Nifedipine-treated Rats Research Articles

Loss of Coronary Dilation to N6-2-(4-Aminophenyl) Ethyladenosine in Isolated Hearts from Chronic Caffeine- and Nifedipine-Treated Rats

Background: The effect of chronic administration of caffeine and/or nifedipine was investigated on functional cardiovascular responses and cardiac adenosine receptor and calcium-handling protein gene expression. Methods: Male Wistar rats (6 weeks) were either administered caffeine 0.06% in their drinking water, given nifedipine 10 mg/(kg·day) intraperitoneal (IP), or provided both caffeine and nifedipine over 14 days and compared with control age-matched rats. Isolated hearts were set up in Langendorff mode. Coronary vasodilation was evaluated using the adenosine receptor agonists 5′-(N-ethylcarboxamido) adenosine (NECA) and N6-2-(4-aminophenyl) ethyladenosine (APNEA). The bradycardic effects were assessed using N6-(l-2-phenylisopropyl) adenosine (R-PIA). In addition, mRNA cardiac expression of adenosine receptors and calcium-handling proteins were investigated using quantitative polymerase chain reaction. Results: Chronic caffeine treatment did not alter functional responses to NECA or R-PIA but enhanced vasodilation mediated by APNEA (p<0.05). Chronic nifedipine treatment did not affect cardiovascular responses to all three adenosine receptor agonists tested (p>0.05). Combined 14-day treatment with both caffeine and nifedipine inhibited vasodilator responses to APNEA without affecting the concentration–response curves of NECA or R-PIA. Chronic caffeine or nifedipine increased the expression of adenosine A2A and A3 receptors without changing adenosine A1 or A2B receptor mRNA levels, whereas chronic caffeine and nifedipine increased adenosine A2B receptor mRNA levels only (p<0.05). Conclusion: In conclusion, vasodilator responses mediated by the adenosine A3 receptor agonist APNEA was lost with chronic caffeine/nifedipine treatment in the rat heart. This was not due to loss of adenosine A3 receptor expression but possibly due to changes in signaling pathways.

Nifedipine Inhibits Vascular Smooth Muscle Cell Dedifferentiation via Downregulation of Akt Signaling

Calcium is an essential signaling molecule that controls vascular smooth muscle cell (VSMC) contraction, proliferation, and differentiation. Here, we show that the calcium antagonist nifedipine inhibits VSMC dedifferentiation in vitro and in vivo. Differentiated VSMCs cultured on laminin-coated dishes were transferred to laminin-free dishes to induce dedifferentiation. Induction of dedifferentiation resulted in the upregulation of nonmuscle myosin heavy chain expression, a marker of dedifferentiation, and the downregulation of smooth muscle myosin heavy chain expression, a marker of differentiation. Nifedipine significantly inhibited both the induction of these phenotypic changes and upregulation of Akt signaling in these cells. Administration of nifedipine at a low concentration that did not affect blood pressure could inhibit the increase in nonmuscle myosin heavy chain expression and decrease in smooth muscle myosin heavy chain expression in a rat balloon-injury model. Furthermore, nifedipine suppressed neointimal hyperplasia and upregulation of Akt signaling. However, phospho-Akt expression was not suppressed in the regenerating arterial endothelium of the nifedipine-treated rats. The inhibitory effect of the downregulation of Akt signaling by dominant-negative Akt on the induction of VSMC dedifferentiation in the intima was identical to that of nifedipine. In contrast, upregulation of Akt signaling by transfection of the cells with a constitutively active Akt reversed the nifedipine-induced inhibition of VSMC dedifferentiation. In conclusion, nifedipine inhibits VSMC dedifferentiation by suppressing Akt signaling, thereby preventing neointimal thickening.

Altered expression of renal aquaporins and Na+transporters in rats treated with L-type calcium blocker

Nifedipine, a calcium antagonist, has diuretic and natriuretic properties. However, the molecular mechanisms by which these effects are produced are poorly understood. We examined kidney abundance of aquaporins (AQP1, AQP2, and AQP3) and major sodium transporters [type 3 Na/H exchanger (NHE-3); type 2 Na-Pi cotransporter (NaPi-2); Na-K-ATPase; type 1 bumetanide-sensitive cotransporter (BSC-1); and thiazide-sensitive Na-Cl cotransporter (TSC)] as well as inner medullary abundance of AQP2, phosphorylated-AQP2 (p-AQP2), AQP3, and calcium-sensing receptor (CaR). Rats treated with nifedipine orally (700 mg/kg) for 19 days had a significant increase in urine output, whereas urinary osmolality and solute-free water reabsorption were markedly reduced. Consistent with this, immunoblotting revealed a significant decrease in the abundance of whole kidney AQP2 (47 +/- 7% of control rats, P < 0.05) and in inner medullary AQP2 (60 +/- 7%) as well as in p-AQP2 abundance (17 +/- 6%) in nifedipine-treated rats. In contrast, whole kidney AQP3 abundance was significantly increased (219 +/- 28%). Of potential importance in modulating AQP2 levels, the abundance of CaR in the inner medulla was significantly increased (295 +/- 25%) in nifedipine-treated rats. Nifedipine treatment was also associated with increased urinary sodium excretion. Consistent with this, semiquantitative immunoblotting revealed significant reductions in the abundance of proximal tubule Na(+) transporters: NHE-3 (3 +/- 1%), NaPi-2 (53 +/- 12%), and Na-K-ATPase (74 +/- 5%). In contrast, the abundance of the distal tubule Na-Cl cotransporter (TSC) was markedly increased (240 +/- 29%), whereas BSC-1 in the thick ascending limb was not altered. In conclusion, 1) increased urine output and reduced urinary concentration in nifedipine-treated-rats may, in part, be due to downregulation of AQP2 and p-AQP2 levels; 2) CaR might be involved in the regulation of water reabsorption in the inner medulla collecting duct; 3) reduced expression of proximal tubule Na(+) transporters (NHE-3, NaPi-2, and Na, K-ATPase) may be involved in the increased urinary sodium excretion; and 4) increase in TSC expression may occur as a compensatory mechanism.

The Ca2+ Channel Blockade Changes the Behavioral and Biochemical Effects of Immobilization Stress

We investigated how the effects of chronic immobilization stress in rats are modified by Ca2+ channel blockade preceding restraint sessions. The application of nifedipine (5 mg/kg) shortly before each of seven daily 2 h restraint sessions prevented the development of sensitized response to amphetamine as well as the stress-induced elevation of the densities of L-type Ca2+ channels in the hippocampus and significantly reduced the elevation of the densities of [3H]nitrendipine binding sites in the cortex and D1 dopamine receptors in the limbic forebrain. Neither stress, nor nifedipine affected the density of α1-adrenoceptors and D1 receptors in the cerebral cortex nor D2 dopamine receptors in the striatum. A single restraint session caused an elevation of blood corticosterone level that remained unaffected by nifedipine pretreatment, but the reduction of this response during the eighth session was significantly less expressed in nifedipine-treated rats. We conclude that L-type calcium channel blockade prevents development of several stress-induced adaptive responses.

Effect of nifedipine on coronary capillary geometry in normotensive and hypertensive rats.

The aim of this study was to describe quantitatively changes in the coronary capillary network resulting from hypertrophy in spontaneously hypertensive rats (SHR) and a potential effect of long-term treatment of these animals with nifedipine. Age-matched male SHR and Wistar-Kyoto (WKY) rats were treated for 27 weeks. Four experimental groups were analyzed: (1) untreated SHR, (2) nifedipine-treated SHR, (3) untreated control WKY rats, and (4) nifedipine-treated WKY rats. Treatment significantly decreased systolic blood pressure in SHR, although normotensive pressures were not reached. SHR had significantly higher cardiac weight, which decreased in nifedipine-treated rats, but values remained above those in control animals. Morphometric evaluation revealed lower capillary density and larger capillary domain area in hearts from SHR, which were partially attenuated by treatment with nifedipine. Capillary domain area was also significantly larger at arteriolar portions compared with domains supplied at venular portions. Capillary segment length was consistently shorter on the venular than arteriolar portion of the capillary, whereas no differences were observed between hearts from WKY rats and SHR. Treatment with nifedipine resulted in a prolongation of segment length. Reconstruction of the three-dimensional capillary supply unit (capillary domain area times capillary segment length) revealed significant differences between the amount of tissue supplied by a capillary at its arteriolar portion than more distally, which was detectable in all experimental groups. In hypertrophic hearts from SHR this tissue volume is increased mainly because of longer intercapillary distances and larger domains, especially on arteriolar portions.(ABSTRACT TRUNCATED AT 250 WORDS)

Nifedipine‐induced gingival overgrowth in the presence or absence of gingival inflammation in rats

One adverse effect of nifedipine, a long-acting vasodilator, is gingival overgrowth. Preexisting gingival inflammation and/or dental plaque has been suggested to be responsible for the progression of this side effect, but the precise mechanism is uncertain because of a lack of suitable animal models. A study was therefore done to establish an experimental model of gingival overgrowth in rats and to investigate the possible involvement of gingival inflammation and/or dental plaque in its development. Specific pathogen-free Fischer rats (male, 14 days old) were used. Gingival inflammation and dental plaque accumulation were induced by infection with Streptococcus mutans MT8148R. The nifedipine-treated rats (experimental group) were fed a caries-inducing diet containing nifedipine either with or without infection, while the nifedipine-untreated rats (control group) were fed the same diet, similarly with or without the infection. Marked gingival overgrowth was induced in the mandibular molar region of nifedipine-treated rats regardless of S. mutans infection, although the infection resulted in a further increase in the degree of gingival overgrowth. Histological examination of the gingival overgrowth revealed the presence of redundant subepithelial connective tissue in the treated rats, and inflammatory cell infiltration was apparent only in the tissue of the S. mutans-infected rats regardless of the nifedipine administration. These findings suggest that nifedipine induces gingival overgrowth in rats either in the presence or absence of gingival inflammation and/or dental plaque, although these factors can augment the effect of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of nifedipine on monocrotaline-induced pulmonary hypertension in rats.

Effective drug therapy for pulmonary hypertension has not yet been developed. This study was designed to estimate the long-term hemodynamic and histopathological effects of nifedipine on severe pulmonary hypertension using animal models. Injection of one dose of monocrotaline produced subacute pulmonary hypertension in 7 week old Sprague-Dawley rats. Nifedipine (10 mg/kg) was administered intraperitoneally every day. For 5 weeks, bodyweight and hemodynamic parameters were measured, and right ventricle (RV) and left ventricle with septum (LV + S) were weighed separately. Medial thickness of the small pulmonary arterial wall was calculated by Suwa's method. Compared with the control group, the increase in right ventricular systolic pressure, total pulmonary resistance index, weight ratio of RV/(LV + S and medial hypertrophy in the nifedipine-treated rats were significantly limited without causing systemic hypotension. These results suggest that treatment with nifedipine may also be effective in attenuation of pulmonary hypertension when applied to humans.

Nifedipine in divided doses does not reverse left ventricular hypertrophy in spontaneously hypertensive rats.

This study investigated whether nifedipine administered in divided daily doses would diminish left ventricular hypertrophy (LVH) in spontaneously hypertensive rats (SHR). We administered nifedipine (12 mg/kg/day) in 3 divided doses by gastric gavage to 15-week-old male SHR (n = 10) for 4 weeks. Age- and sex-matched SHR served as controls (n = 10). Left ventricular (LV) function was evaluated by LV catheterization and cardiac output was determined by the thermodilution method. Plasma renin activity (PRA) and plasma norepinephrine levels were measured. Nifedipine significantly decreased blood pressure (p less than 0.01), shortened time constant T (p less than 0.05), and increased cardiac output (p less than 0.05). Nifedipine did not impair the LV systolic and diastolic indices during acute afterload elevation with angiotensin II. LV weight was similar in the 2 groups of rats. While PRA was unaltered, plasma norepinephrine levels were higher in the nifedipine-treated rats (p less than 0.05). These data indicate that nifedipine in 3 divided doses reduced blood pressure in SHR without compromising cardiac function but did not reverse LVH. The short hypotensive duration of nifedipine and its enhancement of sympathetic nervous activity may be responsible for the failure to reverse LVH, despite adequate blood pressure control.

Effects of Nifedipine on Normotensive Rat Placental Blood Flow, Placental Weight and Fetal Weight

Recently, nifedipine (Ca antagonist) has been used for the treatment of preeclampsia. In this study, we investigated the effects of nifedipine on the normotensive Wistar Kyoto rat's placental blood flow, fetal weight and placental weight. We measured the rat's placental blood flow using clearance of hydrogen gas generated by electrolysis. The placental blood flow, placental and fetal weights of nifedipine-treated rats (5, 10 and 25 mg/kg) were significantly (p less than 0.05) reduced compared with normal pregnant rats. These data suggest that nifedipine might have some reducing effects on placental blood flow, fetal weight and placental weight.

Seizures and wet-dog shakes induced by 4-aminopyridine, and their potentiation by nifedipine

The behavioral and electrographic effects of 4-aminopyridine (4-AP) administered i.p. or microinjected into the hippocampal CA1 region (i.h.) were studied in rats. The modification of such effects by the systemic administration of the Ca2+ antagonist dihydropyridine, nifedipine, was also studied. 4-AP i.p. (5 mg/kg) induced generalized tonic convulsions in 74% of the animals and death in 13%. Convulsions were characterized by electrical discharges of relatively short duration in all structures studied (frontal cortex, amygdala, dorsal hippocampus and dorsal raphe). Limbic seizures and frequent wet-dog shakes were observed when 4-AP was administered i.h. (2-4 nmol) and this behavior was correlated with hippocampal discharges, which rapidly propagated to the other structures. Pretreatment with nifedipine (7.5-50 mg/kg s.c.) markedly potentiated the effects of 4-AP. The percentage of rats that died during generalized convulsion after i.p. 4-AP increased to 56-87% and the frequency of wet-dog shakes increased after i.h. microinjection of 4-AP. Moreover, nifedipine-treated rats showed long-lasting (greater than 60 min) continuous discharges in all structures studied (status epilepticus). These results are discussed in the light of the possible participation of Ca2+ channels in the convulsant effect of 4-AP and its potentiation by nifedipine.

The Effect of Nifedipine on Skin-Flap Survival

Nifedipine, a calcium-channel blocker, is a peripheral vasodilator and has been shown to increase blood flow to skin. The hypothesis that nifedipine would thereby improve skin-flap viability was tested by comparing the extent of necrosis of long pedicle flaps in control and nifedipine-treated rats. Thirty male Sprague-Dawley rats were randomized to receive either 2.5 mg/kg nifedipine in chocolate PO t.i.d. or plain chocolate according to protocols. Serum nifedipine levels were determined by gas chromatography. Dorsal cephalad-based random vascular pedicle flaps (2 X 6 cm) were elevated, sutured to their beds, and photographed for computer-aided surface area determinations. The extent of distal flap necrosis was expressed as a percentage of the total flap area, and differences were studied by one-way analysis of variance. The differences between the mean percentages of necrosis at 1 and 2 weeks for the groups were not statistically significant. We conclude that nifedipine has no effect on the extent of necrosis of the random skin flap in the rat.

Left ventricular function and collagen content after regression of hypertensive hypertrophy.

To determine whether regression of hypertensive hypertrophy through blood pressure control also involves left ventricular collagen and consecutive alterations in left ventricular diastolic and systolic function, antihypertensive treatment with the calcium channel blocker nifedipine (30 mg/kg.day) was employed in 20-week-old spontaneously hypertensive rats (n = 15) for a period of 20 weeks. Age-matched (40 weeks old) untreated (n = 13) and 20-week-old spontaneously hypertensive rats representing the state before therapy (n = 14) were used for comparison. Myocardial stiffness was described by the tangent modulus Km of the elastic stiffness-stress relation. Left ventricular collagen was determined by means of hydroxyproline (OH-proline) concentration. Myocardial working capacity of the left ventricle was measured as the peak developed systolic pressure per weight unit muscle mass and systolic peak pump function as the maximum achievable cardiac output under volume loading. After the 20-week course of nifedipine treatment, systolic aortic pressure dropped from 187 +/- 11 to 144 +/- 6 mm Hg (p less than 0.001). Regression of hypertrophy was shown by a left ventricular muscle/body weight ratio of 2.13 +/- 0.18 mg/g (p less than 0.01) in the 40-week-old nifedipine-treated hypertensive rats, whereas the ratios of the 20-week-old and 40-week-old untreated spontaneously hypertensive rats were 2.3 +/- 0.30 and 2.34 +/- 0.18 mg/g, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic treatment with nifedipine does not change the number of [ 3H]nitrendipine and [ 3H]dihydroalprenolol binding sites

Possible receptor changes occurring after withdrawal of chronic nifedipine treatment or chronic propranolol treatment were examined by administering nifedipine (100 mg/kg per day) or propranolol (45 mg/kg per day) to rats for 2 weeks and then withdrawing treatment [ 3H]Nitrendipine and [ 3H]DHA binding were measured in membrane fragments of the ventricle. In propranolol-treated rats, 8 h after the last administration, the maximum binding for [ 3H]DHA was significantly increased from 79.9 ± 8.0 to 139.8 ± 12.8 fmol/ mg protein (mean ± S.E.); the dissociation constant was significantly increased from 4.9 ± 0.7 to 10.7 ± 1.2 nM . On the other hand, in nifedipine-treated rats, 12 and 48 h after the last administration, [ 3H]nitrendipine binding and [ 3H]DHA binding had not changed significantly. These results indicate that the mechanism of the calcium antagonist withdrawal syndrome may be different from that of β-blocker withdrawal syndrome.

Effects of nifedipine on the hypotensive actions of alpha 2-agonists in conscious spontaneously hypertensive rats.

The present study was designed to examine the effects of the calcium entry blocker, nifedipine, on the acute depressor responses to alpha 2-adrenoceptor agonists. Conscious spontaneously hypertensive rats (SHR) were given nifedipine intravenously (25 micrograms/kg) or vehicle (polyethylene glycol). Subsequent intravenous administration of guanabenz (10, 25, or 50 micrograms/kg) or clonidine (5 micrograms/kg) caused biphasic changes in mean arterial pressure (MAP) in vehicle-treated SHR, an initial pressor response, which was followed by a sustained fall in MAP. In nifedipine-treated rats, the pressor actions of guanabenz and clonidine were virtually abolished, while the onset of the depressor responses were significantly accelerated. The maximal depressor responses to guanabenz and clonidine were similar in vehicle- and nifedipine-pretreated SHR. Central administration of nifedipine (5, 10, or 20 micrograms/kg) in the lateral cerebroventricle significantly attenuated the depressor responses to guanabenz in a dose-dependent manner as compared to vehicle-treated rats. Oral pretreatment with nifedipine (2.5 mg/kg) also significantly blunted the hypotensive actions of guanabenz in the conscious SHR. These data indicate that central and oral administration of nifedipine antagonized the centrally mediated hypotensive actions of guanabenz. Intravenous bolus administration of nifedipine failed to attenuate the maximal depressor responses to guanabenz, suggesting that insufficient nifedipine accumulated centrally to affect central alpha 2-adrenoceptor function.