Renal neurogenic mediation of intracerebroventricular angiotensin II hypertension in rats raised on high sodium chloride diet

TRPV1 (Transient Receptor Potential Vanilloid 1) Cardiac Spinal Afferents Contribute to Hypertension in Spontaneous Hypertensive Rat

Hypertension is associated with increased sympathetic activity. A component of this sympathoexcitation may be driven by increased signaling from sensory endings from the heart to the autonomic control areas in the brain. This pathway mediates the so-called cardiac sympathetic afferent reflex, which is also activated by coronary ischemia or other nociceptive stimuli in the heart. The cardiac sympathetic afferent reflex has been shown to be enhanced in the heart failure state and in renal hypertension. However, little is known about its role in the development or progression of hypertension or the phenotype of the sensory endings involved. To investigate this, we used the selective afferent neurotoxin, resiniferatoxin (RTX) to chronically abolish the cardiac sympathetic afferent reflex in 2 models of hypertension; the spontaneous hypertensive rats (SHRs) and AngII (angiotensin II) infusion (240 ng/kg per min). Blood pressure (BP) was measured in conscious animals for 2 to 8 weeks post-RTX. Epidural application of RTX to the T1-T4 spinal segments prevented the further BP increase in 8-week-old SHR and lowered BP in 16-week-old SHR. RTX did not affect BP in Wistar-Kyoto normotensive rats nor in AngII-infused rats. Epicardial application of RTX (50 µg/mL) in 4-week-old SHR prevented the BP increase whereas this treatment does not lower BP in 16-week-old SHR. When RTX was administered into the L2-L5 spinal segments of 16-week-old SHR, no change in BP was observed. These findings indicate that signaling via thoracic afferent nerve fibers may contribute to the hypertension phenotype in the SHR but not in the Ang II infusion model of hypertension.

Role of afferent and efferent renal nerves in the development of AngII-salt hypertension in rats

Hypertension is the leading modifiable risk factor for death worldwide, yet the causes remain unclear and treatment remains suboptimal. Catheter-based renal denervation (RDNX) is a promising new treatment for resistant hypertension, but the mechanisms underlying its antihypertensive effect remain unclear. We recently found that RDNX attenuates deoxycorticosterone acetate-salt hypertension and that this is dependent on ablation of afferent renal nerves and is associated with decreased renal inflammation. To determine if this is common to other models of salt-sensitive hypertension, rats underwent complete RDNX (n = 8), selective ablation of afferent renal nerves (n = 8), or sham denervation (n = 8). Mean arterial pressure (MAP) and heart rate were measure by telemetry and rats were housed in metabolic cages for measurement of sodium and water balance. Rats were then subjected to angiotensin II (AngII)-salt hypertension (10 ng/kg/min, intravenous + 4% NaCl diet) for 2 weeks. At the end of the study, renal T-cell infiltration was quantified by flow cytometry. AngII resulted in an increase in MAP of ~50 mmHg in all three groups with no between group differences, and a transient bradycardia that was blunted by selective ablation of afferent renal nerves. Sodium and water balance were unaffected by AngII-salt treatment and similar between groups. Lastly, AngII infusion was not associated with T-cell infiltration into the kidneys, and T-cell counts were unaffected by the denervation procedures. These results suggest that AngII-salt hypertension in the rat is not associated with renal inflammation and that neither afferent nor efferent renal nerves contribute to this model.

Central TrkB blockade attenuates ICV angiotensin II-hypertension and sympathetic nerve activity in male Sprague-Dawley rats

Increased sympathetic nerve activity and the activation of the central renin-angiotensin system are commonly associated with cardiovascular disease states such as hypertension and heart failure, yet the precise mechanisms contributing to the long-term maintenance of this sympatho-excitation are incompletely understood. Due to the established physiological role of neurotrophins contributing toward neuroplasticity and neuronal excitability along with recent evidence linking the renin-angiotensin system and brain-derived neurotrophic factor (BDNF) along with its receptor (TrkB), it is likely the two systems interact to promote sympatho-excitation during cardiovascular disease. However, this interaction has not yet been fully demonstrated, in vivo. Thus, we hypothesized that central angiotensin II (Ang II) treatment will evoke a sympatho-excitatory state mediated through the actions of BDNF/TrkB. We infused Ang II (20ng/min) into the right lateral ventricle of male Sprague-Dawley rats for twelve days with or without the TrkB receptor antagonist, ANA-12 (50ng/h). We found that ICV infusion of Ang II increased mean arterial pressure (+40.4mmHg), increased renal sympathetic nerve activity (+19.4% max activity), and induced baroreflex dysfunction relative to vehicle. Co-infusion of ANA-12 attenuated the increase in blood pressure (-20.6mmHg) and prevented the increase in renal sympathetic nerve activity (-22.2% max) and baroreflex dysfunction relative to Ang II alone. Ang II increased thirst and decreased food consumption, and Ang II+ANA-12 augmented the thirst response while attenuating the decrease in food consumption. We conclude that TrkB signaling is a mediator of the long-term blood pressure and sympathetic nerve activity responses to central Ang II activity. These findings demonstrate the involvement of neurotrophins such as BDNF in promoting Ang II-induced autonomic dysfunction and further implicate TrkB signaling in modulating presympathetic autonomic neurons during cardiovascular disease.

Renal Nerves and Long-Term Control of Arterial Pressure

The objective of this review is to provide an in-depth evaluation of how renal nerves regulate renal and cardiovascular function with a focus on long-term control of arterial pressure. We begin by reviewing the anatomy of renal nerves and then briefly discuss how the activity of renal nerves affects renal function. Current methods for measurement and quantification of efferent renal-nerve activity (ERNA) in animals and humans are discussed. Acute regulation of ERNA by classical neural reflexes as well and hormonal inputs to the brain is reviewed. The role of renal nerves in long-term control of arterial pressure in normotensive and hypertensive animals (and humans) is then reviewed with a focus on studies utilizing continuous long-term monitoring of arterial pressure. This includes a review of the effect of renal-nerve ablation on long-term control of arterial pressure in experimental animals as well as humans with drug-resistant hypertension. The extent to which changes in arterial pressure are due to ablation of renal afferent or efferent nerves are reviewed. We conclude by discussing the importance of renal nerves, relative to sympathetic activity to other vascular beds, in long-term control of arterial pressure and hypertension and propose directions for future research in this field. © 2017 American Physiological Society. Compr Physiol 7:263-320, 2017.

Effects of salt intake and potassium supplementation on renalase expression in the kidneys of Dahl salt-sensitive rats

Renalase is currently the only known amine oxidase in the blood that can metabolize catecholamines and regulate sympathetic activity. High salt intake is associated with high blood pressure (BP), possibly through the modulation of renalase expression and secretion, whereas potassium can reverse the high salt-mediated increase in blood pressure. However, whether potassium could also modulate BP through renalase is unclear. In this study, we aim to investigate how salt intake and potassium supplementation affect the level of renalase in rats. Eighteen salt-sensitive (SS) and 18 SS-13BN rats were divided into six groups, receiving normal salt (0.3% NaCl), high salt (8% NaCl) and high salt/potassium (8% NaCl and 8% KCl) dietary intervention for four weeks. At the end of experiments, blood and kidneys were collected for analysis. mRNA level of renalase was measured by quantitative real-time PCR and protein level was determined by Western blot. We found that mRNA and protein levels of renalase in the kidneys of SS and SS-13BN rats were significantly decreased (P < 0.05) after high salt intervention, whereas dopamine in plasma was increased (P < 0.05) compared with rats received normal salt, suggesting that salt may induce salt-sensitive hypertension through inhibition of renalase expression. We also found increased mRNA level and protein level of renalase, decreased catecholamine levels in plasma, and decreased BP in SS rats treated with high salt/potassium, compared with that of the high salt SS group. Taken together, the salt-induced increase and potassium-induced decrease in BP could be mediated through renalase. More studies are needed to confirm our findings and understand the underlying mechanisms.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Acute cannabinoid receptor type 1 (CB1R) modulation influences insulin sensitivity by an effect outside the central nervous system in mice

AIMS/HYPOTHESIS

Modulation of central nervous system (CNS) and extra-CNS cannabinoid receptor type 1 (CB1R) affects metabolic conditions, independently of weight loss. Here we examined the relative contributions of acute CNS and extra-CNS CB1R modulation on insulin sensitivity using pharmacological gain- and loss-of-function of CB1R in mice.

METHODS

We assessed the effects of acute modulation of CB1R on insulin sensitivity and tissue glucose uptake by administering a CB1R agonist (HU210) and antagonist (AM251) (vs vehicle) i.v. in wild-type mice. In addition, we administered a CB1R agonist (vs vehicle) systemically (i.v.) to Cb1r (also known as Cnr1) knockout (Cb1r (-/-)) mice or intracerebroventricularly (i.c.v.) in wild-type mice to elucidate the peripheral vs CNS-mediated regulatory effect of CB1R on insulin sensitivity.

RESULTS

HU210 induced significant insulin resistance in wild-type mice with a reduction of whole-body glucose disappearance rate and muscle Akt phosphorylation, as well as of glucose uptake by skeletal muscle, but not by adipose tissue, changes that were prevented by pretreatment with AM251. HU210 did not affect insulin sensitivity in Cb1r (-/-) mice, suggesting that the observed effects were mediated through CB1R. HU210 administered i.c.v. did not induce insulin resistance, suggesting that acute stimulation of CNS CB1R was not required for this effect.

CONCLUSIONS/INTERPRETATION

Skeletal muscle insulin sensitivity is affected by acute CB1R modulation. These changes are mediated by extra-CNS CB1R, probably by the receptors in skeletal muscle tissue.

Enhanced responses to ganglion blockade do not reflect sympathetic nervous system contribution to angiotensin II-induced hypertension

OBJECTIVE

We examined whether a specific increase in sympathetic nervous system (SNS) activity accounts for the enhanced depressor response to ganglion blockade in angiotensin II (AngII)-induced hypertension in rabbits or whether it reflects a general increased sensitivity of arterial pressure to vasodilatation.

METHODS

Rabbits were renal denervated or sham-operated and 2 weeks later AngII (50 ng/kg per min) infusion commenced. Mean arterial pressure (MAP) responses to ganglion blockade (pentolinium) and vasodilators nitroprusside and adenosine were measured 2-4 weeks later.

RESULTS

Basal MAP was 74 +/- 2 mmHg and maximum hypotensive responses to pentolinium, nitroprusside and adenosine were -17 +/- 2, -17 +/- 1 and -21 +/- 2 mmHg. AngII increased MAP similarly in intact and renal denervated rabbits (+25 +/- 4 mmHg and +31 +/- 4 mmHg, respectively). In intact rabbits, depressor responses to pentolinium were augmented by 75% during AngII infusion but responses to vasodilators also increased by 73-106% suggesting general augmentation of vascular reactivity rather than a specific increase in SNS neural activity. Consistent with this notion, total noradrenaline spillover was similar in normal and AngII-treated rabbits. In renal denervated rabbits, AngII enhanced depressor responses to vasodilators but not pentolinium, suggesting that sympathetic activity may be reduced by AngII hypertension when renal nerves are absent. In anaesthetized rabbits, methoxamine-induced decreases in hindlimb vascular conductance were greater in hypertensive than normotensive rabbits suggesting the presence of vascular hypertrophy of sufficient magnitude to explain increased responses to ganglion blockade and vasodilators.

CONCLUSION

Enhanced depressor responses to ganglion blockade in AngII hypertension do not reflect augmented SNS activity, but rather, augmented sympathetic vasoconstriction mediated by a vascular amplifier effect.

Losartan improves impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type 1 diabetic rats

We examined whether activation of angiotensin-1 receptors (AT1R) could account for impaired responses of cerebral arterioles during type 1 diabetes (T1D). First, we measured responses of cerebral arterioles in nondiabetic rats to eNOS-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists before and during application of angiotensin II. Next, we examined whether losartan could improve impaired responses of cerebral arterioles during T1D. In addition, we harvested cerebral microvessels for Western blot analysis of AT1R protein and measured production of superoxide anion by brain tissue under basal conditions and in response to angiotensin II in the absence or presence of losartan. We found that angiotensin II specifically impaired eNOS-dependent reactivity of cerebral arterioles. In addition, while losartan did not alter responses in nondiabetics, losartan restored impaired eNOS-dependent vasodilatation in diabetics. Further, AT1R protein was higher in diabetics compared to nondiabetics. Finally, superoxide production was higher in brain tissue from diabetics compared to nondiabetics under basal conditions, angiotensin II increased superoxide production in nondiabetics and diabetics, and losartan decreased basal (diabetics) and angiotensin II-induced production of superoxide (nondiabetics and diabetics). We suggest that activation of AT1R during T1D plays a critical role in impaired eNOS-dependent dilatation of cerebral arterioles.

Angiotensin II-based hypertension and the sympathetic nervous system: the role of dose and increased dietary salt in rabbits

There is accumulating evidence that angiotensin II may exert its hypertensive effect through increasing sympathetic drive. However, this action may be dependent on the dose of angiotensin II as well as salt intake. We determined the effect of different doses of angiotensin II and different levels of salt intake on neurogenic pressor activity. We also examined the effect of renal denervation. New Zealand White rabbits were instrumented to continuously measure arterial pressure. The depressor response to the ganglionic blocker pentolinium tartrate (5 mg kg(-1)) was used to assess pressor sympathetic drive on days 0, 7 and 21 of a 20 or 50 ng kg(-1) min(-1) continuous i.v. angiotensin II infusion. A 50 ng kg(-1) min(-1) infusion caused an immediate increase in pressure (23 +/- 5 mmHg), whereas a 20 ng kg(-1) min(-1) infusion caused a slow increase in pressure, peaking by day 12 (17 +/- 4 mmHg). The ganglionic blockade profiles indicated sympathoinhibition in the 50 ng kg(-1) min(-1) group by day 7 and sympathoinhibition in the 20 ng kg(-1) min(-1) group at day 21, corresponding to the development of hypertension. Animals receiving increased dietary salt (0.9% NaCl in drinking water), however, showed a similar slow increase in pressure with 20 ng kg(-1) min(-1) angiotensin II (16 +/- 5 mmHg) but no sympathoinhibition at day 21. Bilateral renal denervation delayed the onset but not the extent of hypertension in this group. We conclude that different doses of angiotensin II produce distinct profiles of hypertension and associated changes in pressor sympathetic drive and that increased dietary salt intake disrupts the normal sympathoinhibitory response to angiotensin II-based hypertension.

Investigation of the mechanisms by which chronic infusion of an acutely subpressor dose of angiotensin II induces hypertension

The mechanisms by which chronic infusion of an initially subpressor low dose of angiotensin II (ANG II) causes a progressive and sustained hypertension remain unclear. In conscious sheep ( n = 6), intravenous infusion of ANG II (2 μg/h) gradually increased mean arterial pressure (MAP) from 82 ± 3 to 96 ± 5 mmHg over 7 days ( P < 0.001). This was accompanied by peripheral vasoconstriction; total peripheral conductance decreased from 44.6 ± 6.4 to 38.2 ± 6.7 ml·min−1·mmHg−1 ( P < 0.001). Cardiac output and heart rate were unchanged. In the regional circulation, mesenteric, renal, and iliac conductances decreased but blood flows were unchanged. There was no coronary vasoconstriction, and coronary blood flow increased. Ganglion blockade (125 mg/h hexamethonium for 4 h) reduced MAP by 13 ± 1 mmHg in the control period and by 7 ± 2 mmHg on day 8 of ANG II treatment. Inhibition of central AT1 receptors by intracerebroventricular infusion of losartan (1 mg/h for 3 h) had no effect on MAP in the control period or after 7 days of ANG II infusion. Pressor responsiveness to incremental doses of intravenous ANG II (5, 10, 20 μg/h, each for 15 min) was unchanged after 7 days of ANG II infusion. ANG II caused no sodium or water retention. In summary, hypertension due to infusion of a low dose of ANG II was accompanied by generalized peripheral vasoconstriction. Indirect evidence suggested that the hypertension was not neurogenic, but measurement of sympathetic nerve activity is required to confirm this conclusion. There was no evidence for a role for central angiotensinergic mechanisms, increased pressor responsiveness to ANG II, or sodium and fluid retention.

Renal denervation attenuates long-term hypertensive effects of Angiotensin ii in the rat

1. It is well accepted that some of the long-term effects of angiotensin (Ang) II are mediated via the central nervous system. Some of these actions that are mediated by the circumventricular organs and the baroreceptor reflex are thought to then alter sympathetic nervous system activity. In particular, there is some debate as to the role of renal nerves in the chronic effects of AngII. The aim of the present study was to assess the contribution of the renal nerves in a long-term model of progressive AngII-induced hypertension. 2. Male Sprague-Dawley rats were subjected to either bilateral renal denervation (RDX; n = 7) or sham surgery (SHAM; n = 8). Rats were instrumented with radiotelemetric transducers and venous catheters for the measurement of blood pressure and AngII infusion, respectively. A 4.0% NaCl diet and distilled water were provided ad libitum. The first 3 days served as the control period (7 mL/day, 0.9% NaCl, i.v.). This was followed by an infusion of AngII for 16 days (10 ng/kg per min, i.v.) and a 3 day recovery period identical to control. 3. Baseline arterial pressure between RDX and SHAM rats did not differ. Following AngII treatment, the arterial pressure of SHAM rats increased more rapidly than that of RDX rats. By Day 10 of treatment, the mean arterial pressure was significantly different between groups, having increased to 166 +/- 4 mmHg in SHAM rats and 135 +/- 11 mmHg in RDX rats. This trend continued for the remainder of AngII treatment. 4. The present results indicate that the renal nerves are necessary for the full expression of AngII-induced hypertension.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Central AT1 and AT2 receptors mediate chronic intracerebroventricular angiotensin II-induced drinking in rats fed high sodium chloride diet from weaning

Intracerebroventricular (ICV) angiotensin (AIl) administration stimulates central AII receptors to induce water consumption in rats. The aim of this study was to determine the role of brain AT1 and AT2 receptors in mediating chronic ICV AII-induced drinking in rats raised on normal or high sodium chloride diets from weaning. Rats were weaned at 21 days of age and placed on normal or high sodium chloride diet for 10-12 weeks. At adulthood, the animals were instrumented with brain lateral ventricular cannulas and femoral arterial catheters. Low dose chronic central AII infusion (20 ng min(-1)) significantly (P < 0.05) increased water intake in both groups of rats when compared with their respective controls of 24 h artificial cerebrospinal fluid infusions. In a separate group of high sodium fed rats, coinfusion of AII with the AT1 receptor antagonist, losartan (0.25 microg min(-1)) or the AT2 receptor blocker, PD 123319 (0.50 microg min(-1)) blocked chronic ICV AII-induced drinking. Upon reinfusion of AII water intake increased above control. Following the cessation of AII infusions, water intake returned to values not significantly different from control (P > 0.05). In contrast, in the normal sodium fed rats losartan, but not PD 123319, blocked the AII-mediated water intake. The data demonstrate that in high sodium chloride fed rats AII stimulates both central AT1 and AT2 receptors to induce drinking, while in the normal sodium chloride fed rats the peptide activates the drinking response primarily by stimulation of central AT1 receptors.

Perinatal dietary NaCl level: effect on angiotensin-induced thermal and dipsogenic responses in adult rats

We have shown previously that administration of angiotensin II (Ang II) produces an apparent decrease in thermoregulatory set point. Exposure to high salt diets either perinatally or later in life has been shown to increase pressor responsiveness to administration of Ang II, so in the present studies we examine whether high dietary NaCl would also increase the thermal responsiveness to Ang II. In the first study, we show that exposure to a basal NaCl diet (0.12%) during gestation through 4 weeks postnatally produced very large elevations in plasma renin activity (PRA) and aldosterone concentrations in the offspring. Exposure to high salt diet (3%) did not decrease the levels of these parameters below those fed mid salt diet (1%). In the second study, we show that rats raised through 4 weeks of age on basal diet, but then fed standard chow until adulthood, showed greater changes in tail skin (T(sk)) and colonic (T(c)) temperatures following administration of Ang II (200 microg/kg sc) than either mid- or high-salt-raised groups. In the third study, we confirmed this finding and extended it to show that rats raised on a very high salt diet (6%) also did not differ from the mid-salt group. In both studies, acute water intake measured in a separate test following administration of Ang II did not differ as a function of perinatal salt diet. In a fourth study, the period of exposure to the diets was extended from the perinatal period through adulthood and, surprisingly, there was no longer an enhanced thermal response to Ang II in basal diet rats compared with rats fed the very high salt diet. In the final study, rats raised on a regular diet but exposed only as adults to the test diets showed a nonsignificant trend toward a decreased thermal response in the basal group. Thus, dietary salt level may have opposite effects on Ang II effects on adult thermoregulation, depending on the age at the exposure.

Alpha-adrenergic systems mediate chronic central AII hypertension in rats fed high sodium chloride diet from weaning

Hypertension is elicited by chronic, low dose intracerebroventricular (ICV) angiotensin II (AII) infusion in rats raised from weaning on relatively high sodium chloride diet (250 mEq kg(-1) food). This experimental model of hypertension is dependent upon renal innervation and associated with neurogenic sodium retention. The present study determined whether this neurogenic ICV AII hypertension is mediated by central alpha-adrenoceptors. Rats were weaned at 21 days of age and fed a 1.5% (250 mg kg(-1) food) sodium chloride diet for 10-12 weeks. At adulthood, animals were instrumented with central nervous system (CNS) lateral ventricular cannulas, femoral artery and vein catheters and housed in metabolic pens for chronic study. Low dose ICV AII infusion (20 ng min(-1)) increased mean arterial pressure (MAP) from 121 +/- 4 to 140 +/- 6 mm Hg on the day of ICV infusion. This increase in arterial pressure was associated with 3 consecutive days of decreased urinary sodium excretion. Subsequent ICV alpha-adrenoceptor blockade with phentolamine (AII + phentolamine) abolished the pressor and antinatriuretic responses to low dose chronic ICV AII infusion. Resumption of ICV AII infusion alone increased in MAP toward pre-alpha-adrenergic blockade values (133 +/- 5 mm Hg) on day 8. Following cessation of ICV AII infusion, arterial pressure and sodium excretion returned to values not significantly different from control. This model of hypertension was not dependent on circulating plasma renin activity (PRA), since PRA decreased during ICV AII infusion. These data confirm that low dose ICV AII causes hypertension and sodium retention in rats raised from weaning on moderately elevated sodium intake. We conclude that AII mediated neurogenic hypertension and antinatriuresis is elicited by stimulation of AT1 receptors on neurons which interact with noradrenergic cell bodies in cardiovascular and autonomic centers that may modulate renal sympathetic outflow via alpha-adrenoceptors.

Chronic intracerebroventricular infusion of angiotensin II increases brain AT1 receptor expression in young rats

The aim of the present study was to determine the effect of chronic intracerebroventricular infusion of angiotensin II (ANG II) on the expression of brain AT1 receptors in young (3-4 weeks) rats. One week of icv ANG II infusion produced a significant increase in brain AT1 receptor protein (Western blot) and mRNA (relative RT-PCR) expression. These data raise the possibility that ANG II may play a role in postnatal expression of brain AT1 receptors.

Prenatal dexamethasone causes oligonephronia, sodium retention, and higher blood pressure in the offspring

Recent reports have shown that low birth weight infants have a higher incidence of adult hypertension. These observations have stimulated a number of studies designed to evaluate the mechanisms of this phenomenon. In this study, fetal growth retardation was induced by treating pregnant rats with dexamethasone. After birth, pups whose mothers were treated with dexamethasone had a lower body and kidney weight and a lower number of glomeruli than control pups. Immunohistochemistry on treated kidneys demonstrated a marked reduction in the number of cells undergoing mitosis in the cortical nephrogenic zone. In the treated group, body and kidney weight normalized by 60 d of age, but blood pressure was significantly higher compared with controls (130+/-4 versus 107+/-1 mm Hg). In addition, GFR was significantly lower, albuminuria was higher, urinary sodium excretion rate and fractional sodium excretion were lower, and sodium tissue content was higher. In contrast, when pregnant rats were treated with a natural glucocorticoid (hydrocortisone) which is metabolized by the placenta, fetal development and adult blood pressure were normal. In conclusion, we found that high levels of maternal glucocorticoids impair renal development and lead to arterial hypertension in offspring. Even though renal mass eventually normalizes, glomerular damage as well as sodium retention occur and these factors may contribute to the development of hypertension.

AT1 receptors mediate chronic central nervous system AII hypertension in rats fed high sodium chloride diet from weaning

CNS angiotensin II (AII) hypertension is induced by chronic, low dose intracerebroventricular (ICV) AII infusion only in rats raised on a relatively high sodium chloride diet (250 meq kg(-1)food) from weaning. This experimental model of hypertension is dependent upon renal sympathetic innervation and associated with neurogenic sodium retention. This study determined whether AT1 and/or AT2 receptor subtypes in the CNS mediate this neurogenic ICV AII hypertension. Rats were weaned at 21 days of age and fed a 1.5% sodium chloride diet for 10-12 weeks. At adulthood, animals were instrumented with CNS lateral ventricular cannulas, femoral arterial and vein catheters and housed in metabolic pens for chronic study. Low dose ICV AII infusion (20 ng min(-1) )increased mean arterial pressure by 12+/-2 mm Hg and decreased urinary sodium excretion for three consecutive days. Subsequent ICV AT1 blockade with losartan abolished both the pressor and antinatriuretic responses to low dose ICV AII. In contrast, ICV AT2 receptor blockade with PD 123319 did not affect either angiotensin induced pressor or antinatriuretic responses. Following cessation of ICV AII infusion, arterial pressure and sodium excretion returned to values not significantly different from control in both groups of rats. These data confirm that low dose ICV AII causes hypertension and sodium retention in rats raised from early age on moderately elevated sodium intakes. This AII mediated neurogenic hypertension and antinatriuresis is transduced by activation of CNS AT1 receptors and not by activation of central AT2 receptors.

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.