Postnatal early overnutrition dysregulates the intrarenal renin-angiotensin system and extracellular matrix-linked molecules in juvenile male rats

Overnutrition during the perinatal period has been associated with susceptibility to obesity and related comorbidities. We examined the effects of postnatal early overnutrition on the development of juvenile obesity and the associated renal pathophysiological changes. Three or 10 pups per mother from rat pup litters were assigned to either the overnutrition or control groups during the first 21 days of life. The effects of overfeeding were measured at 28 days. The smaller male litter pups were heavier than the controls between 4 and 28 days after birth (P<.05). By 28 days of age, the kidney weight per body weight ratio decreased in the small litter group (P<.05). Circulating leptin levels increased in the small litter rats (P<.05). Overnutrition had no effect on renal cell proliferation, apoptosis, macrophages and glomerulosclerosis. In the immunoblots and immunohistochemistry, renin and angiotensin II type (AT) 2 receptor expression increased in the overfed rats (P<.05). By contrast, the plasminogen activator inhibitor (PAI)-1 and matrix metalloproteinase (MMP)-9 expression decreased in the overnutrition group (P<.05). The AT 1 receptor, tissue inhibitor of MMP-1, monocyte chemoattractant protein-1, tumor necrosis factor-α, osteopontin and adiponectin expression was not changed. Our data showed that postnatal early overfeeding led to hyperleptinemia, juvenile obesity and the acquired reset of renal maturation. Up-regulation of renin and AT2 and down-regulation of PAI-1 and MMP-9 might contribute to abnormal programming of renal growth in rats exposed to postnatal early overnutrition.     

The renin-angiotensin system in the perinatal period in rats

Plasma concentrations of renin, angiotensinogen, kininogen, total protein, and renal renin concentration were measured in rats before spontaneous birth, immediately after vaginal delivery, during the subsequent 48 h, as well as at the ages of 10, 20 and 80 days. Preterm rats had a plasma renin concentration about 15 times higher than adults, which increased further in 1 h-old vaginally-delivered rats. Thereafter renin fell to very low levels within 2 h, rose again during the first day and remained at 4 times the adults level until day 10. Renal renin content and concentration increased over the whole observation period, except for a slight fall of renin concentration in the first 3 h after birth. In pre- and full-terms rats, angiotensinogen concentration was only 20% that of adults, reaching even lower values immediately after delivery, due to excessive consumption by renin. Thereafter, angiotensinogen increased more than 10 fold within 48 h. Kininogen concentration in plasma was higher than in adults and stable up to the 10th postnatal day. We conclude that vaginal delivery is a strong stimulus for renin release, the resulting high concentration of renin being responsible both for the increased turnover of angiotensinogen and the subsequent inhibition of renin release. The cause and biological significance of the dramatic increase of angiotensinogen during the first 48 h of life remains obscure.     

Postnatal development of the hepatobiliary transport of phenolsulfonphthalein in rats

1. The postnatal development of the biliary excretion of phenolsulfonphthalein (PSP) was studied in male Wistar rats. 2. Following i.v. injection of PSP at 200 mumol/kg body wt, a maximal biliary excretion of 175 +/- 10 nmol/min/100 g body wt and 32 +/- 5 nmol/min/100 g body wt was reached for unconjugated and conjugated PSP, respectively, in the adult group. 3. The maximal biliary excretion of conjugated PSP was significantly lower in the 20-, 30- and 40-day-old groups as compared to the adults. The excretion of unconjugated dye was also significantly lower in 20- and 30-day-old rats. 4. The postnatal development of PSP excretion was unrelated to changes in the activity of UDP-glucuronosyltransferase. The importance of other factors is also discussed.     

All-trans retinoic acid prevents development of cardiac remodeling in aortic banded rats by inhibiting the renin-angiotensin system

This study was designed to determine the effect of all-trans retinoic acid (RA) on the development of cardiac remodeling in a pressure overload rat model. Male Sprague-Dawley rats were subjected to sham operation and the aortic constriction procedure. A subgroup of sham control and aortic constricted rats were treated with RA for 5 mo after surgery. Pressure-overloaded rats showed significantly increased interstitial and perivascular fibrosis, heart weight-to-body weight ratio, and gene expression of atrial natriuretic peptide and brain natriuretic peptide. Echocardiographic analysis showed that pressure overload induced systolic and diastolic dysfunction, as evidenced by decreased fractional shortening, ejection fraction, stroke volume, and increased E-to-E(a) ratio and isovolumic relaxation time. RA treatment prevented the above changes in cardiac structure and function and hypertrophic gene expression in pressure-overloaded rats. RA restored the ratio of Bcl-2 to Bax, inhibited cleavage of caspase-3 and -9, and prevented the decreases in the levels of SOD-1 and SOD-2. Pressure overload-induced phosphorylation of ERK1/2, JNK, and p38 was inhibited by RA, via upregulation of mitogen-activated protein kinase phosphatase (MKP)-1 and MKP-2. The pressure overload-induced production of angiotensin II was inhibited by RA via upregulation of expression of angiotensin-converting enzyme (ACE)2 and through inhibition of the expression of cardiac and renal renin, angiotensinogen, ACE, and angiotensin type 1 receptor. Similar results were observed in cultured neonatal cardiomyocytes in response to static stretch. These results demonstrate that RA has a significant inhibitory effect on pressure overload-induced cardiac remodeling, through inhibition of the expression of renin-angiotensin system components.     

Postnatal physiological development of rats after acute prenatal hypoxia

The aim of study was to investigate the physiological development of the brain and behaviour in rats subjected to prenatal hypoxia on the 13.5th day of embryogenesis. We have found that such rats manifested a delayed physiological development and a change in nervous tissue of the sensorimotor cortex, as well a disturbed formation of motor responses during the first month of postnatal ontogenesis. During maturation these modifications were in part compensated, however we observed a decrease of the rats' ability to learn new forepaw movements. The destruction of the brain tissue and the modification of neurons composition in the sensorimotor cortex correlated with changes of behaviour at different stages of ontogenesis. Thus, changes of the conditions under which an organism develops during embryogenesis, predetermine a disturbance in ontogenesis and the learning ability.     

Sexual dimorphism in the renin-angiotensin system in aging spontaneously hypertensive rats

In young adult spontaneously hypertensive rats (SHR), mean arterial pressure (MAP) is higher in males than in females and inhibition of the renin-angiotensin system (RAS) eliminates this sex difference. After cessation of estrous cycling in female SHR, MAP is similar to that in male SHR. The purpose of this study was to determine the role of the RAS in maintenance of hypertension in aging male and female SHR. At 16 mo of age, MAP was similar in male and female SHR (183+/-5 vs. 193+/-8 mmHg), and chronic losartan (40 mg.kg-1.day-1 po for 3 wk) reduced MAP by 52% (to 90+/-8 mmHg, P<0.05 vs. control) in males and 37% (to 123+/-11 mmHg, P<0.05 vs. control) in females (P<0.05, females vs. males). The effect of losartan on angiotensin type 1 (AT1) receptor blockade was similar: MAP responses to acute doses of ANG II (62.5-250 ng/kg) were blocked to a similar extent in losartan-treated males and females. F2-isoprostane excretion was reduced with losartan more in males than in females. There were no sex differences in plasma renin activity, plasma angiotensinogen or ANG II, or renal expression of AT1 receptors, angiotensin-converting enzyme, or renin. However, renal angiotensinogen mRNA and protein expression was higher in old males than females, whereas renal ANG II was higher in old females than males. The data show that, in aging SHR, when blood pressures are similar, there remains a sexual dimorphism in the response to AT1 receptor antagonism, and the differences may involve sex differences in mechanisms responsible for oxidative stress with aging.     

Role of cardiac renin-angiotensin system in the development of pressure-overload left ventricular hypertrophy in rats with abdominal aortic constriction

Possible involvement of cardiac renin-angiotensin system (RAS) in pressure overload induced left ventricular hypertrophy (LVH) was investigated. Rats were subjected to abdominal aortic constriction (AAC) and examined the effects of 4 weeks treatments with an angiotensin converting enzyme (ACE) inhibitor, captopril and a vasodilator, hydralazine on haemodynamics and ventricular RNA, DNA, protein and myosin isoform pattern in sham and hypertrophied rats. AAC increased the mean arterial pressure (MAP) and systolic blood pressure (SBP), and resulted in increased left ventricle/body weight ratio, LV thickness, RNA and protein content, however total DNA was not changed. The expression of fetal isogene, -myosin heavy chain (-MHC), was markedly enhanced where as u.-MHC was reduced. High-dose captopril (100 mg/kg p.o.,) significantly prevented the increase in haemodynamics, development of LVH, LV remodeling, increase in total protein, RNA and antithetical expression of myosin isoforms. Hydralazine (15 mg/kg p.o.,), did not modulate hypertrophic changes and low-dose captopril (1.5 mg/kg p.o.,) which has not produced any marked fall in MAP and SBP also modulated favourably the development of LVH and its biochemical markers. Thus, the prevention of the development of LVH and induction of -MHC by non-hypotensive doses of captopril may be related to the blockade of intracardiac production of angiotensin II rather than circulating system. These results suggest that cardiac RAS may play an important role in pressure overload induced LVH.     

Postnatal development of the glycine cleavage system in rat liver

The development of the glycine cleavage system was studied in liver mitochondrial extracts from neonatal and adult rats. The enzyme activity in 2-day-old pups was 29.3% of that measured in the adult and was found to increase in an age-dependent manner. Measurement of hepatic free amino acid concentrations at the neonatal ages showed that glycine levels were highest at 2 days and at 14 days were about 48% of those in the 2-day-old pups. Serine levels did not change between the age of 2 and 14 days. A developmental delay in the glycine cleavage system is responsible for the high levels of glycine in the neonatal rat liver.     

Postnatal development of the circadian rhythm of circulating blood cells in rats

In the present study the variations in the leukocyte and erythrocyte counts were investigated in the peripheral blood within the light and darkness periods during the postnatal development of rats. The animals were kept under an artificial illumination regime (12 hours light, 12 hours darkness), and examined at the ages of 7, 14, 21, 28, 35 and 45 days, and in maturity (56 days). Erythrocyte counts exhibited no light-dark rhythm. The circadian rhythm of leukocyte counts developed in male and female laboratory rats in the fourth week of age.     

Autonomic control in rats with overactivity of tissue renin-angiotensin or kallikrein-kinin system

The renin-angiotensin system (RAS) plays an important role in the regulation of the cardiovascular system and the kallikrein-kinin system (KKS) appears to counteract most of the RAS effects. In this study the vagal and the sympathetic influences on the heart rate and the baroreflex control of the heart rate were evaluated in transgenics rats with human tissue kallikrein gene expression [TGR(hKLK1)], and transgenics rats with tissue renin overexpression [TGR(mREN2)27]. Heart rate was similar in all groups but mean arterial pressure was higher in mREN2 rats than in kallikrein and control rats (149+/-4 vs. 114+/-3 vs. 113+/-3 mm Hg, respectively). The intrinsic heart rate was lower in mREN2 rats than in kallikrein and control rats (324+/-5 vs. 331+/-3 vs. 343+/-7 bpm). The HR response to atropine was similar but the response to propranolol was higher in kallikrein rats than control group (61+/-7 vs. 60+/-9 vs. 38+/-7 bpm, respectively). The vagal tonus was lower in mREN2 than in SD and hKAL rats (18+/-3 vs. 40+/-6 vs. 35+/-6 bpm) whereas the sympathetic tonus was higher in kallikrein rats (118+/-7 vs. 96+/-1 vs. 81+/-9 bpm in the mREN2 and SD rats), respectively. Baroreflex sensitivity to bradycardic responses was attenuated in mREN2 rats (0.37+/-0.05 vs. 1.34+/-0.08 vs. 1.34+/-0,13 bpm/mm Hg) while the tachycardic responses were unchanged. The bradycardic responses to electrical stimulation of the vagal nerve were depressed in both renin and kallikrein rats (129+/-47 vs. 129+/-22 vs. 193+/-25 bpm in control group in response to 32 Hz). In conclusion: 1.The rats with overexpression of renin showed decreased intrinsic heart rate and impairment of vagal function, characterized by decreased vagal tonus, reduced response of HR to electrical stimulation of vagus nerve, and depressed reflex bradycardia provoked by increases of blood pressure. 2. The rats with overexpression of kallikrein showed an increase of sympathetic activity that regulates the heart rate, characterized by increased HR response to propranolol and increased sympathetic tonus, accompanied by decreased bradycardic responses to electrical vagal stimulation.     

Different expression of renin-angiotensin system components in hearts of normotensive and hypertensive rats

Tissue renin-angiotensin systems are known to behave differently from the circulating renin-angiotensin system (RAS). It has already been proposed that not only the circulating RAS, but also RAS localized in the cardiac tissue plays an important role in the heart failure. The objective of this study was to compare the gene expression of individual components of the renin-angiotensin system in hearts of normotensive and hypertensive rats. Two genetically hypertensive rat strains--spontaneously hypertensive rats (SHR) and hereditary hypertriglyceridemic rats (HTG)--were compared with Wistar-Kyoto (WKY) and Lewis (LEW) normotensive controls. In addition, developmental changes in gene expression of individual components of cardiac RAS were studied in 20-day-old fetuses, 2-day-old newborns and 3-month-old HTG and LEW rats. In our study, the angiotensinogen gene expression did not differ either among adult normotensive and hypertensive strains, or during development. In contrast, the renin gene expression was significantly increased in hearts of hypertensive compared to normotensive rats. Moreover, a 5-fold increase of renin mRNA was observed in hearts of HTG rats between day 2 and the third month of age. There was also an age-dependent increase of ACE gene expression in both HTG and LEW rats which was substantially delayed in HTG hearts. In conclusion, the results of our study suggest that overexpression of the cardiac renin gene in hypertensive strains could participate in the structural and functional changes of the heart during the development of hypertension.     

Postnatal development of right atrial injection of capsaicin-induced apneic response in rats.

Apnea and respiratory failure often occur in infants with pulmonary disease. Bronchopulmonary C-fiber (PCF)-mediated apnea is an important component of respiratory dysfunction. This study was undertaken to define the postnatal development of PCF-mediated apnea. The experiments were conducted in five groups of anesthetized, tracheotomized, and spontaneously breathing rats with ages at postnatal days P1-3, P7-9, P14-16, P21-23, and P56-58. Right atrial bolus injection of three doses of capsaicin (Cap), equivalent to 2, 4, and 8 microg/kg used previously in 450-g rats, was applied to stimulate PCFs. We found that 1) Cap-induced apneic response [percent change from the baseline expiratory duration (Te) values (deltaTe%)] and the sensitivity of this response (deltaTe%.microg(-1)) were significantly greater in the rats P10; 2) the Cap-induced apneas were vagally dependent in all rats tested; and 3) bivagotomy-induced prolongation of Te was much greater in the rats P10. From these findings we concluded that, compared with the older rats (>P10), the newborn rats have a stronger PCF-mediated respiratory inhibition that may contribute to infants' vulnerability to respiratory failure.     

大鼠脑干听觉诱发电位和中潜伏期反应的生后发育

目的：探讨大鼠脑干听觉诱发电位（BAEP）和听觉中潜伏期反应(MLR)生后发育模式的异同。方法：在同一批新生SD纯种大鼠连续10周同时观察BAEP和MLR生后发育的变化。结果：BAEP和MLR分别在生后14d和17d出现;BAEP各波峰潜伏期（PL）随鼠龄增长而递减,生后3－4周是PL缩短的主要时期,I波PL在生后29d达成年值,其余各波PL在生后70d全部达成年值;首次出现的MLR,其Po和Na两波PL已达成年值,而Pa、Nb和Pb和PL也随鼠龄增长而缩短,但生后20－23d很快就达成年值;BAEP的Ⅰ、Ⅲ、Ⅳ波和MLR的Nb、Pb波波幅在生后3－4周期间迅速递增,且峰值明显大于成年值,然后逐渐回降。结论：大鼠MLR和BAEP生后发育的模式基本相同,但MLR各波PL较早达成年值。     

Role of adrenal renin-angiotensin system in the control of aldosterone secretion in sodium-restricted rats

This study examined the effect of the pharmacological manipulation of adrenal renin-angiotensin system (RAS) on aldosterone secretion from in situ perfused adrenals of rats kept on a normal diet and sodium restricted for 14 days. Neither the angiotensin-converting enzyme inhibitor captopril nor the nonselective angiotensin II receptor antagonist saralasin and the AT(1) receptor-selective antagonist losartan affected basal aldosterone output in normally fed rats. In contrast, they concentration dependently decreased aldosterone secretion in sodium-restricted animals, with maximal effective concentration ranging from 10(-7) to 10(-6) M. Captopril (10(-6) M), saralasin (10(-6) M), and losartan (10(-7) M) counteracted aldosterone response to 10 mM K(+) in sodium-restricted rats but not in normally fed animals. Collectively, these findings provide evidence that adrenal RAS plays a role in the regulation of aldosterone secretion, but only under conditions of prolonged stimulation of zona glomerulosa probably leading to overexpression of adrenal RAS.     

The CNS renin-angiotensin system

The renin-angiotensin system (RAS) is one of the best-studied enzyme-neuropeptide systems in the brain and can serve as a model for the action of peptides on neuronal function in general. It is now well established that the brain has its own intrinsic RAS with all its components present in the central nervous system. The RAS generates a family of bioactive angiotensin peptides with variable biological and neurobiological activities. These include angiotensin-(1–8) [Ang II], angiotensin-(3–8) [Ang IV], and angiotensin-(1–7) [Ang-(1–7)]. These neuroactive forms of angiotensin act through specific receptors. Only Ang II acts through two different high-specific receptors, termed AT1 and AT2. Neuronal AT1 receptors mediate the stimulatory actions of Ang II on blood pressure, water and salt intake, and the secretion of vasopressin. In contrast, neuronal AT2 receptors have been implicated in the stimulation of apoptosis and as being antagonistic to AT1 receptors. Among the many potential effects mediated by stimulation of AT2 are neuronal regeneration after injury and the inhibition of pathological growth. Ang-(1–7) mediates its antihypertensive effects by stimulating the synthesis and release of vasodilator prostaglandins and nitric oxide and by potentiating the hypotensive effects of bradykinin. New data concerning the roles of Ang IV and Ang-(1–7) in cognition also support the existence of complex site-specific interactions between multiple angiotensins and multiple receptors in the mediation of important central functions of the RAS. Thus, the RAS of the brain is involved not only in the regulation of blood pressure, but also in the modulation of multiple additional functions in the brain, including processes of sensory information, learning, and memory, and the regulation of emotional responses.     

Increased mRNA expression of cardiac renin-angiotensin system and collagen synthesis in spontaneously hypertensive rats

Hypertensive cardiac hypertrophy is associated with the accumulation of collagen in the myocardial interstitium. Previous studies have demonstrated that this myocardial fibrosis accounts for impaired myocardial stiffness and ventricular dysfunction. Although cardiac fibroblasts are responsible for the synthesis of fibrillar collagen, the factors that regulate collagen synthesis in cardiac fibroblasts are not fully understood. We investigated the effects of angiotensin II on cardiac collagen synthesis in cardiac fibroblasts. Cardiac fibroblasts of 10 week old spontaneously hypertensive rats and age-matched Wistar-Kyoto rats were prepared and maintained in culture medium supplemented with 10% fetal calf serum. The expression of mRNA of the renin-angiotensin system (renin, angiotensinogen, angiotensin converting enzyme) was determined by using a ribonuclease protection assay. Basal collagen synthesis in cardiac fibroblasts from spontaneously hypertensive rats was 1.6 fold greater than that in the cell of Wistar-Kyoto rats. Angiotensin II stimulated collagen synthesis in cardiac fibroblasts in a dose-dependent manner. The responsiveness of collagen production to angiotensin II was significantly enhanced in cardiac fibroblasts from spontaneously hypertensive rats (100 nM angiotensin II resulted in 185 ± 18% increase above basal levels, 185 ± 18 versus 128 ± 19% in Wistar-Kyoto rats p < 0.01). This effect was receptor-specific, because it was blocked by the competitive inhibitor saralasin and MK 954. These results indicate that collagen production was enhanced in cardiac fibroblasts from spontaneously hypertensive rats, that angiotensin II had a stimulatory effect on collagen synthesis in cardiac fibroblasts, and that cardiac fibroblasts from spontaneously hypertensive rats were hyper-responsive to stimulation by angiotensin II.Level of angiotensin and renin mRNA expressed in ventricles, and angiotensinogen mRNA expressed in fibroblasts from SHR were higher than those from WKY.These findings suggest that the cardiac renin-angiotensin system may play an important role in collagen accumulation in hypertensive cardiac hypertrophy.