Pharmacological blockade of brain α1-adrenoceptors as measured by ex vivo [H]prazosin binding is correlated with behavioral immobility

The present studies examined the relationship between the blockade of central α₁-adrenoceptors, as measured by ex vivo binding of [³H]prazosin in the cerebral cortex and the inhibition of behavioral activation to a mildly novel environment (cage change). It was found that intraventricular (i.v.t.) terazosin, a saline-soluble α₁-adrenoceptor antagonist, dose dependently inhibited both ex vivo cortical binding and behavioral activation and that there was a highly significant positive correlation between the two with a slope near unity. Prazosin, a nonsaline soluble antagonist which had to be given intraperitoneally (i.p.), was much less potent at blocking both behavioral activity and cortical ex vivo binding, although it blocked ex vivo binding in the lung, indicating that it was effective peripherally but did not readily enter the brain. Despite this, however, the inhibition of cortical binding and behavioral activation that i.p. prazosin did produce were highly correlated with each other and had a slope near unity as with terazosin, whereas the more potent inhibition of lung binding was less well correlated with behavioral inhibition and had a slope significantly less than one. These results confirm our earlier studies, which have shown that α₁-adrenoceptor activity is essential for gross and fine motor behavior in the mouse and that prazosin, which is used extensively in behavioral research, has difficulty entering the mouse brain.     

α-Methyl-5-HT, a 5-HT2 receptor agonist, stimulates β2-adrenoceptors in guinea pig airway smooth muscle

Alpha-methyl-5-HT is widely used as a high-affinity 5-HT(2) receptors agonist, though some studies have postulated that this drug also activates other serotonergic receptors. In the present work, we found that a wide range of concentrations of alpha-methyl-5-HT induced biphasic responses (contraction followed by relaxation) in guinea pig tracheal rings. The relaxing phase caused by 32microM alpha-methyl-5-HT was blocked by 0.1microM propranolol. Furthermore, during an ongoing histamine-induced contraction, alpha-methyl-5-HT (0.1-100microM) produced a concentration-dependent relaxation starting at 10microM. This relaxation was fully abolished by 0.1microM propranolol or 1microM ICI 118,551 (a selective beta(2)-adrenoceptor antagonist). Additionally, in electrophysiological recordings, 32microM alpha-methyl-5-HT also enhanced the membrane K(+) currents of single tracheal myocytes, an effect reverted by propranolol and ICI 118,551, and mimicked by 0.1microM salbutamol. Thus, we concluded that alpha-methyl-5-HT activates beta(2)-adrenoceptors in guinea pig tracheal smooth muscle at concentrations >or=10microM. This effect must be taken into account when this drug is used in airway smooth muscle and in other tissues expressing beta(2)-adrenoceptors.     

Effects of the novel antidepressant S-adenosyl-methionine on α1- and β-adrenoceptors in rat brain

α₁- and β-adrenoceptors were studied ex vivo in the brains of rats receiving repeated daily treatment with the standard antidepressant imipramine or the atypical antidepressant S-adenosyl-L-methionine (SAM), which has minimal effects on monoamine reuptake or turnover. Consistent with past studies, a decrease in the density of β receptors at three weeks and an increase in the affinity of α₁ receptors for the agonist phenylephrine at one week of treatment was observed with imipramine. By comparison, an increase in the density of β receptors and a decrease in the affinity of α₁ receptors for phenylephrine was observed at one week of treatment with SAM. These changes were no longer apparent at three weeks of treatment. The results suggest that treatment with SAM does lead to changes in adrenergic neurotransmission, but that down regulation of β receptors or increased agonist affinity of α₁ receptors may not be necessary for the production of antidepressant effects.     

Isoform specificity of cardiac glycosides binding to human Na,K-ATPase α1β1, α2β1 and α3β1

Cardiac glycosides inhibit the Na⁺,K⁺-ATPase and are used for the treatment of symptomatic heart failure and atrial fibrillation. In human heart three isoforms of Na⁺,K⁺-ATPase are expressed: α₁β₁, α₂β₁ and α₃β₁. It is unknown, if clinically used cardiac glycosides differ in isoform specific affinities, and if the isoforms have specific subcellular localization in human cardiac myocytes. Human Na⁺,K⁺-ATPase isoforms α₁β₁, α₂β₁ and α₃β₁ were expressed in yeast which has no endogenous Na⁺,K⁺-ATPase. Isoform specific affinities of digoxin, digitoxin, β-acetyldigoxin, methyldigoxin and ouabain were assessed in [³H]-ouabain binding assays in the absence or presence of K⁺ (each n = 5). The subcellular localizations of the Na⁺,K⁺-ATPase isoforms were investigated in isolated human atrial cardiomyocytes by immunohistochemistry. In the absence of K⁺, methyldigoxin (α₁ > α₃ > α₂) and ouabain (α₁ = α₃ > α₂) showed distinct isoform specific affinities, while for digoxin, digitoxin and β-acetyldigoxin no differences were found. In the presence of K⁺, also digoxin (α₂ = α₃ > α₁) and β-acetyldigoxin (α₁ > α₃) had isoform specificities. A comparison between the cardiac glycosides demonstrated highly different affinity profiles for the isoforms. Immunohistochemistry showed that all three isoforms are located in the plasma membrane and in intracellular membranes, but only α₁β₁ and α₂β₁ are located in the T-tubuli. Cardiac glycosides show distinct isoform specific affinities and different affinity profiles to Na⁺,K⁺-ATPase isoforms which have different subcellular localizations in human cardiomyocytes. Thus, in contrast to current notion, different cardiac glycoside agents may significantly differ in their pharmacological profile which could be of hitherto unknown clinical relevance.     

The elusive α1D-adrenoceptor: molecular and cellular characteristics and integrative roles

α₁-Adrenoceptors seem to play key roles in cardiovascular, genitourinary, and central nervous system functions. This review will be focused on α_1D-adrenoceptors. These receptors have intrinsic activity, and many of the more commonly used antagonists are in reality inverse agonists. α_1D-Adrenoceptors are phosphorylated in the basal state, and the natural agonists, adrenaline and noradrenaline, increase their phosphorylation; similar effects are induced by direct activation of protein kinase C and through activation of nonadrenergic receptors. Interestingly, a large proportion of α_1D-adrenoceptors are located in intracellular vesicles. Such intracellular location can be changed to surface expression through the use of inverse agonists and coexpression of α_1B-adrenoceptors, which seem to act as pharmacological chaperons for proper plasma membrane insertion. The α_1D-adrenoceptor amino terminus seems to contain a signal that keeps the receptor intracellularly, but interaction with other proteins may also contribute. The precise relationship between the intrinsic activity, phosphorylation, and intracellular location is currently unknown. α_1D-Adrenoceptor activation induces contraction in a variety of vessels, and a role in the control of blood pressure has been suggested. Studies using young prehypertensive and adult spontaneously hypertensive rats as well as knockout mice suggest that vascular α_1D-adrenoceptors are involved in the genesis/maintenance of hypertension.     

Behavioral and receptor binding analysis of the α2-adrenergic agonist, 5-bromo-6 [2-imidazoline-2-YL amino] quinoxaline (UK-14304): evidence for cognitive enhancement at an α2-adrenoceptor subtype

The ability of the α₂-agonists clonidine, B-HT920 (6-allyl-2-amino-5,6,7,8-tetrohydro-4H-thi-azolo-[4,5-d]-azepine) and guanfacine to improve memory in aged monkeys has been related to their affinity to bind at a proposed rauwolscine-insensitive (Ri) subtype of α₂-adrenergic receptor, while their hypotensive and sedating effects have been related to affinity at a rauwolscine-sensitive site (Rs) (Arnsten et al., 1988). The present study examined the α₂-agonist UK-14304 (5-bromo-6 [2-imidazoline-2-yl amino] quinoxaline) for its binding characteristics in tissue from the brain of the rat and for its behavioral effects in aged monkeys. The drug UK-14304 was found to have slightly higher affinity for the Ri than the Rs site (K_i values of 138 and 245 nM, respectively), but was not as selective as the α₂-agonist guanfacine (K_i values of 23 and 340 nM, respectively). Consistent with this binding profile, very small doses of UK-14304 (0.00017–0.17 μg/kg) produced a reliable but modest improvement in memory in the aged monkeys (average improvement of 16.7% ± 2.6% following an optimal dose). No hypotensive or sedating side effects were observed at these small doses. However, hypotension and sedation emerged rapidly when the dose was raised above 1.7 μg/kg and at the largest doses tested (50.0–100.0 μg/kg), hypotension was severe (systolic pressure below 70 mm Hg) and the animals were too sedated to complete cognitive testing. The separation between doses that improved memory and those that produced hypotension and sedation was not as great for UK-14304 as it was for guanfacine, consistent with the greater selectivity of guanfacine for the Ri site. These results offer a fourth example whereby the ability of an α₂-agonist to improve cognitive function, without side effects, could be related to the relative affinities for the Ri and Rs sites.     

Effects of castration on α1-adrenoceptor subtypes in the rat aorta

The expression of α₁-adrenoceptor subtypes in several tissues is regulated by gonadal hormones. In this study, we investigated whether castration regulates the α₁-adrenoceptor subtypes mediating the contractions of the aorta from male rats to noradrenaline. Noradrenaline induced similar concentration-dependent contractions in the aorta from control and castrated rats. Treatment of the aorta from both control and castrated rats with the α_1B/α_1D-adrenoceptor alkylating agent chloroethylclonidine resulted in ≈1600-fold rightward shift in the concentration–response curves to noradrenaline. The pA₂ values found for WB 4101, benoxathian (α_1A-selective) and BMY 7378 (α_1D-selective) indicate that α_1D-adrenoceptors are involved in the contractions of the aorta from control and castrated rats to noradrenaline. However, there was a 15-fold difference between the pK_B estimated through the lowest effective concentrations of the α_1A-adrenoceptor selective antagonist 5-methyl-urapidil in the aorta from control and castrated rats. The pK_B estimated in aorta from control rats is consistent with the interaction with α_1D-adrenoceptors (7.58±0.06), while that calculated in organs from control rats is consistent with α_1A-adrenoceptors (8.76±0.09). These results suggest that castration induces plasticity in the α₁-adrenoceptor subtypes involved in the contractions of the aorta to noradrenaline.     

Behavioral effects of the α2-adrenoceptor antagonist, atipamezole, after focal cerebral ischemia in rats

The present study characterized the behavioral effects of the selective α₂-adrenoceptor antagonist, atipamezole, in a rat model of focal cerebral ischemia. Atipamezole (1 mg/kg, s.c.) or desipramine (5 mg/kg, i.p.), a noradrenaline reuptake blocker, was administered either as a single injection 2 days after ischemia induction or for 10 days thereafter (subacute administration). A subacute atipamezole treatment given 30 min before behavioral assessment improved performance in the limb-placing test (days 5, 7, 9, and 11) and in the foot-slip test (days 3 and 7), but not in the beam-walking test. There was no difference between experimental groups in behavioral performance following a single administration of atipamezole or following single or subacute administration of desipramine. The drug treatments did not attenuate the impairment of spatial cognitive performance of ischemic rats in the Morris water-maze test. These results suggest that repeated use-dependent release of noradrenaline by atipamezole facilitates the sensorimotor recovery following focal cerebral ischemia in rats.     

The rostroventromedial medulla is not involved in α2-adrenoceptor-mediated antinociception in the rat

The aim of the current study was to investigate the role of the rostroventromedial medulla (RVM) in α₂-adrenoceptor-mediated antinociception. Medetomidine or clonidine, selective α₂-adrenoceptor agonists were microinjected into the RVM in unanesthetized rats with a chronic guide cannula. The antinociceptive effects were evaluated using the tail-flick and hot-plate tests. For comparison, medetomidine was microinjected into the cerebellum or the periaqueductal gray (PAG). To study the role of medullospinal pathways, the tail-flick latencies were also measured in spinalized rats. The reversal of the antinociception induced by intracerebral microinjections of medetomidine was attempted by s.c. atipamezole, a selective α₂-adrenoceptor antagonist. The reversal of the antinociception induced by systemic administration of medetomidine was attempted by microinjections of 5% lidocaine or atipamezole into the RVM. When administered into the RVM, medetomidine produced a dose-dependent (1–30 μg) antinociception in the tail-flick and hot-plate tests, which antinociceptive effect was completely reversed by atipamezole (1 mg/kg, s.c.). Also clonidine produced a dose-dependent (3–30 μg) antinociception following microinjection into the RVM. Microinjections of medetomidine into the cerebellum or the PAG produced an identical dose-response curve in the tail-flick test as that obtained following microinjection into the RVM. In spinalized rats the antinociceptive effect (tail-flick test) induced by medetomidine microinjected into the RVM was not less effective than in intact rats. Lidocaine (5%) or atipamezole (5 μg) microinjected into the RVM did not attenuate the antinociception induced by systemically administered medetomidine (100 μg/kg, s.c.). The adapting skin temperature of the tail was increased in a nonmonotonic fashion following medetomidine. The results indicate that the RVM is not a site which is critical for the α₂-adrenergic antinociception. The antinociception following intracerebral microinjections of medetomidine into the RVM, PAG or the cerebellum in the current study can be explained by a spread of the α₂-adrenoceptor agonist into the spinal level to activate directly spinal α₂-adrenoceptors. Also, the antinociception following systemic administration of medetomidine can be explained by spinal α₂-adrenergic mechanisms. The medetomidine-induced increase of the adapting skin temperature may have attenuated the medetomidine-induced increases in the response latencies to noxious heat.     

Bolus Intravenous Injection of Phosphorothioate Oligonucleotides Causes Hypotension by Acting as α1-Adrenergic Receptor Antagonists

Bolus intravenous injections of phosphorothioate oligonucleotides (PS-ODN) into primates cause profound hypotension, which has been attributed to complement activation, the biochemical pathway leading to acute inflammatory response. Because the hypotension was not accompanied by peripheral or pulmonary edema and epinephrine was not effective, but administration of 200 ml Ringer's lactate was effective, we examined the possibility that the 15-base PS-ODN interferes with sympathetic tone. We administered doses ranging from 3.3 to 10 mg/kg of a 15-base PS-ODN as a 30–60 s iv bolus into the right atrium of conscious Macaca mulatta. Blood pressure fell to 27 mm Hg following a 5.0 mg/kg dose, but no hypotension was observed after a 3.3 mg/kg dose; 10 mg/kg was lethal. Adrenergic receptor binding was evaluated in radioligand binding assays using rat cerebral cortex membranes with radiolabeled prazosin. The 15-base PS-ODN competes with prazosin for the α₁-adrenergic receptor with an IC50 of 14 μM, which favors binding over serum albumin (K_d = 37 to 48 μM). Admixing serum albumin with 5.0 mg/kg 15-base PS-ODN prior to injection prevented hypotension, suggesting that unbound PS-ODN interferes with sympathetic tone before binding to plasma proteins. Interactions of the 15-base PS-ODN with the α₁-adrenergic receptor in vivo were confirmed by a decreased response to phenylephrine. Reducing the length from 15 to 9 or 5 bases abolished α₁-adrenergic receptor binding in vitro and bolus infusion of 5.0 mg/kg of 9-base PS-ODN no longer produced hypotension. In conclusion, the 15-base PS-ODN shows cooperative binding to the α₁-adrenergic receptor, which produces cardiovascular effects that are oligomer length, dose, and formulation dependent.     

β2-Adrenoceptor antagonism in anxiety

The relative role of beta 1- and beta 2-adrenoceptor antagonism in the management of anxiety symptoms is not clear. We studied the effect of ICI 118,551, a selective beta 2-antagonist, in 51 patients presenting with acute anxiety symptoms and fulfilling DSM-III criteria for anxiety disorder. All patients received placebo during the first week of treatment followed by thrice daily diazepam (2 mg) or ICI 118,551 (50 mg) or placebo for 4 weeks with double-blind, random allocation. Hamilton anxiety scale scores improved on all treatments but there was no significant difference between treatments. Beta 2-adrenoceptor antagonism does not appear to be effective in acute anxiety neurosis. Some earlier literature suggests that beta 1-antagonism may be more important.     

Conformational investigation of α, β-dehydropeptides

The crystal structure of Ac-Pro-ΔVal-NHCH₃ was examined to determine the influence of the α,β-dehydrovaline residue on the nature of peptide conformation. The peptide crystallizes from methanol-diethyl ether solution at 4° in needle-shaped form in orthorhombic space group P2₁2₁2₁ with a= 11.384(2) Å, b = 13.277(2) Å, c = 9.942(1) Å. V = 1502.7(4) ų Z = 4, D_m= 1.17 g cm^?3 and D_c=1.18 g cm^?3 The structure was solved by direct methods using SHELXS-86 and refined to an R value of 0.057 for 1922 observed reflections. The peptide is found to adopt a β-bend between the type I and the type III conformation with φ₁=?68.3(4)°, ψ₁=? 20.1(4)°, φ₂=?73.5(4)°= and Ψ₂=?14.1(4)°=. An intramolecular hydrogen bond between the carbonyl oxygen of ith residue and the NH of (i+ 3)th residue stabilizes the β-bend. An additional intermolecular N.,.O hydrogen bond joins molecules into infinite chains. In the literature described crystal structures of peptides having a single α,β-dehydroamino acid residue in the (i+ 2) position and forming a β-bend reveal a type II conformation.     

α1-Acid glycoprotein column in the high-performance liquid chromatographic analysis of some groups of chiral drugs

The usefulness of the α₁-acid glycoprotein (Chiral—AGP) column in the analysis of chiral drugs and related materials is illustrated in three different fields. Excellent separations of the enantiomers of pharmacologically active α-ethyl benzhydrols such as 3-trifluoromethyl-α-ethyl benzhydrol (flumecinol) and 11 other derivatives are described. The enantiomers of N-protected amino-acid esters or amides can also be separated. The effect of the derivatization of the free α-amino group on the resolution of the enantiomers is exemplified by the formylation of alanine benzyl ester. As an example of the use of the method for the estimation of the optical purity of chiral drugs, the determination of the “cis(−)” impurity in “cis(+)” diltiazem is presented.     

Identification of α1-adrenoceptor subtypes in rat renal proximal tubules

Although the existence of α₁-adrenoceptor subtypes has been suggested in the kidney, their characterization in the proximal tubules has not been reported. This study was undertaken to characterize the α₁-adrenoceptor subtypes in the renal proximal tubules. [³H]Prazosin bound to proximal tubules with a K_D of 106 ± 17 pM and a B_max of 152 ± 9 fmol/mg protein. Pretreatment of the tubules with chloroethylclonidine, 100 μM, reduced the B_max of [³H]prazosin binding by about 50%, indicating the presence of the α_1B-adrenoceptor subtype. Competition studies performed with the α-adrenoceptor antagonists, WB 4101, (+)-niguldipine, 5-methylurapidil and phentolamine were shallow and could be distinguished into a high affinity (α_1A) and a low affinity site (α_1B) with an approximately equal distribution of both receptors subtypes. These observations clearly demonstrate the existence of α_1A- and α_1B-adrenoceptor subtypes in the renal proximal tubules.     

A threonine residue in the M2 region of the β1 subunit is needed for expression of functional α1β1 GABAA receptors

Although there is a high degree of homology in the M2 transmembrane segments of α₁ and β₁ subunits, subunit-specific effects were observed in α₁β₁ GABA_A receptors expressed in Spodoptera frugipedra (Sf9) cells when the conserved 13′ threonine residue in the M2 transmembrane region was mutated to alanine. When threonine 263 (13′) was mutated to alanine in the β₁ subunit, high-affinity muscimol binding and the response to GABA were abolished. This did not occur when the threonine 263 (13′) was mutated to alanine in the α₁ subunit, but the rate of desensitisation increased and the effect of bicuculline, a competitive inhibitor, was reduced. The results show differential effects of subunits on receptor function and support a role for M2 in desensitisation.     

Bone marrow derived stromal cells modified by adenovirus-mediated HIF-1α double mutant protect cardiac myocytes against CoCl2-induced apoptosis

Bone marrow derived stromal cells (MSCs) can prevent the apoptosis of ischemic cardiomyocytes (CMCs). This anti-apoptosis activity may be related to an activation of the HIF-1α signal pathway in MSCs. Therefore, we investigated protective effects of an adenovirus (Ad)-mediated active form of HIF-1α (HIF-1α-Ala564-Ala803) modified MSCs on CMCs against CoCl₂-induced apoptosis. At normoxia, pAd-HIF1α-Ala564-Ala803 exhibited a stable HIF-1α protein expression in MSCs. Compared with the single CMC culture, the TGF-β1 level and the Bcl-2 expression were significantly increased, concomitant with a reduced expression of caspase-3, the LDH release and TUNEL-positive CMCs in CMC and MSC, β-galactosidase (LacZ)-MSC or HIF-1α-Ala564-Ala803-MSC coculture exposed to CoCl₂. Furthermore, these effects were more prominent in CMC and HIF-1α-Ala564-Ala803-MSC coculture than in CMC and MSC or LacZ-MSC coculture exposed to CoCl₂. Pre-transfection of TGF-β1-small interfering RNA (siRNA) effectively inhibited the TGF-β1 level, resulting in a dramatic reduction in the Bcl-2 expression as well as an increased level of apoptosis in CMC and HIF-1α-Ala564-Ala803-MSC coculture exposure to CoCl₂, whereas pre-transfection of green fluorescent protein (GFP)-siRNA had no such effects. These data suggest that HIF1α-Ala564-Ala803 modified MSCs have better protective effects of CMCs against the CoCl₂-induced apoptosis and these protective effects are at least partly TGF-β1-mediated.     

Conformational investigation of αβ-dehydropeptides

Solution conformations of three series of model peptides, homochiral Ac-Pro-L-Xaa-NHCH₃ and heterochiral Ac-Pro-D-Xaa-NHcH₃ (Xaa = Val, Phe, Leu, Abu. Ah) as well as αβ-unsaturated Ac-Pro-ΔXaa-NHCH₃ [Δ Xaa =ΔVal, (Z)-ΔPhe, (Z)-ΔLeu, (Z)-ΔAbu] were investigated in CDCl₃ and CH₂Cl₂ by ¹H-, ¹³C-NMR, and FTIR spectroscopy. NH stretching absorption spectra, solvent shifts Δδ for NH (Xaa) and NHCH₃ on going from CDCl₃ to (CD₃)₂SO, diagnostic interresidue proton NOEs, and trans-cis isomer ratios were examined. These studies performed showed the essential difference in conformational propensities between homochiral peptides (L-Xaa) on the one hand and heterochiral (D-Xaa) and αβ-dehydropeptides (ΔXaa) on the other. Former compounds are conformationally flexible with an inverse γ-bend, a β-turn, and open forms in an equilibrium depending on the nature of the Xaa side chain. Conformational preferences of heterochiral and αβ-dehydropeptides are very similar, with the type-II β-turn as the dominating structure. There is no apparent correlation between conformational properties and the nature of the Xaa side chain within the two groups. The β-turn formation propensity seems to be somewhat greater in αβ-unsaturated than in heterochiral peptides, but an estimation of β-folded conformers is risky.     

Isolation of subunits, α, β and γ of the complex taipoxin from the venom of Australian taipan snake (Oxyuranus s. scutellatus): characterization of β taipoxin as a potent mitogen

The venom of Australian taipan snake (Oxyuranus s. scutellatus) is extremely potent due to the presence of taipoxin. The intact complex molecule of taipoxin having molecular weight 45.6 kDa is composed of α, β and γ subunits. This report describes the high pressure liquid chromatography (HPLC) separation of α, β (β-1 and β-2) and γ subunits from taipan crude venom. The fractions containing the taipoxin subunits were further purified to obtain homogeneous proteins. The toxicity in mice showed the α subunit as most toxic, the γ subunit as moderately toxic and the β-1 and β-2 subunits were nontoxic. The proteins β-1 and β-2 were found to be mitogenic having neurotrophic activity on PC12 cells in culture similar to nerve growth factor. Immunologically, α, β-1, β-2 and γ subunits were found to be different, showing cross reactivity, and β-1 and β-2 were found to be identical for biological properties and molecular weight. Further characterization of unexpected mitogenic activity of β subunits is underway.     

Conformational investigation of α,β-dehydropeptides

Conformations of three series of model peptides: homochiral Ac-Pro-L-Xaa-NHCH₃ and heterochiral Ac-Pro-D-Xaa-NHCH₃ (Xaa=Phe, Val, Leu. Abu. Ala) as ivell as α,β-dehydro Ac-Pro-ΔXaa-NHCH_s [ΔXaa = (Z)-ΔPhe, ΔVal. (Z)-ΔLeu, (Z)-ΔAbu] were investigated by CD spectroscopy in 2 % dichloromethanecyclohexane, trifluoroethanol. water. and occasionally in other solvents. The spectra of homochiral peptides show a significant solvent dependence. Folded structures are present in 2% dichloromethane-cyclohexane and unordered ones occur in water. The folded conformers are of the inverse γ-turn type for all the peptides but Ac-Pro-L-Phe-NHCH₃ for which the type-I β-turn is preferred. The changes in the spectra of the heterochiral peptides are limited. The compounds adopt the typc-II β–turn in 2% dichloromethanecyclohexane, represented by class B spectra, and retain this conformation in water as well as in fluorinated alcohols but not always to a full extent. The CD spectra of the unsaturated peptides in 2%, dichloromethanecyclohexane, although they cannot be assigned to any common spectral class, must be attributed to the βII-turn conformation as determined for these coinpounds by NMR and IR spectroscopy. The CD spectra of dehydropeptides exhibit a considerable solvent dependence and suggest unordered structures in water.     

Isoeugenodilol: A vasorelaxant α/β‐adrenoceptor blocker with antioxidant activity

Isoeugenodilol, derived from isoeugenol, was investigated under in vivo and in vitro conditions. Isoeugenodilol (0.1, 0.5, 1.0, and 3.0 mg kg^–1, i.v.) produced dose‐dependent hypotensive and bradycardia responses in pentobarbital‐anesthetized Wistar rats. Isoeugenodilol (0.5 mg kg^–1, i.v.) also markedly inhibited both the tachycardia effects induced by (‐) isoproterenol and arterial pressor responses induced by phenylephrine. A single oral administration of isoeugenodilol at doses of 10, 30, and 100 mg kg^–1 dose‐dependently reduced blood pressure, with a decrease in heart rate in conscious spontaneously hypertensive rats (SHRs). In the isolated Wistar rat right atria, left atria, and guinea pig tracheal strips, isoeugenodilol competitively antagonized the (‐) isoproterenol‐induced positive chronotropic effects, inotropic effects, and tracheal relaxation effects in a concentration‐dependent manner. The parallel shift to the right of the concentration–response curve of (‐) isoproterenol suggested that isoeugenodilol was a β₁/β₂‐adrenoceptor competitive antagonist. The apparent pA₂ values were 7.33 ± 0.12 in the right atria, 7.80 ± 0.09 in the left atria, and 7.26 ± 0.11 in the trachea, indicating that isoeugenodilol was a nonselective β‐adrenoceptor blocker. In thoracic aorta experiments, isoeugenodilol also produced a competitive antagonism of norepinephrine‐induced contraction with a pA₂ value of 7.47 ± 0.45. In isolated atria of reserpinized rats, cumulative additions of isoeugenodilol and propranolol produced significantly cardiodepressant responses at high concentrations (10^–5 M) and were without intrinsic sympathomimetic activity (ISA). In isolated rat thoracic aorta, isoeugenodilol more potently relaxed the contractions induced by norepinephrine (3 × 10^–6 M) than those by high K⁺ (75 mM). The vasorelaxant effects of isoeugenodilol on norepinephrine‐induced contractions were attenuated by pretreatment with tetraethylammonium (TEA) and glibenclamide, implying the involvement of K⁺ channel opening. In addition, isoeugenodilol inhibited norepinephrine‐induced biphasic contraction; it affected the fast phase significantly more than the slow phase. Furthermore, the binding characteristics of isoeugenodilol and various β‐adrenoceptor antagonists were evaluated in [³H]CGP‐12177 binding to rat ventricle and lung tissues and [³H]prazosin binding to brain membranes. The ranking order of inhibition for [³H]CGP‐12177 binding on β‐adrenoceptor was propranolol > labetalol > isoeugenodilol, and that for [³H]prazosin binding to α‐adrenoceptors was isoeugenodilol > labetalol. Furthermore, isoeugenodilol inhibited lipid peroxidation induced by Fe²⁺ and ascorbic acid with IC₅₀ of 0.74 ± 0.03 mM, indicating that it possesses the antioxidant activity inherent in isoeugenol. In conclusion, isoeugenodilol was found to be a new generation α/β‐adrenoceptor antagonist with vasorelaxant activity by inhibiting Ca²⁺ channel, receptor‐mediated Ca²⁺ mobilization and by K⁺ channel opening, and to have additional potentially antioxidant effects. Drug Dev. Res. 51:29–42, 2000. © 2000 Wiley‐Liss, Inc.