Ang (1-7) protects islet endothelial cells from palmitate-induced apoptosis by AKT, eNOS, p38 MAPK, and JNK pathways

This study aimed to explore the effect of angiotensin (1-7) (Ang (1-7)) on palmitate-induced apoptosis in islet endothelial cells and the mechanism of action. MS-1 cells were treated with palmitate in the presence or absence of Ang (1-7). The percentage of apoptotic cells was determined by DNA fragmentation and flow cytometry. Reactive oxygen species (ROS) production was measured using a Reactive Oxygen Species Assay Kit. Expression of AKT, eNOS, C-Jun N-terminal kinase (JNK), and p38 was detected by western blotting. Compared with palmitate treated group, palmitate-induced apoptosis was decreased in MS-1 cells which were preincubated with Ang (1-7) (P < 0.05). Palmitate decreased the phosphorylation of AKT and eNOS, and Ang (1-7) increased the phosphorylation of these kinases (P < 0.05), with a concomitant reduction in MS-1 cells apoptosis. Ang (1-7) also inhibited the palmitate-induced ROS production and attenuated the apoptosis-related signaling molecule JNK and p38 activation (all P < 0.05). PI3K/AKT, eNOS, p38 MAPK, and JNK inhibitors blocked the antilipoapoptosis of Ang (1-7) (all P < 0.05). Our findings suggest that Ang (1-7) reduces palmitate-induced islet endothelial cells apoptosis. AKT/eNOS/NO signaling and JNK and p38 pathway are involved in the Ang (1-7)-mediated modulation of islet endothelial cells lipoapoptosis.

Stimulatory effect of allantoin on imidazoline I₁ receptors in animal and cell line

Allantoin is known as the agonist of imidazoline receptor, especially the I₂ subtype. Effect of allantoin on imidazoline I₁ receptor (I₁R) relating to reduction of blood pressure and its merit in steatosis are still obscure. Also, farnesoid X receptor (FXR) plays an important role in lipid homeostasis related to I₁R activation. Thus, we administered allantoin into high fat diet (HFD)-fed mice showing hypertriglyceridemia and hypercholesterolemia. Allantoin significantly improved hyperlipidemia in HFD mice after 4 weeks of administration. Pretreatment with efaroxan, at a dose sufficient to inhibit I₁R activation, attenuated the action of allantoin. In addition, in cultured HepG2 cells, allantoin increased the expression of farnesoid X receptor (FXR). The allantoin-induced FXR expression was blocked by efaroxan. Similar changes were observed in the expressions of FXR-targeted genes. Otherwise, allantoin also lowered systolic blood pressure (SBP) in HFD mice that can be blocked by efaroxan. Taken together, allantoin has an ability to activate I₁R for improvement of metabolic disorders.

Increase in gastric pH reduces hypotensive effect of oral sodium nitrite in rats

The new pathway nitrate-nitrite-nitric oxide (NO) has emerged as a physiological alternative to the classical enzymatic pathway for NO formation from l-arginine. Nitrate is converted to nitrite by commensal bacteria in the oral cavity and the nitrite formed is then swallowed and reduced to NO under the acidic conditions of the stomach. In this study, we tested the hypothesis that increases in gastric pH caused by omeprazole could decrease the hypotensive effect of oral sodium nitrite. We assessed the effects of omeprazole treatment on the acute hypotensive effects produced by sodium nitrite in normotensive and L-NAME-hypertensive free-moving rats. In addition, we assessed the changes in gastric pH and plasma levels of nitrite, NO(x) (nitrate+nitrite), and S-nitrosothiols caused by treatments. We found that the increases in gastric pH induced by omeprazole significantly reduced the hypotensive effects of sodium nitrite in both normotensive and L-NAME-hypertensive rats. This effect of omeprazole was associated with no significant differences in plasma nitrite, NO(x), or S-nitrosothiol levels. Our results suggest that part of the hypotensive effects of oral sodium nitrite may be due to its conversion to NO in the acidified environment of the stomach. The increase in gastric pH induced by treatment with omeprazole blunts part of the beneficial cardiovascular effects of dietary nitrate and nitrite.

Cyclothiazide induces seizure behavior in freely moving rats

We have previously demonstrated that cyclothiazide (CTZ) is a potent convulsant drug inducing robust epileptiform activity in hippocampal neurons both in vitro and in vivo. Here we further establish an animal model for CTZ-induced behavioral seizures in freely moving rats. Microinjection of CTZ into the left ventricle dose-dependently induced robust seizure behaviors within 3h after administration. At a dose of 0.75 μmol, CTZ induced Racine score IV-V seizure behaviors in 71% (n=14) of the rats were tested. In addition, CTZ also induced epileptiform EEG activity accompanying behavioral seizures. The convulsant action of CTZ on both behavior and EEG was blocked by pretreatment with clinical anticonvulsant drug diazepam (n=5). In conclusion, our results demonstrate that CTZ is capable of inducing behavioral seizures in intact animals. Since CTZ acts on both GABAergic and glutamatergic systems, this new animal epilepsy model will be useful for anticonvulsant drug testing and general epilepsy research.

Pharmacological mechanisms underlying the vascular activities of Loranthus ferrugineus Roxb. in rat thoracic aorta

AIM OF THE STUDY

The present study was aimed to investigate the pharmacological basis for the use of Loranthus ferrugineus in hypertension.

MATERIALS AND METHODS

Loranthus ferrugineus methanol extract (LFME) was obtained using Soxhelt extractor and then successively fractionated using chloroform, ethyl acetate and n-butanol. The n-butanol fraction of LFME (NBF-LFME) was studied using isolated rat thoracic aorta.

RESULTS

NBF-LFME (1.0 x 10(-5) to 3.0mg/ml) was found to be the most potent to concentration-dependently relax the endothelium-intact phenyephrine (PE, 1 microM)- and high K(+) (80 mM)-precontracted rat aortic rings. Removal of the endothelium completely abolished the vascular relaxing properties of NBF-LFME. Pretreatment with atropine (1 microM), L-NAME (10 microM), indomethacin (10 microM) and methylene blue (10 microM) significantly blocked NBF-LFME-mediated relaxation. Endothelium-dependent and -independent relaxations induced by acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly enhanced in aortic rings pretreated with NBF-LFME when compared to those observed in control aortic rings. On the contrary, glibenclamide (10 microM), propranolol (1 microM) and prazosin (0.01 microM) did not alter NBF-LFME-induced relaxation.

CONCLUSIONS

The results suggest that NBF-LFME induced vascular relaxation by stimulating muscarinic receptors, activating the endothelium-derived nitric oxide-cGMP-relaxant pathway, promoting prostacyclin release and/or possibly through its ability to lengthen the released nitric oxide half-life. The present data further supports previous in vivo findings and explain the traditional use of Loranthus ferrugineus as an anti-hypertensive agent.

Effect of antitubercular medications on blood pressure control in chronic kidney disease patients with tuberculosis: a prospective cohort study

BACKGROUND

Previous anecdotal reports suggested a decrease in antihypertensive medication potency after starting antitubercular medications. This interaction could be unpredictable in presence of renal failure due to increased half-lives of most commonly used antihypertensive medications.

METHODS

In a cohort study involving 135 patients with chronic kidney disease (CKD), 62 patients with tuberculosis star-ted on antitubercular medications (TB group) were prospectively compared with 73 CKD controls (with no TB and not on antitubercular medications) for a change in antihypertensive medications. Antihypertensive dose was converted to unit score.

RESULTS

The TB group had a greater increase in antihypertensive medication dose as compared with controls (89% vs. 54%, p<0.0001). In absolute terms an overall increase in antihypertensive medications was observed in 60% of pa-tients in the TB group, with a 2-fold dose increase from the baseline (p<0.0001). Four patients from the TB group de-veloped a hypertensive emergency. In multivariate linear regression, the association between TB group and increase in antihypertensives remained significant ( beta =0.38; p<0.0001).

CONCLUSIONS

In CKD patients, antihypertensive medication potency is reduced in TB patients on antitubercular the-rapy in a significant number of patients, to a clinically significant degree with a potential risk for hypertensive emergency.

Effect of non-steroidal anti-inflammatory ophthalmic solution on intraocular pressure reduction by latanoprost in patients with primary open angle glaucoma or ocular hypertension

AIM

To investigate the effects of a non-steroidal anti-inflammatory drug (NSAID) ophthalmic solution on latanoprost induced intraocular pressure (IOP) reduction in glaucoma patients.

METHODS

Examination was conducted on 16 eyes of 16 glaucoma patients who had been given only latanoprost for at least 6 weeks. The NSAID ophthalmic solution, sodium 2-amino-3-(4-bromobenzoyl) phenylacetate sesquihydrate, was additionally given for 12 weeks into one eye (NSAID group), while sodium hyaluronic acid ophthalmic solution was administered into the other eye (control group) in a double masked fashion. The IOP measurement was performed before the start of additional administration of ophthalmic solutions, 2, 4, 6, 8, 10, and 12 weeks after the start of additional administration, and 2, 4, and 6 weeks after discontinuing additional administration.

RESULTS

No significant difference was observed in the IOPs before additional administration of ophthalmic solution between the NSAID group and the control group. Following the additional administration of ophthalmic solution, IOP in the NSAID group was consistently higher than that in the control group, and a maximum difference in IOP between the two groups was 1.08 (SD 1.75) mm Hg (p = 0.03). This trend was observed even after additional administration was discontinued.

CONCLUSION

NSAID ophthalmic solution may partly affect IOP reduction by latanoprost.

Urinary responses to acute moxonidine are inhibited by natriuretic peptide receptor antagonist

We have previously shown that acute intravenous injections of moxonidine and clonidine increase plasma atrial natriuretic peptide (ANP), a vasodilator, diuretic and natriuretic hormone. We hypothesized that moxonidine stimulates the release of ANP, which would act on its renal receptors to cause diuresis and natriuresis, and these effects may be altered in hypertension. Moxonidine (0, 10, 50, 100 or 150 microg in 300 microl saline) and clonidine (0, 1, 5 or 10 microg in 300 microl saline) injected intravenously in conscious normally hydrated normotensive Sprague-Dawley rats (SD, approximately 200 g) and 12-14-week-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) dose-dependently stimulated diuresis, natriuresis, kaliuresis and cGMP excretion, with these effects being more pronounced during the first hour post-injection. The actions of 5 microg clonidine and 50 microg moxonidine were inhibited by yohimbine, an alpha2-adrenoceptor antagonist, and efaroxan, an imidazoline I1-receptor antagonist. Moxonidine (100 microg) stimulated (P<0.01) diuresis in SHR (0.21+/-0.04 vs 1.16+/-0.06 ml h(-1) 100 g(-1)), SD (0.42+/-0.06 vs 1.56+/-0.19 ml h(-1) 100 g(-1)) and WKY (0.12+/-0.04 vs 1.44+/-0.21 ml h(-1) 100 g(-1)). Moxonidine-stimulated urine output was lower in SHR than in SD and WKY. Moxonidine-stimulated sodium and potassium excretions were lower in SHR than in SD, but not WKY, demonstrating an influence of strain but not of pressure. Pretreatment with the natriuretic peptide antagonist anantin (5 or 10 microg) resulted in dose-dependent inhibition of moxonidine-stimulated urinary actions. Anantin (10 microg) inhibited (P<0.01) urine output to 0.38+/-0.06, 0.12+/-0.01, and 0.16+/-0.04 ml h(-1) 100 g(-1) in SD, WKY, and SHR, respectively. Moxonidine increased (P<0.01) plasma ANP in SD (417+/-58 vs 1021+/-112 pg ml(-1)) and WKY (309+/-59 vs 1433+/-187 pg ml(-1)), and in SHR (853+/-96 vs 1879+/-229 pg ml(-1)). These results demonstrate that natriuretic peptides mediate the urinary actions of moxonidine through natriuretic peptide receptors.

Effect of ethanol on reductions in norepinephrine electrochemical signal in the rostral ventrolateral medulla and hypotension elicited by I1-receptor activation in spontaneously hypertensive rats

BACKGROUND

The mechanism of the antagonistic hemodynamic interaction between ethanol and centrally acting sympatholytics is not known. In this study, we tested the hypothesis that the imidazoline (I1)-receptor modulation of norepinephrine (NE) release within the rostral ventrolateral medulla (RVLM) plays a pivotal role in this clinically relevant hemodynamic interaction. METHOD In anesthetized spontaneously hypertensive rats, the effects of centrally acting sympatholytics on RVLM NE electrochemical signal were investigated by in vivo electrochemistry along with cardiovascular responses in the absence and presence of ethanol. In vivo microdialysis in conscious spontaneously hypertensive rats was used to confirm the electrochemical findings. RESULTS Clonidine (30 microg/kg, intravenously) or rilmenidine (400, 600, or 800 microg/kg) significantly reduced RVLM NE electrochemical signal (index of neuronal activity) and mean arterial pressure; rilmenidine effects were dose-related, and ethanol (1 g/kg) counteracted these responses. Ethanol (1 g/kg) pretreatment increased both RVLM NE electrochemical signal and blood pressure but did not influence the reductions in both variables elicited by subsequently administered clonidine. The alpha2-adrenergic antagonist 2-methoxyidazoxan (30 microg/kg) counteracted rilmenidine (800 microg/kg)-evoked responses. In vivo microdialysis in conscious spontaneously hypertensive rats confirmed the electrochemical findings since clonidine- (30 microg/kg, intravenously) evoked reductions in RVLM NE and the associated hypotension were counteracted by ethanol (1 g/kg). CONCLUSIONS (1) Ethanol counteracts centrally mediated hypotension, at least in part, by increasing RVLM NE; (2) the interaction involves the I1 receptor modulation of RVLM neuronal activity; (3) the alpha2-adrenergic receptor contributes to the electrochemical and cardiovascular effects of high doses of rilmenidine, and (4) the RVLM is a neuroanatomical target for systemically administered ethanol.

Angiotensin-(1–7) inhibits the angiotensin II-enhanced norepinephrine release in coarcted hypertensive rats

Since it has been suggested that angiotensin (Ang) (1-7) functions as an antihypertensive peptide, we studied its effect on the Ang II-enhanced norepinephrine (NE) release evoked by K+ in hypothalami isolated from aortic coarcted hypertensive (CH) rats. The endogenous NE stores were labeled by incubation of the tissues with 3H-NE during 30 min, and after 90 min of washing, they were incubated in Krebs solution containing 25 mM KCl in the absence or presence of the peptides. Ang-(1-7) not only diminished the K+-evoked NE release from hypothalami of CH rats, but also blocked the Ang II-enhanced NE release induced by K+. Ang-(1-7) blocking action on the Ang II response was prevented by [D-Ala7]Ang-(1-7), an Ang-(1-7) specific antagonist, by PD 123319, an AT2-receptor antagonist, and by Hoe 140, a B2 receptor antagonist. Ang-(1-7) inhibitory effect on the Ang II facilitatory effect on K+-stimulated NE release disappeared in the presence of Nomega-nitro-L-arginine methylester and was restored by L-arginine. Our present results suggest that Ang-(1-7) may contribute to blood pressure regulation by blocking Ang II actions on NE release at the central level. This inhibitory effect is a nitric oxide-mediated mechanism involving AT2 receptors and/or Ang-(1-7) specific receptors and local bradykinin generation.

[High doses of aspirin reduce natriuresis in hypertensive patients treated with enalapril]

Angiotensin converting enzyme inhibitors have been shown to be useful in the treatment of essential hypertension while anti-platelet agents improve the overall cardiovascular risk profile in this population. Our aim was to assess the interaction of two different aspirin (ASA) doses--81 and 325 mg/day--with the antihypertensive effect of enalapril as well as their impact upon the urinary sodium excretion (Na(u)). A total of 22 patients between 35 and 65 years of age were included in a prospective double blind trial with a partial cross-over design. We excluded patients with secondary hypertension and recent use of anti-inflammatory drugs. Patients were placed on enalapril and a low sodium diet--<6 g of NaCl/day--and, sequentially, on two different doses of aspirin separated by a 10 day wash out period. Blood pressure (BP) was measured at weekly visits. Systolic, diastolic and mean BP levels decreased significantly in enalapril-treated patients (p<0.01) and no difference was detected between the two AAS dosages although a non-statistically significant difference towards better BP control was observed when 81 mg of ASA was used. Na(u) was higher at baseline when compared with the two periods under ASA (p<0.01) and Na(u) was higher with 81 mg than with 325 mg. These results suggest that in essential hypertensive individuals treated with enalapril and two ASA doses, low doses of ASA are associated with better blood pressure control and higher natriuresis.

Blockade of N-methyl-d-aspartate receptors within the rostral ventrolateral medulla antagonizes clonidine-induced cardiovascular effects

There is wide agreement that the rostral ventrolateral medulla (RVLM) plays a crucial role in the regulation of blood pressure (BP), and that there may be a close correlation between the actions of centrally acting antihypertensive agents and N-methyl-D-aspartate (NMDA) receptor functional states. The present study was done to test the hypothesis that NMDA receptors within the RVLM were involved in the cardiovascular effects of centrally acting antihypertensive drug clonidine in anesthetized and paralyzed rats. Prior unilateral microinjection of NMDA receptor antagonist dizocilpine (MK801, 500 pmol) into the RVLM significantly attenuated (p<0.01, n=9) the reductions of BP (-24+/-6 to -8+/-4 mm Hg) and heart rate (-49+/-9 to -14+/-7 bpm) induced by unilaterally injected clonidine (5 nmol) into the RVLM. Prior bilateral microinjection of MK801 (500 pmol for each side) into the RVLM effectively (p<0.01, n=7) antagonized the hypotension (-25+/-5 to -8+/-2 mm Hg) and bradycardia (-43+/-7 to -11+/-4 bpm) of intravenously administered clonidine (10 microg kg(-1)). Importantly, iontophoretic application of MK801 (60 nA) significantly (p<0.01, n=9) prevented the inhibitory effect of intravenously (10 microg kg(-1)) injected clonidine on the discharge of presympathetic neurons in the RVLM (neuronal inhibition: -39+/-6 to -10+/-2%). In conclusion, the present study shows that the RVLM administrated MK801 effectively antagonizes clonidine-induced cardiovascular effects, and suggests that NMDA receptors within the RVLM contribute to clonidine actions.

Aldosterone receptor antagonists: focus on eplerenone

Despite the development of hypertension treatment guidelines, blood pressure control in the general population remains inadequate, indicating the need for ongoing re-evaluation of treatment strategies to further improve blood pressure control. Hypertension results from alterations in cardiac output and/or peripheral resistance. The renin-angiotensin-aldosterone system may be responsible, at least in part, for these alterations. Despite pharmacologic intervention with angiotensin-converting enzyme inhibitors and angiotensin type-1 receptor antagonists, aldosterone continues to be produced. Therapeutic modalities for treating hypertension directed toward antagonizing aldosterone might more effectively control blood pressure. Eplerenone, a new selective aldosterone receptor antagonist, recently received approval from the US Food and Drug Administration for the treatment of hypertension, either alone or in combination with other antihypertensive agents. The objective of this review is to summarize the renin-angiotensin-aldosterone system, emphasizing the role for aldosterone antagonism in the management of hypertension, with a focus on eplerenone.

Long-term treatment with angiotensin II type 1 receptor antagonist, CV-11974, restores beta-catenin mRNA expression in volume-overloaded rabbit hearts

This study aimed to search genes altered in expression after long-term treatment with the angiotensin II type 1 receptor (AT1) antagonist, CV-11974, in volume-overloaded hearts. Arteriovenous shunt was made between the common carotid artery and jugular vein in Japanese White rabbits. Shunt-operated rabbits were randomly treated with CV-11974 or vehicle for 6 weeks, starting 6 weeks after surgery. As controls, sham-operated rabbits were given vehicle. Total RNA was prepared from each left ventricular myocardium. Using differential display, we screened one cDNA encoding human beta-catenin, in which the expression was upregulated after CV-11974 administration in shunt rabbit hearts. Beta-catenin is a molecule that exists in the intercalated disks and also works in cytoplasm as a major component of Wnt signaling. We then examined mRNA expressions of beta-catenin and connexin43 by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). The mRNA expressions of beta-catenin and connexin43 were markedly depressed in shunt-operated animals given vehicle compared with sham-operated animals (P < 0.01). These results suggest that downregulation of beta-catenin and connexin43 expression might be involved in the process of ventricular remodeling by volume overload. The RT-PCR also demonstrated that beta-catenin mRNA expression was significantly higher in shunt rabbits treated with CV-11974 than in those given vehicle (P < 0.05). These data suggest that volume overload may downregulate beta-catenin expression by an AT1 receptor-mediated pathway.

Dissociation between the circulating renin-angiotensin system and angiotensin II receptors in central losartan-induced hypertension

Losartan, an AT1 angiotensin II (ANG II) receptor non-peptide antagonist, induces an increase in mean arterial pressure (MAP) when injected intracerebroventricularly (icv) into rats. The present study investigated possible effector mechanisms of the increase in MAP induced by icv losartan in unanesthetized rats. Male Holtzman rats (280-300 g, N = 6/group) with a cannula implanted into the anterior ventral third ventricle received an icv injection of losartan (90 micro g/2 micro l) that induced a typical peak pressor response within 5 min. In one group of animals, this response to icv losartan was completely reduced from 18 +/- 1 to 4 +/- 2 mmHg by intravenous (iv) injection of losartan (2.5-10 mg/kg), and in another group, it was partially reduced from 18 +/- 3 to 11 +/- 2 mmHg by iv prazosin (0.1-1.0 mg/kg), an alpha1-adrenergic antagonist (P<0.05). Captopril (10 mg/kg), a converting enzyme inhibitor, injected iv in a third group inhibited the pressor response to icv losartan from 24 +/- 3 to 7 +/- 2 mmHg (P<0.05). Propranolol (10 mg/kg), a beta-adrenoceptor antagonist, injected iv in a fourth group did not alter the pressor response to icv losartan. Plasma renin activity and serum angiotensin-converting enzyme activity were not altered by icv losartan in other animals. The results suggest that the pressor effect of icv losartan depends on angiotensinergic and alpha1-adrenoceptor activation, but not on increased circulating ANG II.

Prostaglandins and cystoid macular edema

This review discusses the roles and interactions of prostaglandins and other possible chemical mediators in cystoid macular edema. Prostaglandins have been studied as a potential causative factor of cystoid macular edema following cataract/intraocular lens surgery. The authors' hypothesis and data with regard to the mechanisms of postoperative cystoid macular edema and other inflammatory conditions are presented. The effects of nonsteroidal anti-inflammatory drugs, which are antagonists of prostaglandin biosynthesis, on postoperative inflammatory conditions including cystoid macular edema are also reviewed. Lastly, a mechanism for the induction of cystoid macular edema by anti-glaucoma eyedrops, including prostaglandin analogs is proposed. The results from two clinical trials recently conducted by the authors suggest that the preservative rather than the active ingredient is the causative factor.

Carbamazepine decreases antihypertensive effect of nilvadipine

A 59-year-old male who had suffered from hypertension for 21 years was admitted because of manic and delusional symptoms. He was treated with 12 mg/day of haloperidol for psychotic symptoms and 8 mg/day of nilvadipine for hypertension. Due to insufficient effect of haloperidol on the patient's manic symptoms, carbamazepine was added to these medications. Abnormally high blood pressure was observed during carbamazepine coadministration, and it returned gradually to normal range after its discontinuation. Retrospective analyses revealed that the plasma concentrations of nilvadipine were undetectable during carbamazepine treatment. The clinical course and laboratory findings suggest that carbamazepine decreased the plasma concentration and hence the antihypertensive effect of nilvadipine probably via CYP3A induction. This interaction between nilvadipine and carbamazepine should be kept in mind when these drugs are administered concomitantly.

Effects of adrenomedullin on cyclic AMP formation and on relaxation in iris sphincter smooth muscle

PURPOSE

To determine whether iris sphincter and other tissues of the iris-ciliary body secrete adrenomedullin (ADM), a novel hypotensive peptide that is classified into the calcitonin gene-related peptide (CGRP) family and to determine the binding sites for ADM and compare the effects of ADM and CGRP in the absence and presence of their receptor antagonists on cAMP formation and relaxation in the iris sphincter.

METHODS

Sphincter muscle was incubated in Krebs-Ringer bicarbonate buffer in the absence and presence of ADM for 10 minutes. Accumulation of cAMP in the tissue extract was determined by radioimmunoassay (RIA). The binding of [125I]ADM to iris sphincter membranes was carried out by rapid filtration. Distribution of ADM in the ocular tissues was determined by RIA. Changes in muscle tension were recorded isometrically.

RESULTS

Immunoreactive ADM was present in all tissues of the cat iris-ciliary body. In the isolated cat iris sphincter, ADM increased cAMP accumulation in a time- (t1/2 = 2.2 minutes) and concentration- (EC50 = 13 nM) dependent manner, and this effect was sixfold more efficacious than CGRP. ADM, CGRP, vasoactive intestinal peptide, prostaglandin E2, isoproterenol, and forskolin increased cAMP formation in cat sphincter by 12.5-, 2-, 2.2-, 1-, 2.6-, and 2.4-fold, respectively. The rank of the effects of ADM on cAMP formation in iris sphincter isolated from different animal species was in the following order: cat > dog > bovine > human > rabbit. In the cat iris sphincter, the CGRP antagonist, CGRP(8 to 37), was more effective than the ADM antagonist, ADM (26 to 52), in inhibiting both ADM- and CGRP-induced cAMP formation. ADM and CGRP inhibited carbachol-induced contraction in a concentration-dependent manner with IC50 values of 10 and 90 nM, respectively. Both ADM and CGRP displaced the binding of [125I]ADM to sphincter membranes effectively, with IC50 values of 0.81 and 1.15 nM, respectively.

CONCLUSIONS

In iris sphincter isolated from cat and other mammalian species including human, ADM is a much more efficacious activator of adenylate cyclase and a much more effective relaxant than CGRP. Its biological effects may be due to direct involvement of ADM receptors, but also to activation of CGRP receptors. Activation of ADM receptors by the peptide leads to concentration-dependent increases in cAMP accumulation and subsequent inhibition (relaxation) of smooth muscle contraction. These findings suggest a role for ADM as a local modulator of smooth muscle tone. A possible function for this potent hypotensive peptide in the regulation of intraocular pressure remains to be investigated.

The bradykinin B1 receptor and the central regulation of blood pressure in spontaneously hypertensive rats

1. We evaluated if the brain bradykinin (BK) B1 receptor is involved in the regulation of blood pressure (BP) in conscious rats. 2. Basal mean BP and HR were 115 +/- 2 and 165 +/- 3 mmHg and 345 +/- 10 and 410 +/- 14 beats min in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), respectively. Intracerebroventricular (i.c.v.) injection of 1 nmol B1 receptor agonist Lys-desArg9-BK significantly increased the BP of WKY and SHR by 7+/-1 and 19+/-2 mmHg, respectively. One nmol Sar[D-Phe8]-desArg9-BK, a kininase-resistant B1 agonist, increased the BP of WKY and SHR by 19+/-2 and 17+/-2 mmHg, respectively and reduced HR in both strains. 3. I.c.v. injection of 0.01 nmol B1 antagonists, LysLeu8-desArg9-BK or AcLys[D-betaNal7,Ile8]-desArg9-BK (R715), significantly decreased mean BP in SHR (by 9+/-2 mmHg the former and 14+/-3 mmHg the latter compound), but not in WKY. In SHR, the BP response to R715 was associated to tachycardia. 4. I.c.v. Captopril, a kininase inhibitor, increased the BP of SHR, this response being partially prevented by i.c.v. R715 and reversed into a vasodepressor effect by R715 in combination with the B2 antagonist Icatibant. 5. I.c.v. antisense oligodeoxynucleotides (ODNs) targeted to the B1 receptor mRNA decreased BP in SHR, but not in WKY. HR was not altered in either strain. Distribution of fluorescein-conjugated ODNs was detected in brain areas surrounding cerebral ventricles. 6. Our results indicate that the brain B1 receptor participates in the regulation of BP. Activation of the B1 receptor by kinin metabolites could participate in the pathogenesis of hypertension in SHR.

K+ channel blockers: natriuretic potency correlates to vascular ATP-sensitive K+ channel blockade

Using analogs of known vascular ATP-sensitive K+ channel (KATP) blockers, we identified compounds with a wide range of potencies (over 500-fold) in their capacity to block the hypotensive response of 0.2 mg/kg pinacidil in rats. The most potent of these, U-97025E, belongs to a newly disclosed class of compounds, the cyanoguanidines. U-97025E at 0.04 mg/kg blocked 50% of the depressor response induced by 0.2 mg/kg pinacidil. The maximal natriuresis induced by U-97025E (0.4 mg/kg i.v.) increased Na+ excretion by approximately 60%. This natriuresis is of the same magnitude as that induced by thiazide without any effect on K+ excretion. We found a high degree of correlation between natriuretic potency and the capacity to block the blood pressure lowering effects of pinacidil, both among closely related analogs and dissimilar compounds. These findings imply an obligatory rather than incidental relationship between vascular KATP blockade and natriuresis. The exact molecular link of the vascular and renal effects remains to be determined.

The attenuated effect of ATP-sensitive K+ channel opener pinacidil on renal haemodynamics in spontaneously hypertensive rats

In hypertension, impairment of hyperpolarization by K+ efflux through ATP-sensitive K+ (K(ATP)) channels may contribute to the elevated renal vascular resistance. To elucidate such a role for K(ATP) channels in the renal vasculature, we used micropuncture techniques to examine the effect of K(ATP) channel opener, pinacidil (0.15 mg/h per kg body wt i.v.), on renal and glomerular haemodynamics in spontaneously hypertensive rats (SHR) and in normotensive controls (Wistar Kyoto, WKY). Since pinacidil reduced blood pressure significantly in both groups, the abdominal aorta was clamped before pinacidil administration to yield a renal perfusion pressure equivalent to that during pinacidil infusion. Pinacidil significantly decreased renal vascular resistance in both groups, but the relative change from baseline value was greater in WKY than in SHR. These effects of pinacidil were abolished by pretreatment with glibenclamide (3 mg/kg body wt i.v.). Proximal tubular stop-flow pressure (Psf), an index of glomerular capillary pressure, was significantly elevated by pinacidil infusion in WKY, a response abolished by pretreatment with glibenclamide, but not in SHR. The tubuloglomerular feedback response of Psf was not affected by pinacidil in either group. These data suggest that the activity of K(ATP) channels in SHR may be attenuated in the renal microvasculature. This may contribute to the elevated vascular tone in the renal preglomerular vasculature in SHR.

Preventive effect of rilmenidine on the occurrence of neurogenic ventricular arrhythmias in rabbits

BACKGROUND

Centrally acting antihypertensive drugs bearing an imidazoline or a related chemical structure inhibit sympathetic nervous output to the heart and vascular beds, and enhance parasympathetic tone. Cardiac ischaemia and ventricular arrhythmias that can result from hypertension are likely to benefit from such effects.

OBJECTIVE

To investigate the effects of rilmenidine, an oxazoline with antihypertensive properties, in a model of neurogenically induced ischaemic ventricular arrhythmias.

METHODS AND RESULTS

Bicuculline, a alpha-aminobutyric acid (GABA(A)) receptor antagonist, was administered intracisternally in pentobarbitone anaesthetized rabbits; 10 microg/kg intracisternal bicuculline induced polymorphic ventricular ectopic beats and ventricular tachycardia, while blood pressure increased by about 50-60% and heart rate in sinus rhythm decreased by about 20%. Rilmenidine pretreatment (10 min), either administered intravenously (0.01, 0.1, 1 mg/kg) or intracisternally (3, 10, 30 microg/kg), dose-dependently prevented the occurrence of bicuculline-induced arrhythmias and, because of a lower baseline, the blood pressure values reached were less when compared with controls. Intracisternal idazoxan (15 microg/kg) had no significant antiarrhythmic effect but antagonized, in part, the haemodynamic and antiarrhythmic effects of rilmenidine (1 mg/kg intravenously; 30 microg/kg intracisternally).

CONCLUSION

The antiarrhythmic effects observed with rilmenidine are mainly mediated by blunting the bicuculline-induced increase in the sympathetic nervous output to the heart and the vascular beds. These effects of rilmenidine are likely to originate from action on the central as well as on the peripheral nervous systems. Direct coronary or cardiac effects might also play a role, in particular at low non-hypotensive intravenous doses.

Antihypertensive efficacy of angiotensin converting enzyme inhibition and aspirin counteraction

OBJECTIVE

Blockade of bradykinin breakdown and enhancement of prostaglandin release probably participate in the antihypertensive activity of angiotensin converting enzyme (ACE) inhibitors. Cyclooxygenase blockers may attenuate the efficacy of ACE inhibitors by interfering with prostaglandin synthesis, and patients taking aspirin may not benefit from ACE inhibition. This study was designed to evaluate the incidence of the counteractive phenomenon and to define minimal aspirin dosage that causes an antagonistic effect.

METHODS

These were 26 patients with mild to moderate hypertension (group 1) and 26 patients with severe untreated primary hypertension (group 2). Enalapril (20 mg twice a day) was used as a single drug in group 1 and was added to the combination of long-acting nifedipine (30 mg/day) and atenolol (50 mg/day) in group 2. Aspirin was tested at doses of 100 and 300 mg/day, and an attenuation of more than 20% of the mean blood pressure decrease produced by enalapril was the criteria that defined antagonism.

RESULTS

The 100 mg dose was ineffective. However, 300 mg aspirin had an antagonistic effect in 57% of patients in group 1 and 50% of patients in group 2: mean arterial pressure was lowered by 63% and 91% less, respectively. Results were independent of the drug administration order. In "responders," aspirin significantly attenuated the renin rise associated with ACE inhibition.

CONCLUSIONS

These findings suggest that a number of ACE-inhibited patients are susceptible to 300 mg/day aspirin, regardless of hypertension severity. Antagonism may be mediated through prostaglandin inhibition according to predominance, in an individual patient, of prostaglandin activation (also as a renin secretory stimulus) or angiotensin blockade by enalapril.

Glibenclamide, a specific inhibitor of ATP-sensitive K+ channels, inhibits coronary vasodilation induced by angiotensin II-receptor antagonists

The purpose of our study was test the hypothesis that endogenous angiotensin II contributes to the basal coronary artery tone by acting at vascular ATP-sensitive K+ (K+ATP) channels. Coronary blood flow (CBF) and other hemodynamic parameters were measured in anesthetized dogs. Intracoronary infusion of the selective antagonists of angiotensin II AT1 receptors (L-158,809 and E4177) increased CHF without affecting other hemodynamic parameters, indicating that endogenous angiotensin II caused coronary vaso-constriction through the AT1 subtype receptors. Coronary vasodilation in response to AT1 receptor antagonists was blunted by pretreatment with glibenclamide (a specific inhibitor of K+ATP channels; p < 0.01) but not by either an adenosine-receptor antagonist or an inhibitor of nitric oxide synthesis. Coronary vasodilation in response to AT1-receptor antagonists was partly reduced (p < 0.01) by PD-123319 (the AT2-receptor antagonist). Glibenclamide had no effect on coronary vasodilation induced by sodium nitroprusside. These results indicate that in dogs in vivo, coronary vasodilation in response to AT 1-receptor antagonists inhibited markedly by glibenclamide and partly by PD-123319, suggesting that endogenous angiotensin II contributes to the maintenance of basal coronary vascular tone by acting at K+ATP channels through its receptors.

Pretreatment with the dopamine agonist quinpirole inhibits central antihypertensive mechanisms in rats

1. Intravenous or central treatment of spontaneously hypertensive rats (SHR) with the dopamine D2 receptor agonist quinpirole caused a short-lasting pressor response with little effect on heart rate. 2. At 30 min after intravenous administration of quinpirole, the antihypertensive effect of rilmenidine was significantly inhibited. This interaction of quinpirole and rilmenidine was similarly observed when quinpirole was administered either intravenously (0.3 or 0.1 mg/kg), in the lateral cerebral ventricles (0.1 mg/kg) or intracisternally (0.1 mg/kg) or when rilmenidine was administered intravenously (1 mg/kg) or intracisternally (0.1 mg/kg). 3. The apparent desensitization to the antihypertensive effect of rilmenidine 30 min after pretreatment with quinpirole was not observed after a 4 or 24 h interval. 4. These data suggest that quinpirole has prolonged effects on central sympathetic vasomotor mechanisms that are the target of centrally acting antihypertensive drugs. These and previous results show a functional interaction between central dopamine D2 receptor activation and sympathetic responses mediated by a wide range of different receptors, including imidazoline and 5-hydroxytryptamine 5-HT1A-receptors and alpha 2-adrenoceptors.

[The antagonistic effect of aspirin on the expression of prostaglandin participation in the antihypertensive activity of ACE inhibitors]

ACE-inhibitors antagonize both angiotensin production and bradykinin breakdown, resulting in enhancement of vasodilating prostaglandin release. This provides an explanation for the experimental observation that cycloxygenase blockers (such as aspirin or indomethacin) may counteract the antihypertensive efficacy of the ACE-inhibitors; it may be also possible that hypertensive patients taking aspirin as an antiplatelet agent may fail to benefit from ACE-inhibition. This study was aimed at: evaluating the magnitude and incidence of the inhibitory phenomenon; defining the minimal aspirin dosage that produces an antagonistic effect, as well as the possible reasons for a different individual susceptibility. We have studied untreated patients with mild (10 cases, Group 1), moderate (16 cases, Group 2) or severe (26 cases, Group 3) hypertension. The ACE-inhibitor enalapril was used at doses of 10 mg bid (groups 1 and 2) or 20 mg bid (Group 3). Active drug treatment periods had a 5-day duration. A daily dose of aspirin of 100 mg had no effect on the antihypertensive efficacy of enalapril. On the contrary, when a dose of 300 mg was used, 60, 57 and 50% of patients in Group 1, 2 and 3, respectively, showed a > 20% restraint of the mean arterial pressure fall with enalapril (20% was the lower arbitrary limit for defining antagonism). Inhibition was independent of the sequence of drug administration. In these patients counteraction averaged 60, 70 and 90%, respectively. In them, and not in the remaining patients in each group, aspirin substantially attenuated the renin rise elicited by ACE-inhibition. These data suggest that: a dosage of 100 mg aspirin is devoid of any inhibitory effect; more that 50% of ACE inhibited patients are, at least in the short term, susceptible to the action of 300 mg aspirin, regardless of the severity of hypertension; counteraction is seemingly mediated through a prostaglandin inhibition and depends on the individual predominance of prostaglandin activation (also as a renin secretory stimulus) or angiotensin inhibition by the ACE-inhibitor.

Pretreatment with quinpirole inhibits the central antihypertensive effects of rilmenidine and alpha-methyldopa in conscious rats

Treatment of conscious spontaneously hypertensive rats (SHR) with the dopamine D2 receptor agonist quinpirole causes a short-lasting pressor response and apparent desensitisation to the effects of subsequent injections of quinpirole or central antihypertensives such as clonidine. In the present study, a number of aspects of this apparent desensitisation were investigated. Thirty minutes after intravenous injection of quinpirole into spontaneously hypertensive rats, treatment with the dopamine D2 receptors antagonist raclopride caused a significant fall in blood pressure. At this time point, circulating levels of vasopressin were not significantly different compared to controls. In Brattleboro rats, the pressor response to quinpirole was reduced in the first 15 min after injection, but not difference in blood pressure was observed at later time points. In SHR which had been treated with quinpirole, the central antihypertensive effects of rilmenidine or alpha-methyldopa were significantly inhibited. By contrast, the bradycardia induced by these drugs was similar in quinpirole-treated rats and controls. Quinpirole pretreatment caused an enhancement of the hypotension but a reduction of the reflex tachycardia after intravenous treatment with hydralazine. In SHR treated with methylatropine and quinpirole, the upper plateau of the sympathetic baroreceptor-heart rate reflex curve was reduced. These results show that treatment with quinpirole has marked effects on central sympathetic vasomotor mechanisms which are the target of antihypertensive drugs such as rilmenidine and alpha-methyldopa. At least some of these effects may occur at the level of the sympathetic baroreflex. Moreover, while the effects of quinpirole on sympathetic regulation are prolonged, the initial pressor response is counteracted by an as yet unidentified compensatory mechanism which can be unmasked when quinpirole is displaced from its receptor by dopamine D2 receptor antagonist treatment.

Presynaptic imidazoline receptors and alpha 2-adrenoceptors in the human heart: discrimination by clonidine and moxonidine

The involvement of presynaptic alpha 2-autoreceptors and imidazoline receptors in the modulation of noradrenaline release was investigated in strips from human atrial appendages preincubated with [3H]noradrenaline and superfused with medium containing desipramine and corticosterone. Electrical impulses were applied transmurally at 2 Hz. The imidazoline derivatives moxonidine and clonidine reduced to evoked tritium overflow in a concentration-dependent manner. Moxonidine was 18-fold more potent than clonidine. The concentration-response curve for moxonidine, but not for clonidine was shifted to the right by the alpha 2-adrenoceptor antagonist rauwolscine. The apparent pA2 value of rauwolscine against moxonidine was 8.41. An inhibitory effect was also observed for the imidazoline derivative BDF 6143 (4-chloro-2-(2-imidazolin-2-ylamino)-isoindoline), a mixed alpha 2-adrenoceptor antagonist/imidazoline receptor agonist; BDF 6143 was about 2-fold more potent than clonidine. Rauwolscine (1 microM) did not substantially shift the concentration-response curve of BDF 6143. It is concluded that noradrenaline release in the human atrium is inhibited not only via presynaptic alpha 2-autoreceptors but also via presynaptic non-I1, non-I2 imidazoline receptors. The failure of rauwolscine to antagonize the inhibitory effect of clonidine suggests that clonidine preferentially stimulates the presynaptic imidazoline receptors; the alpha 2-adrenoceptor component of its action is probably suppressed by an inhibitory interaction between the two receptors. In contrast, moxonidine acts via presynaptic alpha 2-autoreceptors, leaving the presynaptic imidazoline receptor unaffected.

Antihypertensive effects of DL-tetrahydropalmatine: an active principle isolated from Corydalis

1. The effects of DL-tetrahydropalmatine (DL-THP) on cardio-vascular function and hypothalamic release of monoamines were assessed in rats under urethane anaesthesia. 2. Intravenous administration of DL-THP (1-10 mg/kg) produced hypotension, bradycardia, a decrease in hypothalamic serotonin and noradrenaline release and an increase in hypothalamic dopamine release in rats. 3. Intrahypothalamic administration of DOI (a serotonergic 5-HT2 receptor antagonist) or apomorphine (a dopamine D2-receptor agonist) produced the opposite effects and reversed DL-THP-induced hypotension and bradycardia. 4. The data suggest that DL-THP acts through the 5-HT2 and/or D2-receptor antagonism in the hypothalamus to induce hypotension and bradycardia in rats.

[Reduction of the antihypertensive effects of enalapril by indomethacin. Its independence from renal sodium retention]

OBJECTIVE

To evaluate in hypertensive patients whether or not the sodium-retaining effects of indomethacin can explain the indomethacin-induced attenuation of enalapril antihypertensive effects.

DESIGN

Randomized, single-blinded, placebo controlled study with a placebo phase (2 weeks) followed by enalapril 20 mg/d (4 weeks, once daily) and enalapril 20 mg + indomethacin 75 mg/d (1 week). Enalapril dose increased up to 40 mg/d if inadequate response to 20 mg.

PATIENTS

Twenty-four patients with mild-moderated hypertension, showing an adequate response to enalapril (20-40 mg/d).

METHODS

Blood pressure evaluated by "casual" methods and by 24-hour ambulatory blood pressure monitoring, measurement of 24-hour urinary sodium excretion and fractional excretion of sodium: at the end of placebo, enalapril and enalapril + indomethacin treatments. Determination of the correlations between the changes induced by indomethacin (when added to enalapril) on the blood pressure and on sodium excretion effects of enalapril.

RESULTS

Enalapril significantly reduced casual blood pressure (systolic/diastolic) by 33/18 mmHg and 24-hour blood pressure by 20/9 mmHg. When added to enalapril, indomethacin attenuated (by 50%) the antihypertensive effects of enalapril and significantly decreased the 24-hour (from 120 +/- 11 mmol to 106 +/- 10 mmol) and fractional excretion of sodium (from 1.11 +/- 0.09% to 0.75 +/- 0.06%). However, the indomethacin-induced attenuation of enalapril hypotensive effects did not correlate with indomethacin-induced changes of sodium excretion.

CONCLUSIONS

When indomethacin is administrated to hypertensive patients that are well controlled with enalapril, it produces a marked attenuation of enalapril hypotensive effects and produces sodium retention. However, the amount of the attenuation of the hypotensive effects of enalapril by indomethacin are completely independent of the amount of the indomethacin-induced sodium retention. These results suggest that the mechanisms involved in interaction between both drugs at the blood pressure domain are probably localized at an extra-renal level.

Inhibition of calcium influx and tonic response to K+ of intestinal smooth muscle by hydralazine

1. Evidence concerning the mechanism of the inhibition of contraction caused by hydralazine has been sought in ileal longitudinal muscle and taenia coli of guinea-pig. Hydralazine (10(-3)-3 x 10(-3) M) markedly inhibited K+ (60 mM) induced tonic response with smaller effects on the phasic response in the ileal muscle. However, 10(-2) M hydralazine completely abolished both responses. 2. Hydralazine increased the threshold for Ca2+ induced contraction in Ca2+ free, K+ depolarized taenia coli and reduced the maximal response size. A low concentration (3 x 10(-10) M) of nifedipine, an L-type Ca2+ channel blocker, further caused a parallel shift to the right in the presence of hydralazine in the concentration-response curves obtained with Ca2+ 3. Hydralazine caused a significant decrease in Ca2+ uptake measured by the lanthanum method during the K+ induced tonic response in ileal muscle; however, it did not affect the Ca2+ efflux. 4. In ileal muscle fibres treated with Triton-X-100, in which the Ca2+ release sites are destroyed, 10(-3) M hydralazine had no effect on the contractions induced by 10(-5) M Ca2+; however, hydralazine at a higher concentration (10(-2) M) had a slight inhibitory effect on the contraction. 5. The present finding indicates that the inhibitory action on contractions produced by hydralazine may result mainly from the interference of calcium permeability at the cell membrane in ileal muscle. There is the possibility that hydralazine of higher concentrations may have a minor action on the contractile system.

The impact of ibuprofen on the efficacy of antihypertensive treatment with hydrochlorothiazide in elderly persons

BACKGROUND

Nonsteroidal antiinflammatory drugs (NSAIDs) may alter blood pressure through their inhibitory effects on prostaglandin biosynthesis. Such potential hypertensive effects of NSAIDs have not been adequately examined in the elderly, who are the largest group of NSAID users.

METHODS

We performed a randomized, double-blind, two-period crossover trial of ibuprofen (1800 mg per day) vs placebo treatment in patients older than 60 years of age with hypertension controlled with hydrochlorothiazide. While continuing their usual thiazide dosage, subjects were randomized to a 4-week treatment period (ibuprofen or placebo) followed by a 2-week placebo wash-out period and a second 4-week treatment period with the alternative therapy. Supine and standing systolic and diastolic blood pressures were measured weekly.

RESULTS

Of 25 randomized subjects, 22 completed the study protocol (mean age = 73 +/- 6.7 years). Supine systolic blood pressure and standing systolic blood pressure were increased significantly with ibuprofen treatment, compared with placebo. Mean supine systolic blood pressures were 143.8 +/- 21.0 and 139.6 +/- 15.9 mmHg on ibuprofen and placebo, respectively (p = .004). Mean standing systolic blood pressures were 148.1 +/- 19.9 and 143.4 +/- 17.9 mmHg on ibuprofen and placebo, respectively (p = .002).

CONCLUSION

We conclude that 1800 mg per day of ibuprofen does induce a significant increase in systolic blood pressure in older hypertensive patients treated with hydrochlorothiazide. NSAID therapy may negatively impact the control of hypertension in elderly patients.

A comparative study of the reversal by different alpha 2-adrenoceptor antagonists of the central sympatho-inhibitory effect of clonidine

1. The recovery of the clonidine-induced hypotension, bradycardia and sympatho-inhibition produced by several putative alpha 2-adrenoceptor antagonists was investigated in pentobarbitone anaesthetized rats. The activity of four substances containing an imidazoline structure: idazoxan, methoxy-idazoxan, BRL44408 and atipamezole was compared with the effect of fluparoxan, yohimbine and L-657,743; in addition the effect of the alpha 1-adrenoceptor antagonist, prazosin, was also studied. 2. Prazosin (0.03-1 mg kg-1, i.v.) failed to alter the sympatho-inhibitory and hypotensive effects of clonidine (10 micrograms kg-1, i.v.). L-657,743 (0.01-1 mg kg-1, i.v.) induced a recovery of blood pressure, heart rate and renal sympathetic nerve activity. Yohimbine (0.03-3 mg kg-1, i.v.) completely reversed the sympatho-inhibitory effect of clonidine but did not alter its hypotensive effect. 3. The four imidazoline drugs: idazoxan (10-300 micrograms kg-1, i.v.), methoxy-idazoxan (1-100 micrograms kg-1, i.v.), BRL44408 (0.1-3 mg kg-1, i.v.) and atipamezole (0.03-1 mg kg-1, i.v.) and fluparoxan (10-300 micrograms kg-1, i.v.) reversed the clonidine-induced hypotension but produced only a partial recovery of the renal sympathetic nerve activity and of the heart rate. After pretreatment with prazosin (0.1 mg kg-1, i.v.), the recovery of the sympathetic nerve activity elicited by these compounds was significantly higher. In hexamethonium (10 mg kg-1, i.v.) pretreated rats, these five drugs induced dose-related hypertension which was reduced by pretreatment with prazosin (0.1 mg kg-1, i.v.). 4. Our results indicate that the putative alpha 2-adrenoceptor antagonists idazoxan, methoxy-idazoxan, BRL44408, atipamezole and fluparoxan also have a peripheral hypertensive effect which is mediated through activation of vascular alpha 1-adrenoceptors; this property of the compounds may be partly responsible for the reversal of the hypotensive action of clonidine. Considering the structure and the affinities of the drugs tested, our data indirectly suggest that alpha 2A-adrenoceptors may be implicated in the central sympatho-inhibitory effects of clonidine.

[The treatability of refractory or resistant hypertension by personalized antihypertensive chronotherapy based on ambulatory monitoring of the arterial pressure]

The present paper is aimed at detecting whether the combination of ambulatory blood pressure monitoring (ABPM) and antihypertensive chronotherapy can be usefully exploited in the treatment of hypertension which appears to be rebel or resistant to pharmacological administration. The study was carried out in 28 hypertensive patients (15 men and 13 women, 45 +/- 10 years old), rebel (10 cases) or resistant (8 cases) to a conventional antihypertensive therapy. The ABPM was performed weekly in order to see when the eventual patient was cured by the therapy which was synchronized to the "relative hypertensive peak" of the antimeridian, postmeridian and nocturnal part of the day. The actuarial analysis documented that at the end of the sixth week no case remained rebel or resistant to the antihypertensive chronotherapy, suggesting that the combination of the ABPM with the chronotherapeutical treatment is highly recommended in presence of apparently refractory cases of hypertension.

Chronic angiotensin II antagonism with losartan in one-kidney, one clip hypertensive rats: effect on cardiac hypertrophy, urinary sodium and water excretion and the natriuretic system

OBJECTIVE

To evaluate the effect of 7-day angiotensin II antagonism with losartan, an AT1-receptor antagonist, on systolic blood pressure, renal sodium and water excretion and on the atrial natriuretic factor system in one-kidney, one clip hypertensive rats.

METHODS

The one-kidney, one clip hypertensive rats were separated into four groups: untreated (group 1), low-sodium diet (group 2), losartan (20 mg/kg orally, group 3) and low-sodium diet with losartan (group 4). All of the rats were kept in metabolic cages with urinary volume, urinary sodium level and water intake being evaluated daily. Body weight and blood pressure were assessed before treatment and at the end of the observation period. Renal glomerular and papillary atrial natriuretic factor receptors were assessed by radioligand binding experiments.

RESULTS

No differences were observed either in body weight or in blood pressure between groups at the outset After 1 week, blood pressure was 184+/-4, 184+/-7, 170+/-5 and 78+/-8 mmHg, in groups 1, 2, 3 and 4, respectively. Group 3 rats failed to gain weight and had high urinary volume. In contrast, group 4 rats lost 15% of their original body weight. Both of the losartan-treated groups presented an apparently reduced cardiac hypertrophy but it was only clear in the low-sodium diet group. Both of the losartan-treated groups had high plasma renin activity. All of the three treated groups showed upregulation of glomerular and no changes in papillary atrial natriuretic factor receptors. Overall, mortality was 18, 27, 0 and 36% in groups 1, 2, 3 and 4, respectively.

CONCLUSION

Losartan administration reduces blood pressure in one-kidney, one clip rats only when combined with a low-sodium diet. Both low-sodium diet and angiotensin II antagonism upregulate renal glomerular but not papillary atrial natriuretic factor receptors, suggesting a divergent regulatory mechanism.

Enalapril does not prevent the myocardial ischemia caused by the chronic inhibition of nitric oxide synthesis

In rats, chronic administration of the nitric oxide (NO) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) causes arterial hypertension, cardiac hypertrophy and myocardial ischemic alterations such as necrosis and fibrosis. In this study, we evaluated the effect of 8 weeks of treatment with enalapril maleate on cardiac weight and on the development of the histological alterations induced by L-NAME. Enalapril significantly inhibited the development of both arterial hypertension (117.2 +/- 5.8, 161.8 +/- 8.8 and 122.0 +/- 10.6 mm Hg, for control, L-NAME- and L-NAME + enalapril-treated animals, respectively) and left ventricular hypertrophy (1.36 +/- 0.13, 1.60 +/- 0.04 and 1.48 +/- 0.05 mg/g, for control, L-NAME- and L-NAME + enalapril-treated animals, respectively), but had no effect on the myocardial lesions. These findings demonstrate that although the renin-angiotensin system plays a major role in the development of arterial hypertension and cardiac hypertrophy, it does not modulate the ischemia-induced myocardial alterations observed in this model.

Metoclopramide blocks bromocriptine induced antihypertensive effect in hypertensive patients

Two groups of patients with essential hypertension were studied at the Vargas Hospital of Caracas. The first group of 9 patients under placebo treatment for 1 week received a single 2.5 mg oral dose of bromocriptine. Cardiovascular and biochemical parameters including arterial pressure, heart rate, plasma renin activity, and plasma aldosterone levels were evaluated during the 6-hour period before and after the administration of drugs. The second experimental design was as follows: 9 patients received 30 mg metoclopramide daily (divided in 3 doses) for 1 week. At the end of the period a single oral dose of 2.5 mg of bromocriptine was given to each patient. The cardiovascular and biochemical parameters were also determined. Bromocriptine reduced both systolic and diastolic arterial pressure. The peak antihypertensive effect was shown 3 hours after administration of the drug, but the reduction of arterial pressure lasted approximately 6 hours. At the same time bromocriptine reduced plasma aldosterone levels and plasma renin activity. This reduction persisted 6 hours after its administration. Metoclopramide reversed the antihypertensive effect of bromocriptine and its effect on aldosterone secretion and plasma renin activity. We conclude from these findings that bromocriptine acts as an antihypertensive agent by stimulating DA2 dopaminergic receptor, the dopaminergic receptor involved in aldosterone and renin secretion is possibly DA2.

Adenosine A2 receptors stimulate c-fos expression in striatal neurons of 6-hydroxydopamine-lesioned rats

The induction of the early-gene c-fos after administration of the adenosine A2a receptor agonist CGS 21680, was studied in the striatum of normal rats or in rats with a unilateral 6-hydroxydopamine lesion of the dopaminergic nigrostriatal neurons. CGS 21680 (2.25 mg/kg) induces c-fos expression in the 6-hydroxydopamine-lesioned striatum, while up to 40 mg/kg fails to induce c-fos in the intact striatum or in the striatum of normal rats. Blockade of muscarine receptors by scopolamine (5 mg/kg) partially prevents, and stimulation of dopamine D2 receptors by quinpirole (0.5 mg/kg) completely reverses, CGS 21680-induced c-fos expression in the 6-hydroxydopamine-lesioned striatum. In turn, CGS 21680 partially reverses c-fos expression induced by quinpirole in the lesioned globus pallidus. CGS 21680, in addition, dose-dependently reduces the turning behavior induced by quinpirole (0.5 mg/kg) in 6-hydroxydopamine-lesioned rats. The results suggest that CGS 21680 induces c-fos expression in the striatum through direct and indirect mechanisms related to the ability of A2a receptors to stimulate cyclic AMP formation or acetylcholine release which in turn would activate c-fos through muscarinic receptors.

NSAIDs, antihypertensive agents and loss of blood pressure control

It is common for patients seen by primary care physicians to be taking both nonsteroidal anti-inflammatory drugs (NSAIDs) and antihypertensive agents. If blood pressure control diminishes in these patients, the physician must evaluate the potential interaction between the two classes of medication. Although the increase in blood pressure secondary to NSAID use may be only 5 to 10 mm Hg, this increase may be enough to justify a change in medication. For this reason, it is important to evaluate the interaction between the two types of drugs and determine its clinical significance in specific patients.

Involvement of imidazoline-preferring receptors in regulation of sympathetic tone

We examined the contribution of imidazoline-preferring receptors (IPR) and alpha 2-adrenoceptors at different levels of the central nervous system in the antihypertensive and sympathoinhibitory actions of rilmenidine in 2 conscious animal models, the spontaneously hypertensive rat (SHR) and the normotensive rabbit. In conscious SHRs, we compared the potency of rilmenidine and clonidine administered intravenously into the lateral cerebral ventricle, the cisterna magna, and into the subarachnoidal space of the thoracolumbar spinal cord. In SHRs, we found that rilmenidine was more potent and more effective by the intrathecal than the intracisternal route. By contrast, clonidine was most effective after administration into the cisterna magna. Intravenous administration of rilmenidine or clonidine induced dose-dependent and prolonged decreases in blood pressure and heart rate. Neither rilmenidine nor clonidine altered mean arterial pressure or heart rate when given into the lateral cerebral ventricle. These data suggest that in SHRs the spinal cord may be an important site for the antihypertensive action of rilmenidine. We therefore characterized the receptor type involved. We observed in conscious SHRs that intrathecal post-treatment with idazoxan, a mixed alpha 2-adrenoceptor and IPR antagonist, abolished the antihypertensive effect of rilmenidine, whereas 2-methoxyidazoxan, a selective alpha 2-adrenoceptor antagonist, caused only a partial reversal of the blood pressure effects of rilmenidine. These results suggest that rilmenidine acts mainly through IPR rather than alpha 2-adrenoceptors in the spinal cord. In view of these findings, we compared the hypotensive actions of rilmenidine and clonidine, administered into the lateral cerebral ventricle, the cisterna magna, and the subarachnoid space of the thoracolumbar spinal cord in conscious normotensive rabbits. Both drugs were less potent and effective when administered intrathecally than intracisternally. These experiments suggest that the hypotensive action of rilmenidine and clonidine in the rabbit is mediated through receptors mainly located in the brainstem. Further, we found that idazoxan reversed the hypotensive action of rilmenidine more readily than 2-methoxyidazoxan. Surprisingly, both idazoxan and 2-methoxyidazoxan completely reversed the depressor effects of clonidine. Therefore, in the rabbit, rilmenidine acts through IPR located in the brainstem and clonidine acts predominantly through alpha 2-adrenoceptors. In conclusion, our studies demonstrate that IPR are involved in the vasodepressor action of rilmenidine in both conscious SHRs and rabbits. However, although the main site of action of rilmenidine in SHRs may be located in the thoracolumbar spinal cord, in the rabbit it appears to be in the brainstem.(ABSTRACT TRUNCATED AT 250 WORDS)

Do nonsteroidal anti-inflammatory drugs affect blood pressure? A meta-analysis

PURPOSE

A meta-analysis of randomized trials studying the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on blood pressure.

DATA SOURCES AND STUDY SELECTION

Eight databases were searched, yielding 38 randomized, placebo-controlled trials and 12 randomized but not placebo-controlled trials (comparing two or more NSAIDs).

DATA EXTRACTION

Pooled mean treatment effects were computed in each trial for blood pressure, weight, creatinine clearance, plasma renin activity, and daily urinary excretion of sodium and prostaglandins. Meta-analyses of these variables were done for all randomized, controlled trials; for all randomized, uncontrolled trials; and for several subgroups.

DATA SYNTHESIS

When pooled, NSAIDs elevated supine mean blood pressure by 5.0 mm Hg (95% CI, 1.2 to 8.7 mm Hg) but had no effect on variables other than blood pressure. Nonsteroidal anti-inflammatory drugs antagonized the antihypertensive effect of beta-blockers (blood pressure elevation, 6.2 mm Hg; CI, 1.1 to 11.4 mm Hg) more than did vasodilators and diuretics. Among NSAIDs, piroxicam produced the most marked elevation in blood pressure (6.2 mm Hg; CI, 0.8 to 11.5 mm Hg), whereas sulindac and aspirin had the least hypertensive effect.

CONCLUSIONS

Nonsteroidal anti-inflammatory drugs may elevate blood pressure and antagonize the blood pressure-lowering effect of antihypertensive medication to an extent that may potentially increase hypertension-related morbidity. Although certain NSAIDs and antihypertensive agents could be more likely to produce these effects, the underlying mechanisms require further study.

Inhibition by imidazoline and imidazolidine derivatives of glibenclamide-sensitive K+ currents in Xenopus oocytes

The effects of imidazoline and imidazolidine derivatives on glibenclamide-sensitive K+ currents induced by the novel K+ channel opener, Y-26763 ((+)-(3S,4R)-4-(N-acetyl-N-benzyloxyamino)-6-cyano-3,4-dihydro-2,2 -dimethyl-2H-1-benzopyran-3-ol), were investigated in voltage-clamped follicle-enclosed Xenopus oocytes. Of 14 imidazoline derivatives and seven imidazolidine derivatives tested, phenotalmine, (-)-cibenzoline, (+)-cibenzoline, alinidine, oxymetazoline, antazoline, midaglizole, xylometazoline, tramazoline and ST91 (2-(2,6-diethylphenylamino)-2-imidazoline hydrochloride) potently suppressed Y-26763-induced K+ currents (IC50 < 80 microM). The compounds which lack an aromatic ring in their structure, 2-methyl-2-imidazole and 2-hydrazino-2-imidazoline, did not affect the K+ currents. Clonidine and idazoxan, which both bind to imidazoline-preferring binding sites with high affinity in various tissues, showed only a small inhibitory effect on Y-26763-induced K+ currents (IC50 780 microM and 955 microM, respectively). The non-imidazoline/non-imidazolidine alpha-adrenoceptor antagonists, WB-4101 (2-(2,6-dimethoxy-phenoxyethyl)-aminomethyl-1,4-benzodioxane hydrochloride), yohimbine and rauwolscine, showed suppressive effects on Y-26763-induced K+ currents (IC50 203 microM, 813 microM and 832 microM, respectively). Octopamine (1 mM), a non-imidazoline/non-imidazolidine alpha-adrenoceptor agonist, was inactive. The results suggest that (1) an aromatic ring or aromatic rings are an essential moiety for imidazoline or imidazolidine derivatives to block glibenclamide-sensitive K+ currents in oocytes, and (2) the K+ current-blocking ability of imidazolines and imidazolidines is related to the alkylation of the benzene ring and the existence of a tertiary amine structure. The K+ current-blocking effects of imidazolines or imidazolidines may not be mediated by alpha-adrenoceptors, at least in follicle-enclosed Xenopus oocytes.

Inhibitory effect of the nonpeptide angiotensin II receptor antagonist losartan and its active metabolite, E-3174, on cAMP phosphodiesterase: additional action of the antagonists

The inhibitory effects of the nonpeptide angiotensin II (AII) receptor antagonist losartan and its active metabolite, E-3174, on bovine brain calcium/calmodulin-dependent 3':5'-cyclic nucleotide phosphodiesterase (cAMP PDE) were investigated. Losartan and E-3174 inhibited cAMP PDE activity competitively with an apparent Ki of 18.7 +/- 2 microM (N = 3) and 70.4 +/- 8 microM (N = 3) with respect to cAMP, respectively. With 1.2 mM cAMP as a substrate, cAMP PDE activities were inhibited by losartan and E-3174 in a concentration-dependent manner. The concentrations of losartan and E-3174 required to obtain 50% inhibition of the enzyme activity (IC50) were estimated to be 38.9 +/- 7 microM (N = 3) and 139.3 +/- 39 microM (N = 3), respectively. These results show that losartan is about four times more potent than E-3174 in inhibiting the enzyme. The Hill coefficient of -1.0 +/- -0.04 (N = 3) for losartan and -1.1 +/- -0.14 (N = 3) for E-3174 was obtained, indicating that one inhibitor binding site is available on cAMP PDE. This study demonstrated that losartan and E-3174 exert additional inhibitory action on cAMP PDE besides AII receptor antagonism.