Effect of Long-Term Treatment with Diltiazem on Atrial Natriuretic Peptides in Spontaneously Hypertensive Rats

ABSTRACT

The present study was designed to examine the possible effect of long-term treatment with diltiazem on plasma and atrial concentrations of atrial natriuretic peptides (ANP) in spontaneously hypertensive rats (SHR). Diltiazem treatment reduced blood pressure and ventricular weight in SHR. Plasma ANP concentration in untreated SHR was higher than Wistar-Kyoto rats (WKY). Diltiazem treatment decreased plasma ANP concentration in SHR near to the level of WKY; moreover, plasma ANP concentration was correlated with blood pressure and ventricular weight in treated and untreated SHR. Left atrial ANP concentration in untreated SHR was lower than WKY. Diltiazem treatment increased left atrial ANP concentration in SHR, but this effect was not noted in WKY. These results suggest that the ANP release from the left atrium is chronically stimulated in adult SHR, and that the prevention of an increase in plasma ANP by diltiazem treatment may be, in part, attributed to the improvement of cardiac overload induced by reductions in blood pressure and cardiac hypertrophy.     

肾血管性高血压大鼠心脏肥厚不同时期血浆及组织心钠素、内皮素含量变化

目的 了解高血压心脏病左室结构、功能变化时血浆及心肌组织中心钠素(atrial natriuretic peptide ANP)、内皮素(endothelin ET)含量变化。方法 应用放免法监测二肾一夹意义型(2K1C)肾血管性高血压大鼠(RHR)血浆及心肌组织中ANP、ET含量变化，并根据超声心动图评价高血压大鼠心脏结构、功能动态变化，将高血压大鼠进行分组。结果 高血压左室向心性肥厚期血浆及心肌组织(左心室)中ANP、ET含量明显升高；左室离心性肥厚期血浆ET较向心性肥厚期组更高，但心肌组织中ET含量与其无显著差别，而血浆及心肌组织中．ANP含量均较向心性肥厚期组低。结论 2K1C型高血压大鼠血浆及心肌组织中ANP、ET含量均升高；血浆ET与．ANP含量变化在左室肥厚中可能起着更为重要作用。     

Enhanced Dilatation by Atrial Natriuretic Peptide of Renal Arcuate Arteries from Young,but not Adult,Spontaneously Hypertensive Rats

The effects of a synthetic atrial natriuretic peptide (sANP) on the contractile response of isolated renal resistance vessels (internal diameter 180–300 um) from young (5 wk) and adult (20 wk) spontaneously hypertensive (SHR) and control Wistar-Kyoto (WKY) rats have been examined. Segments of the vessels were mounted as ring preparations on an isometric myograph and a sub-maximal tone was induced with potassium chloride. All vessels relaxed in a concentration dependent manner when sANP was added to the chamber solution; the threshold concentration was 10^?10 mol/L, but half-maximal relaxation was seen at about 10^?8 mol/L. The vessels from the young SHRs relaxed slightly more than those from the young WKYs. There was no difference in the relaxation of the vessels from the adult SERs and WKYs. The results suggest that although slight differenoes in sensitivity to atrial natriuretic peptide may exist in young SHRs, the greater hypotensive action of infused atrial natriuretic peptide which has been reportd for adult SHRs is not related to a greater relaxing effect of the peptide on the renal resistance vessels.     

Effect of Chronic Treatment with Angiotensin I Converting Enzyme Inhibitors on Circulating Atrial Natriuretic Polypeptide in Spontaneously Hypertensive Rats

We have recently shown that circulating atrial natriuretic polypeptide (ANP) in adult spontaneously hypertensive rats (SHR) is higher than that in age-matched Wistar-Kyoto rats (WKY). The present experiment was designed to examine the possible effects of chronic treatment with angiotensin I converting enzyme inhibitors (ACEI) on plasma ANP levels in SHR. Captopril and enalapril lowered blood pressure and reduced relative ventricular weight in SHR but not to the level of WKY. Plasma ANP levels were decreased by captopril and enalapril compared with untreated SHR. These results suggest that the ANP release may be suppressed in ACEI-treated SHR compared with untreated SHR. We speculate that a reduction of cardiac overload by ACEI may in part explain the decline of circulating ANP.     

Plasma Levels of Atrial Natriuretic Peptides in Conscious Adult Spontaneously Hypertensive Rats

The effects of acute volume expansion and acute salt loading on the plasma levels of immunoreactive atrial natriuretic peptides (ir-ANP's) were investigated in conscious adult (16 weeks) Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Basal plasma concentrations of ir-ANP's were similar (108 ± 9 pg/ml and 105 ± 8 pg/ml, respectively) in hypertensive and normotensive rats. In both strains mean, arterial pressure, heart rate and plasma catecholamines were, unaltered by acute volume expansion but significantly elevated by acute salt loading. However, both acute volume expansion and acute salt loading increased plasma concentrations of ir-ANP's, similarily in SHR and WKY rats, independent of blood pressure or plasma catecholamine levels. Our findings show that chronic hypertension in SHR does not result in changes in basal or VOL- and SAL-stimulated levels of circulating ir-ANP's.     

Different Secretion Patterns of Adrenomedullin,Brain Natriuretic Peptide,and Atrial Natriuretic Peptide During Exercise in Hypertensive and Normotensive Subjects

The purpose of this study was to investigate the effect of exercise on plasma concentrations of adrenomedullin, brain natriuretic peptide (BNP), and atrial natriuretic peptide (ANP) in patients with essential hypertension (n=15) and in normotensive controls (n=10). Exercise consisted of two fixed workloads, 40 and 80 watts of work load using a supine bicycle ergometer. Plasma levels of all three peptides at rest were significantly higher in hypertensives than in controls. Plasma concentrations of ANP increased with exercise in both groups and had greater     

不同抗高血压药物对自发性高血压大鼠左心室肥厚及心钠素mRNA表达的影响

探讨抗高血压药物对自发性高血压大鼠（ＳＨＲ）左心室肥厚与心钠素（ＡＮＰ）ｍＲＮＡ表达的影响。方法成年（１６周龄）雄性ＳＨＲ测定收缩压后随机分为３组，分别给予卡托普利（１００ｍｇ／ｋｇ·ｄ－１），双氢克尿塞（１００ｍｇ／ｋｇ·ｄ－１），普萘洛尔（４０ｍｇ／ｋｇ·ｄ－１）治疗，共１２周，年龄、性别及数量配对的正常血压的ＷＫＹ及未治疗ＳＨＲ作为对照组。治疗结束时测体重、收缩压。动物断头处死，取左心室称重后，采用异硫氰酸胍一步法提取组织总ＲＮＡ，Ｎｏｒｔｈｅｒｎ杂交法检测ＡＮＰｍＲＮＡ相对表达量。结果治疗组动物收缩压及左心室重／体重比均明显低于未治疗ＳＨＲ组。卡托普利与普萘洛尔明显抑制心钠素基因的表达，双氢克尿塞对心钠素基因的表达影响较小。结论不同抗高血压治疗在降低血压和逆转左心室肥厚的同时也不同程度地抑制左心室心钠素基因的表达，利尿剂对心钠素表达的影响较小。     

Comparison of Simultaneous Measurements of Blood Pressure by Tail-Cuff and Carotid Arterial Methods in Conscious Spontaneously Hypertensive and Wistar-Kyoto Rats

We determined the validity of systolic blood pressure (SBP) measured by tail-cuff blood pressure (TCBP) with direct intra-arterial measurements. In conscious, restrained Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR), carotid artery (CA) BP and TCBP were simultaneously measured. In both WKY and SHR strains, highly significant correlations between CABP and TCBP were found and Bland-Altman analyses showed no bias when the two methods were compared. The limits of agreement between CABP and TCBP in WKY and SHR were wide and reproducibility of pressure measurements by either technique was poor, with some evidence for strain-dependent differences. Pressure measurements made over short time frames, however, showed close agreement between CABP and TCBP. Acetylcholine-induced reductions in pressure were equivalently detected by tail-cuff and direct arterial measurement in both strains but angiotensin II-induced pressure elevations were over-estimated by tail-cuff in SHR. Telemetered SBP measurements in conscious rats were highly variable in a strain-dependent manner.     

Lack of Influence of Circulating Adrenaline on Blood Pressure in Normotensive and Hypertensive Rats

The relationship between circulating adrenaline and blood pressure was examined by manipulating plasma adrenaline levels in both normotensive and hypertensive rats: bilateral adrenalmedullectomy was performed in spontaneously hypertensive rats and stroke-prone spontaneously hypertensive rats; adrenaline bitartrate was infused chronically (25-32 μg/kg/h s.c.) into Wistar Kyoto, Sprague Dawley and stroke-prone rats via osmotic minipumps. Arterial and venous catheters were subsequently implanted for direct measurement of mean arterial pressure, blood sampling and drug administration in conscious rats. Adrenaline infusion for 5-6 weeks in Wistar Kyoto rats did not affect resting blood pressure (118 ± 3 versus 119 ± 1 mmHg in controls) even though plasma adrenaline was elevated 12-fold. Plasma noradrenaline was marginally elevated. Blood pressure was also unaffected by adrenaline infusion in Sprague Dawley or stroke-prone hypertensive rats. One week after adrenal medullectomy, plasma adrenaline was reduced 89% in spontaneously hypertensive rats, but blood pressure was unaffected. Ten weeks after adrenal medullectomy in young stroke-prone rats, resting blood pressure was slightly higher (167 ± 2 mmHg) than in control rats (157 ± 2 mmHg), although adrenaline was reduced by 34% in plasma and 67% in adrenal glands. Nitroprusside was infused acutely to lower blood pressure and reflexly elevate plasma noradrenaline. Neither of these responses were affected by chronic adrenaline infusion or adrenal medullectomy. In both adrenaline-infused Wistar Kyoto and medullectomised stroke-prone rats, autonomic blockade reduced blood pressure to a similar extent as in controls, indicating that the degree of sympathetic vasoconstriction was not altered by either treatment. Moreover, pressor responses to i.v. phenylephrine were similar in all groups, indicating that changes in plasma adrenaline did not affect post-synaptic receptor sensitivity. We conclude that elevated plasma adrenaline seen in spontaneous hypertensive rats is unlikely to contribute to their hypertension.     

Effects of Chronic Arachidonate on Blood Pressure of Spontaneously Hypertensive Rats

Three weeks of treatment with arachidonic acid (250 mg/kg/day, s.c.) produced an antihypertensive effect in 16 week-old spontaneously hypertensive rats (SHR) as compared with vehicle treated rats. Indomethacin (4 mg/kg, s.c. B.I.D.), given concurrently with arachidonate, abolished the antihypertensive effect. Plasma catecholamines were not altered by the arachidonate treatment, but blood pressure increments after spinal cord stimulation or after intravenous administration of norepinephrine and angiotensin II in the pithed rat were diminished. Increments in plasma catecholamines in response to spinal cord stimulation were similar in both groups of pithed rats.

These data demonstrate the antihypertensive effect of arachidonic acid in SHR with established hypertension. This beneficial effect seems to be mediated through cyclooxygenase metabolites, and might be related to reduced responsiveness of peripheral blood vessels to pressor stimuli.     

Central Actions of Agmatine in Conscious Spontaneously Hypertensive Rats

Agmatine (decarboxylated arginine) is an endogenous ligand at alpha-2 adrenergic and imidazoline nonadrenergic receptors. In conscious spontaneously hypertensive rats (SHRs), we have studied its central effects on cardiovascular function and its interaction with the second generation centrally acting antihypertensive agent, rilmenidine, and the reference imidazoline, clonidine, which are mixed alpha-2 adrenoceptor/imidazoline receptor agonists. Agmatine, when administered in low doses (30–100 µg/kg) into the fourth ventricle had no effect on blood pressure and caused an increase in heart rate. A higher dose of 1000 µg/kg produced an adverse reaction in conscious SHRs and a marked and long-lasting increase in blood pressure. The effects of fourth ventricular rilmenidine (300 µg/kg) and clonidine (10 µg/kg) were equihypotensive and equibradycardic. The antihypertensive and bradycardic effects of rilmenidine were not reversed by cumulative intracisternal doses (30-100-300 µg/kg) of agmatine. The bradycardia obtained 20 min after intracisternal administration of clonidine in the fourth ventricle was reversed by 30 µg/kg agmatine. Only the highest dose of agmatine (1000 µg/kg) did reverse the antihypertensive effects of rilmenidine and clonidine. Agmatine neither did mimic nor block the antihypertensive response to rilmenidine and clonidine at well-tolerated doses. Yet agmatine produced a small tachycardia at relatively low doses and was able to reverse the bradycardia induced by clonidine. Therefore, its affinity for alpha-2 adrenoceptors in vitro might partially explain its cardiovascular effects in vivo.     

Accelerated Natriuresis Induced by Synthetic Atrial Natriuretic Polypeptide in Spontaneously Hypertensive Rats

Effects of synthetic alpha human atrial natriuretic polypeptide (α-hANP) on diuresis, natriuresis and mean arterial blood pressure (MAP) were compared between 4-5 month-old male spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) under ether anesthesia. In both groups, the peptide injected (0.5 μg/100g body weight, i.v.) caused potent (about ten fold), rapid and short-acting (for 15 min) increases in sodium (Na⁺) and chloride excretions and also an increase in urine flow and potassium excretion with lesser magnitude. Although ratios of the maximum response to basal value were much the same, net increases in urine flow and Na⁺output were significantly greater in SHR than in WKY. As to the effect on MAP, a rapid (within 2 min) fall of 9.5 per cent on the average from control levels was equally observed in the two groups.

These results suggest that the atrial natriuretic peptide may be involved in the altered regulatory mechanism of fluid and electrolyte balance in SHR models with genetic hypertension.     

Hypertensive Diabetic Rats: Different Effects of Streptozotocin Treatment on Blood Pressure in Adult SHR and in Neonatal SHR

The effect of streptozotocin (STZ) treatment on blood pressure in adult spontaneously hypertensive rats (SHR) was compared with that in neonatal SHR. Three-month-old SHR were intravenously given 10, 30 or 50 mg/kg of STZ. When STZ was given in adult SHR, weight loss, overt hyperglycemia and the reduction of blood pressure occurred dose dependently. Two-day-old pups from SHR were subcutaneously injected with 100 mg/kg of STZ. Neonatal STZ treatment did not attenuate the development of hypertension in SHR. Since neonatally STZ-treated SHR develop mild diabetic symptom with hypertension and develop mild diabetic glomerulosclerosis, they are a good model for studying vascular complications or other disorder relating to the synergism between hypertension and diabetes mellitus.     

Comparative Vascular and Renal Excretory Effects of Atrial Natriuretic Factor,Sodium Nitroprusside and 8-BR-cGMP in Spontaneously Hypertensive Rats

ANF (99–126) (1 μg/kg/min x 30 min iv) lowered BP from 198±3 to 140±4 mmHg (P<.05; N=7), in association with marked diuresis (372.2±33.9 vs 48.2±11.5 μ/kg/min in the control) and natriuresis (62.7±6.4 vs 6.6±1.7 μEq/kg/min) in anesthetized SHR. Concomitantly, great increases in plasma cGMP levels and urinary cGMP excretion occurred. Elevation in plasma cGMP due to ANF persisted in SHR with bilateral nephrectomy. SNP (4 μg/kg/min x 30 min iv) decreased BP from 192±3 to 158±5 mmHg (P<.05; N=7). In contrast to ANF, this occurred without significant changes in urine and sodium excretion; alterations in plasma and urinary cGMP were also absent. Furthermore, 8-Br-cGMP (0.3 mg/kg/min x 30 min iv) also lowered BP from 164±9 to 129±7 mmHg (P<.05; N=6) in the absence of diuresis (8.5±1.3 vs 19.8±4.1 μl/kg/min). Intravenous infusion of 8-Br-cAMP at the same rate did not affect BP and produced a modest but significant increase in sodium and water excretion. Our results indicate that the renal excretory responses to exogenous cGMP or SNP differ from those to ANF. The findings are consistent with a mediating role of cGMP in the vascular but not the renal effects of ANF, since at equally effective hypotensive doses both SNP and 8-Br-cGMP failed to register any significant renal excretory effects.     

Effect of Nicorandil on Cardiac Dysfunction During Reperfusion in Normotensive and Spontaneously Hypertensive Rats

The cardioprotective effect of nicorandil, an opener of ATP-sensitive potassium channels, was studied in the isolated perfused hearts of the spontaneously hypertensive rat (SHR) and normotensive Wistar-Kyoto (WKY) rat. The hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. Controls received no drug. In the nicorandil group, the hearts were treated with 0.03 to 0.3 mmol/L nicorandil for 15 min before ischemia. Left ventricular developed pressure (LVDP and end diastolic pressure (LVEDP) at 30 min of reperfusion were significantly lower and larger, respectively, in SHR than in WKY rats. Nicorandil improved LVDP and decreased LVEDP at 30 min of reperfusion in both SHR and WKY rats dose-dependently. The hypertensive heart in the early stage is already susceptible to reperfusion-cardiac dysfunction. Nicorandil has a beneficial effect on the post-ischemic dysfunction in both SHR and WKY rats.     

软脉灵对自发性高血压大鼠心肌纤维化的作用

目的 观察软脉灵对自发性高血压大鼠(SHR)心肌纤维化的影响.方法 选择12周龄雄性SHR 36只,随机分为4组,软脉灵大剂量和小剂量组、空白组、阳性对照组.血压正常的京都Wistar大鼠(WKY)为正常对照组(WKY组).治疗前及治疗12周后用尾袖法测定动脉血压,称重后处死,取心脏,计算左心室重量与体重比(LVM/BW),天狼星红染色,计算心肌胶原容积分数.结果 软脉灵大剂量、小剂量组治疗12周后,收缩压(SBP)均显著低于空白组(P<0.01).与空白组相比,软脉灵大剂量组对SHR心肌外斜层纤维化有明显抑制作用(P<0.01),而软脉灵小剂量组则无影响;与空白组相比,软脉灵大剂量和小剂量组对SHR心肌中环层纤维化及心肌血管周围纤维化均有明显抑制作用(P<0.01).结论 软脉灵可以抑制SHR血压的发展,抑制SHR的心肌纤维化.     

Effect of Atrial Natriuretic Factor on Aldosterone and Its Precursor Steroid Production in Adrenal Zona Glomerulosa Cells from Spontaneously Hypertensive Rats

ABSTRACT

The effect of α-human atrial natriuretic factor(α-hANP, 10^-6M- 10^-8M) on basal, and maximum angiotensin II (AII, 4. 8 x 10^-8 M)-, ACTH (4. 3 × 10^-9M)-, and potassium (8mM)-stimulated levels of corticosterone, 18-hydroxycorticosterone (18-OHB) and aldosterone production were studied in adrenal glomerulosa cells from spontaneously hypertensive rats (SHR) at 14 weeks of age as compared to those in the age-matched Wistar-Kyoto rats (WKY) on a normal sodium diet. Plasma corticosterone, 18-OHB and aldosterone levels and the aldosterone response in vitro to the graded doses of All were similar in SHR and WKY. Basal, and maximum All-, ACTH-, and potassium- stimulated levels of corticosterone, 18-OHB and aldosterone also were similar in the cells from SHR and WKY. Q-hANP similarly inhibited basal and stimulated levels of these corticosteroids in the cells from SHR and WKY.

These results indicate that the inhibitory effect of α-hANP on aldosteronogenesis is unaltered in SHR at 14 weeks of age on a normal sodium diet.     

The Role of Kinins and Atrial Natriuretic Peptide on the Renal Effects of Neutral Endopeptidase Inhibitor in Normotensive and Hypertensive Rats

To further elucidate the renal effects of NEP inhibition, we employed NEP inhibitor UK 73967 (UK), with or without a kinin receptor antagonist Hoe 140 (Hoe), in Sprague-Dawley normotensive rats and DOCA-salt hypertensive rats.

In Sprague-Dawley rats: 1) injected UK significantly decreased NEP, and increased kinins, urine volume (UV) and urinary sodium excretion (UNaV), while none of the variables changed with vehicle treatment; 2) no difference was found in plasma ANP between the vehicle and UK groups; and 3) Hoe canceled the increases of UV and UNaV caused by UK.

In DOCA-salt rats: 1) infused UK significantly decreased NEP, and increased UV and UNaV, while UV and UNaV were slightly decreased, and NEP did not change with vehicle treatment; 2) plasma ANP was significantly higher in UK group than in the vehicle group; and 3) Hoe could not abolish the increase of UV and UNaV induced by UK.

These data indicate that the contributions of renal kinins and plasma ANP to the diuretic and natriuretic mechanisms of NEP inhibition may differ between Sprague-Dawley normotensive rats and DOCA-salt hypertensive rats.     

Contractions to Endothelin in Normotensive and Spontaneously Hypertensive Rats: Role of Endothelium and Prostaglandins

Contractions to endothelin-1 in aortas of the spontaneously hypertensive rats (SHR) were compared with those of normotensive controls (WKY); rings with and without endothelium were studied in organ chambers. Contractions to endothelin were smaller in aortas of SHR compared to WKY, whether the endothelium was present or not. The presence of a functional endothelium reduced contractions to the peptide in both strains. Endothelium-dependent relaxations to acetylcholine and endothelium-independent relaxations to nitric oxide were observed in rings from both strains during contraction with endothelin. Indomethacin reduced the contractions to endothelin in the aorta from SHR with endothelium, but not in those without endothelium; it did not significantly affect endothelin-induced contractions in rings of WKY with or without endothelium. These experiments demonstrate that contractions of the vascular smooth muscle to endothelin are reduced in the aorta of the SHR. The basal and stimulated release of endothelium-derived relaxing factor inhibits contractions to endothelin in the aorta from both strains. The inhibitor of cyclooxygenase indomethacin does not prevent the response of the vascular smooth muscle to endothelin; however, endothelin may stimulate the release of an indomethacin-sensitive endothelium-derived contracting factor in the SHR aorta.     

Actions of L- And D-Arginine and NG-Monomethyl-l-Arginine on the Blood Pressure of Pithed Normotensive and Spontaneously Hypertensive Rats

We have examined the depressor effects of L- and D-arginine on the diastolic blood pressure of pithed normotensive Wistar (NW), Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats after the administration of a single bolus injection of the nitric oxide synthase inhibitor, N^G-monomethyl-L-arginine (L-NMMA). A single bolus intravenous injection of L-NMMA, 30 mg/kg, produced an increase in both the systolic and diastolic blood pressure of pithed rats. Injections of bolus doses, 1–300 mg/kg, of D-arginine did not lead to sustained reductions of the blood pressure in pithed NW rats although slight decreases in the blood pressure of WKY and SH rats were observed, and these transient effects of D-arginine appeared to be more pronounced in the WKY strain. Immediately following the bolus injections of the higher doses of D-arginine a transient decrease in both the systolic and diastolic pressure occurred. In contrast to the actions of D-arginine single bolus injections of L-arginine, 1–300 mg/kg, produced a dose-dependent sustained reduction in both the systolic and diastolic blood pressures of all rats. The threshold for the depressor actions of L-arginine was the same for NW, WKY and SH rats. The final dose of L-arginine (300 mg/kg), produced a significantly greater depressor effect in WKY and SH rats as compared to NW rats. The blood pressure remained elevated after the dose-response curve to D-arginine and, in order to determine whether D-arginine-treated rats are sensitive to the effects of other vasodilators and whether differences in vasoactive actions exist for vasodilators acting other than via nitric oxide synthesis, a dose-response curve to the calcium channel antagonist verapamil was constructed. Injections of verapamil, 0.1–1000 μg/kg, produced a dose-dependent reduction in blood pressure with no difference in either threshold or sensitivity to the actions of verapamil among the three strains of rats. Our results suggest that strain differences exist between the depressor actions of L-arginine and that it is possible that these differences may be due to an alteration in the endogenous levels of nitric oxide synthase and/or the activity of guanylate cyclase, however, no relationship to the hypertensive state of the spontaneously hypertensive rats was apparent.