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J F Smits

Publications and source records attributed to J F Smits.

At least 73 records · Page 4Linked to original sources
PubMed1994

Role of afferent renal nerves in renal adaptation to sodium restriction in uninephrectomized rats.

In the present study we examined the role of the afferent renal nerves in the control of ipsilateral renal adaptation to sodium restriction. Uninephrectomized rats were subjected to selective renal deafferentation or sham operation, instrumented with catheters and housed in metabolism cages to collect urine in 90 min fractions. Only sodium deficient food (0.03% Na+) was allowed. Water and sodium excretion were stabilized via a continuous 48 h infusion (1.25 ml h-1) of a Ringer's solution. During this period water, sodium and potassium excretion were similar in renal deafferented and sham operated rats. Then, the infusion was exchanged for a modified Ringer's solution, in which the sodium ion was replaced by the choline ion. Measurements were performed over 24 h. During the choline C1 infusion, urine flow increased similarly in renal deafferented and sham-operated rats. In both groups of rats, sodium excretion decreased within 24 h by more than 95%, whereas potassium excretion stayed constant. Sodium loss was higher in renal deafferented rats only in the first 90 min period after the exchange of the infusions. These results indicate that afferent renal nerves are not necessary in ipsilateral renal adaptation during 24 h sodium restriction, but may play a modulatory role in correcting transient changes in ipsilateral renal excretory function.

Adaptation, Physiological↗
PubMed1994

Structural alterations in heart valves during left ventricular pressure overload in the rat.

BACKGROUND: Heart valves are an important denominator of the function of the heart but detailed studies of structural alterations of heart valves after hemodynamic changes are lacking. EXPERIMENTAL DESIGN: Structural alterations of heart valves, including DNA synthesis, collagen mRNA, and protein concentration were measured in heart valves of Wistar Kyoto (WKY) rats with acute left ventricular pressure overload, created by intrarenal aortic ligation (AL, N = 18) as well as in heart valves of age-matched spontaneously hypertensive rats, a model of chronic hypertension (N = 18). SHAM aortic ligation and normal WKYs (N = 17 and N = 17) served as controls. All animals received 5'bromo-2' deoxyuridine, during the last 7 days of the experiment, in a dose of 2.4 mg/kg.day. RESULTS: The cumulative labeling fraction (LF) in the mitral valve of AL animals was 47.8 +/- 5.2% as compared with 9.4 +/- 2.6% in SHAM animals (mean +/- SEM, p < 0.01). The LF in the aortic valve of AL animals was 33.3 +/- 2.9% as compared with 7.7 +/- 0.7% in SHAM animals (p < 0.01). The LF in the tricuspid valve was also significantly increased: 11.3 +/- 1.4% in AL versus 5.8 +/- 0.7% in SHAM (p < 0.01). Labeling fractions of heart valves in SHR were not increased as compared with normal WKY. The total collagen concentration in the three heart valves, measured by the hydroxyproline assay, did not change. The mRNA amounts of both collagen type I and III, detected by in situ hybridization, were increased in the heart valves of AL and spontaneously hypertensive animals as compared with the two control groups (SHAM and WKY). In all 3 heart valves, interstitial cells were vimentin-positive, but desmin-negative. A fraction of interstitial cells showed alpha-smooth muscle actin positivity. This immunophenotype did not change during pressure overload. CONCLUSIONS: Heart valves have the capacity to adapt to acute pressure overload, by means of DNA synthesis and increased collagen turnover. The increase in LF in the normotensive tricuspid valve suggests a role for an additional circulating factor. A constant fraction of the interstitial heart valve cells consists of myofibroblasts.

Animals↗
PubMed1993

Role of the baroreflex in beta 2-sympathomimetic induced tachycardia in male rats.

The aim of the study was to determine whether tachycardia which is associated with the use of beta 2-sympathomimetic tocolytic agents is caused by baroreflex activation or by direct stimulation of cardiac beta-adrenoceptors. In conscious male rats, tachycardiac responses following intravenous injection of hexoprenaline, ritodrine and fenoterol were compared following (i) bilateral sinoaortic denervation (SAD) or (ii) sham-operation, and (iii) ganglionic-blockade using hexamethonium. Dose-ranges were chosen to result in similar reductions in diastolic blood pressure (DAP). Furthermore, following ganglionic blockade, the relative contribution of beta 1-adrenoceptor stimulation was assessed using the selective beta 2-receptor antagonist ICI 118,551. In intact rats, increases in HR induced by all beta-adrenoceptor agonist were comparable. In SAD and ganglion-blocked rats, DAP fell more pronounced at even lower doses. The corresponding increases in HR were approximately 3 times smaller than in intact rats but not different between agents. During ganglionic blockade ICI 118,551 significantly inhibited HR responses to fenoterol and hexoprenaline but not ritodrine. The conclusion is that in intact male rats, baroreflex activation is the major determinant of tachycardia following injection of ritodrine, fenoterol or hexoprenaline. Increasing the beta 2-selectivity of these drugs will not limit the tachycardic effects.

Adrenergic beta-Agonists↗
PubMed1993

Evidence for a novel angiotensin II receptor involved in angiogenesis in chick embryo chorioallantoic membrane.

Angiotensin II acts as a growth factor in the cardiovascular system and has been implicated in angiogenesis. The existence of at least two types of angiotensin II receptors, the AT1 and the AT2 receptors, has been suggested by ligand binding studies. We used three different AT receptor antagonists to study the receptor mediating angiotensin II-induced angiogenesis in the chorioallantoic membrane (CAM) of the chick embryo. Angiotensin II caused pronounced angiogenesis of pre- and postcapillary vessels of 30-40%. This response could only be blocked by adding the peptidergic AT2 antagonist CGP-42112A. The nonpeptidergic AT2 antagonist PD123319 and AT1 antagonist losartan (DuP 753) were not effective. In addition, we used radioligand binding studies with a range of ligands to define the nature of the receptor. Our results show a high density of specific single class AT receptor with a total number of binding sites of 1,190 fmol/mg protein and an affinity constant for angiotensin II of 2.7 nM. The inhibitory concentrations (IC50) for CGP-42112A, PD 123319 and losartan were 724, > 100,000, and 59,000 nM, respectively. Our studies suggest that these binding sites act as receptors for angiotensin II-induced angiogenesis. Both functional and radioligand binding studies suggest that the receptor is different from the classical mammalian AT1 and AT2 receptors.

Allantois↗
PubMed1993

Distribution and functional significance of cardiac angiotensin converting enzyme in hypertrophied rat hearts.

BACKGROUND: The intracardiac conversion rate of angiotensin (Ang) I to Ang II and the expression of angiotensin converting enzyme (ACE) mRNA are amplified in rat hearts with left ventricular hypertrophy (LVH). To examine whether the accelerated intracardiac Ang II generation in LVH is related to an induction of cardiac ACE, we studied localization and function of cardiac ACE in hypertrophied rat hearts using specific ACE inhibitors. METHODS AND RESULTS: Cardiac ACE was localized and quantified in hearts from male Wistar rats with LVH due to chronic experimental aortic stenosis and from control rats. With the ACE inhibitor 125I-351A, a derivative of lisinopril, as a radioligand on coronal sections of LVH and control hearts, in vitro autoradiography demonstrated ACE binding in aorta, coronary arteries, atria, and ventricles of both groups. Quantitative analyses revealed that ACE density (counts per minute per cross-sectional area of tissue) was twofold higher within the myocardium of hypertrophied left ventricles compared with controls (p < 0.005). Quantitative morphometry demonstrated a modest increase in the fractional volume of myocytes as well as capillary volume without an increase in the fractional volume of endothelial cells in left ventricular tissue from aortic stenosis rats. These data suggest that an increase in endothelial cell volume per se cannot alone account for the observed doubling of ACE density and support an upregulation of ACE production in hypertrophied tissue. The role of cardiac ACE in intracardiac conversion of Ang I to Ang II and its specific inhibition was studied in isolated, isovolumic beating, buffer-perfused LVH and control hearts. Biochemical conversion rates as well as functional changes in response to 3 x 10(-7) M Ang I were examined in the absence or presence of the ACE inhibitor enalaprilat (4 x 10(-6) M). After a brief stabilization period, groups of LVH and control hearts were subjected to the following infusion protocols: 15 minutes of vehicle followed by 30 minutes of Ang I plus vehicle, 15 minutes of enalaprilat followed by 30 minutes of Ang I plus enalaprilat (enal/Ang I), or 45 minutes of vehicle only to allow comparison with a time control. Intracardiac Ang I-to-Ang II conversion rate was fourfold higher in LVH than in control hearts (p < 0.05). Infusion of enalaprilat reduced the intracardiac Ang I-to-Ang II conversion rate in LVH hearts by 70% (p < 0.05 versus Ang I). At similar levels of constant coronary flow per gram, Ang I increased coronary perfusion pressure by 23 +/- 5 mm Hg (p < 0.01 versus vehicle) in LVH hearts and by 36 +/- 10 mm Hg (p < 0.005 versus vehicle) in control hearts. When enalaprilat was infused with Ang I, the increase in perfusion pressure was limited to 5 +/- 5 mm Hg (NS versus vehicle) in LVH hearts and 12 +/- 3 mm Hg (p < 0.05 versus vehicle) in control hearts and was significantly lower than in hearts infused with Ang I only (p < 0.05 in LVH and p < 0.05 in control hearts, respectively). Systolic function was not affected by either infusion protocol. In contrast, Ang I infusion was associated with diastolic dysfunction. In LVH hearts, left ventricular end-diastolic pressure (LVEDP) increased from 10 +/- 1 mm Hg at baseline to 25 +/- 2 mm Hg at the end of the Ang I infusion (p < 0.001 versus vehicle), which was inhibited by infusion of enalaprilat. In control hearts, there was a lesser increase in LVEDP from 10 +/- 1 mm Hg to 15 +/- 1 mm Hg in response to Ang I (p < 0.05 versus LVH). Control hearts treated with enalaprilat with Ang I displayed no increase in LVEDP: CONCLUSIONS: These observations indicate that ACE protein is increased within the myocardium of LVH hearts, extending recent findings of increased cardiac ACE activity and mRNA levels in this model of pressure-overload LVH in the rat. Blockade of the enzyme by an ACE inhibitor decreases intracardiac Ang I-to-Ang II conversion rate and prevents the functional changes of Ang I-to-Ang II activation

Angiotensin I↗
PubMed1993

Antihypertensive therapy and adaptive mechanisms in peripheral ischemia.

In the present experiments the effect of long-term peripheral ischemia on the capillary of two hind limb skeletal muscles was investigated in spontaneously hypertensive rats. Furthermore, the effect of antihypertensive therapy on changes in capillarity and on the previously observed hyperreactivity of the ischemic vascular bed to vasoconstrictors was investigated in perfused hind limbs of rats after long-term treatment with the angiotensin I converting enzyme inhibitors captopril (0.5 mg/kg.h) or zabiciprilate (0.025 mg/kg.h), the angiotensin II type 1 receptor antagonist losartan (0.625 mg/kg.h), or the calcium antagonist felodipine (0.042 or 0.42 mg/kg.h). Skeletal muscle ischemia in the left hind limb was induced by partial ligation of the left common iliac artery. Long-term (4 weeks) ischemia increased significantly the capillary-to-fiber ratio in the soleus muscle, composed predominantly of type I fibers in spontaneously hypertensive rats, of the ischemic hind limb, whereas capillarity in the contralateral muscle was not affected. Furthermore, capillarity in the gastrocnemius muscle (type II muscle fiber part) of both the ischemic and contralateral hind limb did not change. Long-term treatment with the angiotensin I converting enzyme inhibitors during ischemia abolished the increase in the capillary-to-fiber ratio in the soleus muscle, whereas a comparable antihypertensive dose of felodipine had no effect. Greater blood pressure reductions by both losartan and felodipine prevented increases in capillarization in skeletal muscle ischemia. With respect to vascular hyperreactivity during ischemia, only treatment with losartan normalized reactivity of the ischemic vascular bed to vasoconstrictors.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin Receptor Antagonists↗
PubMed1992

Comparison of angiotensin-converting enzyme inhibitors in the rat in perfused hindlimbs and in vivo.

To investigate the role of local renin angiotensin systems in the functional responses to angiotensin I and II, the effects of angiotensin I and angiotensin II on resistance were measured in perfused hindlimbs of rats under normal conditions and during infusion of enalaprilate, lisinopril, zabiciprilate and captopril at two infusion rates. The angiotensin-converting enzyme (ACE) inhibitors significantly increased ED50 and decreased maximal resistance changes of angiotensin I dose dependently, without effects on angiotensin II responses. Captopril increased the ED50 of angiotensin I significantly more than did the other ACE inhibitors at a low infusion rate. The ACE inhibitors, except for lisinopril, increased the ED50 of angiotensin I pressor responses in vivo to the same extent, and were similarly potent to inhibit plasma ACE activity at 15 min after injection. The ratio of the doses of the ACE inhibitors used in vivo was the same as in perfused hindlimbs. These results suggest that, in the hindlimbs, angiotensin I causes ACE-dependent vasoconstriction. Captopril may be more effective to inhibit local ACE than the other ACE inhibitors investigated.

Angiotensin I↗
PubMed1992

Acute renal vascular response to ACE inhibition in two rat strains with different susceptibility to the development of glomerulosclerosis.

Normotensive male Wistar rats are susceptible to the development of glomerulosclerosis, a process which can be accelerated by partial renal ablation, while normotensive male Wistar Kyoto (WKy) rats are resistant to glomerulosclerosis. Long-term treatment with angiotensin-I-converting enzyme inhibitors prevents the development of glomerulosclerosis. We studied the acute renal vascular response to bolus injections of captopril (1, 3, and 10 mg/kg). Mean arterial blood pressure (MAP) was significantly less in Wistar rats compared to WKy and not influenced by unilateral nephrectomy. Renal vascular resistance (RVR) and the filtration fraction (FF) were significantly greater in sham and unilateral nephrectomy Wistar rats as compared to WKy. Captopril significantly reduced the RVR in all four groups, but at comparable doses, RVR remained greater in the Wistar sham and Wistar rats following unilateral nephrectomy compared to sham and uninephrectomized WKy respectively. Captopril reduced FF in Wistar rats only. These data indicate an enhanced level of activity of the renal renin-angiotensin system in glomerulosclerosis-susceptible Wistar rats compared to glomerulosclerosis-resistant WKy rats, suggesting that vascular reactivity involving the renin-angiotensin system is an important determinant of the genetically determined differences in susceptibility to glomerulosclerosis in these two rats strains. The strain-dependent difference in RVR at the highest dose of captopril indicates that additional, possibly structural features may play a role in the difference in susceptibility to glomerulosclerosis.

Animals↗
PubMed1992

Renal hemodynamic effects of nonhypotensive doses of angiotensin-converting enzyme inhibitors in hypertension and heart failure rats.

Both circulating and local renin-angiotensin systems (RAS) may contribute to cardiovascular homeostasis under normal and pathophysiologic conditions. They may also play a role in the effects of angiotensin-converting enzyme (ACE) inhibitors. In the present study, we compared systemic and regional hemodynamic effects of nonhypotensive doses of captopril and enalaprilate in normal rats, spontaneously hypertensive rats (SHR), and rats with heart failure due to myocardial infarction (MI). Enalaprilate (0.1 mg/kg) or captopril (3 mg/kg) was injected intravenously (i.v.) in conscious rats equipped with miniature Doppler flow probes on renal and mesenteric artery and abdominal aorta or an electromagnetic flow probe on the ascending aorta to measure cardiac output (CO). This resulted in a shift of the angiotensin-I (ANG I) dose-pressor curve (ED50 of ANG I after saline 0.21 +/- 0.33 micrograms, enalaprilate 1.45 +/- 0.26 micrograms, captopril 2.38 +/- 0.73 micrograms; mean +/- SEM; n = 6-12). In the systemic hemodynamic groups, no significant changes in mean arterial pressure (MAP), CO, or total peripheral resistance (TPR) were observed. In the regional hemodynamic groups, enalaprilate caused a slight (-8 +/- 1 mm Hg) reduction in MAP in normal rats. Resistance in the hindquarters was not affected by ACE inhibitors, whereas only enalaprilate reduced mesenteric resistance in MI rats. In contrast, renal resistance was reduced and renal blood flow (RBF) increased after captopril in normal and MI rats and after enalaprilate in MI rats. Effects were greatest in MI rats (RBF: saline -0.05 +/- 1.9%, enalaprilate 10.3 +/- 2.4%, captopril 10.1 +/- 2.0%).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Alpha 1-adrenoreceptor blockade reduces the angiotensin II-induced vascular smooth muscle cell DNA synthesis in the rat thoracic aorta and carotid artery.

We explored effects of alpha 1-adrenoreceptor blockade with prazosin on the increased vascular smooth muscle cell (SMC) DNA synthesis induced by angiotensin II (Ang II) in rats. Ang II was infused with or without prazosin or its solvent. Observations were compared with those in rats receiving saline or solvent. In group A, Ang II was infused for 2 weeks by subcutaneously implanted osmotic minipumps at a rate of 35 ng/100 g per minute. Group B received Ang II together with the alpha 1-adrenoreceptor antagonist prazosin (0.35 micrograms/100 g per minute). Group C received Ang II and 50% dimethyl sulfoxide (DMSO), the solvent of prazosin; group D received 50% DMSO; and group E received 0.9% NaCl (Ang II vehicle). All animals were infused with 5-bromo-2'-deoxyuridine for 2 weeks via separate minipumps to measure DNA synthesis. Ang II significantly increased the fraction of DNA synthesizing SMCs in the media of the thoracic aorta from 0.4 +/- 0.1% (mean +/- SD) in group E (n = 6) to 10.8 +/- 7.0% in group A (n = 8). Addition of prazosin to Ang II reduced the labeling fraction of SMCs to 3.0 +/- 2.2% (group B, n = 9). The remaining SMC DNA synthesis in the prazosin-treated group was probably due to the effects of the solvent of prazosin, i.e., 50% DMSO, since infusion of 50% DMSO alone increased the labeling fraction to 4.1 +/- 2.0% (group D, n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Angiotensin II receptor blockade after myocardial infarction in rats: effects on hemodynamics, myocardial DNA synthesis, and interstitial collagen content.

Angiotensin-converting enzyme (ACE) inhibitors are widely used for treatment of heart failure after myocardial infarction (MI). The beneficial effects consist of a combination of hemodynamic effects and interference with cardiac structural alterations. These effects are believed to depend on inhibition of angiotensin II (AII) formation and thus diminished angiotensin receptor stimulation. We administered the angiotensin II-1 (AT-1) receptor antagonist losartan during and after completion of the repair phase of an MI to investigate involvement of the AT-1 receptor in the above described effects of captopril. MI reduced cardiac output (CO) (sham 94 +/- 4 ml/min, MI 78 +/- 5 ml/min) and maximal CO (sham 154 +/- 4, MI 107 +/- 5 ml/min, respectively). Losartan (15 mg/kg/day) resulted in a rightward shift of the AII pressor dose-response curve by a factor of 32-40. Neither CO nor COVL,max was affected by losartan treatment in either phase (late treatment CO = 78 +/- 5, COVL,max = 118 +/- 9 ml/min). Although early treatment with losartan reduced cardiac hypertrophy measured as heart weight, DNA synthesis was reduced only slightly. In contrast, collagen deposition was inhibited completely. The results suggest that the effects of captopril in rats after MI are not dependent on AT-1 receptor-mediated mechanisms.

Angiotensin II↗
PubMed1991

Microvascular actions of calcium channel antagonists.

The microvascular actions of three calcium channel antagonists were studied in intact spontaneously hypertensive rats (SHR) provided with a dorsal striated muscle microcirculatory chamber. Verapamil and the dihydropyridine derivatives nifedipine and felodipine reduced mean arterial blood pressure (MAP) in a dose-dependent manner. They dilated arterioles of different sizes, with the most pronounced effect being on the smallest precapillary arterioles. Venular diameters were not affected by the calcium antagonists. Approximately 60% of the small arterioles showed a rhythmic pattern of vasodilatation and constriction. This pattern of spontaneous vasomotion was completely blocked by the calcium channel antagonists, especially those of the dihydropyridine type. It is concluded that (a) small precapillary arterioles play an important role in the vasodilator action of calcium channel antagonists, and (b) arteriolar vasomotion depends on vascular smooth muscle cell calcium influx.

Animals↗
PubMed1991

DNA synthesis in the non-infarcted cardiac interstitium after left coronary artery ligation in the rat: effects of captopril.

Effects of Captopril. Journal of Molecular and Cellular Cardiology (1991) 23, 1245-1253. This study was undertaken to investigate the alterations in interstitial DNA synthesis and collagen content in the non-infarcted left and right ventricle after induction of a myocardial infarction (MI) in the rat. MI was induced by ligation of the left anterior descending coronary artery. All animals received 5-Bromo-2'-deoxyUridine (BrdU), via a subcutaneous osmotic minipump, one day before sacrifice, to quantitate DNA synthesis. A transient rise in BrdU incorporation was found in both ventricles. Peak levels were found at day 7 and 14 after infarct induction. BrdU incorporation had returned to control levels 3 weeks after infarct induction. By using anti BRDU--anti-laminin immuno- double staining DNA synthesis was localized mainly in the cardiac interstitium. Concomitantly, a sustained increase in collagen content, measured as the Sirius red positive area on cross sections, was found from day 7 after infarct induction. No changes were found in sham animals. In the second part of the study the effects of the angiotensin I converting enzyme inhibitor captopril and the arteriolar vasodilator hydralazine on MI induced interstitial DNA synthesis and collagen content were investigated. Captopril reduced both the increase in DNA synthesis and collagen content. Hydralazine did not affect interstitial DNA synthesis, but reduced the MI induced collagen content. Both drugs had no effects in sham animals. We conclude that induction of a myocardial infarction stimulates interstitial DNA synthesis and increases the collagen content in the non-infarcted areas of the heart. Interstitial DNA synthesis is dependent on the angiotensin I converting enzyme in a direct manner independent from afterload changes.

Animals↗
PubMed1991

Delayed but not immediate captopril therapy improves cardiac function in conscious rats, following myocardial infarction.

After myocardial infarction, the renin-angiotensin system is found to be activated. While this response may be beneficial in acute failure, it could be detrimental in chronic stages. Therefore effects of captopril therapy were investigated during early and later phases after myocardial infarction in conscious rats, chronically instrumented for hemodynamic measurements. Hemodynamics were measured at baseline and after stimulating the heart by a volume load (cardiac function curve). Myocardial infarction decreased baseline cardiac output and impaired cardiac function, without effects on baseline mean arterial pressure, central venous pressure and heart rate. Captopril given 3 to 5 weeks after infarction improved cardiac function in a dose-dependent manner by increasing stroke volume, whereas stroke work was not affected. In contrast, captopril given from 1 to 21 days after infarction did not lead to improved cardiac function; instead, tachycardia together with a decreased stroke volume suggested deterioration, rather than improvement, of cardiac function. These data indicate that captopril therapy in chronically infarcted conscious rats improved cardiac function when treatment was started after completion of the healing process, but that early treatment not only failed to improve ventricular function, but may have a deleterious effect of the heart.

Animals↗
PubMed1991

Two weeks of intermittent dobutamine therapy restores cardiac performance and inotropic responsiveness in conscious rats with heart failure.

Dobutamine is frequently used for acute therapy in heart failure. In the present study, the hemodynamic effects of long-term intermittent dobutamine therapy were investigated in conscious rats with heart failure. Rats with healed myocardial infarctions received two i.p. injections of dobutamine per day for 2 weeks. Hemodynamic measurements were performed 90-180 min after the last injection. Two weeks of intermittent dobutamine significantly restored all hemodynamic changes induced by infarction. The maximal cardiac output during volume loading was depressed due to infarction and dose-dependently restored by 2 weeks of intermittent dobutamine. An increased stroke volume accounted for this improvement since the heart rate was not altered. In order to investigate changes in adrenergic responsiveness, the effects of acute dobutamine in nontreated and 2 weeks of dobutamine-treated infarcted rats were compared to those in control rats. Whereas chronotropic responses to acute dobutamine were comparable for all experimental groups, the inotropic response was reduced in nontreated infarcted rats but dose-dependently restored after 2 weeks of intermittent dobutamine therapy. From the data, we conclude that 2 weeks of intermittent dobutamine therapy in conscious rats with healed myocardial infarcts improved cardiac performance and restored the inotropic response to acute dobutamine administration. Data indicate that dobutamine has a long-term effect on cardiac function, which differs from the acute inotropic effect.

Animals↗
PubMed1991

Regional hemodynamic effects of rilmenidine and clonidine in the conscious spontaneously hypertensive rat.

Rilmenidine is an oxazoline analogue that has antihypertensive properties that resemble those of clonidine. Since rilmenidine has recently been described to have a relatively greater affinity for imidazoline receptors than clonidine, it was of interest to study whether this has functional consequences with regard to the regional hemodynamic responses. We investigated regional hemodynamics in conscious spontaneously hypertensive rats, equipped with miniature Doppler flow probes on the renal and mesenteric arteries and on the abdominal aorta. Clonidine (3-30 micrograms/kg) and rilmenidine (0.2-3 mg/kg) induced similar, dose-dependent reductions in heart rate. Both also induced an early hypertensive response, which was greater with rilmenidine, and similar later blood pressure reductions, which were maintained over 3 h. The early hypertensive response was associated with generalized vasoconstriction. Rilmenidine caused slightly greater mesenteric and hindquarter constriction than clonidine, whereas renal effects did not differ significantly. During the hypotensive phase, rilmenidine was a less potent mesenteric and hindquarter vasodilator than clonidine. During this phase, renal blood flow was at control levels, probably indicating autoregulation of renal flow. The minor differences in regional hemodynamic effects suggest that clonidine and rilmenidine can both be used as potent antihypertensives. The fact that rilmenidine has been suggested to possess less sedative side-effects suggests that, on this basis, it may be superior for antihypertensive drug therapy.

Animals↗
PubMed1991

Cardiac remodeling in hypertension and following myocardial infarction: effects of arteriolar vasodilators.

Cardiac remodeling constitutes a risk factor in cardiovascular disease. It may occur in a variety of circumstances. In hypertension and following myocardial infarction, pharmacological intervention in the remodeling process has been the subject of several studies. But the mechanisms of action of drugs that do contribute to regression of the remodeling response are still a matter of debate. Much of the confusion around the subject comes from the fact that classic arteriolar vasodilators do not result in such regression in hypertensive cardiac hypertrophy. This paper reviews some of the literature to examine whether there is indeed an exceptional position for vasodilators in hypertensive heart disease. Although, conceptually, arteriolar dilatation, and thus afterload reduction, might also have favorable effects on the remodeling response following myocardial infarction, clinical studies suggest the opposite. In the present paper, possible mechanisms are discussed, and evidence is presented that shows that hydralazine has an unexpected effect on the remodeling response at the level of the extracellular matrix.

Animals↗