Activating autoantibodies to the angiotensin II type I receptor play an important role in mediating hypertension in response to adoptive transfer of CD4+ T lymphocytes from placental ischemic rats

Hypertension in rats with chronic placental ischemia (reduced uterine perfusion pressure, RUPP) is associated with elevated inflammatory cytokines, agonistic autoantibodies to the angiotensin II type I receptor (AT1-AA) and CD4(+) T cells; all of which are elevated in preclamptic women. Additionally, we have shown that adoptive transfer of RUPP CD4(+) T cells increases blood pressure, inflammatory cytokines, and sFlt-1. The objective of this study was to determine the long-term effects of RUPP CD4(+) T cells on AT1-AA, renal and systemic hemodynamics in pregnant rats. To answer this question CD4(+) T splenocytes were magnetically isolated on day 19 of gestation from control RUPP and normal pregnant (NP) rats and injected into a new group of NP rats at day 13 of gestation. On day 19 of gestation mean arterial pressure (MAP) and renal function (glomerular filtration rates, GFR) were analyzed and serum collected for AT1-AA analysis. To determine a role for AT1-AA to mediate RUPP CD4(+) T cell-induced blood pressure increases, MAP was analyzed in a second group of rats treated with AT1 receptor blockade losartan (10 mg·kg(-1)·day(-1)) and in a third group of rats treated with rituximab, a B cell-depleting agent (250 mg/kg) we have shown previously to decrease AT1-AA production in RUPP rats. MAP increased from 101 ± 2 mmHg NP to 126 ± 2 mmHg in RUPP rats (P < 0.001) and to 123 ± 1 mmHg in NP rats injected with RUPP CD4(+) T cells (NP+RUPP CD4(+)T cells) (P < 0.001). Furthermore, GFR decreased from 2.2 ml/min (n = 7) in NP rats to 1.0 ml/min (n = 5) NP+RUPP CD4(+)T cell. Circulating AT1-AA increased from 0.22 ± 0.1 units in NP rats to 13 ± 0.7 (P < 0.001) units in NP+RUPP CD4(+)T cell-treated rats but decreased to 8.34 ± 1 beats/min in NP+RUPP CD4(+) T cells chronically treated with rituximab. Hypertension in NP+RUPP CD4(+)T cell group was attenuated by losartan (102 ± 4 mmHg) and with B cell depletion (101 ± 5 mmHg). Therefore, we conclude that one mechanism of hypertension in response to CD4(+) T lymphocytes activated during placental ischemia is via AT1 receptor activation, potentially via AT1-AA during pregnancy.     

Cytochrome P-450 pathway in renal function of normal rats and rats with bilateral ureteral obstruction.

Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) are decreased and mean arterial pressure (MAP) and renal vascular resistance (RVR) are increased after unilateral release of bilateral ureteral obstruction (BUO) of 24 hr duration. An imbalance between vasoconstrictor and vasodilator substances may explain these hemodynamic changes. We examined the role of the cytochrome P-450 pathway in this setting. After unilateral release of BUO, GFR and ERPF (ml/min/kg body wt) were significantly lower in these rats than in sham-operated rats (SOR) 1.14 +/- 0.09 vs 6.7 +/- 0.5 and 3.09 +/- 0.2 vs 23.5 +/- 3.4, respectively). BUO rats had significantly higher MAP (mm Hg) and RVR (mm Hg/ml/min/kg body wt) than SOR (155 +/- 5 vs 120 +/- 1 and 29.1 +/- 1.7 vs 3.2 +/- 0.4, respectively). SOR given 3-methylcholanthrene and beta-naphthoflavone to induce the cytochrome P-450 system had no significant changes in renal function, RVR, or MAP. SOR given ketoconazole to inhibit the cytochrome P-450 system had significantly lower GFR (4.8 +/- 0.5) than temporal control rats without significant changes in ERPF (21.2 +/- 4.6), MAP (127 +/- 6), or RVR (4.2 +/- 0.9). Rats with BUO given ketoconazole had lower but not significantly different GFR (0.84 +/- .1) and ERPF (2.61 +/- .4) than BUO controls. Values for MAP did not differ in BUO rats given ketoconazole versus BUO temporal controls. BUO rats given 3-methylcholanthrene and beta-naphthoflavone had significantly higher GFR and ERPF (2.01 +/- 0.24 and 6.66 +/- 1.36, respectively) and significantly lower RVR (14.7 +/- 3.9) than control rats with BUO; MAP was unchanged. Microsomal preparations from indomethacin-treated isolated kidneys obtained from BUO rats when compared with preparations obtained from SOR had significantly less activity of the P-450 cytochrome-dependent omega/omega-1 hydroxylase (103 +/- 6 vs 130 +/- 7 pmol hydroxyeicosatetraenoic acids produced per mg of protein/min, P < 0.02) and the P-450 cytochrome-dependent epoxygenase (11 +/- 0.3 vs 30 +/- 4 pmol lipoxyeicosatrienoic acids produced per mg of protein/min, P < 0.04). Indomethacin-treated microsomes prepared from kidneys of BUO rats converted significantly less 14C-arachidonic acid through the P-450-dependent hydroxylases (13.5 +/- 0.8 vs 17.0 +/- 0.1% of 14C-arachidonic acid converted to 19- and 20-hydroxyeicosatetraenoic acids, P < 0.02), and significantly less through the epoxygenases (1.4 +/- 0.4 vs. 3.8 +/- 0.5% of 14C-arachidonic acid converted to epoxyeicosatrienoic acids).(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of chronic treatment with 7-nitroindazole in hyperthyroid rats

This study analyzed the contribution of neuronal nitric oxide synthase (nNOS) to the hemodynamic manifestations of hyperthyroidism. The effects on hyperthyroid rats of the chronic administration of 7-nitroindazole (7-NI), an inhibitor of nNOS, were studied. Six groups of male Wistar rats were used: control, 7-NI (30 mg.kg-1.day-1 by gavage), T(4)50, T(4)75 (50 or 75 microg thyroxine.rat-1.day-1, respectively), T(4)50+7-NI, and T(4)75+7-NI. All treatments were maintained for 4 wk. Body weight, tail systolic blood pressure (SBP), and heart rate (HR) were recorded weekly. Finally, SBP, pulse pressure (PP), and HR were measured in conscious rats, and morphological, metabolic, plasma, and renal variables were determined. Expression of nNOS in the hypothalamus of T(4)75 and control rats was analyzed by Western blot analysis. The response of mean arterial pressure (MAP) to pentolinium (10 mg/kg iv) was used to evaluate the sympathetic contribution to BP in T(4)75 and T(4)75+7-NI rats. T(4) produced an increased hypothalamic nNOS expression and dose-related increases in blood pressure (BP), HR, and PP vs. control rats. 7-NI did not modify BP or any other hemodynamic variable in normal rats. However, 7-NI produced a marked reduction in BP, HR, PP, and food and water intake in both hyperthyroid groups and improved creatinine clearance in the T(4)75 group. Pentolinium produced a greater MAP decrease in the T(4)75+7-NI than in the T(4)75 group. In conclusion, administration of 7-NI attenuates the hemodynamic and metabolic manifestations of hyperthyroidism, suggesting that nNOS contributes to the hyperdynamic circulation of this endocrine disease by modulating sympathetic activity.     

Systemic hemodynamic and regional blood flow changes in response to chronic reductions in uterine perfusion pressure in pregnant rats

Preeclampsia (PE) is associated with increased total peripheral resistance (TPR), reduced cardiac output (CO), and diminished uterine and placental blood flow. We have developed an animal model that employs chronic reductions in uterine perfusion pressure (RUPP) in pregnant rats to generate a "preeclamptic-like" state during late gestation that is characterized by hypertension, proteinuria, and endothelial dysfunction. Although this animal model has many characteristics of human PE, the systemic hemodynamic and regional changes in blood flow that occur in response to chronic RUPP remains unknown. Therefore, we hypothesized that RUPP would decrease uteroplacental blood flow and CO, and increase TPR. Mean arterial pressure (MAP), CO, cardiac index (CI), TPR, and regional blood flow to various tissues were measured using radiolabeled microspheres in the following two groups of conscious rats: normal pregnant rats (NP; n = 8) and RUPP rats (n = 8). MAP was increased (132 +/- 4 vs. 99 +/- 3 mmHg) in the RUPP rats compared with the NP dams. The hypertension in RUPP rats was associated with increased TPR (2.15 +/- 0.02 vs. 0.98 +/- 0.08 mmHg x ml(-1) x min(-1)) and decreased CI (246 +/- 20 vs. 348 +/- 19 ml x min(-1) x kg(-1), P < 0.002) when contrasted with NP dams. Furthermore, uterine (0.16 +/- 0.03 vs. 0.38 +/- 0.09 ml x min(-1) x g tissue(-1)) and placental blood flow (0.30 +/- 0.08 vs. 0.70 +/- 0.10 ml x min(-1) x g tissue(-1)) were decreased in RUPP compared with the NP dams. These data demonstrate that the RUPP model of pregnancy-induced hypertension has systemic hemodynamic and regional blood flow alterations that are strikingly similar to those observed in women with PE.     

Enalapril attenuates endothelin-1-induced hypertension via increased kinin survival

Recent studies have shown that angiotensin-converting enzyme (ACE) inhibitors attenuate endothelin-1 (ET-1)-induced hypertension, but the mechanisms for this effect have not been clarified. Initial experiments were conducted to contrast the effect of the ACE inhibitor enalapril, the combined ACE-neutral endopeptidase inhibitor omapatrilat, and the angiotensin II receptor antagonist candesartan on the hypertensive and renal response to ET-1 in anesthetized Sprague-Dawley rats. Acute intravenous infusion of ET-1 (10 pmol x kg(-1) x min(-1)) for 60 min significantly increased mean arterial pressure (MAP) from 125 +/- 8 to 145 +/- 8 mmHg (P < 0.05) and significantly decreased glomerular filtration rate (GFR) from 0.31 +/- 0.09 to 0.13 +/- 0.05 ml x min(-1) x 100 g kidney wt(-1). Pretreatment with enalapril (10 mg/kg iv) before ET-1 infusion inhibited the increase in MAP (121 +/- 4 vs. 126 +/- 4 mmHg) before and during ET-1 infusion, respectively (P < 0.05) without blocking the effect of ET-1 on GFR. In contrast, neither omapatrilat (30 mg/kg) nor candesartan (10 mg/kg) had any effect on ET-1-induced increases in MAP or decreases in GFR. To determine whether the effect of enalapril was due to the decrease in angiotensin II or increase in kinin formation, rats were given REF-000359 (1 mg/kg iv), a selective B(2) receptor antagonist, with or without enalapril before ET-1 infusion. REF-000359 completely blocked the effect of enalapril on ET-1 infusion (MAP was 117 +/- 5 vs. 135 +/- 5 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 alone had no effect on the response to ET-1 infusion (MAP was 117 +/- 4 vs. 144 +/- 4 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 with or without enalapril had no significant effect on the ability of ET-1 infusion to decrease GFR. These findings support the hypothesis that decreased catabolism of bradykinin and its subsequent vasodilator activity oppose the actions of ET-1 to increase MAP.     

The renal and systemic hemodynamic effects of a nitric oxide-synthase inhibitor are reversed by a selective endothelin(a) receptor antagonist in men.

There is evidence for an interaction between nitric oxide (NO) and endothelin (ET) at the level of the renal vasculature. We hypothesized that acute renal effects of systemic NO synthase inhibition (NG-monomethyl-l-arginine, L-NMMA) may be blunted by coadministration of a specific ET(A) receptor antagonist (BQ-123) in healthy humans. Fifteen healthy young male subjects participated in this randomized, double-blind, placebo-controlled 3-way crossover study. These sodium-repleted volunteers received L-NMMA alone, or BQ-123 alone, or L-NMMA with a subsequent coinfusion of BQ-123. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were determined with the PAH and inulin clearance method, respectively. Mean arterial pressure (MAP) and pulse rate were measured noninvasively at baseline and every 15 min after the start of the study period. L-NMMA alone reduced RPF (-22%, P < 0.001) and GFR (-8%, P < 0.009) and increased MAP (+10%, P < 0.001). BQ-123 alone did not affect these parameters. However, coinfusion of BQ-123 blunted the effects of L-NMMA on RPF (P < 0.001), GFR (P < 0.001), and MAP (P = 0.006). Peripheral and renal hemodynamic effects of acute systemic NO synthase inhibition are at least partially reversed by ET(A) receptor blockade with BQ-123. This indicates a functional antagonism between specific ET(A) receptor antagonist and NO synthase inhibitors at the level of the renal vasculature.     

Pregnancy increases baroreflex-independent GABAergic inhibition of the RVLM in rats

During baroreceptor unloading, sympathoexcitation is attenuated in near-term pregnant compared with nonpregnant rats. Alterations in balance among different excitatory and inhibitory inputs within central autonomic pathways likely contribute to changes in regulation of sympathetic outflow in pregnancy. Both baroreflex-dependent and baroreflex-independent GABAergic inputs inhibit sympathoexcitatory neurons within rostral ventrolateral medulla (RVLM). The present experiments tested the hypothesis that influence of baroreflex-independent GABAergic inhibition of RVLM is greater in pregnant compared with nonpregnant rats. Afferent baroreceptor inputs were eliminated by bilateral sinoaortic denervation in inactin-anesthetized rats. In pregnant compared with nonpregnant rats, baseline mean arterial pressure (MAP) was lower (pregnant = 75 +/- 6 mmHg, nonpregnant = 115 +/- 7 mmHg) and heart rate was higher (pregnant = 381 +/- 10 beats/min, nonpregnant = 308 +/- 10 beats/min). Pressor and sympathoexcitatory [renal sympathetic nerve activity, (RSNA)] responses due to bilateral GABA(A) receptor blockade (bicuculline, 4 mM, 100 nl) of the RVLM were greater in pregnant rats (delta MAP: pregnant = 101 +/- 4 mmHg, nonpregnant = 80 +/- 6 mmHg; delta RSNA: pregnant = 182 +/- 23% control, nonpregnant = 133 +/- 10% control). Unexpected transient sympathoexcitatory effects of angiotensin AT(1) receptor blockade in the RVLM were greater in pregnant rats. Although excitatory responses to bicuculline were attenuated by prior RVLM AT1 receptor blockade in both groups, pressor responses to disinhibition of the RVLM remained augmented in pregnant rats. Increased influence of baroreflex-independent GABAergic inhibition in RVLM could contribute to suppressed sympathoexcitation during withdrawal of arterial baroreceptor input in pregnant animals.     

Adverse effects of pneumoperitoneum on renal function: involvement of the endothelin and nitric oxide systems

Increased intra-abdominal pressure (IAP) during laparoscopy adversely affects kidney function. The mechanism underlying this phenomenon is largely unknown. This study was designed to investigate the involvement of endothelin (ET)-1 and nitric oxide (NO) systems in IAP-induced renal dysfunction. Rats were subjected to IAP of 14 mmHg for 1 h, followed by a deflation for 60 min (recovery). Four additional groups were pretreated with 1) ABT-627, an ET(A) antagonist; 2) A-192621, an ET(B) antagonist; 3) nitroglycerine; and 4) N(G)-nitro-L-arginine methyl ester, a NO synthase inhibitor, before IAP. Urine flow rate (V), absolute Na+ excretion (U(Na)V), glomerular filtration rate (GFR), and renal plasma flow (RPF) were determined. Significant reductions in kidney function and hemodynamics were observed when IAP was applied. V decreased from 8.1 +/- 1.0 to 5.8 +/- 0.5 microl/min, U(Na)V from 1.08 +/- 0.31 to 0.43 +/- 0.10 microeq/min, GFR from 1.84 +/- 0.12 to 1.05 +/- 0.06 ml/min (-46.9 +/- 2.7% from baseline), and RPF from 8.62 +/- 0.87 to 3.82 +/- 0.16 ml/min (-54 +/- 3.5% from baseline). When the animals were pretreated with either ABT-627 or A-192621, given alone or combined, the adverse effects of IAP on GFR, RPF, V, and U(Na)V were significantly augmented. When the animals were pretreated with nitroglycerine, the adverse effects of pneumoperitoneum on GFR and RPF were substantially improved. In contrast, pretreatment with N(G)-nitro-L-arginine methyl ester remarkably aggravated pneumoperitoneum-induced renal dysfunction. In conclusion, decreased renal excretory function and hypofiltration are induced by increased IAP. These effects are related to impairment of renal hemodynamics and could be partially ameliorated by pretreatment with nitroglycerine and aggravated by NO and ET blockade.     

Pregnancy alters hemodynamic responses to hemorrhage in conscious rabbits

Pregnant animals are less able to maintain mean arterial pressure (MAP) during hemorrhage compared with nonpregnant animals, but the hemodynamic basis of this difference is unknown. The hypothesis that pregnancy attenuates responses of cardiac output, as well as total peripheral resistance (TPR) and femoral conductance, to hemorrhage was tested in conscious rabbits in both the pregnant and nonpregnant state (n = 10). During continuous slow blood loss (2% of the initial blood volume per minute), MAP was maintained initially in both groups. However, MAP then abruptly decreased to <45 mmHg in all animals after a smaller percentage of the initial blood volume was removed in pregnant compared with nonpregnant rabbits (43.6 +/- 1.7%, nonpregnant; 29.6 +/- 2.2%, pregnant; P < 0.005). The more rapid transition to hypotension exhibited by pregnant rabbits was associated with greater initial falls in cardiac output (-56 +/- 10 ml/min, nonpregnant; -216 +/- 33 ml/min, pregnant; P < 0.005) and stroke volume (0.8 +/- 0.1 ml/beat, nonpregnant; -1.3 +/- 0.1 ml/beat, pregnant; P < 0.05). In addition, the increase in TPR as a function of the decrease in cardiac output was markedly attenuated (P < 0.0001) during pregnancy. Whereas femoral conductance decreased in nonpregnant rabbits, it did not change significantly in pregnant animals. In conclusion, the lesser ability of conscious pregnant rabbits to maintain MAP during hemorrhage is due largely to a greater decrease in cardiac output but also to inadequate reflex increases in TPR, possibly in part in the femoral vascular bed.     

nNOS gene transfer to RVLM improves baroreflex function in rats with chronic heart failure

We hypothesized that gene transfer of neuronal nitric oxide synthase (nNOS) into the rostral ventrolateral medulla (RVLM) improves baroreflex function in rats with chronic heart failure (CHF). Six to eight weeks after coronary artery ligation, rats showed hemodynamic signs of CHF. A recombinant adenovirus, either Ad.nNOS or Ad.beta-Gal, was transfected into the RVLM. nNOS expression in the RVLM was confirmed by Western blot analysis, NADPH-diaphorase, and immunohistochemical staining. We studied baroreflex control of the heart rate (HR) and renal sympathetic nerve activity (RSNA) in the anesthetized state 3 days after gene transfer by intravenous injections of phenylephrine and nitroprusside. Baroreflex sensitivity was depressed for HR and RSNA regulation in CHF rats (2.0 +/- 0.3 vs. 0.8 +/- 0.2 beats.min-1.mmHg-1, P < 0.01 and 3.8 +/- 0.3 vs. 1.2 +/- 0.1% max/mmHg, P < 0.01, respectively). Ad.nNOS transfer into RVLM significantly increased the HR and RSNA ranges (152 +/- 19 vs. 94 +/- 12 beats/min, P < 0.05 and 130 +/- 16 vs. 106 +/- 5% max/mmHg, P < 0.05) compared with the Ad.beta-Gal in CHF rats. Ad.nNOS also improved the baroreflex gain for the control of HR and RSNA (1.8 +/- 0.2 vs. 0.8 +/- 0.2 beats.min-1.mmHg-1, P < 0.01 and 2.6 +/- 0.2 vs. 1.2 +/- 0.1% max/mmHg, P < 0.01). In sham-operated rats, we found that Ad.nNOS transfer enhanced the HR range compared with Ad.beta-Gal gene transfer (188 +/- 15 vs. 127 +/- 14 beats/min, P < 0.05) but did not alter any other parameter. This study represents the first demonstration of altered baroreflex function following increases in central nNOS in the CHF state. We conclude that delivery of Ad.nNOS into the RVLM improves baroreflex function in rats with CHF.     

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

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

Acute haemodynamic effects of IL-6 treatment in vivo: involvement of vagus nerve in NO-mediated negative inotropism

Interleukin-6 (IL-6) reduces myocardial haemodynamics. However, the intrinsic mechanisms of IL-6 effects are not known. We hypothesized that nitric oxide (NO) synthesised by neuronal synthase (nNOS) can be the molecular mediator of IL-6-mediated cardiac effects. Thus, we investigated in vivo after IL-6 acute administration: (1) the role of NO pathway; (2) the importance of NO derived from nNOS located in intracardiac vagal ganglion in the anterior surface of the left ventricle. Sprague-Dawley (SD) rats (225-250 g) were anaesthetized (sodium pentobarbital 30 mg/kg intraperitoneally administered) and ventilated. The effects of a single IL-6 bolus (100 microg/kg intravenously administered) were studied in four experimental groups: (a) IL-6 (n=6), (b) IL-6 plus 30 mg/kg of L-NAME (an eNOS and nNOS inhibitor; n=6), (c) IL-6 plus 25mg/kg of 7-NI (a specific nNOS inhibitor; n=6), (d) IL-6 plus vagal resection (n=6). We evaluated the following parameters: mean aortic pressure (MAP), left ventricular end systolic pressure (LVESP), left ventricular positive peak dP/dt (PP dP/dt). Data are expressed as mean+/-sem. IL-6 caused a transient but significant reduction of MAP (-21.8% of basal: p<0.05), LVESP (from 130+/-4.2 to 1056.5 mmHg: p<0.05) and PP dP/dt (from 5390+/-158 to 4400+/-223 mmHg/s, p<0.02). Concomitant treatment with L-NAME or 7-NI totally abolished IL-6 effects. Vagal resection significantly reduced the haemodynamic effects (MAP: -10% of basal: p=ns; LVEDS: from 125+/-7.3 to 117+/-6.8 mmHg, p<0.05; PP dP/dt from 5500+/-150 to 5000+/-143 mmHg/s, p<0.05). We conclude that acute administration of IL-6 caused transient but significant cardiac negative inotropism. IL-6 haemodynamic effects are partly due to NO synthesised by nNOS located in vagal left ventricular ganglia.     

Sympathetic-renal interaction in chronic arterial pressure control

The effects of neonatal sympathectomy of donors or recipients on posttransplantation arterial pressure were investigated in spontaneously hypertensive rats (SHR) by renal transplantation experiments. Conscious mean arterial pressure (MAP) and renal vascular resistance were 136 +/- 1 mmHg and 15.5 +/- 1.2 mmHg x ml(-1) x min x g in sympathectomized SHR (n = 8) vs. 158 +/- 4 mmHg (P < 0.001) and 20.8 +/- 1.1 mmHg x ml(-1) x min x g (P < 0.05) in controls (n = 10). Seven weeks after transplantation of a kidney from neonatally sympathectomized SHR donors, MAP in SHR recipients (n = 10) was 20 mmHg lower than in controls transplanted with a kidney from hydralazine-treated SHR (n = 10) (P < 0.05) associated with reduced sodium sensitivity of MAP. Neonatal sympathectomy also lowered MAP in F1-hybrids (F1H; SHR x Wistar-Kyoto rats). Within 6 wk after transplantation, renal grafts from untreated SHR increased MAP by 20 mmHg in sympathectomized F1H (n = 10) and by 35 mmHg in sham-treated F1H (n = 8) (P < 0.05). Neonatal sympathectomy induces chronic changes in SHR kidney function leading to a MAP reduction even when extrarenal sympathetic tone is restored. Generalized reduction in sympathetic tone resets the kidney-fluid system to reduced MAP and blunts the extent of arterial pressure rise induced by an SHR kidney graft.     

Right atrial dimension-pressure relation during volume expansion is unaltered by pregnancy in the rat

Blood volume expands significantly during pregnancy, but afferent signals from cardiac receptors are reduced. In addition, during exogenous volume expansion, right atrial pressure (RAP) increases more for equivalent volumes in pregnant animals, implying reduced atrial compliance. To examine possible gestational alterations in atrial dimension during volume expansion, we compared the effects of volume expansion on RAP and right atrial dimension (RAD) in pregnant vs. virgin rats. Anesthetized animals were ventilated and catheterized for measurement of arterial pressure and RAP and for drug infusion. Through a parasternal incision, ultrasonic crystals were glued to the medial and lateral surfaces of the right atrium for measurement of RAD. Plasma volume and hematocrit were determined before experimentation. RAP, RAD, and arterial pressure were recorded at baseline and during progressive volume expansion (6% dextran, 60% of initial blood volume). Baseline RAP was similar in the two groups: 2.82 +/- 0.40 and 2.72 +/- 0.47 mmHg in pregnant and virgin rats, respectively. Basal RAD was significantly larger in pregnant than in virgin rats: 4.36 +/- 0.66 vs. 3.36 +/- 0.48 mm. Despite increased basal RAD in pregnant rats, the slope of the RAD-RAP relation during volume expansion was similar in the two groups. Results indicate that resting RAD is increased in pregnant rats and that the change in dimension during volume loads is similar to that in virgin rats. Thus, during pregnancy, the right atrium appears to accommodate the increased blood volume, and reduced afferent signaling most likely is due to mechanisms other than mechanical alterations of the atrium by expanded volume.     

Renal interstitial fluid ATP responses to arterial pressure and tubuloglomerular feedback activation during calcium channel blockade

A close relationship between changes in renal interstitial fluid (RIF) ATP concentrations and renal autoregulatory or tubuloglomerular feedback (TGF)-dependent changes in renal vascular resistance (RVR) has been demonstrated, but it has not been determined whether the changes in RIF ATP are a consequence or the cause of the changes in RVR. The present study was performed in anesthetized dogs to assess the changes in RIF ATP following changes in renal arterial pressure (RAP) or stimulation of the TGF mechanism under conditions where changes in RVR were prevented by nifedipine, a calcium channel blocker. RIF ATP levels were measured by using microdialysis probes. Intra-arterial infusion of nifedipine (0.36 microg x kg(-1) x min(-1)) increased renal blood flow (RBF: from 4.49 +/- 0.27 to 5.34 +/- 0.39 ml x min(-1) x g(-1)) and glomerular filtration rate (GFR: from 0.84 +/- 0.07 to 1.09 +/- 0.11 ml x min(-1) x g(-1)). Under conditions of nifedipine infusion, autoregulatory adjustments in RBF, GFR, and RVR were not observed during stepwise reductions in RAP within the autoregulatory range (from 135 +/- 7 to 76 +/- 1 mmHg, n = 7). Furthermore, stimulation of the TGF mechanism with intra-arterial infusion of acetazolamide (100 microg x kg(-1) x min(-1)) did not alter RBF, GFR, and RVR (n = 7). During treatment with nifedipine, RIF ATP levels were significantly decreased in response to reductions in RAP (10.7 +/- 0.7, 5.8 +/- 0.7 and 2.8 +/- 0.3 nmol/l at 135 +/- 7, 101 +/- 4, and 76 +/- 1 mmHg, n = 7) and increased by acetazolamide infusion (from 8.8 +/- 0.8 to 17.0 +/- 1.8 nmol/l, n = 7). These results are similar to those that occurred in dogs not treated with nifedipine and thus demonstrate that the changes in RIF ATP can occur in the absence of autoregulatory or TGF-mediated changes in RVR. The data provide further support to the hypothesis that RIF ATP contributes to adjustments in RVR associated with renal autoregulation and changes in activity of the TGF mechanism.     

Effect of cardiac receptor stimulation on renal vascular resistance in the pregnant rat

Stimulation of cardiac receptors (CR) evokes blunted reflex reductions in mean arterial pressure (MAP) in pregnant compared with virgin rats. Because CR-mediated sympathoinhibition has preferential effects on the kidney, we tested whether, during pregnancy, renal vascular resistance (RVR) changes less in response to CR stimulation and investigated possible mechanisms. MAP, right atrial pressure, renal sympathetic nerve activity (RSNA), renal blood flow (RBF), and RVR were measured in anesthetized animals in response to CR stimulation by graded atrial injections of saline. Baseline MAP and RVR and reflex changes in these variables during CR stimulation were reduced in late-pregnant vs. virgin rats (P<0.05). Reflex changes in RSNA were attenuated in pregnant rats, but changes in RBF as a function of RSNA were similar in both groups. ANG II AT(1)-receptor blockade increased basal RBF more in virgin rats (P<0.05), but between-group differences in reflex changes in MAP, RSNA, and RVR were maintained after AT(1) blockade. Thus during CR simulation, reflex changes in RVR were reduced in pregnant versus virgin rats. This difference does not appear to involve differential effects of ANG II.     

Tempol improves renal hemodynamics and pressure natriuresis in hyperthyroid rats

Hyperthyroidism in rats is associated with increased oxidative stress. These animals also show abnormal renal hemodynamics and an attenuated pressure-diuresis-natriuresis (PDN) response. We analyzed the role of oxidative stress as a mediator of these alterations by examining acute effects of tempol, a superoxide dismutase mimetic. The effects of increasing bolus doses of tempol (25-150 micromol/kg) on mean arterial pressure (MAP), renal vascular resistance (RVR), and cortical (CBF) and medullary (MBF) blood flow were studied in control and thyroxine (T4)-treated rats. In another experiment, tempol was infused at 150 micromol.kg(-1).h(-1) to analyze its effects on the glomerular filtration rate (GFR) and on PDN response in these animals. Tempol dose dependently decreased MAP and RVR and increased CBF and MBF in control and T4-treated rats, but the T4 group showed a greater responsiveness to tempol in all of these variables. The highest dose of tempol decreased RVR by 13.5 +/- 2.1 and 5.5 +/- 1.2 mmHg.ml(-1).min(-1) in hyperthyroid (P < 0.01) and control rats, respectively. GFR was not changed by tempol in controls but was significantly increased in the hyperthyroid group. Tempol did not change the absolute or fractional PDN responses of controls but significantly improved those of hyperthyroid rats, although without attaining normal values. Tempol increased the slopes of the relationship between renal perfusion pressure and natriuresis (T4+tempol: 0.17 +/- 0.05; T4: 0.09 +/- 0.03 microeq.min(-1).g(-1).mmHg(-1); P < 0.05) and reduced 8-isoprostane excretion in hyperthyroid rats. These results show that antioxidant treatment with tempol improves renal hemodynamic variables and PDN response in hyperthyroid rats, indicating the participation of an increased oxidative stress in these mechanisms.     

Chronic Nicotine Exposure Abolishes Maternal Systemic and Renal Adaptations to Pregnancy in Rats

Pregnancy is characterized by maternal systemic and intrarenal vasodilation, leading to increases in the renal plasma flow (RPF) and glomerular filtration rate (GFR). These responses are mainly mediated by nitric oxide (NO) and relaxin. The impact of cigarette smoking on the maternal adaptations to pregnancy is unclear. Here we evaluated the effects of chronic exposure to nicotine on systemic and intrarenal parameters in virgin (V) and 14-day pregnant (P) Wistar rats. V and P groups received saline or nicotine (6 mg·kg^-1·day^-1) respectively, via osmotic minipumps for 28 days, starting 14 days before pregnancy induction. Nicotine induced a 10% increase in blood pressure in the V group and minimized the characteristic pregnancy-induced hypotension. Renal sympathetic nerve activity (rSNA) and baroreflex sensitivity were impaired by nicotine mainly in the P group, indicating that the effect of nicotine on blood pressure was not mediated by nervous system stimulation. Nicotine had no effect on GFR in the V rats but reduced GFR of the P group by 30%. Renal expression of sodium and water transporters was downregulated by nicotine, resulting in increased fractional sodium excretion mainly in the P group, suggesting that nicotine compromised the sodium and water retention required for normal gestation. There was a reduction in the expression of inducible NO synthase (iNOS) in both the kidney tissue and renal artery, as well as in the expression of the relaxin receptor (LGR7). These results clearly show that nicotine induced deleterious effects in both virgin and pregnant animals, and abolished the maternal capacity to adapt to pregnancy.     

Nitric oxide synthase and cGMP-mediated stimulation of renin secretion

The interaction between nitric oxide (NO) and renin is controversial. cAMP is a stimulating messenger for renin, which is degraded by phosphodiesterase (PDE)-3. PDE-3 is inhibited by cGMP, whereas PDE-5 degrades cGMP. We hypothesized that if endogenous cGMP was increased by inhibiting PDE-5, it could inhibit PDE-3, increasing endogenous cAMP, and thereby stimulate renin. We used the selective PDE-5 inhibitor zaprinast at 20 mg/kg body wt ip, which we determined would not change blood pressure (BP) or renal blood flow (RBF). In thiobutabarbital (Inactin)-anesthetized rats, renin secretion rate (RSR) was determined before and 75 min after administration of zaprinast or vehicle. Zaprinast increased cGMP excretion from 12.75 +/- 1.57 to 18.67 +/- 1.87 pmol/min (P < 0.003), whereas vehicle had no effect. Zaprinast increased RSR sixfold (from 2.95 +/- 1.74 to 17.62 +/- 5.46 ng ANG I. h(-1) x min(-1), P < 0.024), while vehicle had no effect (from 4.08 +/- 2.02 to 3.87 +/- 1.53 ng ANG I x h(-1) x min(-1)). There were no changes in BP or RBF. We then tested whether the increase in cGMP could be partially due to the activity of the neuronal isoform of NO synthase (nNOS). Pretreatment with the nNOS inhibitor 7-nitroindazole (7-NI; 50 mg/kg body wt) did not change BP or RBF but attenuated the renin-stimulating effect of zaprinast by 40% compared with vehicle. In 7-NI-treated animals, zaprinast-stimulated cGMP excretion was attenuated by 48%, from 9.17 +/- 1.85 to 13.60 +/- 2.15 pmol/min, compared with an increase from 10.94 +/- 1.90 to 26.38 +/- 3.61 pmol/min with zaprinast without 7-NI (P < 0.04). This suggests that changes in endogenous cGMP production at levels not associated with renal hemodynamic changes are involved in a renin-stimulatory pathway. One source of this cGMP may be nNOS generation of NO in the kidney.     

Role of increased glomerular filtration rate in atrial natriuretic factor-induced natriuresis in the rat

One of the major renal hemodynamic actions of atrial natriuretic factor (ANF) is to increase glomerular filtration rate (GFR). To assess the role of this effect on ANF-induced natriuresis (UNaV), diuresis (V) and kaliuresis (UKV) we performed late clamp experiments in six rats. After control periods (C), synthetic ANF (auriculin A) was infused i.v. (2 micrograms X min-1/kg body wt) throughout the experiment (150 min). After pre-clamp periods, the perfusion pressure of the left kidney (LK) was reduced to 75-80 mmHg. The right kidney (RK) served as a time control. In LK, before the late clamp, ANF increased (p less than 0.01) GFR from 1.5 +/- 0.1 to 1.8 +/- 0.1 ml/min, V from 17 +/- 5 to 53 +/- 5 microliters/min, and UNaV from 2.1 +/- 0.6 to 10.0 +/- 0.9 microEq/min. Almost identical increases occurred in the RK. The late clamp returned all parameters in LK to C values (p greater than 0.05): GFR to 1.4 +/- 0.1 ml/min, V to 6.3 +/- 1.2 microliter/min, and UNaV to 1.0 +/- 0.3 microEq/min. The late clamp also reversed the ANF-induced increase in UKV. In the RK, GFR (1.8 +/- 0.1 ml/min), V (38 +/- 4 microliter/min) and UNaV (7.8 +/- 0.8 microEq/min) remained elevated (p less than 0.01 vs. C) to the end of the experiment. These data demonstrate that upon return of GFR to control levels, the ANF-induced diuresis, natriuresis and kaliuresis is abolished. The results support our previous view that the increase in GFR together with a decrease in inner-medullary hypertonicity account wholly or in great part for the natriuretic action of ANF.