Probing the potential glycoprotein binding site of sindbis virus capsid protein with dioxane and model building

Alphavirus budding from the plasma membrane is initiated by the specific interaction of the nucleocapsid with the cytoplasmic domain of the glycoprotein E2. It was proposed (Lee et al., Structure 4:531-541, 1996) that binding of the capsid protein residues 108 to 110 (the "N-terminal arm" residues) to a hydrophobic pocket on the surface of the neighboring capsid protein in the crystal structure mimics the binding of the E2 C-terminal residues into this pocket. In addition, structural comparisons of wild-type and mutant Sindbis virus capsid protein (SCP) and Semliki Forest virus capsid protein suggested that budding is associated with a switch between two conformations of the hydrophobic pocket. To test the proposed mechanism, SCP(114-264), which is missing the N-terminal arm, was crystallized to examine the pocket conformation when the pocket is empty. However, the pocket was occupied by dioxane molecules from the crystallization solution. The pocket conformation was the same as that when it was occupied by the N-terminal arm, demonstrating that the pocket favors binding ligands of appropriate size and shape.

Organic solvent binding to crystalline subtilisin1 in mostly aqueous media and in the neat solvents

The X-ray crystal structures of the protease subtilisin Carlsberg in 40% acetonitrile and in 20% dioxane have been determined to at least 2.3 A resolution, and their solvent binding patterns have been compared to those observed in the neat organic solvents. The structures of the protein in the two aqueous-organic mixtures are essentially the same as in pure water, acetonitrile, and dioxane. Interestingly, the enzyme-bound organic solvent molecules tend to congregate in the active site. Three of the five bound acetonitrile molecules observed in the structure of subtilisin in 40% acetonitrile are situated in the enzyme active site, as is the single enzyme-bound dioxane molecule observed in 20% dioxane (whose location is distinct from that of any bound acetonitrile molecule). Furthermore, the organic solvent molecules detected in the enzyme active site in the aqueous-organic mixtures are in the same locations as in the structures in the corresponding neat organic solvents.

Capillary electrophoretic and high-performance liquid chromatographic studies of the enantioselective separation of alpha1-adrenoreceptor antagonists

Capillary electrophoresis (CE) and chiral stationary phase (CSP) HPLC methods were investigated for the determination of enantiomeric purity of alpha1-adrenoreceptor antagonists related to WB 4101. In the CE study, the enantioseparation of the analytes was performed by studying the effect of different types of cyclodextrin in the buffer, namely heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DMCD), hydroxypropyl-beta-cyclodextrin (HPCD) and beta-cyclodextrin (beta-CD). HPCD was found to be the most effective chiral selector in the enantioseparation of all the compounds, with high resolution values. A HPLC method, using immobilised serum protein columns, human serum albumin (HSA) and alpha1-acid glycoprotein (AGP), was also investigated. Two benzodioxane racemates were well resolved on a mixed tpe (50% HSA and 50% AGP) column, with enantioselective binding on AGP column.

Lasting increase in serotonin 5-HT1A but not 5-HT4 receptor subtypes in the kindled rat dentate gyrus: dissociation from local presynaptic effects

We examined the effect of kindling on serotonergic neurotransmission in the hippocampus by measuring serotonin (5-HT) release and uptake in hippocampal synaptosomes and 5-HT1A and 5-HT4 receptor subtypes during and at different times after electrical kindling of the dentate gyrus. Using quantitative receptor autoradiography, we found that binding of 8-[3H]hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) to 5-HT1A receptors was selectively increased by 20% on average (p < 0.05) in the dentate gyrus of the stimulated and contralateral hippocampus 2 days after stage 2 (stereotypes and occasional retraction of a forelimb) and by 100% on average (p < 0.05) 1 week after stage 5 (tonic-clonic seizures) compared with sham-stimulated rats. A 20% increase (p < 0.05) was observed 1 month after the last generalized seizure. No changes were found after a single afterdischarge. 5-HT4 receptors, which colocalize with 5-HT1A receptors on hippocampal neurons, were not modified in kindled tissue. [3H]5-HT uptake and its release as well as the 5-HT1B autoreceptor function did not differ from shams in hippocampal synaptosomes at stages 2 and 5. Systemic administration of 100 and 1,000 microg kg(-1) 8-OH-DPAT or 1,000 microg kg(-1) WAY-100,635, 30 min before each electrical stimulation, did not significantly alter kindling progression or the occurrence of stage 5 seizures in fully kindled rats. The changes in 5-HT1A receptor density in the dentate gyrus are part of the plastic modifications occurring during kindling and may contribute to modulating tissue hyperexcitability.

Use of the operational model of agonism and [3H]prazosin binding to assess altered responsiveness of alpha1-adrenoceptors in the vas deferens of spontaneously hypertensive rat

Changes in functional responsiveness to alpha1-adrenoceptor activation with noradrenaline and in [3H]prazosin binding in the epididymal portion of vas deferens from normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) were investigated. The operational model fitting and the nested hyperbolic method were used to analyze the effects of irreversible receptor alkylation by phenoxybenzamine (0.1 microM) on the alpha1-adrenoceptor mediated contractile responses to noradrenaline of vasa deferentia from SHR and WKY rats. Saturation isotherms for [3H]prazosin revealed a significant increase (P < 0.05) in the Bmax in SHR vas deferens (145 +/- 19 fmol/mg protein) compared with vas deferens from normotensive controls (75 +/- 12 fmol/mg protein) without changes in the K(D). No differences in the proportion of high and low affinity binding sites for WB-4101 and 5-methylurapidil were observed. The maximum contractile response, alpha, (P < 0.001) and the pEC50 (P < 0.05) values for noradrenaline were greater for SHR than for WKY rat tissues. The apparent affinity (pK(A)) determined by the nested hyperbolic method and by the operational model of agonism was found to be similar in the two strains. In agreement with relative pEC50, the efficacy (tau) value for SHR was greater than for WKY rats. However, the difference in the tau estimates did not reach statistical significance. In summary, in the epididymal portion of SHR vas deferens, the increased maximum contractile response to noradrenaline is due to an increase of Em. Taken together, the tau values and the results from binding experiments lead to the assumption that the transducer constant K(E) must be greater in SHR than in WKY rats, suggesting a deterioration in the transduction of the stimulus provided by the agonist in hypertensive animals.

Multiple [3H]-nemonapride binding sites in calf brain

[3H]-Nemonapride has been the ligand of choice to label D4 dopamine receptors. Its specificity was questioned when it was discovered that sigma (sigma) sites were also labeled by [3H]-nemonapride. To further characterize the binding of [3H]-nemonapride, three areas of calf brain (striatum, frontal cortex and cerebellum) were examined. In all three areas, [3H]-nemonapride labeled multiple sites. Dopaminergic and sigma sites were the most prominent. The sigma binding profile was sigma-1 like with a Ki binding profile as follows (in order of decreasing potency): haloperidol, PPAP, pentazocine, DTG, U-50488, R(+)-3-PPP. Experiments using sulpiride and pentazocine to block striatal dopaminergic and sigma sites, respectively, revealed additional, not previously characterized binding sites for [3H]-nemonapride. One component which was present in striatum but not in frontal cortex or cerebellum, had affinity for some neuroleptics and WB-4101, but not for typical serotonergic agents. Thus, [3H]-nemonapride has no selectivity for dopamine receptors unless stringent experimental conditions are met.

Heterogeneity and complexity of alpha 1-adrenoceptors in the ovine uterine artery and umbilical vein

To understand the subtypes of alpha 1-adrenoceptors in the regulation of uterine and umbilical vascular function, the subtypes of alpha 1-adrenoceptors in the ovine uterine artery and umbilical vein were investigated pharmacologically. The use of the irreversible alpha 1B-adrenoceptor antagonist, chloroethylclonidine, revealed the heterogeneity of alpha 1-adrenoceptors in these two tissues. Chloroethylclonidine showed different patterns of action. While it depressed the maximal contraction to norepinephrine in the umbilical vein, it did not decrease the maximal response in the uterine artery. The alpha 1A-adrenoceptor antagonist, 2-(2,6-dimethoxyphenoxyethyl) aminomethyl-1,4-benzodioxane (WB 4101), competitively inhibited norepinephrine-induced contractile responses in the ovine uterine artery and umbilical vein with intermediate pA2 values of 8.30 and 8.45, respectively. Combined use of chloroethylclonidine with either prazosin or WB 4101 produced an additive inhibition of norepinephrine-induced contractions in both tissues, suggesting an interaction of WB 4101 with a chloroethylclonidine-insensitive alpha 1-adrenoceptor. However, the chloroethylclonidine-insensitive alpha 1-adrenoceptor differed on the affinity for prazosin in the uterine artery and umbilical vein. The Ca2+ channel blocker, nifedipine, inhibited contractions to both the chloroethylclonidine-sensitive alpha 1-adrenoceptor (alpha 1B subtype) and the chloroethylclonidine-insensitive alpha 1-adrenoceptor in both tissues. Prazosin, WB 4101 and chloroethylclonidine all inhibited norepinephrine-induced contraction due to the release of calcium from intracellular stores in both tissues. Our results suggest that there is heterogeneity and complexity of alpha 1-adrenoceptors in the ovine uterine artery and umbilical vein. Both the chloroethylclonidine-sensitive and insensitive alpha 1-adrenoceptor may use both intracellular and extracellular Ca2+ sources.

Hydrophobic properties of NAD glycohydrolase from neurospora crassa conidia and interaction with dioxane

NAD glycohydrolase (NADase, EC 3.2.2.5) from Neurospora crassa conidia shows marked hydrophobic properties which are related to the self inhibition of the enzyme. Both aliphatic amines and carboxylic acids are able to inhibit noncompetitively the catalytic activity of the enzyme and the inhibition depends on the non-polar moiety of the substances. Also dioxane is an inhibitor of NAD glycohydrolase even though it apparently increases the specific activity of the enzyme. This effect can be explained by the fact that NADase is present as a dimer when the enzyme is concentrated or at high temperature, and dioxane binds the enzyme breaking the hydrophobic bonds in the dimeric enzyme and yielding the most active monomeric form which is only slightly inhibited by the organic solvent.

Two district alpha(1)-adrenoceptor subtypes in the human prostate: assessment by radioligand binding assay using 3H-prazosin

1. We showed that there were two distinct alpha(1)-adrenoceptor subtypes (alpha(1H) and alpha(IL)) in the human prostate which show different affinities for 3H-prazosin. 2. WB4101, tamsulosin, 5-methylurapizil, phentolamin, and terazosin, but not nifedipine, had significantly higher pKi values for the alpha(1H)-subtype than for the alpha(IL)-subtypes. 3. There was good correlation (r = 0.92, P < 0.05) between the pKi values obtained for the alpha(1H)-receptors in membrane fractions and the cloned human alpha(1c)-adrenoceptor subtype.

Identification of critical extracellular loop residues involved in alpha 1-adrenergic receptor subtype-selective antagonist binding

alpha 1-Adrenergic receptor (AR) subtypes mediate many effects of the sympathetic nervous system. Although structurally similar, the three cloned subtypes (alpha 1a-AR, alpha 1b-AR, and alpha 1d-AR) bind a series of ligands with different relative potencies. This is particularly true for the alpha 1a-AR, which recognizes a number of ligands with 10-100-fold higher affinity than the alpha 1b or alpha 1d subtypes. Because ligands are hypothesized to bind to receptor residues that are located in the transmembrane (TM) spanning domains, subtype differences in ligand recognition are likely the result of differences in the binding properties of nonconserved TM residues. We previously reported on the identification of two TM residues in the alpha 1b-AR that converted the agonist binding profile entirely to that of the alpha 1a-AR when mutated to corresponding alpha 1a-AR residues. We now report on the determinants of antagonist selectivity between these two alpha 1-AR subtypes. Construction of a chimera in which the entire fifth TM and a portion of the putative second extracellular loop of the hamster alpha 1b-AR was replaced with the corresponding region of the rat alpha 1a-AR revealed that the chimera accounted for all of the higher binding affinity (8-29-fold) seen in the alpha 1a-AR for two antagonists, phentolamine and WB4101. Using site-directed mutagenesis, we further analyzed individual point mutations making up this chimera. We found that three adjacent residues, which were located on the extracellular loop of the fifth TM, are fully responsible for this higher antagonist binding affinity in the alpha 1a-AR. These three point mutations (G196Q, V1971, T198N) in the alpha 1b-AR were additive and sufficient in their effects on changing antagonist-binding profiles to that of the alpha 1a-AR. Reversal of these three residues in the alpha 1a-AR to their corresponding residues in the alpha 1b-AR completely reversed the antagonist affinity to wild-type alpha 1b-AR values. To aid in molecular modeling, the use of organic chemicals that mimic key structures of the antagonists were used in competitive ligand-binding studies with the mutated receptors. These results indicated the orientation of both phentolamine and WB4101 in the alpha 1-AR binding pocket. Together, the data indicate that alpha 1-antagonists may bind near the surface of the receptor, much like the peptide hormone receptors, and not deep within the TM regions, where the ligand-binding pocket was first proposed and identified for alpha 1 agonists.

The effects of SB 216469, an antagonist which discriminates between the alpha 1A-adrenoceptor and the human prostatic alpha 1-adrenoceptor

1. The affinity of the alpha 1-adrenoceptor antagonist SB 216469 (also known as REC 15/2739) has been determined at native and cloned alpha 1-adrenoceptor subtypes by radioligand binding and at functional alpha 1-adrenoceptor subtypes in isolated tissues. 2. In radioligand binding studies with [3H]-prazosin, SB 216469 had a high affinity at the alpha 1A-adrenoceptors of the rat cerebral cortex and kidney (9.5-9.8) but a lower affinity at the alpha 1B-adrenoceptors of the rat spleen and liver (7.7-8.2). 3. At cloned rat alpha 1-adrenoceptor subtypes transiently expressed in COS-1 cells and also at cloned human alpha 1-adrenoceptor subtypes stably transfected in Rat-1 cells, SB 216469 exhibited a high affinity at the alpha 1a-adrenoceptors (9.6-10.4) with a significantly lower affinity at the alpha 1b-adrenoceptor (8.0-8.4) and an intermediate affinity at the alpha 1d-adrenoceptor (8.7-9.2). 4. At functional alpha 1-adrenoceptors, SB 216469 had a similar pharmacological profile, with a high affinity at the alpha 1A-adrenoceptors of the rat vas deferens and anococcygeus muscle (pA2 = 9.5-10.0), a low affinity at the alpha 1B-adrenoceptors of the rat spleen (6.7) and guinea-pig aorta (8.0), and an intermediate affinity at the alpha 1D-adrenoceptors of the rat aorta (8.8). 5. Several recent studies have concluded that the alpha 1-adrenoceptor present in the human prostate has the pharmacological characteristics of the alpha 1A-adrenoceptor subtype. However, the affinity of SB 216469 at human prostatic alpha 1-adrenoceptors (pA2 = 8.1) determined in isolated tissue strips, was significantly lower than the values obtained at either the cloned alpha 1a-adrenoceptors (human, rat, bovine) or the native alpha 1A-adrenoceptors in radioligand binding and functional studies in the rat. 6. Our results with SB 216469, therefore, suggest that the alpha 1-adrenoceptor mediating contractile responses of the human prostate has properties which distinguish it from the cloned alpha 1a-adrenoceptor or native alpha 1A-adrenoceptor. Since it has previously been shown that the receptor is not the alpha 1B- or alpha 1D-adrenoceptor, the functional alpha 1-adrenoceptor of the human prostate may represent a novel receptor with properties which differ from any of the alpha 1-adrenoceptors currently defined by pharmacological means.

The crystal structure of TGF-beta 3 and comparison to TGF-beta 2: implications for receptor binding

Transforming growth factors beta belong to a group of cytokines that control cellular proliferation and differentiation. Five isoforms are known that share approximately 75% sequence identity, but exert different biological activities. The structure of TGF-beta 3 was solved by X-ray crystallography and refined to a final R-factor of 17.5% at 2.0 A resolution. Comparison with the structure of TGF-beta 2 (Schlunegger MP, Grütter MG, 1992, Nature 358:430-434; Daopin S, Piez KA, Ogawa Y, Davies DR, 1992, Science 257:369-373) reveals a virtually identical central core. Differences exist in the conformations of the N-terminal alpha-helix and in the beta-sheet loops. In TGF-beta 3, the N-terminal alpha-helix has moved approximately 1 A away from the central core. This movement can be correlated with the mutation of Leu 17 to Val and Ala 47 to Pro in TGF-beta 3. The beta-sheet loops rotate as a rigid body 9 degrees around an axis that runs approximately parallel to the dimer axis. If these differences are recognized by the TGF-beta receptors, they might account for the individual cellular responses. A molecule of the precipitating agent dioxane is bound in a crystal contact, forming a hydrogen bond with Trp 32. This dioxane may occupy a carbohydrate-binding site, because dioxane possesses some structural similarity with a carbohydrate. The dioxane is in contact with two tryptophans, which are often involved in carbohydrate recognition.

Rat pineal alpha 1-adrenoceptor subtypes: studies using radioligand binding and reverse transcription-polymerase chain reaction analysis

1. The pharmacological characteristics of alpha 1-adrenoceptor binding sites in rat pineal gland membranes, detected by use of a selective alpha 1-adrenoceptor antagonist ([125I]-iodo-2-[beta-(4-hydroxyphenyl) ethylaminomethyl]tetralone, [125I]-HEAT), were investigated with the alkylating agent, chloroethylclonidine (CEC), and in competition experiments with a number of adrenoceptor agonists and antagonists. 2. Chloroethylclonidine (CEC) treatment (10 microM, 10 min) of rat pineal membranes inactivated approximately 70% of specific [125I]-HEAT binding sites. Higher concentrations of CEC (up to 100 microM) or longer treatment periods (up to 40 min) were no more effective. 3. Adrenoceptor agonists and antagonists competitively inhibited [125I]-HEAT binding with Hill coefficients close to unity indicating a single alpha 1-adrenoceptor subtype is present. The affinity (Ki) of subtype selective agonists (oxymetazoline, SDZ NVI-085) and antagonists (5-methylurapidil, WB4101, benoxathian, phentolamine) was consistent with binding to an alpha 1B-adrenoceptor subtype. 4. The (-)- and (+)-enantiomers of niguldipine had an equal and low affinity for alpha 1-adrenoceptor binding sites both in untreated (log Ki-6.66 and -6.90 respectively) and CEC-treated membranes in which approximately 70% of sites had been inactivated (log Ki-6.41 and -6.86 respectively). This indicates that the small proportion of alpha 1-adrenoceptors insensitive to CEC are not alpha 1A-adrenoceptors. 5. mRNA was isolated from rat pinealocytes, cDNA was synthesized and then amplified by the polymerase chain reaction with alpha 1-adrenoceptor subtype specific primers. These experiments identified both alpha 1A- and alpha 1B-adrenoceptor mRNA, but not alpha 1D-mRNA in rat pinealocytes, although all three adrenoceptor subtypes were readily identified in rat brain cortex. 6. These data indicate that although both alpha 1A- and alpha 1B-adrenoceptor mRNAs are present in the pineal the major subtype of alpha 1-adrenoceptor expressed is the alpha 1B.

Synthesis, absolute configuration, and biological profile of the enantiomers of trans-[2-(2,6-dimethoxyphenoxy)ethyl] [(3-p-tolyl-2,3-dihydro-1,4-benzodioxin-2-yl)methyl]amine (mephendioxan), a potent competitive alpha 1A-adrenoreceptor antagonist

The enantiomers of trans-[2-(2,6-dimethoxyphenoxy)ethyl] [(3-p-tolyl-2,3-dihydro-1,4-benzodioxin-2-yl) methyl]amine (mephendioxan, 2) were synthesized from the chiral trans-3-p-tolyl-2,3-dihydro-1,4-benzodioxin-2-carboxylic acids [(+)-3 and (-)-3] which in turn were obtained through the resolution of the racemic acid with (R)- and (S)-alpha-methylbenzylamine. Comparison of CD spectra of the enantiomers of 2 with that of (2S,3S)-3-methyl-2-phenyl-1,4-benzodioxane allowed the assignment of the 2S,3S configuration to the (-)-enantiomer of 2 and of the 2R,3R configuration to the other enantiomer. The binding profile of the enantiomers of 2 was assessed at alpha 1, alpha 2, D2, and 5-HT1A receptors, in comparison to WB 4101 (1), 5-methylurapidil, and (+)-niguldipine. In addition, the two enantiomers were investigated at native and cloned alpha 1-adrenoreceptor subtypes. (-)-2 was 10-30 times as potent as the (+)-enantiomer at alpha 1-adrenoreceptor subtypes in both functional and binding assays. It was 36-fold selective for the alpha 1A- versus alpha 1B-adrenoreceptor and 60- and 20-fold selective in binding to the alpha 1a-adrenoreceptor relative to alpha 1b and alpha 1d subtypes, respectively. Furthermore, the enantiomer (-)-2 displayed selectivities of 12000-, 2500-, and 250-fold in binding to alpha 1a-adrenoreceptors relative to alpha 2-adrenoreceptors and 5-HT1A and D2 receptors. These results indicate that (-)-2 may be a valuable tool in the characterization of alpha 1-adrenoreceptor subtypes.

Comparison of the densities of 5-HT4 receptors, beta 1- and beta 2-adrenoceptors in human atrium: functional implications

We measured in human atrium the density of 5-HT4 receptors, labelled with [125I]-SB 207710 (1-butyl-4-piperidinyl) methyl 8-amino-7-iodo-1, 4-benzodioxan-5-carboxylate), and compared it with the density of beta1- and beta2-adrenoceptors, labelled with (-)-[125I]-cyanopindolol. [125I]-SB 207710 (5-1200 pmol/l) labelled a small population of saturable binding sites (Bmax approximately 4 fmol/mg protein) with a pK(D) of 9.7 and with 5-HT4 receptor characteristics, as assessed with competing ligands. The density of atrial binding sites with 5-HT4 receptor characteristics was 10 and 5 times lower, respectively, than the density of beta 1- and beta 2-adrenoceptors. We suggest that the small 5-HT4 receptor population may in part explain why the positive inotropic effects of 5-HT are smaller than those of catecholamines mediated through beta 1- and beta 2-adrenoceptors.

Sustained increase in rat myocardial alpha 1A-adrenoceptors induced by 6-hydroxydopamine treatment involves a decelerated receptor turnover

The biochemical mechanisms involved in the alpha 1-adrenoceptor up-regulation and possible changes in subtypes of adrenoceptors in the rat heart after chemical denervation were investigated. The effects of acute 6-hydroxydopamine treatment (two increasing doses 24 h apart) on the pseudo-steady state densities and turnover rates of alpha 1-adrenoceptors were studied in ventricular myocardium of the rat. We have assessed the repopulation kinetics of [3H]prazosin binding sites after irreversible inactivation of alpha 1-adrenoceptors induced by a single dose of phenoxybenzamine (1 mg/kg i.p.) in rats acutely treated either with 6-hydroxy-dopamine or with vehicle (control animals). Seven days after the last administration of 6-hydroxydopamine an enhanced density of [3H]prazosin binding sites (Bmax 58.7 +/- 3.6 fmol/mg protein vehicle-treated rats versus 82.6 +/- 5.3 fmol/mg protein 6-hydroxydopamine-treated rats) was observed. This was not accompanied by changes in the dissociation constant value. Furthermore, the proportion of high affinity sites for WB-4101 was altered (21 +/- 2% versus 72 +/- 3% for animals treated with vehicle and 6-hydroxydopamine, respectively). In rat myocardium, alpha 1-adrenoceptor turnover, evaluated during the 6-hydroxydopamine-induced up-regulation (7-19 days after the completion of treatment with 6-hydroxydopamine) revealed an increase in the half-life of the alpha 1-adrenoceptor (t1/2 of 67.2 h versus 38.7 h in control animals). The present study confirms an increase in alpha 1-adrenoceptors in rat myocardium after chemical denervation and reveals that the effect is almost completely confined to the alpha 1A-adrenoceptor subtype. Furthermore, the up-regulation of alpha 1A-adrenoceptors is the result of a decrease in the cellular processes that control the rate of receptor degradation.

Expression of I2-imidazoline sites in rat prostate. Effect of castration and aging

Clonidine, idazoxan, and related imidazoline adrenergic drugs bind to non-adrenergic sites in brain and several peripheral tissues. These sites, termed imidazoline receptors, appear to exist in two major subclasses, I1 sites labeled by clonidine and I2 sites labeled by idazoxan. In this study, we investigated whether rat prostate expresses imidazoline receptors and, if so, whether their expression can be regulated by circulating testosterone. Studies in rat ventral prostate membrane revealed that [3H]idazoxan, but not [3H]p-aminoclonidine, bound to non-adrenergic sites. The binding of [3H]idazoxan was saturable (Bmax: 941 +/- 105 fmol/mg protein) and high affinity (KD: 16.4 +/- 2.3 nM). The rank order of the inhibition of binding by imidazoline ligands was cirazoline > clonidine > UK 14,304 > guanabenz, indicating an I2 subclass of imidazoline receptors. Bilateral orchiectomy increased the number of binding sites (Bmax) for [3H]idazoxan without changing the affinity (KD). Testosterone replacement, while completely restoring the plasma testosterone levels, only partially reversed the increase in Bmax. In contrast, the binding of [3H]idazoxan to prostate membranes of rats in different age groups (4, 7, and 16 months) revealed a progressive decrease in the Bmax without any change in KD. We conclude that the rat prostate expresses the I2 subclass of imidazoline receptors and that the expression is regulated by circulating testosterone.

I2-imidazoline binding sites: relationship with different monoamine oxidase domains and identification of histidine residues mediating ligand binding regulation by H+1

We have shown that I2-imidazoline binding sites (I2BSs) are located on both monoamine oxidases A (MAO-A) and B (MAO-B) and are selectively regulated by H+ and K+ in vitro. In the present study we used chemical modifying agents to investigate the localization of I2BSs with respect to different MAO domains and the mechanisms of ligand binding regulation by K+ and H+. In mitochondrial or solubilized preparations from rabbit kidney and liver, modification of cysteine residues, which are critical for MAO activity, did not affect [3H]idazoxan binding, indicating that I2BS is not associated to the cysteine-containing flavin adenine dinucleotide (FAD) prosthetic group or to the catalytic site of MAOs. Among various chemical modifying agents, only diethylpyrocarbonate and 4-bromophenacyl bromide, two histidine modifying agents, inhibited [3H]idazoxan binding to I2BS. The pH profile of diethylpyrocarbonate effect was consistent with the specific modification of histidine residues. In protection experiments, the effect of diethylpyrocarbonate was not prevented in the presence of saturating concentrations of amiloride, guanabenz or KCl, suggesting that these residues are not located within the ligand or K+ binding sites. In contrast, histidine residues appear to be within a MAO domain involved in regulation of [3H]idazoxan binding by H+. Indeed, the pH-dependent increase in [3H]idazoxan binding was fully abolished after treatment of solubilized material with diethylpyrocarbonate. In conclusion, our results show that MAO I2BSs are not located within the flavin adenine dinucleotide prosthetic group or the catalytic site. Histidine(s) residue(s) involved in the regulation of ligand binding to I2BS by H+ also has been identified.

Antagonists that differentiate between alpha 2A-and alpha 2D-adrenoceptors

Four antagonists were examined for their ability to differentiate alpha 2A-from the orthologous alpha 2D-adrenoceptors. The antagonists were (2S,12bS)1',3'-dimethylspiro(1,3,4,5',6,6',7,12b-octah ydro-2H- benzo[b]furo[2,3-a]quinolizine)-2,4'-pyrimidin-2'-one (MK912), 2-[2-(methoxy-1,4-benzodioxanyl)imidazoline (RX 821002), efaroxan and benoxathian. The alpha 2-autoreceptors in rabbit brain cortex were chosen as alpha 2A-and the alpha 2-autoreceptors in guinea-pig brain cortex as alpha 2D-adrenoceptors. Slices of the brain cortex were preincubated with 3H-noradrenaline and then superfused and stimulated electrically by brief pulse trains (4 pulses, 100 Hz) that led to little, if any, alpha 2-autoinhibition. 5-Bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) was used as an alpha 2-adrenoceptor agonist. UK 14, 304 decreased the stimulation-evoked overflow of tritium. The antagonists shifted the concentration-inhibition curve of UK 14, 304 to the right in an apparently competitive manner. Dissociation constants of the antagonists were calculated from the shifts. MK 912, RX 821002 and efaroxan had markedly higher affinity for (guinea-pig) alpha 2D-adrenoceptors (pKd values 10.0, 9.7 and 9.1, respectively) than for (rabbit) alpha 2A-adrenoceptors (pKd 8.9, 8.2 and 7.6, respectively). Benoxathian had higher affinity for alpha 2A-(pKd 7.4) than for alpha 2D-adrenoceptors (pKd 6.9). Ratios calculated from the Kd values of the four compounds differentiated between alpha 2A and alpha 2D up to 100 fold. It is concluded that MK 912, RX 821002, efaroxan and benoxathian are antagonists with high power to differentiate alpha 2A-from alpha 2D-adrenoceptors.

Chronic imipramine treatment induces downregulation of alpha-2 receptors in rat's locus coeruleus and A2 region of the tractus solitarius

Imipramine is an effective antidepressant agent that blocks the reuptake of monoamines. In order to understand some of its basic mechanisms of action, we investigated the effects of chronic imipramine administration (10 mg/kg, i.p.; 21 days) on the alpha-2 receptor population of several brain sites. Alpha-2 receptor density was estimated by in vitro autoradiography using [3H]Idazoxan. The densitometric analysis revealed a decreased receptor density in the A2 region of the tractus solitarius (20%) and locus coeruleus (16%). No changes were observed in the amygdala, pyriform cortex, periacueductal gray and the bed nucleus of the stria terminalis. These results suggest that chronic imipramine treatment selectively modulates the alpha-2 receptor population localized in the brain stem norepinephrine-rich nuclei and not in the population present on limbic structures innervated by noradrenergic terminal projections. The possible physiological consequences of this selective modulation of alpha-2 receptors are discussed.

Monocryl suture, a new ultra-pliable absorbable monofilament suture

Synthetic absorbable sutures are available as braided constructions or as monofilaments. Braided absorbable sutures are made either from 90:10 poly(glycolide-co-L(-)-lactide), sold by Ethicon, Inc. under the trade name Vicryl, or from polyglycolide, as sold, for instance, by Davis and Geck under the trade name Dexon. There are, however, some concerns with braided sutures that relate to tissue drag and the trauma this may cause, as well as the possible potentiation of infection through the interstices of the braid structure. Absorbable monofilaments, such as the monofilament sutures derived from p-dioxanone homopolymer (PDS II, an Ethicon, Inc. product), or a copolymer of trimethylene carbonate and glycolide (Maxon, a Davis and Geck product), eliminate many of these concerns, but generally monofilaments do not handle as well as braids. This paper describes the research leading to the introduction of Monocryl (poliglecaprone 25) monofilament sutures, based on segmented block copolymers of epsilon-caprolactone and glycolide. Monocryl sutures will be shown to display excellent handling properties, minimal resistance during passage through tissue and excellent tensile properties. These sutures provide an in vivo breaking strength retention of approximately 20-30% after 2 weeks, considered by many to be the critical wound healing period. Absorption data on these sutures are presented; absorption is complete between the 91st and 119th days of implantation, with slight or minimal tissue reaction.

Identification of drugs subtype-selective for alpha 2A-, alpha 2B-, and alpha 2C-adrenoceptors in the pig cerebellum and kidney cortex

The radioligands [3H]MK912 and [3H]RX821002 were used to label alpha2A-, alpha2B-, and alpha2C-adrenoceptors of the pig cerebellum and kidney cortex. By inclusion of the alpha2A-adrenoceptor-selective drug, BRL44408, and using a 'multi-curve' experimental design all the three porcine alpha2-adrenoceptor subtypes could be characterized pharmacologically. The data indicate that the pig alpha2-adrenoceptor subtypes are pharmacologically more related to human alpha2-adrenoceptor subtypes than to the rodent alpha2-adrenoceptors. We suggest a set of drugs that are useful for the delineation of the pig alpha2-adrenoceptor subtypes.

Actions of terazosin and its enantiomers at subtypes of alpha 1- and alpha 2-adrenoceptors in vitro

Terazosin and its enantiomers, antagonists of alpha 1-adrenoceptors, were studied in radioligand binding and functional assays to determine relative potencies at subtypes of alpha 1- and alpha 2-adrenoceptors in vitro. The racemic compound and its enantiomers showed high and apparently equal affinity for subtypes of alpha 1-adrenoceptors with Kl values in the low nanomolar range, and showed potent antagonism of alpha 1-adrenoceptors in isolated tissues, with the enantiomers approximately equipotent to the racemate at each alpha 1-adrenoceptor subtype. At alpha 2b sites, R(+) terazosin bound less potently than either the S(-) enantiomer or racemate. R(+) terazosin was also less potent than the S(-) enantiomer or the racemate at rat atrial alpha 2B receptors. These agents were not significantly different in their potencies at alpha 2a or alpha 2A sites. Since the high affinity for alpha 2B sites of quinazoline-type alpha-adrenoceptor antagonists has been used to differentiate alpha 2-adrenoceptor subtypes, the low affinity of R(+) terazosin for these sites was unexpected. Because terazosin or its enantiomers are approximately equipotent at alpha 1-adrenoceptor subtypes, the lower potency of R(+) terazosin at alpha 2B receptors indicates a somewhat greater selectivity for alpha 1-compared to alpha 2B adrenoceptor subtypes. The possible pharmacological significance of this observation is discussed.

Identification of alpha 1-adrenoceptor subtypes in the rabbit prostate

1. The alpha 1-adrenoceptor subtypes of rabbit prostate were characterized in binding and functional experiments. 2. In saturation experiments, [3H]-prazosin bound to two distinct affinity sites in the rabbit prostate (pKD = 11.20 +/- 0.22 and 8.39 +/- 0.11, Bmax = 15.3 and 736 fmol mg protein-1). 3. In the displacement experiments, the binding was inhibited with shallow displacement curves by unlabelled prazosin, WB4101, and 5-methylurapidil, suggesting the presence of two distinct affinity sites for prazosin, WB4101, or 5-methylurapidil. On the other hand, HV723 displaced the [3H]-prazosin binding monophasically with a low affinity. From the results, the presence of two distinct alpha 1-adrenoceptor subtypes was suggested; presumably one is the classical alpha 1A (cloned alpha 1C) subtype with high affinity for prazosin, WB4101 and 5-methylurapidil but not for HV723 and the other corresponds to the alpha 1L subtype, which shows low affinity for the four antagonists. 4. In the functional experiments, prazosin, WB4101, HV723 and 5-methylurapidil competitively antagonized the contractile response to noradrenaline with low affinities close to those for the alpha 1L subtype determined in binding experiments. These results suggest that contractile response to noradrenaline in the rabbit prostate is predominantly mediated through the alpha 1L subtype.