Assessment of Perfusion and Oxygenation of the Human Renal Cortex and Medulla by Quantitative MRI during Handgrip Exercise.

BACKGROUND: Renal flow abnormalities are believed to play a central role in the pathogenesis of nephropathy and in primary and secondary hypertension, but are difficult to measure in humans. Handgrip exercise is known to reduce renal arterial flow (RAF) by means of increased renal sympathetic nerve activity. METHODS: To monitor medullary and cortical oxygenation under handgrip exercise-reduced perfusion, we used contrast- and radiation-free magnetic resonance imaging (MRI) to measure regional changes in renal perfusion and blood oxygenation in ten healthy normotensive individuals during handgrip exercise. We used phase-contrast MRI to measure RAF, arterial spin labeling to measure perfusion, and both changes in transverse relaxation time (T2*) and dynamic blood oxygenation level-dependent imaging to measure blood oxygenation. RESULTS: Handgrip exercise induced a significant decrease in RAF. In the renal medulla, this was accompanied by an increase of oxygenation (reflected by an increase in T2*) despite a significant drop in medullary perfusion; the renal cortex showed a significant decrease in both perfusion and oxygenation. We also found a significant correlation (R2=0.8) between resting systolic BP and the decrease in RAF during handgrip exercise. CONCLUSIONS: Renal MRI measurements in response to handgrip exercise were consistent with a sympathetically mediated decrease in RAF. In the renal medulla, oxygenation increased despite a reduction in perfusion, which we interpreted as the result of decreased GFR and a subsequently reduced reabsorptive workload. Our results further indicate that the renal flow response's sensitivity to sympathetic activation is correlated with resting BP, even within a normotensive range.

Autonomic innervation of the periglomerular arteries.

OBJECTIVE: To explore spatial and volume relations of the calcitonine gene-related peptide (CGRP)-positive and tyrosine hydroxylase (TH)-positive nerve fibers in the wall of cortical blood vessels. STUDY DESIGN: Kidney specimens from 10 rats were processed for confocal microscopy. Nerve fibers were stained with anti-CGRP and anti-TH antibodies and image stacks were collected. Three-dimensional reconstruction and quantification of labeled fibers were performed to reveal their distribution and spatial relations. RESULTS: CGRP- and TH-immunoreactive nerve fibers were distributed throughout the kidney cortex. TH-positive fibers were dominant in the small periglomerular arteries (up to 4.6-fold). Examined nerves were finely intertwined in the wall of small blood vessels of the kidney and ran in the same nerve bundle but without co-localization. Extensive, web-like branching and varicosities of the TH nerves were observed. Sensory fibers prevailed in the wall of the larger arteries "embedded" into tubules near the medullary rays, and their endings can be verified in the muscularis layer of the interlobular arteries. CONCLUSION: Characteristics of the investigated fibers emphasize their role in the regulation of kidney blood vessel diameter and their influence on hypertension onset.

The protective effects of DA-9801 (Dioscorea extract) on the peripheral nerves in streptozotocin-induced diabetic rats.

It has been reported that DA-9801, an extract mixture of Dioscorea japonica Thunb and Dioscorea nipponica Makino, produces a neurotrophic activity. Therefore, this study was conducted to examine the neuroprotective effects of DA-9801 in streptozotocin-induced diabetic rats. The experimental rats were divided into six groups: the control group, Group I (non-diabetic rats treated with DA-9801), Group II (diabetic, non-treated rats) and Groups III, IV, and V (diabetic rats treated with DA-9801 at doses of 10, 50 or 100 mg/kg/d). Following a 16-wk course of oral treatment with DA-9801, functional parameters (von Frey filament test, hot plate test), biochemical parameters (nerve growth factor (NGF), tumor necrosis factor (TNF)-α, interleukin (IL)-6) were measured. An immunohistochemical staining was done to assess the neuroprotective effects of DA-9081 in the skin, sciatic nerve, gastric mucosa and renal cortex. In Week 8, pain was evoked by either tactile or thermal stimuli, whose threshold was significantly higher in Group III, IV and V than Group II. Western blot analysis showed a more significant increase in NGF and decrease in TNF-α and IL-6 in Group III, IV and V than in Group II (p<0.05). Moreover, following the treatment with DA-9801, a loss of intraepidermal nerve fibers (IENFs) was inhibited to a significant level in the skin, myelinated axonal fibers of the sciatic nerve and small nerve fibers innervating the gastric mucosa or renal cortex (p<0.05). Our results demonstrated that DA-9801 is a beneficial agent that protects the peripheral nerves in diabetic rats.

Comparison of peripheral nerve damages according to glucose control timing in experimental diabetes.

OBJECTIVE: In addition to tight glucose control, early intensive therapy has been reported to be more important for the prevention of diabetic micro- and macro-vascular complications. What is not known exactly is the quantitative difference according to timing delay in glucose control and whether early period control is really better than late control in terms of diabetic peripheral neuropathy. In this study, we investigated the effect of timing differences in glucose control on the peripheral nerves in an experimental diabetic model. METHODS: 5 groups (6-8 rats in each group) were comprised of normal glucose rats (designated control), rats with hyperglycemia (designated DM), rats with glucose control for the entire 28-week study period (designated DM + INS [W0-28]), rats with glucose control for the early 14-week period followed by hyperglycemia for the late 14-week period (designated DM + INS [W0-14]), and rats with hyperglycemia for the early 14-week period followed by glucose control in the late 14-week period (designated DM + INS [W15-28]). RESULTS: We found that the current perception threshold (CPT) was lower in the DM + INS (W0-28) and DM + INS (W15-28) groups than in the DM + INS (W0-14) or DM groups (P<0.05). The mean myelinated fiber area of the sciatic nerve was significantly greater in the DM + INS (W0-28) and DM + INS (W15-28) groups (63.5±2.32 and 60.1±2.14 um, respectively) than in the DM + INS (W0-14) or DM groups (55.5±2.81 or 51.5±2.64 um, respectively) (P<0.05), and the intraepidermal nerve fiber (IENF) density was significantly higher in the DM + INS (W0-28) and DM + INS (W15-28) groups (6.9±0.46 and 6.8±0.11, respectively) than in the DM + INS (W0-14) or DM groups (59.5±0.32 and 5.3±0.39/mm, respectively) (P<0.05). CONCLUSION: Our results indicate that continuous glucose control is necessary to alleviate peripheral nerve damage and that glycemic control during the later period may be more important than early period management. The importance of continuous glucose control, including the later period of diabetes, should therefore be emphasized in diabetic peripheral neuropathy.

Sulodexide prevents peripheral nerve damage in streptozotocin induced diabetic rats.

We investigated whether sulodexide has additional protective effects against peripheral nerve damage caused by microvascular dysfunction in a rat model of diabetes. Female Sprague-Dawley (SD) rats were divided into the following 4 groups (n=7-9/group): Normal, Normal+Sulodexide (sulodexide 10mg/kg), diabetic group, and diabetic+Sulodexide (sulodexide 10mg/kg). We assessed current perception threshold, skin blood flow, superoxide dismutase, and proteinuria in experimental rats after oral administration of sulodexide for 20 weeks. We also performed morphometric analysis of sciatic nerves and intraepidermal nerve fibers of the foot. Superoxide dismutase activity in the blood and sciatic nerve were increased significantly after sulodexide treatment in the diabetic group. Current perception threshold was reduced at 2000 Hz (633.3 ± 24.15 vs 741.2 ± 23.5 µA, P<0.05) and skin blood flow was improved (10.90 ± 0.67 vs 8.85 ± 0.49 TPU, P<0.05) in the diabetic+Sulodexide group compared with the diabetic group. The mean myelinated axon area was significantly larger (56.6 ± 2.2 vs 49.8 ± 2.7 µm(2), P<0.05) and the intraepidermal nerve fiber density was significantly less reduced (6.27 ± 0.24 vs 5.40 ± 0.25/mm, P<0.05) in the diabetic+Sulodexide group compared to the diabetic group. Our results demonstrate that sulodexide exhibits protective effects against peripheral nerve damage in a rat experimental model of diabetes. Therefore, these findings suggest that sulodexide is a potential new therapeutic agent for diabetic peripheral neuropathy.

Do distinct populations of dorsal root ganglion neurons account for the sensory peptidergic innervation of the kidney?

Peptidergic afferent renal nerves (PARN) have been linked to kidney damage in hypertension and nephritis. Neither the receptors nor the signals controlling local release of neurokinines [calcitonin gene-related peptide (CGRP) and substance P (SP)] and signal transmission to the brain are well-understood. We tested the hypothesis that PARN, compared with nonrenal afferents (Non-RN), are more sensitive to acidic stimulation via transient receptor potential vanilloid type 1 (TRPV1) channels and exhibit a distinctive firing pattern. PARN were distinguished from Non-RN by fluorescent labeling (DiI) and studied by in vitro patch-clamp techniques in dorsal root ganglion neurons (DRG; T11-L2). Acid-induced currents or firing due to current injection or acidic superfusion were studied in 252 neurons, harvested from 12 Sprague-Dawley rats. PARN showed higher acid-induced currents than Non-RN (transient: 15.9 +/- 5.1 vs. 0.4 +/- 0.2* pA/pF at pH 6; sustained: 20.0 +/- 4.5 vs. 6.2 +/- 1.2* pA/pF at pH 5; *P < 0.05). The TRPV1 antagonist capsazepine inhibited sustained, amiloride-transient currents. Forty-eight percent of PARN were classified as tonic neurons (TN = sustained firing during current injection), and 52% were phasic (PN = transient firing). Non-RN were rarely tonic (15%), but more frequently phasic (85%), than PARN (P < 0.001). TN were more frequently acid-sensitive than PN (50-70 vs. 2-20%, P < 0.01). Furthermore, renal PN were more frequently acid-sensitive than nonrenal PN (20 vs. 2%, P < 0.01). Confocal microscopy revealed innervation of renal vessels, tubules, and glomeruli by CGRP- and partly SP-positive fibers coexpressing TRPV1. Our data show that PARN are represented by a very distinct population of small-to-medium sized DRG neurons exhibiting more frequently tonic firing and TRPV1-mediated acid sensitivity. These very distinct DRG neurons might play a pivotal role in renal physiology and disease.

Mechanosensitive N-methyl-D-aspartate receptors contribute to sensory activation in the rat renal pelvis.

The N-methyl-D-aspartate (NMDA) subtype of the ionotropic glutamate receptor is found in the periphery. The present study tested whether NMDA receptors (NMDARs) are present in the ends of afferent renal nerves in the renal pelvis, an area concerned mainly with transmitting sensation and the to reflex regulation of body fluid. The main NMDAR subunit, NMDAzeta1, was found to be more abundant in the renal pelvis than the renal cortex and medulla, and was mainly colocalized with the pan-neuronal marker PGP9.5 or the sensory nerve marker, the neurokinin-1 receptor. However, NMDAzeta1 mRNA was undetectable, suggesting that it might be synthesized outside the renal pelvis. Intrarenal arterial administration of the specific ion channel blocker (+)-MK-801, but not the inactive enantiomer (-)-MK-801, decreased urine output and sodium excretion. High doses of (+)-MK-801 also caused regional vasoconstriction in the renal cortex, as determined by laser-Doppler flowmetry. Intrapelvic administration of the NMDAR ligand D-serine caused a dose-dependent increase in substance P (SP) release and afferent renal nerve activity, but had no effect on arterial pressure. The D-serine-induced sensory activation and SP release were abrogated by (+)-MK-801, the SP receptor blocker L-703,606, or dorsal rhizotomy. Increasing intrapelvic pressure resulted in an increase in afferent renal nerve activity and a diuretic/natriuretic response. Interestingly, these effects were attenuated by prior administration of (+)-MK-801. These results indicate that NMDAR-positive sensory nerves are present in the renal pelvis and contribute to the renorenal reflex control of body fluid.

Effects of mitral regurgitation on the reflex diuresis to pulmonary lymphatic obstruction in rabbits.

Increasing the extravascular fluid of the airways acutely by obstructing pulmonary lymph drainage causes a reflex diuresis mediated by neuronal nitric oxide synthase in the renal medulla. The authors examined this reflex in rabbits with a chronic increase in extravascular fluid of the airways resulting from surgically induced mitral regurgitation. Intact rabbits served as controls. Renal neuronal (nNOS) and endothelial (eNOS) nitric oxide synthase expressions were also examined. The reflex was absent in rabbits with mitral regurgitation. There were significant increases in medullary and cortical nNOS mRNA compared to controls. The observed changes in mRNA levels correlated with nNOS protein levels. eNOS mRNA was unaffected.

Temporal relationship between renal cyst development, hypertension and cardiac hypertrophy in a new rat model of autosomal recessive polycystic kidney disease.

BACKGROUND/METHODS: We have examined the hypothesis that cyst formation is key in the pathogenesis of cardiovascular disease in a Lewis polycystic kidney (LPK) model of autosomal-recessive polycystic kidney disease (ARPKD), by determining the relationship between cyst development and indices of renal function and cardiovascular disease. RESULTS: In the LPK (n = 35), cysts appear at week 3 (1.1 +/- 0.1 mm) increasing to week 24 (2.8 +/- 2 mm). Immunostaining for nephron-specific segments indicate cysts develop predominantly from the collecting duct. Cyst formation preceded hypertension (160 +/- 22 vs. Lewis control 105 +/- 20 mm Hg systolic blood pressure (BP), n = 12) at week 6, elevated creatinine (109 +/- 63 vs. 59 +/- 6 micromol/l, n = 16) and cardiac mass (0.7 vs. 0.4% bodyweight, n = 15) at week 12, and left ventricular hypertrophy (2,898 +/- 207 vs. 1,808 +/- 192 mum, n = 14) at week 24 (all p < or = 0.05). Plasma-renin activity and angiotensin II were reduced in 10- to 12-week LPK (2.2 +/- 2.9 vs. Lewis 11.9 +/- 4.9 ng/ml/h, and 25.0 +/- 19.1 vs. 94.9 +/- 64.4 pg/ml, respectively, n = 26, p < or = 0.05). Ganglionic blockade (hexamethonium 3.3 mg/kg) significantly reduced mean BP in the LPK (52 vs. Lewis 4%, n = 9, p < or = 0.05). CONCLUSION: Cyst formation is a key event in the genesis of hypertension while the sympathetic nervous system is important in the maintenance of hypertension in this model of ARPKD.

Impaired response of the denervated kidney to endothelin receptor blockade in normotensive and spontaneously hypertensive rats.

BACKGROUND: As yet, there are only limited data available on the exact role of endothelin (ET) acting through endothelin-A (ETA) receptors in renal sodium and water regulation and the potential functional implications of an interaction of the renal ET system with renal nerves in normotensive and spontaneously hypertensive rats. METHODS: Experiments were carried out in 64 male conscious spontaneously hypertensive rats and in 56 normotensive Wistar-Kyoto (WKY) rats. Bilateral renal denervation (BRD) was performed in 32 spontaneously hypertensive rats and 28 WKY rats 7 days before the experiments. The ETA receptor antagonist, BQ-123 (16.4 nmol/kg x min intravenously) or the endothelin-B (ETB) receptor antagonist, BQ-788 (25 nmol/kg x min intravenously) were infused at a rate of 25 microL/min for 50 minutes. RESULTS: Renal papillary ET-1 concentration in intact spontaneously hypertensive rats was 67.8% lower than in intact WKY rats (154 +/- 40 fmol/mg protein vs. 478 +/- 62 fmol/mg protein, P < 0.01). BRD decreased papillary ET-1 by 73.5% in WKY rats to 127 +/- 19 fmol/mg protein (P < 0.001), but had no effect in spontaneously hypertensive rats (122 +/- 37 fmol/mg protein). BRD, BQ-123, or BQ-788 did not affect glomerular filtration rate (GFR) or renal blood flow (RBF) in any of the groups. In intact WKY, BQ-123 decreased urine flow rate (V) from 4.65 +/- 0.44 microL/min.100 g body weight to 2.44 +/- 0.35 microL/min.100 g body weight (P < 0.01), urinary excretion of sodium (UNaV) from 238.2 +/- 27.4 to 100.2 +/- 17.0 (P < 0.01) and potassium (UKV) from 532.1 +/- 62.6 nmol/min.100 g body weight to 243.0 +/- 34.2 nmol/min.100 g body weight (P < 0.001), whereas BQ-788 decreased only V and UNaV. In renal denervated WKY, BQ-123 or BQ-788 did not alter V, UNaV, or UKV. In intact spontaneously hypertensive rats BQ-123 but not BQ-788 decreased V from 3.94 +/- 0.48 microL/min.100 g body weight to 2.55 +/- 0.44 microL/min.100 g body weight (P < 0.05). In renal denervated spontaneously hypertensive rats neither BQ-123 nor BQ-788 affected V, UNaV, or UKV. CONCLUSION: An interaction between ET and renal nerves is involved in the control of renal function. Moreover, renal nerves participate in the regulation of ET-1 production within the kidney. Finally, decreased synthesis of ET-1 in the renal papilla of spontaneously hypertensive rats may contribute to development and/or maintenance of hypertension due to modulation of renal excretory function.

Role of renal nerves in stimulation of renin, COX-2, and nNOS in rat renal cortex during salt deficiency.

We investigated a possible involvement of the sympathetic nervous system in the parallel increase of renin, cyclooxygenase-2 (COX-2), and neuronal nitric oxide synthase (nNOS) gene expression in the juxtaglomerular apparatus of rat kidneys induced by salt deficiency. Therefore, we determined the effects of renal denervation and the beta-adrenoreceptor antagonist metoprolol (50 mg/kg body wt po, twice a day) on renocortical expression of renin, COX-2, and nNOS in rats fed a low-salt (0.02% wt/wt) diet or treated for 1 wk with ramipril (10 mg/kg body wt) in combination with a low-salt diet. We found that a low-salt diet in combination with ramipril strongly increased renocortical mRNA levels of renin, COX-2, and nNOS 9-, 7-, and 2.5-fold, respectively. Treatment with metoprolol did not change basal expression of the three genes or induction of renin and COX-2 gene expression, while induction of nNOS expression was clearly attenuated. Similarly, unilateral renal denervation attenuated induction of nNOS expression but had no effect on all other parameters. These findings suggest that beta-adrenergic stimulation is not required for stimulation of renin and COX-2 gene expression in the juxtaglomerular apparatus during salt deficiency. However, beta-adrenoreceptor activity or renal nerve activity appears to be required for the full stimulation of nNOS expression by low salt intake or combined with angiotensin-converting enzyme inhibition.

Importance of the renal nerves for basal and stimulated renin mRNA levels in fetal and adult ovine kidneys.

OBJECTIVE: To investigate the effect of renal denervation on renin mRNA levels in fetal and nonpregnant adult ovine renocortical tissue and in isolated juxtaglomerular cells under basal conditions and after stimulation. METHODS: The left kidney was denervated and the right kidney subjected to a sham procedure in nine ovine fetuses (136-141 days' gestation) and 20 nonpregnant ewes. After 5-7 days the denervated and intact kidneys were obtained, and renin-containing renal cortical cells were isolated and cultured overnight. Then cells were treated with isoproterenol, forskolin, or isomethylbutyl xanthine (IBMX) for 4 hours. Total RNA was isolated and renin mRNA measured by RNase protection assay. Cyclic adenosine monophosphate (cAMP) levels were measured in the incubation medium with a competitive enzyme immunoassay. RESULTS: In adults, basal renin mRNA levels were significantly lower in denervated than in sham-operated kidneys. No difference was noted between denervated and intact fetal kidneys. Renin mRNA levels were significantly higher in fetal than in adult kidney tissue, and cells from fetuses had greater increases in renin mRNA after stimulation than did cells from adults. Fetal cells also released more cAMP into the incubation medium, and there was a correlation between cAMP and renin mRNA levels. CONCLUSIONS: The data indicate the effects of renal denervation on renin mRNA expression in the kidney are age dependent and that the fetus in late gestation has a mechanism for maintaining renin mRNA levels after denervation, which is absent or nonfunctional in the adult.

Differential control of intrarenal blood flow during reflex increases in sympathetic nerve activity.

The role of renal sympathetic nerve activity (RSNA) in the physiological regulation of medullary blood flow (MBF) remains ill defined, yet regulation of MBF may be crucial to long-term arterial pressure regulation. To investigate the effects of reflex increases in RSNA on intrarenal blood flow distribution, we exposed pentobarbital sodium-anesthetized, artificially ventilated rabbits (n = 7) to progressive hypoxia while recording RSNA, cortical blood flow (CBF), and MBF using laser-Doppler flowmetry. Another group of animals with denervated kidneys (n = 6) underwent the same protocol. Progressive hypoxia (from room air to 16, 14, 12, and 10% inspired O(2)) significantly reduced arterial oxygen partial pressure (from 99 +/- 3 to 65 +/- 2, 51 +/- 2, 41 +/- 1, and 39 +/- 2 mmHg, respectively) and significantly increased RSNA (by 8 +/- 3, 44 +/- 25, 62 +/- 21, and 76 +/- 37%, respectively, compared with room air) without affecting mean arterial pressure. There were significant reductions in CBF (by 2 +/- 1, 5 +/- 2, 11 +/- 3, and 14 +/- 2%, respectively) in intact but not denervated rabbits. MBF was unaffected by hypoxia in either group. Thus moderate reflex increases in RSNA cause renal cortical vasoconstriction, but not at vascular sites regulating MBF.

Differential neural control of intrarenal blood flow.

To test whether renal sympathetic nerve activity (RSNA) can differentially regulate blood flow in the renal medulla (MBF) and cortex (CBF) of pentobarbital sodium-anesthetized rabbits, we electrically stimulated the renal nerves while recording total renal blood flow (RBF), CBF, and MBF. Three stimulation sequences were applied 1) varying amplitude (0.5-8 V), 2) varying frequency (0.5-8 Hz), and 3) a modulated sinusoidal pattern of varying frequency (0. 04-0.72 Hz). Increasing amplitude or frequency of stimulation progressively decreased all flow variables. RBF and CBF responded similarly, but MBF responded less. For example, 0.5-V stimulation decreased CBF by 20 +/- 9%, but MBF fell by only 4 +/- 6%. The amplitude of oscillations in all flow variables was progressively reduced as the frequency of sinusoidal stimulation was increased. An increased amplitude of oscillation was observed at 0.12 and 0.32 Hz in MBF and to a lesser extent RBF, but not CBF. MBF therefore appears to be less sensitive than CBF to the magnitude of RSNA, but it is more able to respond to these higher frequencies of neural stimulation.

Downregulation of neuronal nitric oxide synthase in the rat remnant kidney.

Chronic renal failure is associated with disturbances in nitric oxide (NO) production. This study was conducted to determine the effect of 5/6 nephrectomy (5/6 Nx) on expression of intrarenal neuronal nitric oxide synthase (nNOS) in the rat. In normal rat kidney, nNOS protein was detected in the macula densa and in the cytoplasm and nuclei of cells of the inner medullary collecting duct by both immunofluorescence and electron microscopy. Western blot analysis revealed that 2 wk after 5/6 Nx, there were significant decreases in nNOS protein expression in renal cortex (sham: 95.42+/-15.60 versus 5/6 Nx: 47.55+/-12.78 arbitrary units, P<0.05, n = 4) and inner medulla (sham: 147.70+/-26.96 versus 5/6 Nx: 36.95+/-17.24 arbitrary units, P<0.005, n = 8). Losartan treatment was used to determine the role of angiotensin II (AngII) AT1 receptors in the inhibition of nNOS expression in 5/6 Nx. Losartan had no effect on the decreased expression of nNOS in the inner medulla, but partially increased nNOS protein expression in the cortex of 5/6 Nx rats. In contrast, in sham rats losartan significantly inhibited nNOS protein expression in the cortex (0.66+/-0.04-fold of sham values, P<0.05, n = 6) and inner medulla (0.74+/-0.12-fold of sham values, P<0.05, n = 6). nNOS mRNA was significantly decreased in cortex and inner medulla from 5/6 Nx rats, and the effects of losartan on nNOS mRNA paralleled those observed on nNOS protein expression. These data indicate that 5/6 Nx downregulates intrarenal nNOS mRNA and protein expression. In normal rats, AngII AT1 receptors exert a tonic stimulatory effect on expression of intrarenal nNOS. These findings suggest that the reduction in intrarenal nNOS expression in 5/6 Nx may play a role in contributing to hypertension and altered tubular transport responses in chronic renal failure.

Exaggerated natriuresis in transgenic (mRen2)27 rats.

BACKGROUND: Hypertension features an exaggerated natriuresis after acute volume expansion. In humans, the degree of exaggerated natriuresis appears to be correlated inversely to the level of angiotensin (Ang) II. OBJECTIVE: To test the hypothesis that the degree of exaggerated natruresis is correlated to the level of Ang II by studying two rat models, transgenic rats (TGR) with and extra renin gene (TGR mRen2)27 and desoxycorticosterone acetate (DOCA)-salt rats, in comparison with Sprague-Dawley Hannover (SDH) rat controls. METHODS: All of the rats were uninephrectomized for 1 month. DOCA-salt rats were implanted with a DOCA pallet and drank 1% saline. Rats were anesthetized and their left kidneys were instrumented with renal sympathetic nerve activity (RSNA) electrodes and laser-Doppler cortical and medullary flow probes. The glomerular filtration rate, diuresis, and natriuresis were measured for 120 min after sodium loading (5% body weight 0.9% saline administered during 3 min). Kidneys were examined histologically. RESULTS: The blood pressure in TGR and DOCA-salt rats was 40-50 mmHg higher than that in SDH rats, and decreased briefly after volume expansion for all groups. The diuresis and natriuresis of TGR and DOCA-salt rats were greater than those of SDH rats. The medullary blood flow increased and the cortical blood flow in SDH decreased, whereas the cortical blood flow in TGR and DOCA-salt rats remained high. The RSNA in rats of all groups decreased; however, this decrease was greater in SDH than it was in TGR and DOCA-salt rats. The histology was affected most severely for the DOCA-salt rats. CONCLUSIONS: Exaggerated natriuresis occurred in hypertensive rats regardless of their Ang II status. Both strains were characterized by a smaller decrease in RSNA and a preserved cortical blood flow in the face of volume expansion. These data do not support the notion that exaggerated natriuresis is a function of renin-level suppression for rats.

Neonatal ureteral obstruction stimulates recruitment of renin-secreting renal cortical cells.

Unilateral ureteral obstruction (UUO) in the neonate increases ipsilateral renal renin gene expression, an effect which is mediated by renal nerves. To determine whether neonatal UUO alters the number of renal cortical cells secreting renin and whether this change is modulated by renal nerve activity, newborn Sprague-Dawley rats were subjected to left UUO, right uninephrectomy, or sham operation and studied four weeks thereafter. To evaluate the importance of renal nerves in this response, an additional group of animals underwent chemical sympathectomy with guanethidine. Ureteral obstruction was associated with marked reduction in renal mass in the obstructed kidney and contralateral compensatory hypertrophy, changes which were not altered by sympathectomy. Renin messenger RNA and renal renin content were elevated in the obstructed kidney. The number of cells secreting renin, measured by the reverse hemolytic plaque assay, was markedly increased in the obstructed kidney (45 +/- 18 plaques/slide vs. 11 +/- 1 plaques/slide in sham animals), but not in the opposite kidney or following uninephrectomy. This effect was not significantly altered by sympathectomy. There was no change in the amount of renin secreted per cell or in the secretory response to Ca++. These results show that UUO results in recruitment of cells not previously secreting renin by a mechanism independent of renal nerve activity. This recruitment occurs without alteration of the quantity of renin secreted per cell or in the normal regulatory effect of Ca++ on renin secretion. An increase in the number of renin-secreting cells may contribute to the activation of the renin-angiotensin system, and thus to the vasoconstriction observed following ureteral obstruction.

Dopamine receptor modulation of noradrenaline release by carmoxirole in human cortical kidney slices.

The effect of the dopamine D2-receptor agonist carmoxirole on noradrenaline release was investigated in human and rat cortical kidney slices. After preincubation with 3H-noradrenaline, the slices were electrically stimulated at 5 Hz in superfusion chambers, and the stimulation-induced (S-I) outflow of radioactivity was taken as the index of noradrenaline release. In human but not in rat cortical kidney slices, carmoxirole (0.03 microM) inhibited the S-I outflow of radioactivity. Carmoxirole (0.3 microM) also failed to inhibit the S-I outflow of radioactivity from human kidney slices. When alpha-adrenoceptors were blocked by the non-selective alpha-adrenoceptor antagonist phentolamine (1 microM), carmoxirole (0.03 microM, 0.3 microM) inhibited S-I outflow to a similar extent. The inhibitory effect of carmoxirole (0.03 microM) was prevented by the D2-receptor antagonist (-)-sulpiride (10 microM) but not by the D1-receptor antagonist SCH 23390 (1 microM) in human kidney slices. Phentolamine (1 microM) by itself induced a five-fold greater enhancement of the S-I outflow of radioactivity in rat than in human cortical kidney slices. The data suggest that activation of prejunctional D2-receptors by carmoxirole inhibits noradrenaline release from human renal sympathetic nerves. Carmoxirole in higher concentrations (0.3 microM) blocks inhibitory prejunctional alpha-autoreceptors, which seems to mask the inhibitory D2-receptor mediated effect. The different effects of phentolamine and carmoxirole in human and rat kidney may indicate a difference of the prejunctional alpha-autoreceptor mechanism in the two species.

Two patterns of dopa decarboxylase immunoreactivity in sympathetic axons supplying rat renal cortex.

Three ultrastructural cytochemical methods have been used to classify the innervation of the rat renal cortex. Every axon seen contained chromaffin-reactive, dense core vesicles and stained for tyrosine hydroxylase, indicating that they were all catecholaminergic. About 10% of the axons associated with smooth muscle and juxtaglomerular cells of the arteriolar vessels also contained dopa decarboxylase, but this enzyme was not present in any of the peritubular axons. Our results are compatible with the possibility that, in the rat, the juxtaglomerular blood vessels, but not the renal tubules, are supplied by dopaminergic as well as by noradrenergic nerves.