaction between angiotensin II and adenosine in producing afferent arteriolar vasoconstriction. In the intact rat kidney, we observed that 1) peritubular infusion of the adenosine1-receptor blocker 8-cyclopentyl-1,3-dipropylxanthine (CPX, 10(-4) M) blocked the fall in stop-flow pressure (PSF) induced by angiotensin II (5 x 10(-7) M) but not that caused by vasopressin (10(-5) M) or norepinephrine (10(-5) M), 2) peritubular infusion of saralasin (5 x 10(-5) M) attenuated the fall in PSF caused by N6-cyclohexyladenosine (CHA, 10(-5) M) 3) the fall in PSF following luminal application of CHA (10(-5) M) was reduced in angiotensin II-depleted states (volume expansion and converting enzyme inhibition) and this could be reversed by infusion of low doses of angiotensin II, and 4) the reduction in PSF in response to luminal infusion of CHA was augmented in a greater-than-additive fashion when angiotensin was simultaneously administered at low intravenous infusion rates. In isolated afferent arterioles of the rabbit, we noted that 1) addition of 10(-5) M CPX to the bath significantly blunted the constrictor effect of angiotensin II (10(-8) M), 2) presence of the converting enzyme inhibitor quinaprilate (10(-7) M) caused a right shift in the constrictor-response curve to increasing concentrations of CHA (10(-9)-10(-5) M) but 10(-5) M saralasin did not affect vasoconstriction caused by 10(-6) M adenosine, 3) simultaneous administration of submaximal constrictor doses of angiotensin II (10(-10) M) and adenosine (10(-6) M) produced vasoconstriction that was greater than additive, and 4) 10(-5) M CHA and angiotensin II (10(-7) M) constricted afferent arterioles after removal of the glomerulus, whereas either agent alone had no constrictor effect in this preparation. Our results suggest that adenosine and angiotensin cooperate in a mutually dependent and synergistic fashion in producing afferent arteriolar vasoconstriction.

Cyclic AMP selectively increases renin mRNA stability in cultured juxtaglomerular granular cells

This study was undertaken to examine the regulation of renin release and gene expression in primary cultures of juxtaglomerular granular (JGG) cells. JGG cells, isolated from mouse kidney, demonstrated high purity and showed regulated renin release in vitro. Changes in steady-state renin mRNA levels were assessed by quantitative polymerase chain reaction techniques, with polymerase chain reaction amplification efficiency monitored by co-amplification of experimental samples with a dilution series of cDNA for a mutant template. When the cells were incubated in the presence or absence of forskolin, isoproterenol, or 8-bromo-cAMP plus 3-isobutyl-1-methylxanthine for 24 h or cholera toxin for 12 h, renin mRNA levels were increased 3.9-, 4.4-, 5.1-, and 3.3-fold, respectively (all, p < 0.05). A significant increase in renin mRNA levels was observed 8 h after treatment with forskolin, but no change was detectable at 4 h. Cycloheximide did not prevent the increase in renin mRNA by isoproterenol. When RNA synthesis was inhibited by incubation with actinomycin D (5 micrograms/ml), renin mRNA levels declined with a half-life of 3.0 +/- 0.8 h. Treatment with forskolin increased renin mRNA half-life to 10.8 +/- 2.7 h (p < 0.025). The half-life of beta-actin, endothelin-1, or the facilitative glucose transporter-1 (GLUT-1) mRNA expressed in the same cells was not altered, although the steady-state levels of GLUT-1 mRNA increased 2.2-fold after treatment with forskolin. These data demonstrate that cAMP increases renin release and mRNA levels in JGG cells in vitro, that the stimulatory effect of cAMP on renin mRNA is delayed but does not require new protein synthesis, and that the increased renin mRNA levels induced by cAMP are due in part to a selective increase in renin mRNA stability.

The macula densa mechanism for control of renin secretion

Many questions remain concerning the precise mechanism by which the luminal signal for renin secretion is transmitted from the MD to the JG granular cell. It appears likely that a number of pathways may participate in MD-mediated changes in renin release, some of the agents serving to modulate release, others participating directly in signal transmission. Collectively, the current information suggests a transmission pathway that involves several steps. First, changes occurring in MD NaCl transport, which result directly from alterations in luminal NaCl concentration, act to initiate the response. Second, conveyance of this signal to the extraglomerular mesangial cells via a change in the ionic environment of the EGM field and/or a paracrine factor produced by the MD (perhaps NO) appear likely to be the next step. The subsequent steps probably include changes in prostaglandin production by the EGM, and possible participation of other paracrine factors produced by both endothelial and extraglomerular mesangial cells.

Effect of prostaglandin synthesis inhibition on macula densa-stimulated renin secretion

The purpose of the present studies was to evaluate directly the role of prostaglandins in macula densa-mediated renin release. Individual juxtaglomerular apparatus specimens were microdissected from rabbit kidney and perfused with a solution containing either high NaCl (Na+ = 141 meq/l; Cl- = 122 meq/l) or low NaCl (Na+ = 26 meq/l; Cl- = 7 meq/l) concentration. With a step decrease in perfusate NaCl (high to low), renin secretion rate was markedly stimulated (from 15.06 to 63.1 nGU/min, P < 0.01), and the response was almost fully reversible. When specimens were bathed with cyclooxygenase inhibitors flurbiprofen (10(-5) M) or flufenamic acid (10(-4) M), this macula densa-activated increase in renin release was largely or completely abolished (flurbiprofen, 3.5-10.5 nGU/min, not significant; flufenamic acid, 9.0-12.3 nGU/min, not significant). Exposing the macula densa to a step increase in perfusate NaCl concentration (low to high) resulted in a significant and reversible suppression of renin secretion in control specimens, but no significant suppression was seen in specimens treated with flufenamic acid. These data provide direct evidence to support the hypothesis that locally produced prostaglandins may act as a primary mediator of the renin response to macula densa activation.

Endothelin-1 mRNA in glomerular and epithelial cells of kidney

To examine the question of the tubular localization of renal endothelin-1 (ET-1) mRNA, cDNA generated by reverse transcription of isolated rat tubule RNA was amplified by polymerase chain reaction using rat ET-1-specific oligonucleotides. Product identity was determined by restriction enzyme digestion or direct product sequencing. ET-1 mRNA was found to increase in renal tissue in a corticomedullary direction. High levels of ET-1 mRNA were found in dissected glomeruli and in juxtaglomerular cells in short-term primary culture. Among tubule segments, ET-1 mRNA was most abundant in inner medullary collecting ducts (IMCD), but products were also found with cDNA derived from proximal convoluted and straight tubules, thick ascending limbs, and outer medullary collecting ducts. In kidneys of untreated, homozygous Brattleboro rats, the increase of ET-1 mRNA along the corticomedullary axis as well as the preponderance of tubular ET-1 mRNA in IMCD was not observed. Our data show that ET-1 mRNA is present in all nephron segments studied and that its expression may be dependent on the functional state of the kidney. Our results are consistent with the proposal that ET-1 modifies tubular function in an autocrine or paracrine fashion.

Effects of adenosine and angiotensin on macula densa-stimulated renin secretion

The present studies were performed to assess, in the isolated perfused juxtaglomerular apparatus of the rabbit kidney, the effect of exogenous adenosine on renin secretion stimulated by a low NaCl concentration at the macula densa. Addition of adenosine to the bath resulted in a change of renin secretion from 30.4 to 23.9 nGU/min at an adenosine concentration of 10(-6) M (n = 7; P = NS), from 38.6 to 17.9 nGU/min at a concentration of 10(-4) M (n = 7; P = 0.038), and from 18.4 to 5.8 nGU/min at 10(-2) M (P = 0.0053). Addition of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine at 10(-5) M fully reversed the effect of adenosine at 10(-4) M, but not at 10(-2) M. Inhibition of adenosine breakdown by the adenosine deaminase inhibitor pentostatin (10(-6) M) enhanced the inhibitory effect of adenosine with renin secretion falling from 61.7 to 19.5 nGU/min at 10(-6) M adenosine (P = 0.035) and from 44.7 to 13.5 nGU/min at 10(-4) M adenosine (n = 0.027). A marked inhibition of NaCl-dependent renin secretion was caused by both angiotensin II (P = 0.011) and angiotensin III (P = 0.006), both at 10(-8) M. These results show that adenosine is capable of reducing macula densa-mediated renin secretion, but that this effect, even at very high concentrations or during adenosine deaminase blockade, does not fully mimic the inhibitory potency of increasing luminal NaCl concentration. Because the marked effect caused by angiotensins establishes the potential of this preparation to demonstrate inhibitory hormonal influences, it is concluded that adenosine does not appear to be the sole paracrine factor responsible for the NaCl-induced reduction of renin secretion.

Distribution of mineralocorticoid and glucocorticoid receptor mRNA along the nephron

In the present study, a competitive polymerase chain reaction (PCR) technique was used to quantitate the relative levels of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) mRNA in microdissected nephron segments from the rat kidney and of MR mRNA from isolated principal and intercalated collecting duct cells from rabbit. RNA was isolated from cells and isolated tubules, cDNA was synthesized, and receptor cDNA was coamplified by PCR with a competitive control template. beta-Actin PCR products were also obtained from each nephron segment studied, to assess variations in RNA extraction and cDNA synthesis. MR mRNA, as determined by this competitive PCR technique, was 10-fold more abundant in cortical collecting duct (CCD), outer medullary collecting duct, and inner medullary collecting duct segments than in the proximal tubule and thick ascending limb segments (P < 0.05). Both principal and beta-intercalated cells of the CCD contained detectable levels of MR mRNA, although the levels in the principal cells were threefold higher (P < 0.01). GR mRNA was twofold more abundant in glomeruli, proximal tubule, and thick ascending limb segments than in the collecting duct segments (P < 0.05). In general, the distribution pattern of MR and GR mRNA is consistent with the distribution of adrenal corticosteroid function along the nephron.