Isolated Rabbit Aortic Strips Research Articles

Organic nitrates and tolerance in cardiovascular diseases: effects of isosorbide-2-mononitrate compared to traditional nitrates

Nitrates are a cornerstone in the treatment of coronary heart disease and heart fail- ure. Although they are widely used in clinical practice, their therapeutic value is partially com- promised by the rapid development of tolerance. The effect of different nitrates, nitroglycerin (NTG), isosorbide dinitrate (ISDN), 5-mononitrate (5MN) and 2-mononitrate (2MN) and the mech- anism responsible for nitrate tolerance were investigated on isolated rabbit hearts and aortic strips. Preparation was stimulated by different spasmogenic agents: KCl, angiotensin II (A) and noradrenaline (NA); nitrates were administered on the plateau contraction, at the concentration of maximum inhibitory effect. Nitrates produced the following maximum inhibitions on NA-in- duced contraction: NTG 90% (10 -6 M), ISDN 60% (10 -4 M), 5MN 55% (10 -4 M) and 2MN 80% (10 -4 M). In another series of experiments, preparations were pre-incubated with the maximum inhibitory concentration of each nitrate to evaluate the induction of tolerance. After incubation a loss of vasodilator effect of nearly 50-60% was observed for all the nitrates considered except 2MN, in which the loss of effect was significantly lower (36%). The cyclic GMP (cGMP) levels measured in the preparations were lower in the presence of 2MN than in the other compounds. These data suggest that 2MN is able to induce a lesser cGMP increase and a lesser tolerance in- duction; since these observations seem to be correlated the vasodilator effect of 2MN probably in- volves mechanisms other than guanylyl cyclase stimulation. (Heart International 2007; 3: 112-21)

190 Smooth Muscle Tone-Dependent Hydraulic Conductance of Aortic Media to Water Filtration

Atherosclerotic plaques are focal accumulations of lipids, fibrous proteins and inflammatory cells in the intima and inner media of the arterial wall and therefore cannot be explained entirely by systemic risk factors (e.g. elevated blood pressure, plasma cholesterol, etc.). Variation in the accumulation of plasma macromolecules within the inner wall may be one localising factor but the basic transport mechanisms involved in such accumulation are incompletely understood. Transmural water transport, driven by pressure gradients, plays a major role in the transport of the largest macromolecules (eg: lipoproteins): they are predominantly transported by advection. Studying the factors affecting the hydraulic conductance (L­­ p ) of the arterial wall is therefore the first step in discovering the transport routes of large molecules within the arterial wall and has an impact on both our understanding of the mechanisms behind the lipid accumulation that characterises atherosclerosis and on the design of drugs of similar molecular size targeted at the arterial wall. One such factor is the role of smooth muscle cell tone. We have developed an ex vivo preparation of the rat aortic bifurcation in which it is excised and placed in a bath of physiological buffer while its lumen is maintained at a steady pressure of 100mmHg; it is then treated with increasing concentrations of noradrenaline. By measuring hydraulic flux we can calculate L p , averaged over the whole vessel, and can determine the effects of muscle contraction on it. Additionally, we place a fluorescent protein tracer, rhodamine-albumin, in the luminal space. It is transported through the wall and can be measured in the abluminal bath. Allowing this tracer’s transport to reach a steady state before formaldehyde fixation and 3D confocal microscopy gives us a realistic structure of the available space for mobile water in the vessel wall, with which we can perform numerical simulations of water transport. L p was found to be significantly lower at noradrenaline concentrations ≥100 nM than in controls. This threshold concentration corresponds to previously reported findings on the tension-concentration relationship of isolated rabbit aortic strips. 1 We are currently performing numerical simulations on small regions within the media to determine the permeability of the structure as it changes with noradrenaline concentration. This will give us an estimate of the L p of the media alone and, by subtraction, the L p of the endothelium. Funding BHF, BHF Centre of Research Excellence and EU. Reference Furchgott RF, Bhadrakom S. J Pharmacol Exp Ther . 1953; 108(2):129–43

Nonpeptidic angiotensin II AT1 receptor antagonists derived from 6-substituted aminocarbonyl and acylamino benzimidazoles

Both 6-substituted aminocarbonyl and acylamino benzimidazole derivatives were designed and synthesized as nonpeptidic angiotensin II AT1 receptor antagonists. Compounds 6f, 6g, 11e, 11f, 11g, and 12 showed nanomolar AT1 receptor binding affinity and high AT1 receptor selectivity over AT2 receptor in a preliminary pharmacological evaluation. Among them, the two most active compounds 6f (AT1 IC50 = 3 nM, AT2 IC50 > 10,000 nM, PA2 = 8.51) and 11g (AT1 IC50 = 0.1 nM, AT2 IC50 = 149 nM, PA2 = 8.43) exhibited good antagonistic activity in isolated rabbit aortic strip functional assay. In addition, they were orally active AT1 receptor antagonists in spontaneous hypertensive rats.

Effects of methanolic extract of yohimbe bark (<i>Pausinystalia yohimbe</i>) on isolated rabbit aortic strip and rat uterus

Background: Medicinal plants contain physiologically active principles that over the years have been exploited in traditional medicine for the treatment of various ailments. Objectives and Methods: This study aimed to investigate the effects of the methanolic extract of Pausinystalia yohimbe bark (5 mg/ml) on isolated rabbit aortic strip and rat uterus. Results: methanolic extract of P. yohimbe bark (5 mg/ml) produced relaxation of the phenylephrine precontracted-rabbit aortic strip. This relaxation may be resulted through nitric oxide (NO), since the pretreatment of the isolated rabbit aortic strip with methylene blue inhibited the NO-mediated relaxation. Moreover, the extract exhibited relaxation of rat uterine muscles, which appeared to be not mediated by activation of β2-adrenoceptors and/or H2 receptors, since the relaxant effect continued even after the pretreatment of the tissue with propranolol and ranitidine respectively. Conclusion: The obtained results revealed that methanolic extract of P. yohimbe bark caused relaxation of both isolated rat uterus and rabbit aortic strip through facilitating the role of endogenous compounds such as NO.

English

The leaf of Acalypha torta Muell. (Euphorbiaceae) is used as folk remedy in Nigeria for the treatment of hypertension. Effects of extracts of A. torta leaf on the blood pressure of anaesthetized cats were studied to examine this claim. The ethanol extract produced a significant (p < 0.0001) and dose - dependent fall in arterial blood pressure. The extract inhibited adrenaline - induced contraction of isolated rabbit aortic strips and produced a significant (p < 0.0001) and dose - dependent increase in the rate of flow of physiologic fluid through the rat hind-quarters preparation. Both evidences indicate relaxant effect of the ethanol extract on vascular smooth muscle. Calcium chloride - induced tachycardia was abolished following administration of the extract. It had no effect on the rate of contraction of the isolated rabbit heart, but reduced the force of contraction. Column chromatography was performed and Fraction L, eluted with distilled water, was found to be responsible for the reduction in blood pressure.   Key words: Acalypha torta, hypertension, antihypertensive, cat.

SMOOTH MUSCLE RELAXANT ACTIVITY OF A DIHYDROPYRIMIDINE DERIVATIVE 5-ACYL-6-METHYL-4-PHENYL-2-S-ETHYL-1, 4-DIHYDROPYRIMIDINE (BK- VI) ON ISOLATED RAT UTERUS AND RABBIT AORTIC STRIP.

ABSTRACT Objective : To investigate the smooth muscle relaxant activity of a newly synthesized dihydropyrimidine derivative 5-acyl-6-methyl-4-phenyl-2-S-ethyl-1,4-dihydropyrimidine (BK- VI) and nifedipine on isolated rat uterus and rabbit aortic strip. Material and Methods : Effect of the test compound BK-VI on the smooth muscles of isolated rat uterus and isolated rabbit aortic strip was observed and compared with that of nifedipine. Observations were made with increasing bath concentrations of BK-VI and nifedipine.Six preparations were used for each dose of BK-VI and nifedipine.Mean effect of increasing doses of BK-VI and nifedipine on the height of calcium-induced contraction of depolarized isolated rabbit aortic strip and on K + -induced contraction of isolated rat uterus were noted and IC-50 calculated. Results : Test compound BK-VI had a significant dose-dependent relaxant effect on K + -induced contractions of isolated rat uterus. Significant relaxation was seen at bath concentration starting from 9.34x10 -4 M (IC-50=12.2x10 -4 M).Nifedipine showed significant relaxation at all bath concentrations starting from 2.8X10 -7 M(IC 50 =7.5X10 -7 M).Compound BK-VI produced potentiation of Ca 2+ -induced contractions of K+-depolarized rabbit’s aortic strip at bath concentration of 0.7×10 -5 M while significant inhibition was observed at higher bath concentrations. Nifedipine showed dose-dependent significant inhibition at all bath concentrations. Conclusion : BK-VI has a calcium channel blocking activity like nifedipine and it can inhibit the Ca 2+ dependent contractions of smooth muscles of uterus and aorta. KEY WORD: Calcium channel blockers, Dihydropyrimidines, Voltage dependent calcium channels.

Design, synthesis and biological activity of 6-substituted carbamoyl benzimidazoles as new nonpeptidic angiotensin II AT1 receptor antagonists

A series of 6-substituted carbamoyl benzimidazoles were designed and synthesised as new nonpeptidic angiotensin II AT1 receptor antagonists. The preliminary pharmacological evaluation revealed a nanomolar AT1 receptor binding affinity for all compounds in the series, and a potent antagonistic activity in an isolated rabbit aortic strip functional assay for compounds 6f, 6g, 6h and 6k was also demonstrated. Furthermore, evaluation in spontaneous hypertensive rats and a preliminary toxicity evaluation showed that compound 6g is an orally active AT1 receptor antagonist with low toxicity.

Design, synthesis and biological evaluation of 6-substituted aminocarbonyl benzimidazole derivatives as nonpeptidic angiotensin II AT1 receptor antagonists

A series of 6-substituted aminocarbonyl benzimidazole derivatives were designed and synthesized as nonpeptidic angiotensin II AT1 receptor antagonists. The preliminary pharmacological evaluation revealed nanomolar AT1 receptor binding affinity and good AT1 receptor selectivity over AT2 receptor for all compounds of the series, a potent antagonistic activity in isolated rabbit aortic strip functional assay for compounds 6b, 6d and 6i was also demonstrated. Furthermore, evaluation in spontaneous hypertensive rats and a preliminary toxicity evaluation showed that compound 6i is an orally active AT1 receptor antagonist with low toxicity.

Effect of Tiangou Jiangya capsule on rabbit aortic strip contraction

To observe the effect of Tiangou Jiangya capsule on isolated rabbit aortic strips, and to discuss its antihypertensive mechanism. The isolated rabbit aortic strips were placed in perfusion baths, and induced to contract by norepinephrine (NE), KCl and CaCl2 respectively, then Tiangou Jiangya capsule extraction was added to observe its effect on the contraction. The effect on intracellular Ca2+ dependent contraction and extracellular Ca2+ dependent contraction induced by NE were also studied. The Tiangou Jiangya capsule (1, 3, 5 g x L(-1)) can reduce the largest contract reaction of aortic strips induced by NE or CaCl2 (P < 0.01). It can reduce both intracellular Ca2+ dependent contraction and extracellular Ca2+ dependent contraction induced by NE (P < 0.01), and the effect on extracellular Ca2+ dependent contraction is more significant. But the Tiangou Jiangya capsule has no significant effect on KCl induced contraction. Tiangou Jiangya capsule can regulate intracellular Ca2+ concentration and help to relax the vascular smooth muscle. The mechanism could be regulating the receptor-operated Ca2+ channel. The effect on extracellular Ca2+ dependent contraction is more obvious than on intracellular Ca2+ dependent contraction induced by NE.

Erectogenic Effects ofClerodendron capitatum: Involvement of Phosphodiesterase Type-5 Inhibition

Clerodendron capitatum (Willd) (family: verbenaceae) is locally named as Gung and used traditionally to treat erectile dysfunction. Therefore, the current study was designed to investigate the erectogenic properties of C. capitatum. The relaxation effect of this plant was tested on phenylephrine precontracted rabbit corpus cavernosum smooth muscle (CCSM). The effects of C. capitatum were also examined on isolated Guinea pig atria alone, in the presence of calcium chloride (Ca2+ channel blocker), atropine (cholinergic blocker), and glibenclamide (ATP-sensitive K+ channel blocker). These effects were confirmed on isolated rabbit aortic strips. The extract, when tested colorimetrically for its inhibitory activities on phosphordiesterase-5 (PDE-5) in vitro towards p-nitrophenyl phenyl phosphate (PNPPP), was observed to induce significant dose-dependent inhibition of PDE-5, with an ID50 of 0.161 mg/ml (P < .05). In conclusion, our results suggest that C. capitatum possesses a relaxant effect on CCSM, which is attributable to the inhibition of PDE-5, but not mediated by the release calcium, activation of adrenergic or cholinergic receptors, or the activation of potassium channels.

Smooth Muscle Relaxant Activity of a Synthetic Dihydropyrimidine Derivative 5-acyl-6-methyl-4(2,3methylenedioxy)phenyl-2-s-benzyl-1,4-dihydro Pyrimidine (bk- vii) on Isolated Rat Uterus and Rabbit Aortic Strip

ObjectivesTo investigate the smooth muscle relaxant activity of a newly synthesised dihydropyrimidine derivative 5-acyl-6-methyl-4(2,3 methylenedioxy) Phenyl-2-S-benzyl-1,4-dihydropyrimidine(code named as BK- VII) and comparing with nifedipine on isolated rat uterus and rabbit aortic strip.Effect of the test compound BK-VII on the smooth muscles of isolated rat uterus and isolated rabbit aortic strip was observed and compared with that of nifedipine. Observations were made with increasing bath concentrations of BK-VII and nifedipine. Six preparations were used for each dose of BK-VII and nifedipine. Mean effect of increasing doses of BK-VII and nifedipine on the height of calcium (Ca²⁺) induced contraction of depolarised isolated rabbit aortic strip and on potassium (K⁺) induced contraction of isolated rat uterus were noted and median inhibitory concentration (IC-50) calculated.ResultsTest compound BK-VII had a significant dose-dependent relaxant effect on K⁺-induced contractions of isolated rat uterus. Significant relaxation was seen at bath concentration starting from 4.2X10⁻⁵M (IC₅₀ -12.2X10⁻⁵M). Nifedipine showed significant relaxation at all bath concentrations starting from 2.8X10⁻⁷M (IC₅₀-7.5X10⁻⁷M). Compound BK-VII produced potentiation of Ca²⁺-induced contractions of K⁺-depolarized rabbit's aortic strip at bath concentration of 0.6X10⁻⁵M while significant inhibition was observed at higher bath concentrations. Nifedipine showed dose-dependent significant inhibition at all bath concentrations.BK-VII has a calcium channel blocking activity like nifedipine and it can inhibit the Ca²⁺ dependent contractions of smooth muscles of uterus and aorta.

In Vitro Antagonistic Properties of a New Angiotensin Type 1 Receptor Blocker, Azilsartan, in Receptor Binding and Function Studies

The angiotensin II (AII) antagonistic action of azilsartan (AZL) [2-ethoxy-1-{[2'-(5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]methyl}-1H-benzimidazole-7-carboxylic acid] was investigated in radioligand binding and function studies. AZL inhibited the specific binding of ¹²⁵I-Sar¹-Ile⁸-AII to human angiotensin type 1 receptors with an IC₅₀ of 2.6 nM. The inhibitory effect of AZL persisted after washout of the free compound (IC(50) value of 7.4 nM). Olmesartan, telmisartan, valsartan, and irbesartan also inhibited the specific binding with IC₅₀ values of 6.7, 5.1, 44.9, and 15.8 nM, respectively. However, their inhibitory effects were markedly attenuated with washout (IC₅₀ values of 242.5, 191.6, >10,000, and >10,000 nM). AZL also inhibited the accumulation of AII-induced inositol 1-phosphate (IP1) in the cell-based assay with an IC₅₀ value of 9.2 nmol; this effect was resistant to washout (IC₅₀ value of 81.3 nM). Olmesartan and valsartan inhibited IP1 accumulation with IC₅₀ values of 12.2 and 59.8 nM, respectively. The activities of these compounds were markedly reduced after washout (IC₅₀ value of 908.5 and 22,664.4 nM). AZL was defined as an inverse agonist in an experiment by using a constitutively active mutant of human angiotensin type 1 receptors. In isolated rabbit aortic strips, AZL reduced the maximal contractile response to AII with a pD'₂ value of 9.9. The inhibitory effects of AZL on contractile responses induced by AII persisted after the strips were washed; these inhibitory effects were more potent than those of olmesartan. These results suggest that AZL is a highly potent and slowly dissociating AII receptor blocker. Its tight receptor binding might be expected to produce potent and long-lasting antihypertensive effects in preclinical and clinical settings.

Design, Synthesis, and Biological Evaluation of AT1 Angiotensin II Receptor Antagonists Based on the Pyrazolo[3,4-b]pyridine and Related Heteroaromatic Bicyclic Systems

Novel AT 1 receptor antagonists bearing the pyrazolo[3,4- b]pyridine bicyclic heteroaromatic system (or structurally related moieties) were designed and synthesized as the final step of a large program devoted to the development of new antihypertensive agents and to the understanding of the molecular basis of their pharmacodynamic and pharmacokinetic properties. The preliminary pharmacological characterization revealed nanomolar AT 1 receptor affinity for several compounds of the series and a potent antagonistic activity in isolated rabbit aortic strip functional assay for 7c and 8a. These results stimulated the study of the biopharmaceutical properties of some selected compounds, which were found to be characterized by a permeability from medium to high. Remarkably, the least permeable 7c showed both permeability and oral bioavailability (80%) higher than losartan, but its terminal half-life was shorter. These results suggest that the permeability is not a limiting factor in the pharmacokinetics of these AT 1 receptor antagonists.

Synthesis of Recombinant Atrial Natriuretic Peptide (rANP) Using Hybrid Fusion Protein-Phage fr Coat/ANP (CP/ANP)

Baumanis, V., I. Jansone, A. Skangals, I. Mandrika and V. Berzins. Synthesis of recombinant atrial natriuretic peptide (rANP) using hybrid fusion protein-phage fr coat/ANP (CP/ANP). Peptides 18(8) 1229–1235, 1997.—Recombinant atrial natriuretic peptide (rANP) was expressed in and isolated from E. coli. rANP was purified using HPLC. Amino acid analysis, partial sequencing, and molecular mass were determined. Fused protein was used to rise polyclonal antibodies and to develop of immunoenzymatic assays of rANP and CP/ANP. Experiments were designed to study rANP effects on isolated rabbit aortic strips and to examine hypotensive, diuretic, and natriuretic activity, as well as renal creatinine clearance, in an in vivo rat model. Identity of recombinant and commercial ANP has been confirmed. Physiological activity of CP/ANP has allowed the investigators to predict the conformation of CP/ANP, pro-ANP processing, and the method by which fusion protein interacts with ANP receptors.

Pharmacological Profiles of a Novel Non-peptide Angiotensin II Type I Receptor Antagonist HR720 In Vitro and In Vivo

The pharmacological properties of 2-butyl-4-(methylthio)-1-[[2’-[[[(propylamino)carbonyl] amino]sulfonyl](1,1′-biphenyl)-4-yl]methyl]-1H-imidazole-5-carboxylate (HR720), a novel non-peptide angiotensin (Ang)II type I (AT1) receptor antagonist, were characterized in both in vitro and in vivo systems. In vitro autoradiography using 125I-[Sar1,Ile8]Ang II as a ligand revealed that HR720 competitively inhibited the specific binding of the ligand to the adrenal cortex. The IC50 value for the adrenal cortex was 1.5 × 10-8 M, and the IC50 for medulla was 1.4 × 10-6 M. Similar results were obtained in the adrenal cortex with CV-11974, a known potent AT1-receptor antagonist. Since AT1 receptors are known to predominate in the adrenal cortex and AT2-receptors in the adrenal medulla, it is considered that HR720 is highly selective for AT1 receptors. HR720 inhibited the Ang II-induced contraction of isolated rabbit aortic strips and human gastroepiploic arteries in a noncompetitive manner, pD’2=9.40 and 9.62 for rabbit aorta and human artery, respectively. With CV-11974, pD’2 values of 9.84 in isolated rabbit aorta and 10.00 in human artery were obtained. HR720 did not affect the norepinephrine-, serotonin- or KCl-induced contraction even at a concentration of 1 × 10-5 M. In anesthetized hamsters, HR720 induced a dose-dependent inhibition of the pressure response to Ang II. The potency of HR720 to antagonize the Ang II-induced pressure response was similar to that of CV-11974. These results demonstrate that HR720 is a potent and selective AT1-receptor antagonist.

In vitro pharmacological characterization of UP 269-6, a novel nonpeptide angiotensin II receptor antagonist.

f1p4in vitro pharmacology of UP 269-6, a novel nonpeptide angiotensin II antagonist, was examined in radioligand binding and functional isolated tissue assays. UP 269-6 bound selectively to AT1 receptors as evidenced by the inhibition of specific [125I] Sar1, Ile8-AII binding in rat adrenal membranes (IC50 = 35.8 nM) and in cultured vascular smooth muscle cells (IC50 = 23.8 nM). UP 269-6 displayed a very high selectivity for the AT1 compared to the AT2 receptor subtype (IC50 > 10,000 nM). UP 269-6 inhibited the AII-induced contraction of isolated rabbit aortic strips. The pattern of AII antagonism suggested competitive antagonism at low concentrations (10(-10), 3 x 10(-10), 10(-9) M) of UP 269-6 and insurmountable antagonism at higher concentrations (3 x 10(-9), 10(-8), 3 x 10(-8) M). Based on the calculated pA2 values, UP 269-6 (9.86 +/- 0.25) was an angiotensin II receptor antagonist as potent as L-158,809 (9.82 +/- 0.37) and much more potent than losartan (7.96 +/- 0.38). UP 269-6 was devoid of affinity (IC50 > 10,000 nM) for many other receptors, ion channels and uptake sites, demonstrating its high specificity for AII receptors. Furthermore, this compound did not affect the contractile response to KCl or phenylephrine in rabbit aorta and exhibited no effect on angiotensin converting enzyme activity. These data demonstrate that UP 269-6 is a highly potent, selective and specific AT1 receptor antagonist.

Pharmacological effects of butylidenephthalide

AbstractThe pharmacological effects of synthetic butylidenephthalide (Bdph), the most potent antispasmodic agent found in the neutral oil of Ligusticum wallichii Franch., were examined in this study. In vivo, Bdph exerted a significant antihypertensive effect in anaesthetized renal hypertensive rats at a dose of 30 mg/kg (i.v. or i.p.), or 60 mg/kg (p.o.). Bdph antagonized noradrenaline (NA) induced increases in blood pressure in anaesthetized normotensive rats. In addition, Bdph prevented the pituitrin‐induced T‐wave lowering of the ECG in anaesthetized rats. It also dose‐dependently decreased coronary arterial pressure in dogs. It is concluded that Bdph dilates coronary vessels. In vitro, Bdph non‐competitively antagonized adrenaline‐induced contraction in isolated rabbit aortic strips. It also significantly antagonized the NA‐induced maximum decrease in perfusion rate of isolated rabbit ears. However, the vasodilator effect may cause a heat loss because Bdph significantly lowered the rectal temperature of rats at ambient temperature of 20°C, but not at 30°C. Bdph might be a useful coronary dilator and antihypertensive drug.

Synthesis, calcium-channel-blocking activity, and antihypertensive activity of 4-(diarylmethyl)-1-[3-(aryloxy)propyl]piperidines and structurally related compounds

A series of 4-(diarylmethyl)-1-[3-(aryloxy)propyl]piperidines and structurally related compounds were synthesized as calcium-channel blockers and antihypertensive agents. Compounds were evaluated for calcium-channel-blocking activity by determining their ability to antagonize calcium-induced contractions of isolated rabbit aortic strips. The most potent compounds were those with fluoro substituents in the 3- and/or 4-positions of both rings of the diphenylmethyl group. Bis(4-fluorophenyl)acetonitrile analogue 79 was similar in potency to bis(4-fluorophenyl)methyl compound 1. The methylene analogue of 1 (78) and derivatives of 1 that contained a hydroxyl (76), carbamoyl (80), amino (81), or acetamido (82) substituent on the methyl group were less potent. In most cases, substituents on the phenoxy ring, changes in the distance between the aryloxy group and the piperidine nitrogen, and the substitution of S, N(CH3), or CH2 for the oxygen atom of the aryloxy group had only a small to moderate effect on the potency. The best compounds in this series were more potent than verapamil, diltiazem, flunarizine, and lidoflazine, but were less potent than nifedipine. Compounds were evaluated for antihypertensive activity in spontaneously hypertensive rats (SHR) at an oral dose of 30 mg/kg. Of the 55 compounds tested, only nine produced a statistically significant (p less than 0.05) reduction in blood pressure greater than 20%; all of these compounds had fluoro substituents in both rings of the diphenylmethyl group. One of the most active compounds in the SHR at 30 mg/kg was 1-[4-[3-[4-[bis(3,4-difluorophenyl)methyl]-1- piperidinyl]propoxy]-3-methoxyphenyl]ethanone (63), which produced a 35% reduction in blood pressure and was similar in activity to nifedipine. At lower doses, however, 4-[bis(4-fluorophenyl)methyl]-1-[3-(4-chlorophenoxy)propyl]piperidine (93) was one of the most effective antihypertensive agents, producing reductions in blood pressure of 17 and 11% at oral doses of 10 and 3 mg/kg, respectively; 63 was inactive at 10 mg/kg.

Comparison of isobutyl nitrate and isobutyl nitrite: tolerance and cross-tolerance to glyceryl trinitrate

This study includes the first systematic comparison of an organic nitrate with the corresponding organic nitrite - isobutyl nitrate and isobutyl nitrite. The spasmolytic activity of the nitrite on isolated rabbit aortic strips was stronger, more rapid in onset, but less stable than the activity of the nitrate. In vitro tolerance to glyceryl trinitrate and isobutyl nitrite greatly weakened the activity of isobutyl nitrate, respectively, but had much less effect on isobutyl nitrite. Possible reasons for these differences are discussed.

Biotransformation of Glyceryl Trinitrate and Elevation of Cyclic GMP Precede Glyceryl Trinitrate-Induced Vasodilation

In this study, we examined glyceryl trinitrate (GTN) biotransformation and cyclic GMP elevation in vascular smooth muscle before onset of GTN-induced relaxation. Isolated rabbit aortic strips (RAS) and strips of bovine pulmonary artery (BPA) and bovine pulmonary vein (BPV) were contracted submaximally and incubated with [3H]GTN. Before onset of GTN-induced vasodilation, the tissues were freeze-clamped and then analyzed for GTN, glyceryl-1,2-dinitrate (1,2-GDN), and glyceryl-1,3-dinitrate (1,3-GDN) and for cyclic GMP. Before onset of relaxation of RAS, BPA, and BPV, there was significant biotransformation of GTN to GDN and significant elevation of cyclic GMP. There was significantly greater biotransformation of GTN and elevation of cyclic GMP by BPV than by BPA incubated with the same concentration of GTN, which was temporally related with the more rapid onset of relaxation induced in BPV than in BPA. These results are consistent with the hypothesis that the magnitude of GTN biotransformation before vasodilation is the important determinant of subsequent tissue relaxation. In GTN biotransformation before vasodilation, there was preferential formation of 1,2-GDN. These data indicate that the mechanism of GTN biotransformation to 1,2-GDN is related to elevation of cyclic GMP and subsequent vasodilation.