Maria Luisa Kurnjek

Effect of chronic angiotensin II inhibition on the nitric oxide synthase in the normal rat during aging

Objective To assess the effect on the cardiovascular system, of enalapril (E) or losartan (L) given since weaning during 6 or 18 months to normal rats. Methods Animals were divided in three groups: control (C), E-treated and L-treated; treated rats received 10 mg/kg per day of drug. Systolic blood pressure (SBP), body weight, water and food intake (WI, FI), cardiac, left ventricular and aortic weight as well as the length of the tail were recorded. NADPH-diaphorase activity was determined as a marker of nitric oxide synthase (NOS) activity in aorta, arterioles of small intestine, heart and kidney of normal rats. NOS activity was measured as optical density (OD) in the stained tissue. Nitrate + nitrite urinary excretion was measured in 24 h urine. Only significant differences (P < 0.05) are reported. Results SBP, absolute cardiac, left ventricular and aortic weight increased with age. Both treatments delayed these increments. At 6 and 18 months, NOS activity was higher in aortic endothelium (Em) of L- and E-treated animals. Losartan treatment during 6 months also increased NOS activity in aortic smooth muscle (SM). Aortic Em NOS activity fell in the 18 months-treated and untreated animals. E increased NOS activity in the SM of intestinal arterioles at 6 months but reduced it at 18 months. Conclusions The fact that both E and L delayed cardiac hypertrophy/hyperplasia and aortic growth and raised aortic endothelium NOS activity indicates a protective effect on cardiovascular damage due to aging, exerted through inhibition of angiotensin II.

Effect of chronic angiotensin II inhibition on the cardiovascular system of the normal rat

Previous studies have demonstrated in normal rats that chronic treatment, from weaning to 30 days, with either enalapril or losartan, induced significant changes in cardiovascular structure and function. The present study was performed to assess the effect of either enalapril or losartan on the structure and function of the heart and arteries given to normal rats from weaning until 6 months of age. Animals (n = 48) were divided into three groups: control, enalapril treated, and losartan treated; treated rats received 10 mg/kg/day of drug. Blood pressure, body weight, and water intake were recorded for that time period. DNA, cGMP, collagen, degree of fibrosis, and nitric oxide synthase-NADPH-diaphorase-dependent activity in the heart and arteries were determined. Only significant differences (P < .05) are reported. Blood pressure increased only in control rats (13 +/- 1 mm Hg), enalapril treatment enhanced water intake and reduced the rate of body growth (control, 672.9 +/- 15.4 g; losartan, 692.4 +/- 21.8 g; enalapril, 541.8 +/- 13.8 g). In the heart, DNA (control, 120 +/- 5; losartan, 99 +/- 4; enalapril, 93 +/- 6 microg/100 mg), collagen (control, 2.5 +/- 0.2; enalapril, 1.85 +/- 0.08 microg/100 mg), and fibrosis (control, 3.5 +/- 0.4%; losartan, 2.2 +/- 0.3%; enalapril, 2.1 +/- 0.4%) were reduced by treatment. In the aorta, cGMP (control, 0.15 +/- 0.01; losartan, 0.24 +/- 0.02 pmol/mg), and NADPH-diaphorase (control, 0.114 +/- 0.003; losartan, 0.148 +/- 0.006; enalapril, 0.169 +/- 0.003 as optical density) were enhanced. The enzyme was also higher in the aortic endothelium of treated animals (control, 0.193 +/- 0.010; losartan, 0.228 +/- 0.009; enalapril, 0.278 +/- 0.005). The lower rate of body weight increase, the enhanced water intake, and the reduced cardiac and left ventricular weight attributable to enalapril treatment do not seem to be related to inhibition of the renin-angiotensin system. On the other hand, renin-angiotensin system inhibition induces a protective effect on the heart and aorta through structural and functional changes. Most of this action seems to be exerted through angiotensin II type 1 receptors.

Divergent Regulation of Circulating and Intrarenal Renin-Angiotensin Systems in Response to Long-Term Blockade

Background/Aims: Long-term treatment with angiotensin-converting enzyme (ACE) inhibitors or angiotensin (Ang) II type I (AT1) receptor blockers can improve kidney function and attenuate the progressive decline in kidney function associated with age. In this study in Wistar rats medicated for 22 months, we determined the effects of enalapril (10 mg/kg/day) and losartan (30 mg/kg/day) treatment, in comparison with vehicle (tap water), on renal AngII receptor density and circulating and urinary components of the renin-angiotensin system (RAS). Methods: Kidney sections were incubated with [125I-sarcosine1-threonine8]AngII (0.6 nM) for Ang receptor density, and Ang peptides were determined using radioimmunoassays. Results: Receptor density was ∼50% higher in vasa recta, glomeruli, and tubulointerstitium in enalapril-treated rats and lower in vasa recta and glomeruli in losartan-treated relative to vehicle-treated rats. Losartan and enalapril treatment elevated plasma levels of AngI and Ang-(1–7) while AngII increased only in losartan-treated rats. In contrast, both treatments were associated with a reduction in urinary excretion of all three Ang peptides as compared with control rats. Conclusion: The reduction in urinary Ang peptides with losartan and enalapril treatment suggests that blockade of intrarenal AngII may be an important mechanism underlying the renoprotection seen with such treatments.

The Brain Renin—Angiotensin System and the Development of Doc - Salt Hypertension

UNLABELLED The effect of captopril, given in the drinking fluid, on the development of DOC-salt hypertension was analyzed. Although captopril did not prevent an increase in blood pressure (BP) elicited by DOC-salt, captopril did diminish BP in both DOC-salt and control animals. From the first week of treatment DOC-salt rats increased their fluid intake (FI). At the end of the experiment, captopril reduced this increment (655% to 357%). At the same time plasma angiotensinogen was diminished (-35%; p less than 0.001) and cerebrospinal fluid (CSF) substrate concentration increased (+33%; p less than 0.02) in DOC-salt rats, captopril did not modify these changes. In control rats captopril did not alter FI, depleted plasma angiotensinogen, (-73%; p less than 0.001), did not change the central prohormone and increased plasma renin activity (PRA) (+260%; p less than 0.001). IN CONCLUSION CSF angiotensinogen concentration changes as previously found in CNS while a clear dissociation between plasma and CSF angiotensinogen was found in DOC-salt rats. In these animals the hypertension was not clearly affected by captopril treatment. However the effect of the converting enzyme inhibitor suggests that the central renin-angiotensin system could participate in the increase in FI.

Effect of EXP 3174 on Blood Pressure of Normoreninemic Renal Hypertensive Rats

This study examined the effect on mean blood pressure of a new orally active nonpeptide angiotensin II (Ang II) receptor antagonist, EXP 3174, in doses that completely block exogenous Ang II action. Anesthetized and conscious two-kidney, two clip chronic renovascular hypertensive rats and sham-operated animals were used. In anesthetized hypertensive rats, intracerebroventricular administration of the inhibitor had no effect on blood pressure, whereas blood pressure was normalized by intravenous injection of the antagonist (163 +/- 12 to 110 +/- 9 mm Hg, P < .05). In sham anesthetized rats, intravenous injection of EXP 3174 also lowered blood pressure (112 +/- 6 to 96 +/- 6mm Hg, P < .05). In conscious rats, intravenous EXP 3174 induced a fall in pressure that was larger in hypertensive (156 +/- 9 to 132 +/- 5 mm Hg, P < .05) than in sham (104 +/- 3 to 94 +/- 4 mm Hg, P < .05) rats. Plasma renin activity was very high in anesthetized animals (hypertensive versus sham, 87.8 +/- 8.3 versus 95.7 +/- 10.2 ng Ang I/mL per hour); differences were not significant either between anesthetized hypertensive and sham or in conscious animals (hypertensive versus sham, 9.42 +/- 1.58 versus 6.74 +/- 2.32 ng Ang I/mL per hour). Angiotensinogen concentration was higher in cerebrospinal fluid in anesthetized hypertensive rats (36.4 +/- 3.0 versus 26.0 +/- 2.4 ng Ang I/mL, P < .05) and in the artery wall of hypertensive conscious rats (103.1 +/- 10.3 versus 75.2 +/- 7.8 ng Ang I/g, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Water-salt balance, plasma renin activity and catecholamine excretion in renovascular hypertension in the rat

Water-electrolyte balance, plasma renin activity and urinary catecholamine excretion were studied for a period of 10 weeks after clipping the renal artery in the rat. Two groups of rats were examined; in Group I, a silver clip was applied on the left renal artery leaving the contralateral kidney untouched; in Group II, both renal arteries were clipped. Neither water-salt retention nor the increase inthe activity of the renin-angiotensin system or in the neural tone seem to be essential in the development of high arterial pressure after renal ischemia. All these factors would seem to be secondary mechanisms the contribution of which would depend on the experimental model or the hypertensive period under consideration.

Neonatal 6-Hydroxydopamine Treatment and the Development of Renal Hypertension in the Rat

The onset and development of 2 kidney-2 clip renal hypertension was studied in chronically sympathectomized rats treated with 6-hydroxydopamine (6-OHDA) immediately after birth and with adrenal demedullation performed at the time of clipping. Blood pressure (BP) was lower in 6-OHDA treated animals than in untreated controls and the rate of hypertension development was similar in both groups. Urinary excretion of norepinephrine (NE) was significantly decreased during the 15th week and normal by the end of the 20th week. The cardiac NE content reached negligible levels while the mesenteric arteries retained 50% of its content. In the central nervous system (CNS) the 6-OHDA treatment induced a significant increase in NE concentration in the brain stem and medulla oblongata and a significant decrease in cerebellum. Hypertension produced a significant decrease in NE content in the brain stem while 6-OHDA treatment in hypertensive rats resulted in a generalized NE depletion in all the CNS areas. Results have shown that 6-OHDA treatment does not produce a complete and generally distributed sympathectomy; treatment reduces the level of BP but does not change the slope in BP increase.

Chronic administration of ketanserin and the development of two-kidney-two-clip Goldblatt renovascular hypertension in the rat.

The effect of ketanserin (Kt) has been analyzed during the development of two-kidney–wo-clip (2k–2c) reno-vascular hypertension in the rat. Male Wistar rats were divided into four experimental groups: (1) clip Kt (ClKt) (n = 12)—A silver clip (0.25 mm width) was placed in each renal artery 3 days after beginning the administration of Kt (10 mg/kg/day) in the drinking water; (2) sham Kt (ShKt) (n = 13)—Similar to group 1, but the clips were placed in, and immediately removed from, the renal arteries; (3) untreated clip (UCl) (n = 10)—Similar to group 1, but the rats drank water; (4) untreated sham (USh) (n = 10)—Similar to group 2, but the rats drank water. Blood pressure (BP) was measured before surgery and was followed weekly for 7 weeks. At the end of this period, blood and cerebrospinal fluid (CSF) samples were obtained in all the animals. Plasma renin activity (PRA) and plasma and CSF angiotensinogen concentration (AoC) were evaluated. The results have shown that Kt partially inhibited the increase in BP induced by bilateral renal ischemia (BP: UCl rats 180.5 ± 12.4 versus ClKt rats 149.8 ± 5.1 mm Hg;p < 0.01; USh rats 116.7 ± 3.7; ShKt rats 114.4 ± 5.0 mm Hg). PRA was similar in hypertensive and control rats whether or not they had received Kt. AoC in plasma was decreased in clipped treated and untreated rats. AoC was in-creased in the CSF of UCl animals (60.8 ± 3.8 ng Ang I/ml) when compared with USh rats (46.5 ± 2.0 ng Ang I/ml); no changes were observed in treated rats (ClKt rats 44.4 ± 1.1 versus ShKt rats 44.4 ± 3.8 ng Ang I/ml). The effect of chronic KT treatment resulted in (a) partial inhibition in the BP increase due to bilateral renal ischetnia and (b) prevention of CSF AoC increase observed in 2k–2c untreated renal hypertensive rats.

Effect of ketanserin and prazosin on blood pressure and cardiovascular reactivity to vasopressor agents during the development of two kidney ― two clip renal hypertension in the conscious rat

The present experiment was performed in order to evaluate some of the actions of ketanserin, a blocking agent active at the serotonin 2 (S2) receptors. Male rats were divided into: 1. Two kidney-two clip (2K-2C) renal hypertensive: a silver clip (0.25 mm width) was placed in both renal arteries. 2. Sham-operated: a similar operation without placing the clip was performed. Blood pressure (BP), heart rate and pressor responses to tyramine, angiotensin II and norepinephrine (NE), and the hypotensive effect of prazosin (Pz) and ketanserin (Kt) were recorded in the conscious animals 8 weeks later. Results showed that Pz produced a similar decrease in BP in hypertensive and sham animals while Kt lowered BP much more in hypertensive than in normotensive rats. Prazosin abolished the pressor response to tyramine while ketanserin only diminished tyramine effect. Both hypotensive agents shifted the dose-response curve to NE to the right. Present data have shown that ketanserin and prazosin are effective hypotensive agents in 2K - 2C renovascular hypertension in the rat. They also suggest that both hypotensive compounds have an alpha 1-blocking effect, somehow they seem to have some differences in their pattern of pharmacological action.

Norepinephrine turnover in the heart and blood vessels of rats subjected to bilateral renal infarction.

The total norepinephrine (NE) content, the uptake of [3H]NE, the turnover rate and the synthesis rate of the neurotransmitter at the heart and blood vessels have been studied during the development of hypertension in rats subjected to bilateral renal infarction. Normal and sham-operated rats were used as controls. Fifty percent of the rats with renal infarction became hypertensive. The weight of the hearts and blood vessels of the experimental animals was significantly increased 15 days after renal infarction. Changes were greater in hypertensive animals. NE concentration in the heart was slightly decreased without achieving statistical significance, while total NE content was unchanged. In the artery wall NE concentration was significantly decreased in normotensive and hypertensive operated rats. [3H]NE uptake in the heart and blood vessels was similar in experimental and control animals. In relation to NE turnover, in both the heart and blood vessels, normal and sham-operated animals behaved as one population while normotensive and hypertensive rats behaved as another population. The rate constant of NE turnover was increased in both tissues of operated experimental animals without achieving statistical significance in the case of the heart. NE synthesis rate was unchanged in the cardiac muscle but was significantly increased in the blood vessels of operated animals. Present data indicate that results describing NE dynamics in the heart cannot be extrapolated for the blood vessels level; on the other hand changes in the neurotransmitter do not seem to be related to the development of high blood pressure after renal infarction in the rat.