Effect of sodium nitroprusside on norepinephrine overflow and antidiuresis induced by stimulation of renal nerves in anesthetized dogs

Effect of reactive oxygen species and nitric oxide in the neural control of intrarenal haemodynamics in anaesthetized normotensive rats

AIMS

This study examined the interaction between reactive oxygen species and nitric oxide (NO) in mediating the decrease in renal blood flow (RBF) evoked by sympathetic renal nerve stimulation (RNS).

METHODS

Groups of male Wistar rats were subjected to RNS at different frequencies prior to, and following, an infusion of: (i) tempol, the superoxide dismutase (SOD) mimetic, (ii) tempol plus the hydrogen peroxide-degrading enzyme catalase (tem + cat), (iii) diethyldithiocarbamic acid (DETC), a SOD inhibitor, (iv) the nitric oxide synthase (NOS) inhibitor, L-nitro-arginine methyl ester (L-NAME) alone, or (v) L-NAME followed by tempol, into the kidney cortico-medullary border (CMB). Blood perfusion within the cortical (CBP) and medullary (MBP) regions of the kidney was measured using Laser-Doppler flowmetry.

RESULTS

Infusion of tempol CMB significantly attenuated RNS-evoked reductions in CBP (by 22% at 8 Hz; P < 0.05), but not MBP. When tempol and catalase were co-infused to reduce both ROS and hydrogen peroxide (H2 O2 ), respectively, there was a significantly greater attenuation of the RNS-evoked reduction in CBP compared with that of tempol alone. Infusion of either DETC or L-NAME alone did not significantly affect the CBP or MBP responses to RNS. Similarly, RNS following tempol infusion with L-NAME also had no effect on CBP and MBP over and above the group that received tempol alone.

CONCLUSION

These results suggest that reactive oxygen species such as superoxide and H2 O2 have a direct role in reducing renal vascular compliance in response to RNS, rather than indirectly through scavenging NO.

Protective effect of 17β-estradiol on ischemic acute kidney injury through the renal sympathetic nervous system

Enhanced renal sympathetic nerve activity during an ischemic period and renal venous norepinephrine overflow after reperfusion play important roles in the development of ischemic acute kidney injury. In this study, we examined the effect of 17β-estradiol on the renal sympathetic nervous system and kidney function in ischemia/reperfusion-induced acute kidney injury in anesthetized rats. Ischemic acute kidney injury was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after a contralateral nephrectomy. Intravenous injection of 17β-estradiol (100 μg/kg) 15 min before reperfusion suppressed enhanced renal sympathetic nerve activity during renal ischemia, also suppressed renal venous norepinephrine overflow after reperfusion, and attenuated ischemia/reperfusion-induced renal dysfunction with histological damage. The above renoprotective effects of 17β-estradiol were reversed by pretreatment with tamoxifen (5 mg/kg), an estrogen receptor antagonist, or N(G)-nitro-L-arginine methyl ester (0.3 mg/kg), a non-selective nitric oxide synthase inhibitor. These results indicate that 17β-estradiol can suppress enhanced renal sympathetic nerve activity during renal ischemia, and its consequent effect on norepinephrine overflow from nerve endings, by nitric oxide production via estrogen receptors. These effects appear to contribute to renoprotection against ischemia/reperfusion-induced renal injury.

Nitric oxide inhibition and the impact on renal nerve-mediated antinatriuresis and antidiuresis in the anaesthetized rat

The contribution of nitric oxide (NO) to the antinatriuresis and antidiuresis caused by low-level electrical stimulation of the renal sympathetic nerves (RNS) was investigated in rats anaesthetized with chloralose-urethane. Groups of rats, n= 6, were given i.v. infusions of vehicle, l-NAME (10 microg kg(-1) min(-1)), 1400W (20 microg kg(-1) min(-1)), or S-methyl-thiocitrulline (SMTC) (20 microg kg(-1) min(-1)) to inhibit NO synthesis non-selectively or selectively to block the inducible or neuronal NOS isoforms (iNOS and nNOS, respectively). Following baseline measurements of blood pressure (BP), renal blood flow (RBF), glomerular filtration rate (GFR), urine flow (UV) and sodium excretion (U(Na)V), RNS was performed at 15 V, 2 ms duration with a frequency between 0.5 and 1.0 Hz. RNS did not cause measurable changes in BP, RBF or GFR in any of the groups. In untreated rats, RNS decreased UV and U(Na)V by 40-50% (both P < 0.01), but these excretory responses were prevented in l-NAME-treated rats. In the presence of 1400W i.v., RNS caused reversible reductions in both UV and U(Na)V of 40-50% (both P < 0.01), while in SMTC-treated rats, RNS caused an inconsistent fall in UV, but a significant reduction (P < 0.05) in U(Na)V of 21%. These data demonstrated that the renal nerve-mediated antinatriuresis and antidiuresis was dependent on the presence of NO, generated in part by nNOS. The findings suggest that NO importantly modulates the neural control of fluid reabsorption; the control may be facilitatory at a presynaptic level but inhibitory on tubular reabsorptive processes.

Angiotensin II and nitric oxide in neural control of intrarenal blood flow

We investigated the roles of the renin-angiotensin system and the significance of interactions between angiotensin II and nitric oxide, in responses of regional kidney perfusion to electrical renal nerve stimulation (RNS) in pentobarbital sodium-anesthetized rabbits. Under control conditions, RNS (0.5–8 Hz) reduced total renal blood flow (RBF; −89 ± 3% at 8 Hz) and cortical perfusion (CBF; −90 ± 2% at 8 Hz) more than medullary perfusion (MBF; −55 ± 5% at 8 Hz). Angiotensin II type 1 (AT1)-receptor antagonism (candesartan) blunted RNS-induced reductions in RBF ( P = 0.03), CBF ( P = 0.007), and MBF ( P = 0.04), particularly at 4 and 8 Hz. Nitric oxide synthase inhibition with NG-nitro-l-arginine (l-NNA) enhanced RBF ( P = 0.003), CBF ( P = 0.001), and MBF ( P = 0.03) responses to RNS, particularly at frequencies of 2 Hz and less. After candesartan pretreatment, l-NNA significantly enhanced RNS-induced reductions in RBF ( P = 0.04) and CBF ( P = 0.007) but not MBF ( P = 0.66). Renal arterial infusion of angiotensin II (5 ng·kg−1·min−1) selectively enhanced responses of MBF to RNS in l-NNA-pretreated but not in vehicle-pretreated rabbits. In contrast, greater doses of angiotensin II (5–15 ng·kg−1·min−1) blunted responses of MBF to RNS in rabbits with intact nitric oxide synthase. These results suggest that endogenous angiotensin II enhances, whereas nitric oxide blunts, neurally mediated vasoconstriction in the renal cortical and medullary circulations. In the renal medulla, but not the cortex, angiotensin II also appears to be able to blunt neurally mediated vasoconstriction.

Prostaglandins and nitric oxide in regional kidney blood flow responses to renal nerve stimulation

We examined the roles of cyclooxygenase products and of interactions between the cyclooxygenase and nitric oxide systems in the mechanisms underlying the relative insensitivity of medullary perfusion to renal nerve stimulation (RNS) in anaesthetized rabbits. To this end we examined the effects of ibuprofen and N(G)-nitro-L: -arginine (L-NNA), both alone and in combination, on the responses of regional kidney perfusion to RNS. Under control conditions, RNS produced frequency-dependent reductions in total renal blood flow (RBF; -82+/-3% at 6 Hz), cortical laser-Doppler flux (CLDF; -84+/-4% at 6 Hz) and, to a lesser extent, medullary laser-Doppler flux (MLDF; -46+/-7% at 6 Hz). Ibuprofen did not affect these responses significantly, suggesting that cyclooxygenase products have little net role in modulating renal vascular responses to RNS. L-NNA enhanced RBF (P=0.002), CLDF (P=0.03) and MLDF (P=0.03) responses to RNS. As we have shown previously, this effect of L-NNA was particularly prominent for MLDF at RNS frequencies < or = 1.5 Hz. Subsequent administration of ibuprofen, in L-NNA-pretreated rabbits, did not affect responses to RNS significantly. We conclude that counter-regulatory actions of NO, but not of prostaglandins, partly underlie the relative insensitivity of medullary perfusion to renal nerve activation.

Nitric oxide and renal nerves: Comparison of effects on renal circulation and sodium excretion in anesthetized rats

BACKGROUND

An array of vasoconstrictor and vasodilator agents have the potential to control intrarenal circulation; however, their relative functional importance is unclear. We compared here the importance of nitric oxide and renal nerves in studies involving sequential blockade of nitric oxide synthesis and renal denervation.

METHODS

In anesthetized rats, N-nitro-L-arginine methylester (L-NAME) was used for nonselective inhibition of nitric oxide synthesis and 7-nitroindazole (7-NI) for inactivation of neuronal isoform of nitric oxide synthase (nNOS). Acute unilateral renal denervation was performed noninvasively enabling observation of rapid changes. Renal cortical and medullary blood flow was determined by laser Doppler flowmetry.

RESULTS

L-NAME decreased medullary blood flow and cortical blood flow, by 22% to 24%, whereas after 7-NI, medullary blood flow decreased by 22% and cortical blood flow about 10% (all changes significant). In untreated rats denervation significantly increased cortical blood flow (10% to 15%) but not medullary blood flow. In rats treated with L-NAME denervation partly prevented the post-inhibitor decrease in cortical blood flow but not in medullary blood flow. After 7-NI treatment, the decrease in cortical blood flow and medullary blood flow did not occur or a partial restoration of flow was seen. The denervation natriuresis was intact under L-NAME but attenuated following 7-NI.

CONCLUSION

A reduction of medullary blood flow after 7-NI, similar as after L-NAME, suggests that nitric oxide generated by nNOS is mainly responsible for adequate perfusion of the medulla whereas activity of nNOS and other isoform(s) is required to maintain cortical blood flow. Renal denervation partly restored cortical blood flow reduced by nitric oxide blockade. For medullary blood flow, such restoration was seen only after inactivation of nNOS alone, suggesting an intrinsic interaction of this isoform and renal nerves.

Parentally biased favouritism: why should parents specialize in caring for different offspring?

'Parentally biased favouritism' occurs when the two parents differentially care for individual offspring or kinds of offspring. Examples in birds include brood division and differential investment by the two parents in relation to the size or sex of the offspring. This paper uses mathematical models to investigate which ideas can, in theory, explain parentally biased favouritism. One previous explanation is that the parents differ in their cost of reproduction and that the parent who consequently invests least concentrates its care on the more valuable offspring. However, a mathematical model predicts the total care given by each parent and received by each offspring, not how much each parent cares for each offspring, and hence does not explain parentally biased favouritism. Parentally biased favouritism towards particular types of offspring can be explained by a difference between the parents in the benefits of caring for a given type of offspring or in the effort incurred in providing care to a given type of offspring, but then it is extreme, with at least one of the parents providing care to only one type of offspring. Parentally biased favouritism towards particular individual offspring (brood division) can be explained by parent-offspring conflict or sexual conflict.

Nitric oxide modulation of neurally induced proximal tubular fluid reabsorption in the rat

This study investigated the role of NO in mediating the renal sympathetic nerve-mediated increases in proximal tubular fluid reabsorption (Jva). In inactin-anesthetized Wistar rats, renal sympathetic nerve stimulation (15 V, 2 ms) at 0.75 and 1.0 Hz did not change blood pressure or glomerular filtration rate but did decrease urine flow and sodium excretion in a frequency-related fashion by 40% to 50% at 1.0 Hz (both, P<0.01). Renal nerve stimulation in control animals increased Jva by 11% at 0.75 Hz (P<0.05) and 31% at 1.0 Hz (P<0.01). Intraluminal N(omega)-nitro-L-arginine methyl ester (L-NAME) resulted in a higher basal Jva (19%, P<0.05), and renal nerve stimulation had no effect on Jva. When L-NAME plus sodium nitroprusside was present intraluminally, however, there were frequency-dependent increases in Jva that were similar in pattern and magnitude to the control rats. Introduction of the relatively selective nNOS blocker 7-nitroindazole intraluminally, at 10(-6) and 10(-4) M, raised basal Jva by 18% and 24%, respectively (P<0.01), and renal nerve stimulation did not change Jva. Intraluminal aminoguanidine (10(-4) M), a relatively selective iNOS blocker, did not affect basal Jva, which remained unchanged during renal nerve stimulation. These data are consistent with NO exerting a tonic inhibitory action on the basal levels of Jva, which, in part, is caused by NO generated by the nNOS isoform. Moreover, the findings have revealed that the presence of NO is necessary to ensure that renal nerves can stimulate fluid reabsorption by the proximal tubules, requiring NO generated from both nNOS and iNOS.

Effects of bradykinin on renal nerve stimulation-induced antidiuresis and norepinephrine overflow in anesthetized dogs

We examined effects of bradykinin on antidiuresis and norepinephrine overflow induced by renal nerve stimulation (RNS) in anesthetized dogs, with or without blockade of the B2 receptor by Hoe 140 (D-Arg-[Hyp3, Thi5, D-Tic7, Oic8]bradykinin) or the endogenous nitric oxide generation by N(G)nitro-L-arginine (NOARG), a nitric oxide synthase inhibitor. RNS (0.5-2.0 Hz) produced significant decreases in urine flow, urinary and fractional excretions of sodium, and increases in norepinephrine secretion rate (NESR), without affecting systemic and renal hemodynamics. Intrarenal arterial infusion of bradykinin (5 ng/kg per minute) significantly suppressed the RNS-induced antidiuresis and increase in NESR. Hoe 140 (100 ng/kg per minute) did not affect the RNS-induced renal actions, but in the presence of Hoe 140, bradykinin-induced suppressive actions on reductions in urine formation and increases in NESR in response to RNS were abolished. RNS during intrarenal arterial infusion of NOARG (40 microg/kg per minute) led to potent reductions in urine formation and decreased renal blood flow and glomerular filtration rate. Simultaneously, NESR was markedly increased. During NOARG infusion, bradykinin-induced decreases in renal actions elicited by RNS were markedly attenuated. These findings suggest that bradykinin suppresses the RNS-induced norepinephrine overflow and renal actions via nitric oxide production mediated by activation of B2 receptor. Renal noradrenergic neurotransmission may be inhibited by bradykinin at the prejunctional level, when its local production in the kidney is enhanced.

Intensity of nest defence is related to offspring sex ratio in the great tit Parus major

Nest-defence behaviour of passerines is a form of parental investment. Parents are selected, therefore, to vary the intensity of their nest defence with respect to the value of their offspring. Great tit, Parus major, males were tested for their defence response to both a nest predator and playback of a great tit chick distress call. The results from the two trials were similar; males gave more alarm calls and made more perch changes if they had larger broods and if they had a greater proportion of sons in their brood. This is the first evidence for a relationship between nest-defence intensity and offspring sex ratio. Paternal quality, size, age and condition, lay date and chick condition did not significantly influence any of the measured nest-defence parameters.

Effects of sodium nitroprusside on renal functions and NO-cGMP production in anesthetized dogs

Although the renal nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) system plays an important role in maintaining urinary sodium and water excretion, effects of an authentic NO donor sodium nitroprusside (SNP) on urine formation have been controversial. In this study, we examined whether SNP increases renal NO release and cGMP production and induces natriuresis in the denervated kidney of anesthetized dogs. The intrarenal arterial infusion of SNP at 10, 30, and 100 ng/kg/min did not affect renal function or NO-cGMP production. The higher dose of SNP (1,000 ng/kg/min) reduced systemic blood pressure and urine flow rate. The antidiuresis was observed also in the contralateral control kidney, the degree of which was larger than that observed in the ipsilateral SNP-infused kidney. During the SNP infusion, reductions in urinary Na+ excretion, fractional Na+ excretion, and urinary nitrite + nitrate excretion occurred in the control kidney but not in the SNP-infused kidney. Urinary cGMP excretion and renal venous plasma cGMP concentration were significantly increased during the SNP infusion in the SNP-infused kidney but not in the control kidney. These renal effects of SNP were similar to those obtained by intrarenal arterial infusion of a specific NO donor, NOC 7 (300 ng/kg/min). These results suggest that SNP can produce nitric oxide and increase cGMP levels in the kidney and suppress sodium reabsorption, but the natriuretic property of SNP may be masked by its counteracting effects including the systemic hypotension in anesthetized dogs.

Effects of zaprinast on renal nerve stimulation-induced anti-natriuresis in anaesthetized dogs

1. We examined whether zaprinast, a putative cGMP-specific phosphodiesterase inhibitor, affects neural control of renal function in pentobarbital-anaesthetized dogs. 2. Renal nerve stimulation (1 Hz, 1 ms duration) reduced urine flow rate, urinary Na+ excretion (UNaV) and fractional excretion of Na+ (FENa) with little change in either renal blood flow (RBF) or glomerular filtration rate (GFR). 3. Intrarenal arterial infusion of zaprinast (10 and 100 micrograms/kg per min) increased basal urine flow rate, UNaV and FENa but not RBF or GFR. Zaprinast infusion (100 micrograms/kg per min) also increased renal venous plasma cGMP concentration and urinary cGMP excretion. 4. Renal nerve stimulation-induced reductions in UNaV and FENa were attenuated during zaprinast infusion, whereas the reduction in urine flow rate was resistant to zaprinast. 5. Renal nerve stimulation increased the renal venous plasma noradrenaline concentration and renal noradrenaline efflux, which remained unaffected during infusion of zaprinast (100 micrograms/kg per min). 6. The results of the present study suggest that zaprinast induces natriuresis and counteracts adrenergically induced antinatriuresis by acting on renal tubular sites in the dog kidney in vivo.

Effects of FK409, a nitric oxide donor, on renal responses to renal nerve stimulation in anesthetized dogs

We examined the effects of (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409), a nitric oxide (NO) donor, on renal actions and norepinephrine overflow induced by renal nerve stimulation in anesthetized dogs, with or without N(G)-nitro-L-arginine (NOARG), a NO synthase inhibitor. Renal nerve stimulation at a low frequency (0.5-2.0 Hz) produced significant decreases in urine flow and urinary excretion of Na+ and increases in norepinephrine secretion rate. Renal nerve stimulation at a high frequency (2.5-5.0 Hz) which diminishes renal hemodynamics, elicited more marked decreases in urine formation and increases in norepinephrine secretion rate. Intrarenal arterial infusion of FK409 (0.25 microg/kg/min) failed to alter renal actions and increases in norepinephrine secretion rate in response to both low- and high frequency renal nerve stimulation. When NOARG (40 microg/kg/min) was administrated intrarenally, low-frequency renal nerve stimulation caused a potent antidiuresis and renal vasoconstriction. The renal nerve stimulation-induced increase in norepinephrine secretion rate was markedly enhanced by NOARG infusion. Simultaneous infusion of FK409 markedly attenuated the NOARG-induced enhancement of renal actions and increases in norepinephrine secretion rate, in response to low-frequency renal nerve stimulation. These results suggest that exogenous NO suppresses the renal nerve stimulation-induced norepinephrine overflow and renal actions in NO-depleted conditions. We also propose that endogenous NO functions tonically as an inhibitory modulator of renal noradrenergic neurotransmission.

Involvement of nitric oxide in endothelin ETB receptor-mediated inhibitory actions on antidiuresis and norepinephrine overflow induced by stimulation of renal nerves in anesthetized dogs

We examined the effect of sarafotoxin S6c (S6c), a selective endothelin ETB-receptor agonist, on renal actions and norepinephrine (NE) overflow induced by renal nerve stimulation (RNS) in anesthetized dogs, with or without blockade of endogenous nitric oxide (NO) generation by NG-nitro-L-arginine (NOARG), a NO synthase inhibitor. RNS (0.5-2.0 Hz) produced significant decreases in urine flow, urinary and fractional excretion of sodium, and increased NE secretion rate, without affecting systemic and renal hemodynamics. When S6c (1 ng/kg/min) was infused intrarenally, there was a slight and transient increase in renal blood flow at 1-2 min after the start of the infusion, without any change in systemic hemodynamics and this response was followed by a gradual reduction. There was a significant increase in the basal level of urine flow with no effects on urinary and fractional excretion of sodium. In addition, S6c administration elicited an increase in urinary excretion of NO metabolites. NO2- and NO3-. During S6c infusion, RNS-induced antidiuretic action and increases in NE secretion rate were significantly attenuated. RNS during intrarenal arterial infusion of NOARG (40 micrograms/kg/min) led to potent reductions in urine formation and decreased renal blood flow and glomerular filtration rate. Simultaneously. NE secretion rate was markedly increased. In the presence of NOARG, S6c-induced suppressive actions on reductions in urine formation and increase in NE secretion rate in response to RNS were markedly attenuated. The peptide did not increase urinary excretion of NO metabolites. These findings suggest that ET functions as an inhibitory modulator of renal noradrenergic neurotransmission through ETB-receptor mechanisms, events that may be caused by NO production induced by the peptide.

Neural control of renal function

The renal nerves are the communication link between the central nervous system and the kidney. In response to multiple peripheral and central inputs, efferent renal sympathetic nerve activity is altered so as to convey information to the major structural and functional components of the kidney, the vessels, glomeruli, and tubules, each of which is innervated. At the level of each of these individual components, information transfer occurs via interaction of the neurotransmitter released at the sympathetic nerve terminal-neuroeffector junction with specific postjunctional receptors coupled to defined intracellular signaling and effector systems. In response to normal physiological stimuli, changes in efferent renal sympathetic nerve activity contribute importantly to homeostatic regulation of renal blood flow, glomerular filtration rate, renal tubular epithelial cell solute and water transport, and hormonal release. Afferent input from sensory receptors located in the kidney participates in this reflex control system via renorenal reflexes that enable total renal function to be self-regulated and balanced between the two kidneys. In pathophysiological conditions, abnormal regulation of efferent renal sympathetic nerve activity contributes significantly to the associated abnormalities of renal function which, in turn, are of importance in the pathogenesis of the disease.

Inhibitory effects of endothelin-3 on antidiuresis and norepinephrine overflow induced by stimulation of renal nerves in anesthetized dogs

The effects of endothelin-3 (ET-3) on changes in renal hemodynamics, urine formation, and norepinephrine (NE) overflow induced by renal nerve stimulation (RNS) were examined in anesthetized dogs. RNS at a low frequency (0.5-2.0 Hz) produced significant decreases in urine flow (UF), urinary excretion of sodium (UNaV), and fractional excretion of sodium (FENa), and increased the NE secretion rate (NESR) without affecting systemic or renal hemodynamics. RNS at a high frequency (2.5-5.0 Hz), which diminishes renal hemodynamics by causing renal vasoconstriction, affected urine formation and NESR more potently than did low-frequency RNS. When ET-3 (2.0 ng/kg/min) was infused into the renal artery, there was a slight and transient increase in renal blood flow (RBF); this response was followed by a gradual reduction. ET-3 infusion tended to increase the basal levels of UF without affecting UNaV, indicating the excretion of hypotonic urine with administration of this peptide. During ET-3 infusion, low-frequency RNS-induced antidiuretic action was significantly attenuated. Simultaneously, increase in NESR elicited by low-frequency RNS was markedly suppressed. Qualitatively similar results were observed in the case of high-frequency RNS. In addition, high-frequency RNS-induced decreases in the glomerular filtration rate (GFR) and the filtration fraction (FF) were suppressed by ET-3 infusion. These findings suggest that ET-3 suppresses renal responses to stimulated renal noradrenergic neurotransmission by inhibiting the release of NE. These findings, together with our previous findings, suggest that ET-3 (and/or ET-1) functions as an inhibitory modulator of the renal noradrenergic nervous system through the prejunctional ETB-receptor mechanism.