[Exploring the causality between intestinal flora and hyperplastic scars of human based on two-sample Mendelian randomization analysis]

Objective: To investigate the causality between intestinal flora and hypertrophic scars (HS) of human. Methods: This study was a study based on two-sample Mendelian randomization (TSMR) analysis. The data on intestinal flora (n=18 473) and HS (n=208 248) of human were obtained from the genome-wide association study database. Genetically variable genes at five levels (phylum, class, order, family, and genus) of known intestinal flora, i.e., single nucleotide polymorphisms (SNPs), were extracted as instrumental variables for linkage disequilibrium (LD) analysis. Human genotype-phenotype association analysis was performed using PhenoScanner V2 database to exclude SNPs unrelated to HS in intestinal flora and analyze whether the selected SNPs were weak instrumental variables. The causal relationship between intestinal flora SNPs and HS was analyzed through four methods of TSMR analysis, namely inverse variance weighted (IVW), MR-Egger regression, weighted median, and weighted mode. Scatter plots of significant results from the four aforementioned analysis methods were plotted to analyze the correlation between intestinal flora SNPs and HS. Both IVW test and MR-Egger regression test were used to assess the heterogeneity of intestinal flora SNPs, MR-Egger regression test and MR-PRESSO outlier test were used to assess the horizontal multiplicity of intestinal flora SNPs, and leave-one-out sensitivity analysis was used to determine whether HS was caused by a single SNP in the intestinal flora. Reverse TSMR analyses were performed for HS SNPs and genus Intestinimonas or genus Ruminococcus2, respectively, to detect whether there was reverse causality between them. Results: A total of 196 known intestinal flora, belonging to 9 phyla, 16 classes, 20 orders, 32 families, and 119 genera, were obtained, and multiple SNPs were obtained from each flora as instrumental variables. LD analysis showed that the SNPs of the intestinal flora were consistent with the hypothesis that genetic variation was strongly associated with exposure factors, except for rs1000888, rs12566247, and rs994794. Human genotype-phenotype association analysis showed that none of the selected SNPs after LD analysis was excluded and there were no weak instrumental variables. IVW, MR-Egger regression, weighted median, and weighted mode of TSMR analysis showed that both genus Intestinimonas and genus Ruminococcus2 were causally associated with HS. Among them, forest plots of IVW and MR-Egger regression analyses also showed that 16 SNPs (the same SNPs number of this genus below) of genus Intestinimonas and 15 SNPs (the same SNPs number of this genus below) of genus Ruminococcus2 were protective factors for HS. Further, IVW analysis showed that genus Intestinimonas SNPs (with odds ratio of 0.62, 95% confidence interval of 0.41-0.93, P<0.05) and genus Ruminococcus2 SNPs (with odds ratio of 0.62, 95% confidence interval of 0.40-0.97, P<0.05) were negatively correlated with the risk of HS. Scatter plots showed that SNPs of genus Intestinimonas and genus Ruminococcus2 were protective factors of HS. Both IVW test and MR-Egger regression test showed that SNPs of genus Intestinimonas (with Q values of 5.73 and 5.76, respectively, P>0.05) and genus Ruminococcus2 (with Q values of 13.67 and 15.61, respectively, P>0.05) were not heterogeneous. MR-Egger regression test showed that the SNPs of genus Intestinimonas and genus Ruminococcus2 had no horizontal multiplicity (with intercepts of 0.01 and 0.06, respectively, P>0.05); MR-PRESSO outlier test showed that the SNPs of genus Intestinimonas and genus Ruminococcus2 had no horizontal multiplicity (P>0.05). Leave-one-out sensitivity analysis showed that no single intestinal flora SNP drove the occurrence of HS. Reverse TSMR analysis showed no reverse causality between HS SNPs and genus Intestinimonas or genus Ruminococcus2 (with odds ratios of 1.01 and 0.99, respectively, 95% confidence intervals of 0.97-1.06 and 0.96-1.04, respectively, P>0.05). Conclusions: There is a causal relationship between intestinal flora and HS of human, in which genus Intestinimonas and genus Ruminococcus2 have a certain effect on inhibiting HS.

Eicosapentaenoic acid reduces inflammation and apoptosis by SREBP1/TLR4/MYD88

AIM

Podocytes dysfunction including the cell integrity, apoptosis and inflammation plays crucial role in diabetic nephropathy. Current exploration evaluated the protective role of eicosapentaenoic acid (EPA) in high glucose-treated podocytes and the underlying mechanisms.

METHOD

MPC5 cell were stimulated by high glucose or treated by EPA of different concentrations. CCK8 assay was utilized to assess MPC5 cell viability, flow cytometry analyzed cell apoptosis.

RESULTS

Data showed that EPA prominently alleviated the high glucose-induced apoptosis and inflammation. Besides, the disruption of the podocytes structure certifying by podocin and synaptopodin induced by hyperglycemia was hindered by EPA administration. In addition, overexpression of the sterol regulatory element-binding protein-1 (SREBP-1) reversed the protective effects of EPA in high glucose-treated podocytes. EPA inhibits the SREBP-1/TLR4/MYD88 signaling in high glucose treated cells.

CONCLUSIONS

This study suggests that EPA protects against podocytes dysfunction by regulating SREBP-1 and these findings provide a better understanding for diabetic nephropathy and a novel therapeutic strategy (Fig. 7, Ref. 24).

Correlation of increased MALAT1 expression with pathological features and prognosis in cancer patients: a meta-analysis

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been identified as a potential cancer biomarker, yet the mechanism by which it influences the development of cancer remains unknown. In this study, we aimed to correlate MALAT1 expression with pathological features and prognosis in cancer patients. Several databases were searched using combinations of keywords relating to MALAT1 and cancer. After selection of relevant cohort studies according to strict criteria, a meta-analysis was conducted. Twelve studies were analyzed, involving 958 cancer patients. Elevated MALAT1 expression was associated with poor prognosis and larger tumors [prognosis: hazard ratio = 3.11, 95% confidence interval (CI) = 1.98-4.23, P = 0.000; tumor size: odds ratio (OR) = 0.40, 95%CI = 0.21-0.74, P = 0.003]. However, no connection with histological grade, T-stage, lymph node (LN) metastasis, or distant metastasis was established (all P > 0.05). A correlation between increased expression and poor prognosis was observed in the large and small sample-size subgroups (all P< 0.05), as was a relationship with large tumor size (OR = 0.30, 95%CI = 0.13-0.71, P = 0.006). Expression was correlated with T-stage and distant metastasis in the small sample-size subgroup (all P < 0.05), but no association was detected regarding histological grade, LN metastasis in either subgroup (all P > 0.05). Our findings demonstrate that elevated MALAT1 expression correlates with large tumor size, advanced tumor stage, and poor prognosis, and might therefore be utilized to evaluate clinical pathological features and prognostic out come for cancer patients.

INPP4B is an oncogenic regulator in human colon cancer

Inositol polyphosphate 4-phosphatase type II (INPP4B) negatively regulates phosphatidylinositol 3-kinase signaling and is a tumor suppressor in some types of cancers. However, we have found that it is frequently upregulated in human colon cancer cells. Here we show that silencing of INPP4B blocks activation of Akt and serum- and glucocorticoid-regulated kinase 3 (SGK3), inhibits colon cancer cell proliferation and retards colon cancer xenograft growth. Conversely, overexpression of INPP4B increases proliferation and triggers anchorage-independent growth of normal colon epithelial cells. Moreover, we demonstrate that the effect of INPP4B on Akt and SGK3 is associated with inactivation of phosphate and tensin homolog through its protein phosphatase activity and that the increase in INPP4B is due to Ets-1-mediated transcriptional upregulation in colon cancer cells. Collectively, these results suggest that INPP4B may function as an oncogenic driver in colon cancer, with potential implications for targeting INPP4B as a novel approach to treat this disease.

MicroRNA-497 targets insulin-like growth factor 1 receptor and has a tumour suppressive role in human colorectal cancer

Past studies have shown that amplified insulin-like growth factor 1 (IGF1)/IGF1 receptor (IGF1-R) signalling has an important role in colorectal cancer (CRC) development, progression and resistance to treatment. In this report, we demonstrate that downregulation of microRNA-497 (miR-497) as a result of DNA copy number reduction is involved in upregulation of IGF1-R in CRC cells. MiR-497 and miR-195 of the miR-15/16/195/424/497 family that share the same 3′ untranslated region (3′UTR) binding seed sequence and are predicted to target IGF1-R were concurrently downregulated in the majority of CRC tissues relative to paired adjacent normal mucosa. However, only overexpression of miR-497 led to suppression of the IGF1-R 3′UTR activity and downregulation of the endogenous IGF1-R protein in CRC cells. This was associated with inhibition of cell survival, proliferation and invasion, and increased sensitivity to apoptosis induced by various stimuli including the chemotherapeutic drugs cisplatin and 5-fluorouracil, and the death ligand tumour necrosis factor-related apoptosis-inducing ligand. The biological effect of miR-497 on CRC cells was largely mediated by inhibition of phosphatidylinositol 3-kinase/Akt signalling, as overexpression of an active form of Akt reversed its impact on cell survival and proliferation, recapitulating the effect of overexpression of IGF1-R. Downregulation of miR-497 and miR-195 appeared to associate with copy number loss of a segment of chromosome 17p13.1, where these miRs are located at proximity. Similarly to miR-195, the members of the same miR family, miR-424 that was upregulated, and miR-15a, miR-15b and miR-16 that were unaltered in expression in CRC tissues compared with paired adjacent normal mucosa, did not appear to have a role in regulating the expression of IGF1-R. Taken together, these results identify downregulation of miR-497 as an important mechanism of upregulation of IGF1-R in CRC cells that contributes to malignancy of CRC.

Determination of low-level mercury based on a renewable-drops sensing technique

The design and characteristics of a novel drop-based fluorescence-detection technique for the determination of mercury(II) are described. The method, using a flow injection technique, is based on the renewable-drops of 3,3',5,5'-tetramethylbenzidine(TMB), which are formed at the bottom tip of a silica capillary tube connected to the end of the flow system. An excitation beam from a high-pressure Hg lamp directly illuminates the drops, the fluorescence emission is conducted to a photodiode (PD) to convert the photocurrent into a voltage signal (mV). Optimum analytical conditions for Hg(II) assays have been established. In NaAc/HAc buffer at pH 3.09 this assay has a wide linear range for Hg(II) from 8.0 x 10(-8) to 2.0 x 10(-5) mol/L with a detection limit of 2.0 x 10(-8) mol/L. The use of renewable drops allowing a fresh reaction surface for each sample is of particular value to solving the problems of irreversible reactions. Besides its high sensitivity, the method permits a simple, fast, and inexpensive measurement with only micro-quantities of reagent consumption. The technique described provides a simple and sensitive way to fabricate sensors of feasible prospects and commercial advantages.

Pressor and bradycardic effects of centrally administered relaxin in conscious rats

The current study tested the hypothesis that centrally administered relaxin elevates arterial pressure in conscious rats and that this hypertensive effect is mediated, at least in part, by central or peripheral vasopressin. Injection of human relaxin (0.068 or 0.34 microgram in 200 nL artificial cerebrospinal fluid) into the right lateral ventricle of conscious, unrestrained Sprague-Dawley rats caused significant dose-related increases in arterial pressure and decreases in heart rat. The pressor and bradycardic responses to intracerebroventricular injections of relaxin were significantly blunted by pretreatment with either intracerebroventricular or intravenous injection of a vasopressin receptor (V1) antagonist, suggesting that the cardiovascular effects of central relaxin are mediated, at least in part, by V1 receptors in the brain and perhaps also by vasopressin released into the peripheral circulation. Neither intracerebroventricular injection of the vehicle alone nor intravenous injection of relaxin (0.34 microgram) altered arterial pressure or heart rate. In contrast to the above, intravenous injections of relaxin (40 micrograms/kg) elicited pressor and tachycardic responses that were not blunted by pretreatment with either intracerebroventricular or intravenous injection of the V1 receptor antagonist. Together, these data suggest that in the central nervous system relaxin contributes to the regulation of cardiovascular function and that the mechanisms for the cardiovascular effects of central and peripheral relaxin are distinct.

Electromagnetic imaging for complex cylindrical objects

Electronic imaging of complex cylindrical objects with arbitrary cross sections was investigated, assuming an incident wave upon both penetrable inhomogeneous dielectric cylinders and perfectly conducting cylinders with known shape, and external measurements of the scanned field. By properly processing the scattered held measurements, the dielectric permittivity distribution of the scanned object can be reconstructed. A theoretical formulation was based on proper arrangement of the incident field directions resulting in a set of integral equations derived and solved by the moment method and the unrelated illumination method. Numerical results demonstrate the capability of the imaging algorithm. Good reconstruction results were obtained even in the presence of additive random noise. In addition, noise effects on the reconstruction results were investigated.

Sodium-proton (Na+/H+) exchange inhibition increases blood pressure in spontaneously hypertensive rat

The current study was designed to determine the role of sodium-proton (Na+/H+) exchange in blood pressure regulation in sodium chloride (NaCl)-sensitive and NaCl-resistant spontaneously hypertensive rats and control Wistar-Kyoto rats (WKY) using 5-(N,N-hexamethylene)amiloride (HMA), a potent and selective inhibitor of Na+/H+ exchange. The response of mean arterial pressure to intravenous infusion of HMA was examined in conscious, unrestrained male rats maintained on normal (1%) or high (8%) NaCl diets for 3 weeks beginning at age 7 weeks. The HMA significantly increased mean arterial pressure in NaCl-sensitive spontaneously hypertensive rats and NaCl-resistant spontaneously hypertensive rats that were fed 1% NaCl, but not in WKY rats that were fed 1% NaCl; the 8% NaCl diet enhanced this pressor response in all 3 strains. The pressor response was accompanied by significant increases in plasma norepinephrine levels in NaCl-sensitive spontaneously hypertensive rats on both diets, but not in NaCl-resistant spontaneously hypertensive rats or WKY rats on either diet. There were no differences in steady-state levels (30-60 nM) of plasma HMA between diet groups in any strain. Therefore, administration of HMA in a dose at which it is highly selective for the Na+/H+ exchanger (Ki = 160 nM) caused a systemic pressor response in spontaneously hypertensive rats that was enhanced by dietary NaCl supplementation. With these data, it is suggested that inhibition of Na+/H+ exchange in vivo has a pressor effect greater in spontaneously hypertensive rats than in WKY rats and is further enhanced by NaCl supplementation.

Role of anterior hypothalamic angiotensin II in the pathogenesis of salt sensitive hypertension in the spontaneously hypertensive rat

Selective alterations in noradrenergic mechanisms in the anterior hypothalamic area (AHA) of NaCl-sensitive spontaneously hypertensive rats (SHR-S) have been demonstrated during dietary NaCl supplementation. To test the hypothesis that endogenous angiotensin II (Ang II) in the AHA also plays a role in blood pressure regulation and in NaCl sensitive hypertension in the SHR-S, Type 1 Ang II (AT1) receptors in the AHA were blocked by local microinjection of losartan, a selective nonpeptide AT1 receptor antagonist, and the effects of the intervention on blood pressure were observed. Microinjection of losartan into the AHA of conscious rats caused a significant dose-related decrease in mean arterial pressure in SHR-S but not in Wistar-Kyoto (WKY) rats. To test the hypothesis that the depressor response to AHA AT1 receptor blockade is enhanced by high (8%) NaCl feeding in SHR-S, losartan was microinjected into the AHA of conscious SHR-S and WKY rats that had been fed 1% or 8% NaCl diets for 3 weeks. The magnitude and duration of the depressor response to losartan were significantly greater in the 8% NaCl fed SHR-S than in the 1% NaCl fed rats. These findings, along with the observation that Ang II receptor numbers are increased in neurons isolated from brain of SHR compared with WKY rats, suggest that endogenous Ang II acting on AT1 receptors in the AHA participates in the tonic control of blood pressure in SHR-S but not in normotensive WKY rats. In addition, it is involved in the pathogenesis of NaCl sensitive hypertension in the SHR-S.

Blocking hypothalamic AT1 receptors lowers blood pressure in salt-sensitive rats

Previous studies from our laboratory have shown that microinjection of DuP 753 (2-n-butyl-4-chloro-5-(hydroxymethyl)-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl]methyl]imidazole, potassium salt), a highly selective nonpeptide antagonist of type 1 angiotensin II receptors, into the anterior hypothalamic area produces a dose-related depressor response in salt-sensitive spontaneously hypertensive rats fed a basal (1%) salt diet. The current study tested the hypothesis that the depressor response to anterior hypothalamic type 1 angiotensin II receptor blockade with DuP 753 or its metabolite EXP 3174 is enhanced by high (8%) salt feeding in this model. DuP 753 or EXP 3174 (40 micrograms in 100 nl artificial cerebrospinal fluid vehicle) or vehicle alone was microinjected into the anterior hypothalamic area of conscious salt-sensitive spontaneously hypertensive and Wistar-Kyoto rats that had been fed 1% or 8% salt diets for 3 weeks. Both DuP 753 and EXP 3174 caused significant decreases in mean arterial pressure in spontaneously hypertensive but not in Wistar-Kyoto rats fed either diet. The magnitude and duration of the depressor responses to DuP 753 and EXP 3174 were significantly greater in the 8% salt-fed spontaneously hypertensive rats than in 1% salt-fed rats. Vehicle injections had no effect on blood pressure in either strain-diet group. Microinjection of angiotensin II (2 micrograms in 100 nl artificial cerebrospinal fluid vehicle) into the anterior hypothalamic area caused significant pressor and bradycardiac responses in all strain-diet groups; dietary salt supplementation enhanced these effects in salt-sensitive spontaneously hypertensive rats but not in Wistar-Kyoto rats. These responses were blocked by pretreatment with EXP 3174.(ABSTRACT TRUNCATED AT 250 WORDS)

Normobaric hypoxia stimulates endothelin-1 gene expression in the rat

The current study tested the hypothesis that exposure to hypoxia enhances endothelin-1 (ET-1) gene expression and elevates circulating ET-1 levels in the rat. Rats were exposed to normobaric hypoxia (10% O2) or room air for 24 or 48 h. ET-1 in arterial blood was measured by radioimmunoassay. ET-1 gene transcript levels were measured by the slot blot technique on total RNA isolated from lung, right and left atria, right and left ventricles, kidney, spleen, liver, brain, main trunk of pulmonary artery, and thoracic aorta. Blots were probed with a 0.5 kb rat prepro ET-1 cDNA that does not cross-hybridize with mRNA for ET-2 or ET-3. Plasma ET-1 levels were increased significantly at 24 (10.03 +/- 2.33 pg/ml) and 48 h (14.02 +/- 3.44 pg/ml) of hypoxia compared with air controls (4.14 +/- 0.66 pg/ml). ET-1 mRNA levels were increased significantly (2-fold) in lung and right atrium after 48 h of hypoxia; no change was seen in organs perfused by the systemic vascular bed. These findings suggest that the hypoxia-induced increase in circulating ET-1 levels is mainly of pulmonary origin. A paracrine effect of ET-1 produced by lung endothelial cells could account for hypoxic pulmonary hypertension.

Atrial natriuretic peptide modulates baroreceptor reflex in spontaneously hypertensive rat

Our previous studies have suggested that atrial natriuretic peptide in the caudal nucleus tractus solitarii is involved in the centrally mediated regulation of blood pressure in the salt-sensitive spontaneously hypertensive rat (SHR). The current study tested the hypothesis that endogenous atrial natriuretic peptide in the caudal nucleus tractus solitarii participates in baroreceptor reflex control of heart rate in this hypertensive model. Salt-sensitive SHR and control Wistar-Kyoto (WKY) rats maintained on basal (1%) salt intake were studied. Arterial baroreceptor reflex-mediated changes in heart rate were recorded in conscious unrestrained rats during phenylephrine (5-40 micrograms.kg-1.min-1 infusion; 30 minutes later, atrial natriuretic peptide (50 ng), monoclonal antibody to atrial natriuretic peptide (0.55 micrograms), purified mouse immunoglobulin G (0.55 micrograms), or artificial cerebrospinal fluid vehicle (50 nl) was microinjected into the caudal nucleus tractus solitarii. Phenylephrine infusion was then repeated and mean arterial pressure and heart rate were monitored as before. The slope of the heart rate/mean arterial pressure relation was significantly less (p less than 0.05) in the salt-sensitive SHR than in the WKY control, indicating that baroreceptor reflex control of heart rate was blunted in this hypertensive model. Microinjection of atrial natriuretic peptide into the caudal nucleus tractus solitarii further blunted (p less than 0.05) baroreceptor reflex control of heart rate in salt-sensitive SHR but not in WKY rats. In contrast, microinjection of the monoclonal antibody enhanced the sensitivity of baroreceptor reflex control of heart rate in salt-sensitive SHR but not in WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Cicletanine blunts the pulmonary pressor response to acute hypoxia in rats

Cicletanine (CIC) recently has been shown to lower systemic arterial pressure in hypertensive animals and man by a mechanism that may involve potentiation of the vasodilator effect of atrial natriuretic peptide (ANP). We previously have shown that ANP prevents acute hypoxia-induced pulmonary vasoconstriction and modulates the severity of chronic hypoxic pulmonary hypertension. The current study tested the hypothesis that CIC inhibits the pulmonary pressor response to acute hypoxia by a cyclic guanosine monophosphate (cGMP)-dependent mechanism. Catheters were placed in the pulmonary arteries of Sprague-Dawley rats through the right jugular vein using a closed chest technique, and in the aorta through the right femoral artery. After a 24 hour recovery, CIC (600 mg/kg) or vehicle was administered orally by gavage to conscious rats 4 hours prior to exposure to 10% oxygen at ambient pressure or to room air. Mean pulmonary arterial pressure (MPAP) and mean systemic arterial pressure (MSAP) and heart rate (HR) were monitored for 3 hours. CIC attenuated the acute pulmonary pressor response to hypoxia (MPAP = 24.5 +/- 1.0 mm Hg in the "hypoxic+CIC" group vs. 29.9 +/- 1.0 mm Hg in the "hypoxic+vehicle" group; p less than 0.05 at 3 hours of hypoxic exposure), but had no significant effect on MSAP or HR. CIC had no effect on MPAP, MSAP, or HR in air control rats. Acute hypoxia caused significant increases in plasma ANP and cGMP and in kidney cGMP content, but CIC administration did not alter these parameters further. This is the first demonstration that acute administration of CIC attenuates the pulmonary pressor response to acute hypoxia in conscious rats.

Depressor effect of blocking angiotensin subtype 1 receptors in anterior hypothalamus

Previous studies have shown that the anterior hypothalamic area participates in the centrally mediated pressor response to exogenous angiotensin II. The current study was designed to test the hypothesis that endogenous anterior hypothalamic angiotensin II plays a significant role in blood pressure control. Type 1 angiotensin II receptors in the anterior hypothalamic area were blocked by local microinjection of DuP 753 (2-n-butyl-4-chloro-5-(hydroxymethyl)-1-[(2'-(1H-tetrazol-5-yl) biphenyl-4-yl)methyl]imidazole, potassium salt), a highly selective nonpeptide antagonist. DuP 753 (20 or 40 micrograms; in 100 nl artificial cerebrospinal fluid) or vehicle alone was microinjected into the anterior hypothalamic area of conscious NaCl-sensitive spontaneously hypertensive rats and Wistar-Kyoto controls. DuP 753 caused significant dose-related decreases in mean arterial pressure (maximal decrease, 22.5 +/- 1.8 mm Hg) with unchanged heart rate in NaCl-sensitive spontaneously hypertensive rats but effected no change in Wistar-Kyoto rats. Injections of equal volumes of artificial cerebrospinal fluid into the anterior hypothalamic area had no effect in either strain. Further, microinjection of DuP 753 into the posterior hypothalamic area produced no significant effect on blood pressure or heart rate in NaCl-sensitive spontaneously hypertensive rats. Microinjection into the anterior hypothalamic area of the selective type 2 angiotensin II receptor antagonist PD 123319 did not affect blood pressure or heart rate in NaCl-sensitive spontaneously hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Pressor effect of blocking atrial natriuretic peptide in nucleus tractus solitarii

Previous studies have shown that microinjection of atrial natriuretic peptide into the caudal nucleus tractus solitarii produces significant increases in local neuronal firing rate associated with reductions in arterial pressure in anesthetized Wistar rats. Single units excited by microinjection of atrial natriuretic peptide into the caudal nucleus tractus solitarii were also excited by activation of arterial baroreceptors and inhibited by baroreceptor unloading. To test the hypothesis that endogenous atrial natriuretic peptide in caudal nucleus tractus solitarii is involved in the tonic control of blood pressure in the rat, we administered a blocking monoclonal antibody to atrial natriuretic peptide in a volume of 50 nl artificial cerebrospinal fluid via microinjection into the caudal nucleus tractus solitarii of spontaneously hypertensive and Wistar-Kyoto rats and observed the effects on mean arterial pressure and heart rate. Control injections of monoclonal antibody were administered into the rostral nucleus tractus solitarii, hypoglossal nucleus, spinal trigeminal nucleus, and cuneate nucleus of spontaneously hypertensive rats. Microinjection of monoclonal antibody into the caudal nucleus tractus solitarii caused significant increases in mean arterial pressure in spontaneously hypertensive rats but not in Wistar-Kyoto rats. There was no concomitant change in heart rate. Control injections of purified mouse immunoglobulin into the caudal nucleus tractus solitarii and of monoclonal antibody into the control neuronal groups listed above had no effect on mean arterial pressure. These results suggest that endogenous atrial natriuretic peptide in the caudal nucleus tractus solitarii mediates tonic control of blood pressure in spontaneously hypertensive rats but not in normotensive Wistar-Kyoto rats.

Atrial natriuretic peptide in acute hypoxia-induced pulmonary hypertension in rats

To test the hypothesis that exogenous atrial natriuretic peptide (ANP) prevents the acute pulmonary pressor response to hypoxia, ANP (20-micrograms/kg bolus followed by 1-microgram.kg-1.min-1 infusion) or vehicle was administered intravenously to conscious rats beginning 3 min before exposure to hypoxia or room air for 90 min. Exogenous ANP abolished the acute pulmonary pressor response to hypoxia in association with marked and parallel increases in plasma ANP and guanosine 5'-cyclic monophosphate (cGMP) and with a significant increase in lung cGMP content. To examine whether endogenous ANP modulates the acute pulmonary pressor response to hypoxia, rats were pretreated with a monoclonal antibody (Ab) to ANP and exposed to hypoxia. Mean pulmonary arterial pressure (MPAP) in the Ab-treated rats was not different from control over the first 6 h of hypoxic exposure. Thereafter, the Ab-treated group had significantly higher MPAP than control. Our data suggest that 1) exogenous ANP blocks the pulmonary pressor response to acute hypoxia via stimulation of cGMP accumulation in the pulmonary vasculature, and 2) endogenous ANP may modulate the subacute, but not acute, phase of hypoxic pulmonary hypertension.

Intrahypothalamic clonidine infusion prevents NaCl-sensitive hypertension

We have previously shown that dietary NaCl supplementation increases blood pressure and sympathetic nervous system activity in association with decreased norepinephrine release and increased alpha 2-adrenergic receptor number in the anterior hypothalamic area of salt-sensitive spontaneously hypertensive rats (SHR-S) but not in salt-resistant spontaneously hypertensive rats (SHR-R) or Wistar-Kyoto (WKY) rats. Further, acute microinjection of clonidine into the anterior hypothalamic area produced depressor responses that were augmented by high salt feeding in SHR-S but not in SHR-R or WKY rats. The current study tested the hypothesis that chronic infusion of clonidine into the anterior hypothalamic area prevents salt-sensitive hypertension in SHR-S. Beginning at age 7 weeks, immediately before initiation of 1% or 8% salt diets, clonidine (2 ng/min) or saline vehicle was infused into the anterior hypothalamic area or femoral vein of male SHR-S via osmotic minipump for 20 days. In SHR-S fed an 8% salt diet, chronic microinfusion of clonidine into the anterior hypothalamic area offset the hypertensive effect of the dietary salt supplementation and reduced the enhancing effects of dietary salt on left ventricular weight and plasma norepinephrine levels. In contrast, chronic microinfusion of clonidine into the anterior hypothalamic area did not significantly affect any of these measures in 1% salt-fed SHR-S. Intravenous infusion of clonidine at the rate used for the anterior hypothalamic area infusion did not alter any of these measures in 8% salt-fed SHR-S.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary Ca2+ prevents NaCl-sensitive hypertension in spontaneously hypertensive rats via sympatholytic and renal effects

NaCl-sensitive spontaneously hypertensive rats (SHR-S) were used to test the hypotheses that dietary Ca2+ supplementation 1) prevents NaCl-sensitive hypertension via a sympatholytic mechanism, and 2) increases diuretic and natriuretic responses to acute volume loading. SHR-S and control WKY rats were begun on one of four diets at age 8 wk: control, high NaCl, high Ca2+, or high NaCl and high Ca2+. In SHR-S, dietary Ca2+ supplementation prevented the NaCl-induced increases in blood pressure and plasma norepinephrine concentrations, the reductions in anterior hypothalamic norepinephrine stores and turnover, and the secondary increases in alpha 2 adrenoceptor number. Thus, Ca2+ prevented NaCl-sensitive hypertension in SHR-S by increasing noradrenergic input to the anterior hypothalamus. High-NaCl-fed SHR-S had impaired diuretic and natriuretic responses to an isotonic volume load; Ca2+ enhanced the ability of these animals to adjust fluid volume rapidly via diuresis and natriuresis. This alteration in renal function may contribute to the hypotensive effect of a high Ca2+ diet in NaCl-sensitive hypertension.

Antihypertensive effect of cicletanine is exaggerated in NaCl-sensitive hypertension

Cicletanine (CIC), a furopyridine derivative, lowers blood pressure in hypertensive animals and humans. We have previously identified an NaCl-sensitive substrain of spontaneously hypertensive rat (SHR-S) that displays enhanced sensitivity to the depressor effects of exogenous atrial natriuretic peptide (ANP) when fed a high NaCl diet. The current study tested the hypotheses that CIC has an exaggerated antihypertensive effect in NaCl-supplemented SHR-S and that this effect might be ANP dependent. CIC (40 mg/kg/day) or vehicle was administered by gavage in a single daily dose for three weeks beginning immediately prior to initiation of 1% or 8% NaCl diets in seven-week-old male SHR-S. CIC significantly decreased mean arterial pressure (MAP) and the ratio of left ventricular and septum weight to body weight (LV + S/BW) in both 8% NaCl- and 1% NaCl-fed SHR-S. The depressor effect of CIC was greater in the 8% NaCl group (-26 mmHg) than in the 1% NaCl group (-13 mmHg). CIC was associated with significant reduction in RAP in the 8% NaCl group but not in the 1% NaCl group. Neither CIC treatment nor 8% NaCl significantly altered plasma ANP or cyclic guanosine monophosphate (GMP) levels in plasma, aorta, or kidney. CIC was associated with significant decreases in plasma norepinephrine (NE) levels in the 1% NaCl group but not in the 8% NaCl group. The data demonstrate that the antihypertensive effect of CIC is exaggerated in NaCl-sensitive hypertension. The antihypertensive effect of CIC appears not to be related to ANP or cyclic GMP but may be related to a combination of a sympatholytic and natriuretic/diuretic effects in SHR-S.

Altered stores of atrial natriuretic peptide in specific brain nuclei of NaCl-sensitive spontaneously hypertensive rats

Previous studies from our laboratories have demonstrated a selective increase in stores of atrial natriuretic peptide (ANP) in the anterior hypothalamus of NaCl-sensitive spontaneously hypertensive rats (SHR-S) compared to NaCl-resistant Wistar-Kyoto (WKY) controls and have suggested that anterior hypothalamic ANP contributes to the pathogenesis of NaCl-sensitive hypertension in SHR-S by local inhibition of norepinephrine release. We have also observed blunting of cardiopulmonary and arterial baroreflex function in SHR-S compared to WKY. In the current study, ANP stores in 12 brain nuclei thought to participate in the pathogenesis of hypertension, including locus coeruleus (LC), A1/C1 area (A1/C1), nucleus tractus solitarii (NTS), medial preoptic nucleus (MPON), suprachiasmatic nucleus (SCN), supraoptic nucleus (SON), anterior hypothalamic area (AHA), paraventricular hypothalamic nucleus (PVN), ventromedial hypothalamic nucleus (VMN), dorsomedial hypothalamic nucleus (DMN), lateral hypothalamic nucleus (LN), and posterior hypothalamic area (PHA), were compared in 10-week-old male SHR-S and WKY rats following 3 weeks of 1% v 8% NaCl feeding. Individual brain nuclei were obtained by the micropunch technique and ANP content of bilateral brain nuclei from individual rats was measured by radioimmunoassay. ANP content was significantly decreased in NTS and LC and elevated in AHA of SHR-S compared to WKY rats on either diet. Dietary NaCl supplementation was associated with increased ANP content in PVN of both strains. These alterations in ANP content in SHR-S may be related to the reduced release of norepinephrine from nerve terminals in AHA and to the presumed central defect in baroreceptor function.

Blockade of endogenous anterior hypothalamic atrial natriuretic peptide with monoclonal antibody lowers blood pressure in spontaneously hypertensive rats

We have previously shown that the atrial natriuretic peptide (ANP) content of the anterior hypothalamic region of NaCl-sensitive spontaneously hypertensive rats (SHR-S) is higher than that of Wistar-Kyoto (WKY) rats. ANP has been shown to inhibit neuronal norepinephrine release and to reduce the excitability of hypothalamic neurons. This study tested the hypothesis that blockade of endogenous ANP in the anterior hypothalamus by local microinjection of a monoclonal antibody to ANP (MAb KY-ANP-II) lowers blood pressure in SHR-S. Purified MAb KY-ANP-II (0.055 and 0.55 micrograms) or control mouse IgG in 200 nl saline was microinjected into the anterior hypothalamic area (AHA) of conscious SHR-S and control WKY rats. As a further control, Mab KY-ANP-II (0.55 microgram) was microinjected into the posterior hypothalamic area (PHA) of SHR-S. Anterior hypothalamic microinjection of MAb KY-ANP-II caused significant dose-related decreases in mean arterial pressure (MAP) and heart rate (HR) in SHR-S but not in WKY rats. Control injections of equal volumes of IgG had no effect on MAP or HR. Microinjection of Mab KY-ANP-II into PHA produced no significant alteration in MAP or HR in SHR-S. These data provide the first demonstration that endogenous ANP in a region of brain known to influence cardiovascular function mediates BP and HR control in the rat. These findings suggest that the increased endogenous ANP in the anterior hypothalamus of SHR-S may be involved in the central regulation of BP in the model.

Lesions of the anterior hypothalamic area increase arterial pressure in NaCl-sensitive spontaneously hypertensive rats

In NaCl-sensitive spontaneously hypertensive rats, diets high in NaCl increase arterial pressure and peripheral sympathetic nervous system activity and decrease the sympatho-inhibition mediated by the anterior hypothalamic area. To test the importance of the defect in anterior hypothalamic area-mediated sympatho-inhibition in the pathogenesis of NaCl-sensitive hypertension, bilateral ibotenic acid lesions of the anterior hypothalamic area were made in NaCl-sensitive spontaneous hypertensive rats, in NaCl-resistant spontaneously hypertensive rats and in normotensive, NaCl-resistant Wistar Kyoto rats. In NaCl-sensitive spontaneous hypertensive rats on a basal NaCl diet, the anterior hypothalamic area lesions caused a rapid rise in arterial pressure within the first week after surgery; by 21 days after surgery, mean systolic arterial pressure of the lesion group was 24 mmHg higher than that of the sham-operated group. In a second experiment, NaCl-sensitive spontaneous hypertensive rats were placed on an 8% NaCl diet 1 day after the lesion of the anterior hypothalamic area. 5 days after the operation, the lesion group of NaCl-sensitive spontaneous hypertensive rats on the 8% NaCl diet had a significantly higher arterial pressure than the sham-operated group, but by 1 week after the lesion, arterial pressures were not significantly different between the lesion and sham-operated NaCl-sensitive spontaneous hypertensive rats on the high NaCl diet. In Wistar Kyoto rats on a basal NaCl diet, lesions of the anterior hypothalamic area resulted in a small, transient elevation of arterial pressure, but no sustained effect. In NaCl-resistant spontaneous hypertensive rats, the anterior hypothalamic area lesions did not affect arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary Ca2+ prevents NaCl-sensitive hypertension in spontaneously hypertensive rats by a sympatholytic mechanism

The current study tested the hypothesis that dietary Ca2+ supplementation reverses the NaCl-sensitive component of hypertension and the associated neurochemical abnormalities in the NaCl-sensitive spontaneously hypertensive rat (SHR-S). Male SHR-S were begun on one of four diets at 8 weeks of age: control (0.75% NaCl/0.68% Ca2+); high NaCl (8.00% NaCl/0.68% Ca2+); high Ca2+ (0.75% NaCl/2.00% Ca2+); and high NaCl/high Ca2+ (8.00% NaCl/2.00% Ca2+). High NaCl SHR-S (X2 weeks) had higher mean arterial pressure (MAP) (161 +/- 4 mm Hg) than controls (149 +/- 3 mm Hg; P less than .05). Supplementation with Ca2+ prevented the rise in MAP in high NaCl rats, but did not alter MAP in controls. The 8% NaCl diet elevated plasma norepinephrine and reduced anterior hypothalamic (AHA) norepinephrine stores and turnover; concomitant Ca2+ supplementation restored both plasma norepinephrine and AHA norepinephrine turnover to normal. Clonidine was microinjected into the AHA of rats maintained on the four diets for 2 weeks to test the hypothesis that dietary Ca2+ supplementation prevents the previously observed NaCl-induced upregulation of alpha 2-adrenoceptors in AHA. Clonidine caused dose-dependent decreases in MAP that were greater in high NaCl rats than in controls. The Ca2+ supplementation prevented the exaggerated depressor response to clonidine in the high NaCl group, but not in the controls. The Ca2+ supplementation had no effect on pretreatment MAP or on MAP responses to clonidine in control NaCl-resistant SHR (SHR-R) or Wistar-Kyoto (WKY) rats. Thus, dietary Ca2+ supplementation prevents the NaCl-induced exacerbation of hypertension and augmented depressor response to clonidine in SHR-S by increasing noradrenergic input to AHA, thereby preventing the upregulation of AHA alpha 2-adrenoceptors.

Atrial natriuretic peptide clearance receptor agonist lowers pulmonary pressure in hypoxic rats

We demonstrated previously that intravenous administration of exogenous atrial natriuretic peptide (ANP) lowers mean pulmonary arterial pressure (MPAP) in hypoxia-adapted rats. To test the hypothesis that endogenous ANP may also lower MPAP in this model, C-ANP-(4-23), a ring-deleted analogue of ANP that binds to the biologically silent ANP clearance receptor (C-ANP receptor) but not to the ANP biological receptor (B-ANP receptor), was administered intravenously as a bolus injection (10 micrograms/kg) followed by an infusion (1 micrograms.kg-1.min-1 for 60 min) to rats adapted to hypoxia (10% O2) for 4 wk and to air control rats. C-ANP-(4-23) significantly lowered MPAP in hypoxic rats but not in air controls. A statistically insignificant reduction in mean systemic arterial pressure was found in both groups after C-ANP-(4-23) administration. C-ANP-(4-23) significantly (two- to threefold) increased endogenous plasma ANP levels in both groups; the increase was not significantly different between groups. Both basal and post-C-ANP-(4-23) levels of plasma ANP were greater in hypoxia-adapted animals than in air controls; the C-ANP-induced increase in plasma ANP was not significantly different between groups. These results suggest that the endogenous ANP may modulate pulmonary vascular tone in rats with hypoxic pulmonary hypertension.

Atrial natriuretic factor prevents NaCl-sensitive hypertension in spontaneously hypertensive rats

Our previous studies demonstrated that acute infusion of atrial natriuretic factor (ANF) produces an enhanced depressor response in NaCl-sensitive spontaneously hypertensive rats (SHR-S) fed a high (8%) NaCl diet compared with control SHR-S fed a normal (1%) NaCl diet and that dietary NaCl loading increases circulating ANF levels in Wistar-Kyoto (WKY) rats but not in SHR-S. The current study tested the hypotheses that 1) long-term infusion of ANF at a dose that elevates plasma ANF to levels comparable with those seen in high NaCl-fed WKY rats prevents the NaCl-induced exacerbation of hypertension in SHR-S and 2) ANF lowers blood pressure in this model by a sympatholytic effect. Male SHR-S received infusions of ANF (0.1 microgram/hr) or vehicle intravenously via osmotic minipump for 3 weeks beginning immediately before initiation of 1% or 8% NaCl diets at age 7 weeks. Chronic ANF infusion prevented the increase in arterial pressure in response to a high NaCl diet in SHR-S but had no effect in 1% NaCl-fed SHR-S. Thus, the NaCl-sensitive component of hypertension in SHR-S was more sensitive to ANF than the non-NaCl-sensitive component. Plasma norepinephrine was significantly increased in ANF-treated, 8% NaCl-fed SHR-S compared with vehicle controls, suggesting that ANF did not prevent NaCl-sensitive hypertension by a sympatholytic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine D2 receptors in the posterior region of the nucleus tractus solitarius mediate the central pressor action of quinpirole (LY171555)

Our previous studies demonstrated that intravenous (IV) administration of the selective dopamine (DA) D2 receptor agonist quinpirole (LY171555) induces a pressor response in conscious Sprague-Dawley (S-D) rats through a central mechanism. The present study was designed to identify the neurons which medicate this pressor response. Injection of quinpirole (1-150 micrograms/kg) into the 4th ventricle produced a greater pressor response of a more rapid onset than similar injections into the lateral ventricle in conscious, freely moving S-D rats, suggesting a site of action in brainstem. Further, microinjections (5-10 micrograms/kg in 200 nl) of quinpirole into major hypothalamic nuclei of conscious, freely moving rats elicited no pressor response. Uni- or bilateral microinjections of quinpirole (5 micrograms/200 nl) into the posterior region of nucleus tractus solitarius (P-NTS) caused a consistent increase in mean arterial pressure (MAP) (Max = 12.4 +/- 1.1 mmHg, n = 12) with a rapid onset (less than 30 sec) in unanesthetized decerebrate S-D rats, while microinjections into the anterior region of NTS, area postrema, C1/A1 regions, raphe obscurus nucleus, locus coeruleus or regions 0.5 mm lateral, superior or inferior to P-NTS produced little or no response. The pressor response induced by bilateral microinjections of quinpirole into P-NTS was not different from that of unilateral microinjection. The pressor response to microinjection of quinpirole into P-NTS was abolished by pretreatment with metoclopramide (5 mg/kg, IV or 25 micrograms/200 nl, P-NTS injection; 5 min before), a selective DA D2 antagonist that crosses the blood-brain barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide attenuates the development of pulmonary hypertension in rats adapted to chronic hypoxia

To test the hypothesis that chronic infusion of atrial natriuretic peptide (ANP) instituted before hypoxic exposure attenuates the development of pulmonary hypertension in hypoxia adapted rats, ANP (0.2 and 1.0 microgram/h) or vehicle was administered intravenously via osmotic minipump for 4 wk beginning before exposure to 10% O2 or to room air. Low dose ANP increased plasma ANP levels by only 60% of vehicle controls after 4 wk and significantly decreased mean pulmonary arterial pressure (MPAP) (P less than 0.01), the ratio of right ventricular weight to body weight (RV/BW) (P less than 0.01), and the wall thickness of small (50-100 microns) pulmonary arteries (P = 0.01) in hypoxia-adapted rats. ANP did not alter any of these parameters in air-control rats. High dose ANP increased plasma ANP levels by 230% of control and produced greater reductions in MPAP (P less than 0.001) and RV/BW) (P less than 0.05), but not in pulmonary arterial wall thickness, than the low dose. Neither dose of ANP altered mean systemic arterial pressure in either hypoxic or normoxic rats. The data demonstrate that chronic infusion of exogenous ANP at a dose that does not affect MPAP or RV weight in air-control rats attenuates the development of pulmonary hypertension and RV enlargement in rats adapted to chronic hypoxia.

Vasopressin lowers pulmonary artery pressure in hypoxic rats by releasing atrial natriuretic peptide

The authors previously demonstrated that arginine vasopressin (AVP) lowers pulmonary artery pressure in rats with hypoxic pulmonary hypertension by activation of the V1 receptor. The pulmonary depressor effect of AVP in hypoxia-adapted rats is not due to its effect on cardiac output. The current study tested two alternative hypotheses: that AVP lowers pulmonary artery pressure in the hypoxia-adapted lung by (1) dilating pulmonary vasculature directly, or (2) releasing atrial natriuretic peptide (ANP) from the heart. The first hypothesis was tested by injecting AVP into the pulmonary arteries of isolated, buffer perfused lungs and monitoring pulmonary artery pressure, and by exposing preconstricted pulmonary artery rings to graded doses of AVP and monitoring the tension generated. AVP caused minimal vasodilation in perfused lungs and only a small vasodilator effect in pulmonary artery rings. The second hypothesis was tested by injecting AVP (160 ng/kg) or vehicle intravenously in conscious hypoxia-adapted (4 weeks) or air control rats and measuring ANP in arterial blood and atria, and by testing pretreatment with the V1 receptor antagonist d(CH2)5 Tyr(Me)AVP (130 micrograms/kg) on the AVP-induced increase in plasma ANP. AVP produced a 7-fold increase in plasma ANP (209 +/- 33 to 1346 +/- 233 pg/ml; p less than 0.05) in hypoxia-adapted rats and a 5-fold increase in ANP (122 +/- 22 to 573 +/- 174 pg/ml; p less than 0.05) in air controls. ANP release was abolished by pretreatment of both groups with d(CH2)5 Tyr(Me)AVP. The AVP-induced ANP release came mainly from left atrium. These data strongly suggest that the pulmonary depressor effects of AVP in hypoxia-adapted rats is due to augmented V1 receptor-induced release of ANP from left atrium.

Atrial natriuretic factor in NaCl-sensitive and NaCl-resistant spontaneously hypertensive rats

Our previous studies demonstrated that chronic dietary NaCl supplementation is associated with significant increases in plasma atrial natriuretic factor in Wistar-Kyoto (WKY) rats but not in NaCl-sensitive spontaneously hypertensive rats (SHR-S). The current study tested the hypotheses that 1) acute volume-induced atrial natriuretic factor release is impaired in SHR-S compared with control NaCl-resistant SHR (SHR-R) and WKY rats maintained on basal (1%) NaCl diets; 2) dietary NaCl supplementation (8% NaCl for 2 weeks) alters acute volume-dependent atrial natriuretic factor release in these strains; and 3) replacement of the deficiency in circulating atrial natriuretic factor seen in NaCl-supplemented SHR-S can reverse the NaCl-sensitive component of hypertension. SHR-S and control SHR-R and WKY rats were placed on 1% or 8% NaCl diets at age 7 weeks; 2 weeks later, right atrial pressure and plasma atrial natriuretic factor were measured in conscious rats before and after acute volume expansion (7, 20, and 60 ml/kg, 5% dextrose, for 1 minute). The slopes of the right atrial pressure x plasma atrial natriuretic factor linear regression for the SHR-S fed both 1% and 8% NaCl were significantly shallower (p less than 0.01) than those of 1% NaCl-fed SHR-R or WKY rats. Dietary NaCl supplementation did not alter right atrial pressure in any strain and blunted acute volume-induced atrial natriuretic factor release in WKY rats, but not in SHR-S or SHR-R, suggesting the dietary NaCl-induced elevation in plasma atrial natriuretic factor levels in WKY rats may be related to impaired clearance, as well as enhanced release, of the peptide. The plasma levels of exogenous atrial natriuretic factor required to abolish the NaCl-induced pressor effect in SHR-S were 12-fold greater than endogenous plasma atrial natriuretic factor levels in 8% NaCl-fed WKY rats, suggesting that impairment of atrial natriuretic factor release does not play a major role in the pathogenesis of NaCl-sensitive hypertension in SHR-S.

Central mechanisms of hypertension

Central monoaminergic neurons, particularly noradrenergic neurons, are involved in the pathogenesis of hypertension. Dietary NaCl supplementation in NaCl-sensitive spontaneously hypertensive rats (SHR-S) elevates blood pressure, increases peripheral sympathetic nervous system activity, and depresses endogenous noradrenaline stores and noradrenaline release in the anterior hypothalamus (AHA). NaCl-resistant spontaneously hypertensive rats (SHR-R) and normotensive Wistar-Kyoto (WKY) rats are resistant to the NaCl-induced alterations in blood pressure and central and peripheral noradrenergic activity, whereas uninephrectomized Sprague-Dawley rats treated with DOCA + NaCl and Dahl-S rats receiving dietary NaCl supplementation develop NaCl-induced increments in blood pressure, but not depressed AHA noradrenaline release. The AHA is a major cardiovascular regulatory region, and depressor responses elicited by pharmacological (alpha 2-adrenoceptor) stimulation of this area are exaggerated in SHR-S fed a high NaCl diet compared to SHR-S fed a basal diet and SHR-R and WKY fed a high or basal NaCl diet. alpha 2-Adrenoceptors in the AHA are increased in number in SHR-S fed a high NaCl diet, presumably reflecting upregulation in response to reduced local noradrenaline release. These findings are consistent with the hypothesis that decreased noradrenergic activity of sympathoinhibitory neurons in the AHA may mediate the exacerbation in hypertension that occurs in SHR-S during dietary NaCl supplementation.

Dietary NaCl loading enhances antihypertensive effect of guanabenz in spontaneously hypertensive rats

Our previous studies demonstrated that high dietary NaCl intake causes increases in blood pressure and plasma norepinephrine (NE) levels and a decrease in NE release associated with local upregulation of alpha 2-adrenoceptor number in the anterior hypothalamic area (AHA) of NaCl-sensitive spontaneously hypertensive rats (SHR-S). Further, acute microinjection of clonidine into the AHA of SHR-S fed a high NaCl diet resulted in greater depressor and bradycardic responses than in SHR-S receiving a normal NaCl diet. The current study tested the hypothesis that the antihypertensive effect of chronic systemic administration of guanabenz (0.24 micrograms/kg/min, IV) is enhanced in SHR-S maintained on a high (8%) NaCl diet than in control rats on a normal (1% NaCl) diet. After two weeks on the diets, mean arterial pressure (MAP) and heart rate (HR) were measured and blood for NE and epinephrine (E) assay was collected from intra-arterial cannulas in conscious, unrestrained rats. The ratio of left ventricle and septum to body weight (LV + S/BW) was determined. Chronic infusion of guanabenz significantly decreased MAP (P less than .05), HR (P less than .01) and LV + S/BW (P less than .01) in 8% NaCl fed SHR-S, but not in 1% NaCl fed SHR-S (P greater than .1). Guanabenz tended to reduce plasma NE levels in 8% NaCl fed SHR-S (.1 greater than P greater than .05), but not in 1% NaCl fed rats (P greater than .1).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic effects of arginine vasopressin in rats adapted to chronic hypoxia

Acute and chronic pulmonary and systemic hemodynamic responses to arginine vasopressin (AVP) were examined in 4-wk hypoxia-adapted and air control rats. AVP, administered intravenously as bolus injections or sustained infusions, produced major dose-dependent V1-receptor-mediated reductions in mean pulmonary arterial pressure in hypoxia-adapted rats. These effects were comparable in pentobarbital-anesthetized, thoracotomized animals and in conscious, intact rats. Chronic infusions of AVP induced a sustained reduction in mean pulmonary arterial pressure and partially prevented the development of pulmonary hypertension without changing systemic arterial pressure. AVP induced significant decreases in cardiac output in both groups; the cardiac output response was not significantly different in hypoxia-adapted and air control animals. AVP induced almost no change in MPAP in air control rats. Furthermore the systemic pressor effects of AVP were significantly blunted in hypoxia-adapted rats compared with air controls. We conclude that the pulmonary depressor and blunted systemic pressor effects of AVP observed in hypoxia-adapted rats may be related to release of a vasodilator, such as endothelium-derived relaxing factor, vasodilator prostaglandins, or atrial natriuretic peptides. Further study is needed to elucidate these mechanisms and assess the usefulness of AVP and/or its analogues in the treatment and prevention of hypoxia-induced pulmonary hypertension.

Dietary Ca2+ supplementation prevents the exaggerated responsiveness of anterior hypothalamic alpha 2-adrenoceptors in NaCl-loaded spontaneously hypertensive rats

Our previous studies demonstrated that (a) dietary Ca2+ supplementation prevents the rise in blood pressure, activation of sympathetic outflow, and reductions in anterior hypothalamic norepinephrine (NE) content and release induced in NaCl-sensitive spontaneous hypertensive rats (SHR-S) by dietary NaCl loading; and (b) stimulation of alpha 2-adrenoceptors by microinjection of clonidine into the anterior hypothalamic area (AHA) results in an exaggerated depressor response in SHR-S fed a high NaCl diet as compared with SHR-S on a basal diet. The current study tested the hypothesis that dietary Ca2+ supplementation prevents these NaCl induced defects in AHA noradrenergic neurons. SHR-S were placed on diets containing: (a) high NaCl; (b) high Ca2+; (c) high Ca2+, high NaCl; or (d) basal NaCl, basal Ca2+ (control). Two weeks later, clonidine (0.6, 1.2, or 2.5 micrograms) was microinjected into the AHA of conscious rats. Clonidine caused dose-dependent decreases in mean arterial pressure (MAP) and heart rate (HR) that were greater in SHR-S on the high NaCl diet than on the control diet. Ca2+ supplementation prevented the exaggerated depressor response to clonidine in high NaCl-fed SHR-S, but did not reduce the response in SHR-S on the basal NaCl diet. Ca2+ supplementation had no effect on blood pressure (BP) or HR responses to clonidine in control NaCl-resistant SHR (SHR-R) or in normotensive Wistar Kyoto (WKY) rats.

Hypothalamic microinjection of alpha 2-adrenoceptor agonists causes greater sympathoinhibition in spontaneously hypertensive rats on high NaCl diets

We tested the hypothesis that in NaCl-sensitive spontaneously hypertensive rats (SHR-S) maintained on high NaCl diets, sympathoinhibitory neurons in the anterior hypothalamic area display increased responsiveness to alpha 2-adrenergic receptor stimulation, giving rise to exaggerated depressor responses. Clonidine (0.6-2.5 micrograms) was microinjected directly into the anterior hypothalamic area of SHR-S maintained for 2 weeks on high (8%) and normal (1%) NaCl diets, and blood pressure and heart rate responses were monitored. Controls were NaCl-resistant SHR (SHR-R) and normotensive Wistar-Kyoto (WKY) rats. Clonidine microinjection into the anterior hypothalamic area resulted in dose-dependent rapid-onset depressor and bradycardic responses that were significantly greater in SHR-S fed on a high NaCl diet. In SHR-R and WKY rats, the high NaCl diet had no significant effect on blood pressure or heart rate responses to clonidine. Further studies demonstrated that the response to microinjection of clonidine into the rat anterior hypothalamic area was location-specific, since injections into surrounding hypothalamic nuclei gave a longer latency in the onset of either depressor and bradycardic responses or pressor and tachycardic responses. The response of clonidine was blocked by concurrent microinjection of the selective alpha 2-adrenergic antagonist rauwolscine but not by the alpha 1-adrenergic antagonist prazosin, confirming that the response was alpha 2-adrenoceptor-specific. Microinjection of the selective alpha 2-agonist guanabenz into the anterior hypothalamic area produced depressor and bradycardic responses in SHR-S and Sprague-Dawley rats, while microinjection of the selective alpha 1-agonist phenylephrine into the anterior hypothalamic area had no effect on either blood pressure or heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide lowers pulmonary arterial pressure in hypoxia-adapted rats

To test the hypothesis that atrial natriuretic peptide (ANP) has a direct vasodilator effect on the pulmonary vasculature that is enhanced in hypoxia-induced pulmonary hypertension in the rat, we determined the effects of ANP on mean pulmonary (MPAP) and systemic arterial pressure (MSAP) in intact conscious Sprague-Dawley rats exposed to 10% O2 or room air for 4 wk. Catheters were placed in the pulmonary artery through the right jugular vein by means of a closed-chest technique. MPAP and MSAP were monitored before and after intravenous injections of graded doses of ANP. ANP produced dose-related decreases in MPAP that were greater in the hypoxic group than in air controls. There were no significant between-group differences in the systemic depressor responses to ANP or in the ANP-induced reduction in cardiac output. ANP lowered MPAP significantly in isolated perfused lungs from both hypoxia-adapted and air control rats, and this effect was significantly greater in the hypoxic than the air control lungs. These data indicate that ANP lowers pulmonary arterial pressure in rats with hypoxia-induced pulmonary hypertension, mainly by a direct vasodilator effect on the pulmonary vasculature.

Exaggerated depressor response to 6-iodoamiloride in NaCl-sensitive spontaneously hypertensive rats

The current study tested the hypothesis that NaCl-sensitive hypertension may result from increased membrane sodium channel activity. The effect of 6-iodoamiloride, and analog of the sodium channel blocker amiloride, on mean arterial pressure (MAP) was examined in conscious, freely moving NaCl-sensitive spontaneously hypertensive rats (SHR-S) fed high (8%) or normal (1%) NaCl diets. SHR-S and age-matched NaCl-resistant SHR (SHR-R) and normotensive Wistar-Kyoto (WKY) control rats were studied at 9 weeks of age after 2 weeks on either high (8%) NaCl or control (1%) NaCl diets. 6-iodoamiloride was infused intravenously in doses of 0.38 or 0.76 mg/100 g body weight, and MAP and heart rate (HR) were monitored from a femoral arterial cannula for 2 hours. The 8% NaCl diet caused a significant elevation in MAP in SHR-S but not in SHR-R or WKY. Administration of 6-iodoamiloride (both doses) produced a significant, sustained decrease in MAP in both SHR-S and SHR-R. Maximal depressor responses to high dose 6-iodoamiloride were significantly enhanced in SHR-S fed 8% NaCl (31.2 +/- 3.7 mm Hg) compared to SHR-S fed 1% NaCl (14.8 +/- 2.4 mm Hg) or SHR-R fed either 8% or 1% NaCl diets (15.6 +/- 4.2 and 10.2 +/- 3.0 mm Hg, respectively). In contrast, feeding an 8% NaCl diet had no significant effect on the depressor responses to 6-iodoamiloride in either SHR-R or WKY rats. In WKY, these doses of 6-iodoamiloride had no significant effect on MAP in either diet group. 6-iodoamiloride had no significant effect on heart rate in any group. These results support the hypothesis that the exacerbation of hypertension in SHR-S fed a high NaCl diet may result from increased membrane sodium channel activity.

Impaired release of atrial natriuretic factor in NaCl-loaded spontaneously hypertensive rats

Our previous studies demonstrated that NaCl-sensitive spontaneously hypertensive rats (SHR) of the Okamoto strain exhibit increased blood pressure and reduced noradrenergic input to the anterior hypothalamus area when fed high NaCl diets. The current study tested the hypotheses that 1) release of atrial natriuretic factor (ANF) into the plasma is impaired in NaCl-loaded SHR, a defect that would tend to elevate blood pressure, and 2) ANF levels in regions of brain involved in blood pressure regulation, such as the anterior hypothalamic area, are altered in SHR. SHR and control Wistar-Kyoto rats (WKY) were placed on 1% or 8% NaCl diets at age 7 weeks; 2 weeks later, ANF levels were measured in plasma, left and right atria, anterior hypothalamic area, ventral hypothalamic area, posterior hypothalamic area, pons, and medulla by radioimmunoassay. Blood for ANF assay was obtained from intra-arterial cannulas in conscious, unrestrained rats studied in the resting state. The 8% NaCl diet produced an increase in blood pressure in the SHR, but not in the WKY. Plasma ANF levels were significantly greater in WKY fed 8% NaCl than in WKY fed 1% NaCl, but dietary NaCl loading did not produce similar increases in plasma ANF in the SHR. Plasma ANF levels were not significantly different between SHR and WKY fed the 1% NaCl diet. The observation that dietary NaCl loading stimulated ANF release into the plasma in WKY but not in SHR suggests that the exacerbation in hypertension seen in NaCl-loaded SHR may be related to an impairment in ANF release.(ABSTRACT TRUNCATED AT 250 WORDS)

The neural basis of salt sensitivity in the rat: altered hypothalamic function

Dietary NaCl supplementation in NaCl-sensitive spontaneously hypertensive rats (SHR-S) elevates blood pressure, increases peripheral sympathetic nervous system activity and depresses endogenous noradrenaline stores and noradrenaline release in the anterior hypothalamus. NaCl-resistant spontaneously hypertensive rats (SHR-R) and normotensive Wistar Kyoto (WKY) rats are resistant to the NaCl-induced alterations in blood pressure and central and peripheral noradrenergic activity, suggesting that the alterations observed in the SHR-S during NaCl loading are genetically mediated. The anterior hypothalamus is a major cardiovascular regulatory region, and depressor responses elicited by pharmacologic (alpha 2 adrenoceptor) stimulation of this area are exaggerated in SHR-S fed a high NaCl diet compared with SHR-S fed a basal diet and compared with SHR-R and WKY fed a high or basal NaCl diet. Membrane-binding techniques confirm that alpha 2 adrenoceptors in the anterior hypothalamic area are increased in number in SHR-S fed a high NaCl diet, presumably reflecting upregulation in response to reduced local noradrenaline release. These findings are consistent with the hypothesis that decreased noradrenergic activity of sympathoinhibitory neurons in the anterior hypothalamic area may mediate the exacerbation in hypertension that occurs in SHR-S during dietary NaCl supplementation.