Development of immunoreactive atrial natriuretic peptide in fetal hearts of spontaneously hypertensive and Wistar-Kyoto rats

Summary The development of immunoreactive atrial natriuretic peptide (ANP) was studied in fetal hearts of spontaneously hypertensive (SHR) and compared to normotensive Wistar-Kyoto (WKY) rats. While SHR fetal hearts were noticeably less developed than those of WKY at 10 and 11 days gestation, both strains showed ANP immunoreactive cells in some but not all primitive heart tubes. At 12 days additional ANP immunoreactive cells appeared in formative trabeculae of the ventricle and atrium. ANP cells were also observed in the myogenic layer of the truncus and bulbus arteriosus and their derivatives from 11 through 16 days, but not at 18 days. In both strains, there were more ANP cells in the left ventricle than in right beginning at day 13. There were no obvious strain differences in the developmental pattern and timing of ANP producing cells. However, on the day of birth, staining was reduced in hearts from some WKY newborn pups compared with hearts from SHR newborns and ventricular staining was reduced in both strains when compared to fetal hearts. These observations indicate that ANP is one of the earliest peptide hormones produced and that the predisposition to genetic hypertension does not appear to influence the development of ANP.     

Effects of chronic salt loading on plasma atrial natriuretic peptide (ANP) in the spontaneously hypertensive rat

Plasma concentrations of immunoreactive atrial natriuretic peptide (ANP) was measured in spontaneously hypertensive rats (SHR) during chronic salt loading (1.5% NaCl in drinking water). During the 3-week experimental period mean arterial blood pressure, heart rate, urinary sodium excretion and body weight was assessed in salt-loaded as well as in control rats. The sodium excretion was more than 10-fold increased in the rats on the high salt diet. The plasma ANP concentration was significantly increased only 24 h after the start of the high salt intake. Thereafter plasma ANP concentrations were not significantly different from values obtained in control rats. The blood pressure was significantly increased after 3 weeks on the high salt diet. At the end of the 3-week experimental period the rats were subjected to a 10 and 20% acute volume expansion with homologous whole blood. During this intervention the increase in plasma ANP concentrations was blunted in the high salt rats compared to the control group. It is concluded that during chronic salt loading in SHR there is an initial rise in plasma ANP levels and that other hormonal and neuronal systems are more important in the long term maintenance of fluid and electrolyte balance.     

Differential haemodynamic effects of atrial natriuretic peptide (ANP) in normotensive and spontaneously hypertensive rats

Central haemodynamic parameters and cardiac performance were measured in conscious spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) control rats after a 10-min infusion of rat ANP (103-125), 1 micrograms kg-1 min-1. Mean Arterial blood pressure (MAP) decreased by approximately 10% in both groups of rats. Heart rate (HR) increased slightly in both strains during the infusion. In the normotensive group the fall in MAP was due to a reduction in cardiac output (CO) while in the SHR there was a decrease in CO as well as in total peripheral resistance (TPR). The ANP infusion also reduced central blood volume (CBV) and stroke volume (SV) in both groups of rats. The reduction in CBV and CO was significantly more pronounced in the WKY strain. Left ventricular end diastolic pressure (LVEDP) and cardiac contractility (dP/dt) did not change while central venous pressure (CVP) was slightly decreased in the WKY group as a result of the ANP infusion. We conclude that ANP reduces MAP in normotensive animals by a reduction in CO. In the SHR a reduction in TPR also contributes to the fall in MAP. Atrial natriuretic peptide did not exert any negative inotropic effects, but the reduction of CO was due to an increased venous compliance.     

Effects of calcium supplementation and deoxycorticosterone on plasma atrial natriuretic peptide and electrolyte excretion in spontaneously hypertensive rats

The effects of calcium and the mineralocorticoid deoxycorticosterone (DOC) on blood pressure were studied in four groups of spontaneously hypertensive rats (SHR): (1) control; (2) calcium; (3) deoxycorticosterone and; (4) deoxycorticosterone + calcium. Calcium was given as 1.5% calcium chloride in drinking fluid and deoxycorticosterone by weekly subcutaneous injections (25 mg kg^-1). During the nine weeks of treatment the increase in systolic blood pressure was enhanced in the deoxycorticosterone and attenuated in the calcium group, whereas the deoxycorticosterone + calcium group did not deviate from control. Total plasma calcium was elevated in the calcium group. Plasma concentrations of sodium and atrial natriuretic peptide (ANP) were increased by deoxycorticosterone while neither of the calcium-treated groups differed from control in these respects. Urinary excretions of calcium and sodium were increased in both groups receiving calcium, and also the deoxycorticosterone group excreted more calcium into urine than the control. Adrenergic nerve density in a section of the mesenteric artery and the urinary excretion of noradrenaline and adrenaline were similar in all study groups. The results indicate that calcium supplementation can attenuate the development of hypertension and prevent the deoxycorticosterone-induced blood pressure rise in SHR, possibly by influencing sodium metabolism as seen in increased natriuresis, and by preventing the actions of deoxycorticosterone on sodium balance.     

Central blood volume in spontaneously hypertensive rats and Wistar-Kyoto normotensive rats

Central blood volume and total blood volume were determined in spontaneously hypertensive rats and Wistar Kyoto rats at two ages, 6 and 12 weeks, representing ‘borderline’ hypertension and early ‘established’ hypertension, respectively. A technique was used where plasma and erythrocyte indicators were injected into conscious rats. Blood volume in the cardiopulmonary compartment, present in the ‘resting’ awake steady-state, could then be estimated by sudden freezing of the entire rat. 12 week-old spontaneously hypertensive rats showed a decreased total blood volume, while the fraction of blood contained in the cardiopulmonary area was significantly increased compared with that of normotensive Wistar Kyoto rats. In 6-week-old spontaneously hypertensive rats, total blood volume was only marginally decreased but also here a tendency towards centralization of the blood was seen. Thus, along with the development of hypertension in the spontaneously hypertensive rat their decreasing blood volume tends to become increasingly centralized to the cardiopulmonary area. Both neurohormonal influences and structural wall changes in the low-pressure capacitance side may contribute to this.     

Effects of calcium supplementation and deoxycorticosterone on plasma atrial natriuretic peptide and electrolyte excretion in spontaneously hypertensive rats.

The effects of calcium and the mineralocorticoid deoxycorticosterone (DOC) on blood pressure were studied in four groups of spontaneously hypertensive rats (SHR): (1) control; (2) calcium; (3) deoxycorticosterone and; (4) deoxycorticosterone + calcium. Calcium was given as 1.5% calcium chloride in drinking fluid and deoxycorticosterone by weekly subcutaneous injections (25 mg kg-1). During the nine weeks of treatment the increase in systolic blood pressure was enhanced in the deoxycorticosterone and attenuated in the calcium group, whereas the deoxycorticosterone + calcium group did not deviate from control. Total plasma calcium was elevated in the calcium group. Plasma concentrations of sodium and atrial natriuretic peptide (ANP) were increased by deoxycorticosterone while neither of the calcium-treated groups differed from control in these respects. Urinary excretions of calcium and sodium were increased in both groups receiving calcium, and also the deoxycorticosterone group excreted more calcium into urine than the control. Adrenergic nerve density in a section of the mesenteric artery and the urinary excretion of noradrenaline and adrenaline were similar in all study groups. The results indicate that calcium supplementation can attenuate the development of hypertension and prevent the deoxycorticosterone-induced blood pressure rise in SHR, possibly by influencing sodium metabolism as seen in increased natriuresis, and by preventing the actions of deoxycorticosterone on sodium balance.     

人类心房利钠肽基因在自发性高血压大鼠体内表达及其对血压的影响

目的研究人类心房利钠肽（hANP）基因在自发性高血压大鼠（SHRs）体内表达、持续时间和对血压的影响。方法 12只8周龄雄性SHRs,随机分为两组,于左腿股四头肌注射pcDNA3.1-hANP质粒的为实验组,在同一部位注射pcDNA3.1空质粒的为对照组,每周测量大鼠尾动脉收缩压,及利用放射免疫方法监测血中hANP水平。结果转基因后第1周起与对照组比较,实验组血压开始下降,两组动物一直相差（13±3.1）mmHg（P〈0.05）,其作用可持续10周;且放射免疫方法监测实验组血中hANP水平较高;RT-PCR和Western印迹杂交技术检测显示实验组hANP基因在肌肉组织中高效表达,对照组则未见表达。结论肌肉注射法将hANP基因导入SHRs,hANP基因可在肌肉组织中高效表达,且hANP可释放入血,降低SHRs的血压,显示了hANP基因对高血压患者治疗的可能性。     

Circulating and local visfatin/Nampt/PBEF levels in spontaneously hypertensive rats,stroke-prone spontaneously hypertensive rats and Wistar-Kyoto rats

Visfatin (also known as nicotinamide phosphoribosyltransferase and pre-B cell colony-enhancing factor) is a multifunctional protein. Visfatin has been reported to be involved in several biological processes in the cardiovascular system, . However, the role of visfatin in hypertension is still unclear. In this study, we examined the circulating and local adipose visfatin levels in spontaneously hypertensive rats (SHR), stroke-prone spontaneously hypertensive rats (SHR-SP), and in their normotensive control Wistar-Kyoto (WKY). SHR and SHR-SP rats exhibited lower body weight, lower fat tissue and hypolipidemia. No differences of serum visfatin levels were observed in SHR/SHR-SP and WKY. Serum visfatin levels did not correlate to serum glucose, lipids, insulin, and fat pad weights, but significantly correlated to weights of skeletal muscle. Visfatin expression in visceral fat tissue was slightly lower in SHR-SP compared with that in WKY. Moreover, there were no significant differences of visfatin expression in skeletal muscles among WKY, SHR and SHR-SP. Finally, visfatin protein was detected in L6 rat skeletal muscle cell culture medium, indicating that visfatin was secreted from skeletal muscle cells. Thus, our results may provide useful information for understanding the characteristic of visfatin in hypertensive models, and support the view that visfatin may be a myokine.     

Haemodynamics and plasma ANP (atrial natriuretic peptide) after acute blood volume expansion in normotensive and spontaneously hypertensive rats

Atrial natriuretic peptide (ANP) was measured in plasma during acute volume load in conscious, spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. During basal conditions immunoreactive ANP were similar in the SHR (630 +/- 56 pmoles l-1) and the WKY (657 +/- 114 pmoles l-1) groups. An acute 10% and 20% whole blood volume expansion resulted in a linear increase in immunoreactive plasma ANP in the WKY. In the SHR the increase in plasma ANP was attenuated during the 20% volume load. During the 10% and 20% volume load central venous pressure (CVP), central blood volume (CBV) and cardiac output increased relatively more in the SHR compared with the WKY group. In contrast, the increase in peripheral blood volume (PBV) and decrease in heart rate (HR) was attenuated in the SH rats. In the SHR group there was a shift of the ANP vs. CVP and ANP vs. CBV curves to the right compared with the WKY. We conclude that acute volume loading is a potent stimulus for ANP release in WKY as well as SHR. However, in the SHR, ANP release was blunted in spite of the increased centralization of the volume load in this rat strain. Thus, the decreased responsiveness of the ANP hormonal system may contribute to the development and maintenance of hypertension in this genetic form of hypertension.     

Preweanling behavioral development in spontaneously hypertensive, borderline hypertensive, and Wistar-Kyoto normotensive rats

Preweanling physical and behavioral development was studied in spontaneously hypertensive (SHR), borderline hypertensive (BHR), and Wistar-Kyoto normotensive (WKY) rat pups. Measures of physical development included body weight, onset of various morphological landmarks, and speed of surface righting. Behavioral tests assessed locomotor development, exploratory behavior, and cliff avoidance in pups of the 3 groups. On all measures employed, SHR pups exhibited a delay in physical maturation compared to age-matched BHR and WKY pups. Results from the locomotor development test revealed that young WKY pups (ages 1-7 days) spent more time locomoting than SHR pups, with BHR times being intermediate. In contrast, older SHR pups (ages 17-30 days) displayed greater activity in an exploratory maze than WKY pups, with BHR values again intermediate. Finally, SHR pups were more behaviorally reactive in the cliff avoidance task compared to BHR and WKY pups. These group differences may be useful in understanding the development of genetic hypertension and may serve as early behavioral markers of a predisposition to cardiovascular disease.     

Patterns of behavioral development in spontaneously hypertensive rats and Wistar-Kyoto normotensive controls

We have examined the behavior of spontaneously hypertensive (SHR) rats and stroke-prone hypertensive (SP-SHR) male rats during the development and maintenance of elevated blood pressure and compared this pattern with age- and gender-matched normotensive (WKY) rats of the same Wistar-Kyoto strain as controls. Rats of each strain (n = 10/age group) were isolated in individual cages and observed for 60 min at 3,4,6,8,10, or 20 weeks of age using a scan sampling technique. At all ages SHR rats were significantly more active than WKY rats whereas SP-SHR rats were intermediate in level of activity. In a 2nd series, activity of male rats of each strain was monitored continuously for 24 hr in the home cage. No strain differences in amount or pattern of total daily activity were evident at either 4-6 or 16-18 weeks of age. These results indicate that SHR rats are more reactive to environmental change, but the intermediate level of activity of SP-SPHR rats suggests that this response is not related to the degree of blood pressure elevation,     

Concomitant increase in plasma atrial natriuretic peptide and cyclic GMP during volume loading

Summary To investigate the effects of fluid expansion on endogenous atrial natriuretic peptide (ANP) and cyclic 3,5-guanosine monophosphate (cGMP), four male volunteers were studied before, during and after intravasal volume loading. Volume expansion was performed by intravenous infusion of 2,000 ml isotonic saline solution within 30 min. Mean plasma ANP levels increased 2.5-fold from 31.2 pg/ml to 81.7 pg/ml 40 min after the start of infusion. Plasma cGMP levels paralleled the rise in ANP, shwoing a mean cGMP increment from 2.7 pmol/ml to a maximum of 8.2 pmol/ml. Both ANP and cGMP levels were back to basal levels 120 min after termination of the infusion. Stimulation of endogenous ANP release by volume loading suggests that ANP is involved in the regulation of fluid homeostasis in man. The parallel rise in plasma cGMP levels supports the idea that cGMP is a mediator for the effects of ANP.Abbreviations ANP atrial natriuretic peptid - cGMP cyclic 3,5-guanosine monophosphate - PRA plasma renin activity     

Tubuloglomerular feedback and autoregulation of glomerular filtration rate in Wistar-Kyoto spontaneously hypertensive rats

Experiments were done in Wistar-Kyoto spontaneously hypertensive rats (SHR) to examine the efficiency of autoregulatory adjustments of kidney and nephron filtration rate (GFR) to acute changes in blood pressure (BP) over a broad blood pressure range. When BP of the SHR was reduced from 158±7 to 118 ±3 mm Hg by aortic clamping, kidney-GFR remained unchanged from 1.19±0.11 to 1.17±013 ml·min^–1·g^–1 kidney weight (KW), respectively. Single nephron GFR (SNGFR) measured at early distal tubule sites was similarly unchanged with the same BP change, 27.9±1.5 vs. 24.9±2.1 nl·min^–1·g^–1 KW (P>0.10). Proximal and distal estimates of SNGFR were significantly different from each other at high BP (7 nl·min^–1·g^–1,P<0.025), but were not different at low BP (2.0 nl·ml^–1·g^–1,P>0.10). Studies assessing tubuloglomerular feedback activity were done with orthograde perfusion of the loop of Henle using recollections of early proximal flow rate (EPFR) as an index of change of glomerular filtration rate. A change in perfusion rate from 0 to 45 nl·min^–1 induced a reduction in early proximal flow rate of 40.5 ±4.5%. Juxtaglomerular renin activity of superficial nephrons was 36.2±4.3 in the SHR, a value insignificantly different from 23.7±4.4 ng Angiotensin II amide·0.1 ml^–1·h^–1. 5 glomeruli^–1 in normal controls (P>0.05). The SHR appears to behave as a normal animal with respect to tubologlomerular feedback and autoregulatory renal vascular adjustments. Like normal rat models, the SHR demonstrated dependence on maintenance of distal filtrate delivery to achieve single nephron GFR autoregulation.Financial support for these studies and for Dr. Ploth were made available by funds from the Deutsche Forschungsgemeinschaft     

Renal medullary effects of transient prehypertensive treatment in young spontaneously hypertensive rats

Aim: Transient angiotensin II receptor blockade (ARB) leads to prolonged blood pressure (BP) lowering, but the underlying mechanism remains uncertain. Long‐term BP control is regulated by the medullary microcirculation with the pericyte as contractile cell. We hypothesize that the prolonged BP effect is caused by increased medullary blood flow (MBF) associated with structural alterations based on reduced medullary pericyte number. Methods: Four‐week‐old spontaneously hypertensive rats (SHR) were treated for 4 weeks with losartan (SHR‐Los: 20 mg kg^?1 day^?1), hydralazine (SHR‐Hyd: 15 mg kg^?1 day^?1), losartan and pan‐caspase inhibitor zVAD (SHR‐Los + 1 mg kg^?1 day^?1 zVAD), losartan and glycogen synthase kinase‐3β (GSK) inhibitor valproate (SHR‐Los + 10 mg kg^?1 day^?1 Val) or placebo. BP, MBF and pericyte number were determined under and after treatment (8 and 12 weeks). Apoptotic pericytes were determined with α‐actin and TUNEL double staining. Sodium concentration was determined in renal medulla and urine. Results: Antihypertensive treatment equipotently reduced BP at 8 weeks of age. After drug withdrawal (12 weeks of age) BP reduction was restricted to SHR‐Los (SHR‐Los: 153 ± 5, SHR‐Hyd: 177 ± 2, SHR: 184 ± 3 mmHg). Simultaneously, MBF was increased and pericyte number reduced, while medullary and urinary sodium concentration increased. Transient ARB in combination with zVAD or valproate resulted in more medullary pericytes and higher BP (SHR‐Los/zVAD: 164 ± 7; SHR‐Los/Val: 168 ± 6 mmHg) compared with transient ARB alone. Conclusion: After drug withdrawal, transient ARB leads to increased MBF and is associated with a reduction in medullary pericytes. This may be associated with pericyte apoptosis as anti‐apoptosis during transient ARB increases pericyte number and BP.     

Renal interstitial pressure and tubuloglomerular feedback control in rats during infusion of atrial natriuretic peptide (ANP)

Atrial natriuretic peptide (ANP), injected at physiological concentrations, is known to induce both natriuresis and diuresis. It has been suggested by some investigators that these changes result from an increasing glomerular filtration rate (GFR), but others have been unable to demonstrate an increased GFR. The tubuloglomerular feedback (TGF) mechanism is an important regulator of GFR, and the sensitivity of TGF is decreased during ANP administration. Furthermore, resetting of TGF is, in most instances, related to changes in renal interstitial hydrostatic and oncotic pressures. It is also known that ANP may increase capillary permeability which may change renal interstitial pressure. The present study was performed to examine renal interstitial pressures and the TGF mechanism during ANP infusion. In accordance with previous studies, TGF sensitivity was found to be decreased. The tubular flow rate which elicited half the maximal drop in stop-flow pressure (P_sf) was increased from 18.5 to 25.7 nl min^-1. In contrast, ANP infusion resulted in a decreased interstitial hydrostatic pressure and an increased interstitial oncotic pressure. From previous experiments, such changes in interstitial pressures would be expected to increase TGF sensitivity. The changes in interstitial pressure cannot, therefore, directly explain the resetting of the feedback mechanism. In conclusion, the present paper shows a decreased renal net interstial pressure after intravenous administration of ANP.