Rabbit Aortic Strips Research Articles

Pitavastatin and Lovastatin Exhibit Calcium Channel Blocking Activity Which Potentiate Vasorelaxant Effects of Amlodipine: A New Futuristic Dimension in Statin's Pleiotropy.

Background and Objectives: We have recently reported that Fluvastatin, Atorvastatin, Simvastatin and Rosuvastatin have calcium channel antagonistic activities using rabbits' intestinal preparations. The current study is focused on the effects of Pitavastatin and Lovastatin for possible inhibition of vascular L-Type calcium channels, which may have vasorelaxant effect(s). Combined effects of Pitavastatin and Lovastatin in the presence of Amlodipine were also tested for vasorelaxation. Materials and Methods: Possible relaxing effects of Pitavastatin and Lovastatin on 80 mM Potassium chloride (KCL)-induced contractions and on 1 µM norepinephrine (N.E)-induced contractions were studied in isolated rabbit's aortic strips preparations. Relaxing effects on 80 mM KCL-induced vascular contractions were further verified by constructing Calcium Concentration Response Curves (CCRCs), in the absence and presence of three different concentrations of Pitavastatin and Lovastatin using CCRCs as negative control. Verapamil was used as a standard drug that has L-Type calcium channel binding activity. In other series of experiments, we studied drug interaction(s) among Pitavastatin, Lovastatin, and amlodipine. Results: The results of this study imply that Lovastatin is more potent than Pitavastatin for having comparatively lower EC50 (7.44 × 10-5 ± 0.16 M) in intact and (4.55 × 10-5 ± 0.10 M) in denuded aortae for KCL-induced contractions. Lovastatin amplitudes in intact and denuded aortae for KCL-induced contractions were, respectively, 24% and 35.5%; whereas amplitudes for Pitavastatin in intact and denuded aortae for KCL-induced contractions were 34% and 40%, respectively. A left shift in the EC50 values for the statins was seen when we added amlodipine in EC50 (Log Ca++ M). Right shift for CCRCs state that Pitavastatin and Lovastatin have calcium channel antagonistic effects. Lovastatin in test concentration (6.74 × 10-7 M) produced a right shift in relatively lower EC50 (-2.5 ± 0.10) Log Ca++ M as compared to Pitavastatin, which further confirms that lovastatin is relatively more potent. The right shift in EC50 resembles the right shift of Verapamil. Additive effect of Pitavastatin and Lovastatin was noted in presence of amlodipine (p < 0.05). Conclusions: KCL (80 mM)-induced vascular contractions were relaxed by Pitavastatin and Lovastatin via inhibitory effects on L-Type voltage-gated calcium channels. Lovastatin and Pitavastatin also relaxed Norepinephrine (1 µM)-induced contractions giving an insight for involvement of dual mode of action of Pitavastatin and Lovastatin.

Abstract P1123: The Pharmacological Basis for Vasodilator Effect of Sisymbrium Irio Linn. Validates it's Folkloric Use in Hypertension

Traditionally seeds of Sisymbrium irio Linn has been used in different regions of Pakistan for the treatment of gastrointestinal, airways and vascular system ailments. To insight the pharmacological basis in vitro study was conducted in order to validate its folkloric uses in hypertension. 70% aqueous-methanolic extract of seeds from Sisymbrium irio (Si.MEs) was tested on isolated rabbit aorta, jejunum and trachea strip hanged in tissue bath having physiological solutions aerated with carbogen and their responses were measured and recorded via Power Lab. The Si.MEs exhibited the transient spasmogenic effect (0.01-1.0 mg/mL) on spontaneous jejunum contractions, followed by the spasmolytic effect. The addition of atropine resulted in blocking in spasmogenic effect while the spasmolytic effect was originated, suggesting the presence of an antimuscarinic effect. Likewise verapamil, Si.MEs (0.03-5 mg/mL) repressed the high concentration K + (80 mM)-induced contraction and also drifted the Ca 2+ concentration-response curves toward right (0.3-3.0 mg/mL), possibly signifying the Ca 2+ channel blockade. Furthermore, Si.MEs exhibited nonspecific relaxant effect on carbachol (1 μM)- and high concentration K + (80 mM)-induced tracheal contractions in a way comparable to dicyclomine, suggesting the coexistence of Ca 2+ antagonistic and/or antimuscarinic properties. Additionally, Si.MEs also relaxed the phenylephrine(1 μM)- and high concentration K + (80 mM)-induced aortic contraction (0.01-3 mg/mL), suggesting blockade of Ca 2+ channel. Moreover, oral administration of Si.MEs, as high as 6 g per kg, did not produce lethality among the treated groups of mice. Aqueous-methanolic extract of seeds from S. irio (Si.MEs) exhibited the bronchodilator and gut modulator (spasmogenic and spasmolytic) activities, probably through dual blockade of muscarinic receptors and Ca 2+ channels, whereas, vasodilator effect may be due to Ca 2+ channels blockade validates its use in hypertension.

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)

EFFECTS OF ROSUVASTATIN IN EXPERIMENTALLY-INDUCED CARDIAC ISCHEMIA AND ON AORTIC VASCULAR REACTIVITY.

Myocardial infarction (MI) continues to be a major public health problem in the world. The present study aimed to elucidate the protective effect of different doses of rosuvastatin and cilostazol, as well as their combination on isoprenaline-induced MI in rats as well as their effects on isolated aorta. Methods: I- Adult rats received different doses of rosuvastatin (1,2,5,10, & 20mg/kg), cilostazol (18mg/kg) and combination of rosuvastatin 1mg/kg and cilostazol 18mg/kg by oral gavage daily for 16 days, then rats were subcutaneously injected with two doses 24-h apart of 150mg/kg isoprenaline in the last two days. ECG pattern was monitored, myocardial injury markers (CK-MB and LDH) and inflammatory biomarker (CRP) were measured in serum. MDA, catalase and SOD were quantified in cardiac homogenates and heart tissue damage was examined by histopathology. II- Effects of rosuvastatin (0.2 µg/ml – 6.4 µg/ml), cilostazol (7.5 µg/ml – 480 µg/ml) and combination cilostazol (30 µg/ml) and rosuvastatin (0.2 µg/ml – 6.4 µg/ml) on NE-induced contraction in rabbit aortic strip were recorded. Each dose of either rosuvastatin or cilostazol were incubated for 10 min and 15min respectively then NE (0.5 µg/ml) was added and the contraction was recorded for one and half min. Results: I- Pretreatment with different doses of rosuvastatin (1,2,5 & 10), cilostazol 18mg/kg and the combination markedly ameliorated ISO-induced alterations in ECG, cardiac markers, inflammatory marker, oxidative markers and heart architecture. However, protection disappeared at higher dose of rosuvastatin 20mg/kg. II- Addition of either rosuvastatin (0.2-6.4 µg/ml), cilostazol (7.5-480µg/ml) or combination rosuvastatin (0.2-6.4 µg/ml) and cilostazol 30µg/ml produced a significant decrease in the height of NE-induced contraction in a dose dependent manner. Conclusion: I-This study provides evidence that rosuvastatin, cilostazol and their combination possess cardioprotective effect on isoprenaline-induced myocardial infarction. II- The drugs had vasorelaxant effect on aorta. Mechanism of drug action are discussed.

PHARMACOLOGICAL EFFECTS OF GEMFIBROZIL ON SOME CARDIOVASCULAR PREPARATIONS OF EXPERIMENTAL ANIMALS

Gemfibrozil (member of fibrates) is Peroxisome proliferator activated receptors (PPAR-α) agonist which improves lipid profiles particulary very low density lipoprotein and high density lipoprotein in patients with dyslipidemia.Objective: Studying the pharmacological effects of Gemfibrozil on some cardiovascular preparations of experimental animals. Materials and Methods: The experiments were conducted to study the effect of different doses of gemfibrozil on isolated perfused rabbit heart & coronary flow, isolated rabbit aortic spiral strip and mean arterial blood pressure of anaesthetized cats. Each experiment was done on six preparations. Results: In-vitro study: onisolated perfused rabbit heart, gemfibrozil (25-800µg/ml) produced a dose-dependent reduction on the amplitude of myocardial contractions. The inhibitory effect of gemfibrozil (100µg/ml) was not abolished after complete blockade of nicotinic and muscarinic receptors while it was completely abolished after inhibition of nitric oxide synthase by N-methyl L-arginine. On the other hand the stimulatory effects of calcium gluconate, isoprenaline, histamine and serotonin were not abolished after administration of gemfibrozil (100µg/ml). On coronary flow of isolated perfused rabbit heart, gemfibrozil (25-800μg/ml) produced also a dose-dependent reduction of coronary flow. On isolated spiral aortic strips of rabbit , gemfibrozil produced dose-dependent significant reduction on nor-epinpherine (NE) induced contraction. In-vivo study gemfibrozil produced a dose-dependent significant reduction in mean arterial blood pressure (MABP) of anaesthetized cats. Conclusion: Gemfibrozil produced a negative inotropic effect through nitric oxide release with a decrease in coronary flow. It also reduced NE- induced contractions of aortic spiral strips with reduction in mean arterial blood pressure. So it must me used cauciously in cases of heart failure, but it could be beneficial in hypertensive patient with atherosclerosis.

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

Effects of Peroxyl Radicals on Contractility of Rabbit Aorta and Guinea Pig Atria

High-fat meals may lead to hypotension, oxidative stress and increases of lipopolysaccharide (LPS). Contrasting results have been reported after treatment of isolated tissues with hydrogen peroxide and LPS, whereas the effects of peroxyl radicals, involved in the propagation reaction of lipoperoxidation, have not been investigated previously. In the present study, we aimed to evaluate the effects of peroxyl radicals on the contractile responses in isolated rabbit aorta and guinea pig atria. We treated isolated guinea pig atria, rabbit aorta strips and rings with 2,2'-Azobis (2- amidinopropane) dihydrochloride (AAPH). AAPH did not affect isoprenaline-induced contraction in guinea pig atria, whilst it dose-dependently reduced the contractile responses induced in rabbit aorta strips by cumulative doses of adrenaline (ADR) and induced an endothelium-independent relaxation of noradrenaline (NA)-contracted aorta rings. The effects of KCl-induced and BaCl2-induced contractions were small. Furthermore, alkalinization with NH4Cl of NA-contracted aorta rings significantly reduced the vasodilatatory activity of AAPH. The present study suggests that peroxyl radicals induce acute functional alterations on vascular contraction through intracellular pH regulation. This finding could be related to the documented after meal increase in oxidative burst and endotoxin and the related hypotension.

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.

Calcium channel blocking activity of a dihydropyrimidine derivative (BKVIII) on rabbit's aortic strip

Calcium channel blocking activity of a dihydropyrimidine derivative (BKVIII) on rabbit's aortic strip

Effects of methanolic extract of yohimbe bark (&amp;lt;i&amp;gt;Pausinystalia yohimbe&amp;lt;/i&amp;gt;) 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&nbsp;Acalypha torta&nbsp;Muell. (Euphorbiaceae) is used as folk remedy in Nigeria for the treatment of hypertension. Effects of extracts of&nbsp;A. torta&nbsp;leaf on the blood pressure of anaesthetized cats were studied to examine this claim. The ethanol extract produced a significant (p &lt; 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 &lt; 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. &nbsp; Key words:&nbsp;Acalypha torta,&nbsp;hypertension, antihypertensive, cat.

A Novel Bioassay for the Activity Determination of Therapeutic Human Brain Natriuretic Peptide (BNP)

BackgroundRecombinant human brain natriuretic peptide (rhBNP) is an important peptide-based therapeutic drug indicated for the treatment of acute heart failure. Accurate determination of the potency of therapeutic rhBNP is crucial for the safety and efficacy of the drug. The current bioassay involves use of rabbit aortic strips, with experiments being complicated and time-consuming and markedly variable in results. Animal-less methods with better precision and accuracy should be explored. We have therefore developed an alternative cell-based assay, which relies on the ability of BNP to induce cGMP production in HEK293 cells expressing BNP receptor guanylyl cyclase-A.Methodology/Principal FindingsAn alternative assay based on the measurement of BNP-induced cGMP production was developed. Specifically, the bioassay employs cells engineered to express BNP receptor guanylyl cyclase-A (GCA). Upon rhBNP stimulation, the levels of the second messager cGMP in these cells drastically increased and subsequently secreted into culture supernatants. The quantity of cGMP, which corresponds to the rhBNP activity, was determined using a competitive ELISA developed by us. Compared with the traditional assay, the novel cell-based assay demonstrated better reproducibility and precision.Conclusion/SignificanceThe optimized cell-based assay is much simpler, more rapid and precise compared with the traditional assay using animal tissues. To our knowledge, this is the first report on a novel and viable alternative assay for rhBNP potency analysis.

Some Pharmacodynamic Aspects of Cefepime.

Some pharmacodynamic effects of cefepime, a new injectable semisynthetic cephalosporin, were studied in laboratory animals and the following results were obtained. Cefepime maximally stimulated isolated guinea pig's ileum, rat's colon (80 μg/mL bath), and rabbit's duodenum (400 μg/mL bath). Contrarily, complete relaxation of isolated rat's fundic strip was produced by 80 μg/mL bath. Effects of cefepime on isolated rat's uterine muscle were different according to stage of sex cycle. Cefepime did not induce any effects on the resting tonus of isolated guinea pig's tracheal chain and rabbit's aortic strip. Concentrations of 200 and 400 μg/mL bath induced marked inhibition in the force of muscular twitches of the isolated frog's gastrocnemius muscle which was less potent than that induced by procaine hydrochloride 2%. Cefepime completely blocked the neuromuscular transmission of frog's rectus abdominis muscle (40 μg/mL bath) and rat's phrenic nerve hemidiaphragm preparation (200 μg/mL bath). This blockade was reversed by acetylcholine and neostigmine. Cefepime produced dose-dependent negative inotropic effect on isolated rabbit's heart and guinea pig's auricles. There were no changes in blood pressure and rate of respiration in anaesthetized dog after cefepime injection. These findings indicate that cefepime has a low potential to produce adverse reactions at therapeutic doses.

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.

Effects of convulsant barbiturates on vascular smooth muscle.

Abstract The convulsant barbiturate, 5-(2-cyclohexylidene-ethyl)-5-ethyl barbituric acid (cheb), produces contraction in rabbit aortic strips. Contractions effected by either cheb or tyramine were preceded by a lag time and both agents induced tachyphylaxis; however, cross-tachyphylaxis could not be demonstrated. Phenoxybenzamine and atropine failed to affect cheb-induced responses, whereas pentobarbitone selectively blocked and also reversed cheb contractions. Prevention, but not reversal, of tachyphylaxis was also accomplished with pentobarbitone. These results suggest that cheb does not act through the release of noradrenaline or acetylcholine; nor does it exert an effect on the receptors for these amines or on those for histamine. Pentobarbitone, however, appears to compete with cheb for common receptors. Another convulsant barbiturate, 5-ethyl-5-(dimethylbutyl)barbituric acid (dmbb), and its optical isomers were also examined. The racemic mixture had no contractile activity, but the (+)-isomer elicited cheb-like effects. The (-)-isomer, on the other hand, was like pentobarbitone in that it antagonized both cheb- and (+)-dmbb-induced contractions. These studies illustrate that convulsant barbiturates are able to stimulate vascular smooth muscle; therefore, it is suggested that the rabbit aortic strip may serve as an in vitro working model for study of the mechanism of action of these drugs in the central nervous system.

The Effect of α1-Acid Glycoprotein on the Pharmacological Activity of α1-Adrenergic Antagonists in Rabbit Aortic Strips

The pharmacological activity of three alpha 1-adrenergic antagonists, prazosin, tiodazosin and WB4101 has been studied in the presence and absence of 20 microM alpha 1-acid glycoprotein (AAG) in rabbit aortic strips, and measured as the ability to increase the EC50 value of the alpha 1-adrenergic agonist phenylephrine. For all three drugs, the presence of AAG diminished the pharmacological activity when compared with equivalent unbound concentrations in the absence of AAG. In the presence of AAG the EC50 value of phenylephrine at 5.69 nM unbound prazosin was on average 47% lower than in the absence of AAG (P less than 0.002), at 122 nM unbound tiodazosin, 39% lower (P less than 0.01), and at 25.6 nM unbound WB4101, 68% lower (P less than 0.002). Albumin showed no ability to modify the alpha 1-adrenergic blocking activity of prazosin (P greater than 0.7). The EC50 value for phenylephrine in the absence of antagonists was not affected by AAG. The effect of AAG on the antagonistic activity of prazosin was concentration-dependent with a maximum suppression of prazosin activity of 79% and with a half-maximum concentration of 1.1 microM AAG. AAG significantly decreased prazosin's ability to reduce alpha 1-adrenergic stimulation of calcium influx (P less than 0.05), while it had no effect on prazosin's ability to decrease alpha 1-adrenergic-stimulated formation of inositol phosphate. These results suggest that the effect of AAG on adrenoceptors appears to act selectively via alpha 1 a-receptors. Consistent with these observation was the observation that WB4101, a selective alpha 1a-antagonist was more affected by AAG than was prazosin or tiodazosin.