The role of alpha 1-adrenoceptor subtypes in the regulation of arterial blood pressure.

The effect of chlorethylclonidine on alpha 1-adrenoceptor subtypes and arterial blood pressure has been evaluated. Chlorethylclonidine significantly reduced the alpha 1-adrenoceptor population. Chlorethylclonidine treatment had no significant effect on resting systemic arterial blood pressure or heart rate and shifted the phenylephrine pressor dose-response curve only 2.4-fold to the right. These data suggest that only one of the alpha 1-adrenoceptor subtypes plays a major role in the regulation of arterial blood pressure.

Heterogeneity of alpha 1 receptors associated with vascular smooth muscle: evidence from functional and ligand binding studies.

The nature of the alpha 1 receptor associated with rabbit aorta has been examined in functional and receptor binding studies. In isolated aortic rings the dose-response curve for (-)metaraminol was not parallel to that of (-)epinephrine, (-)norepinephrine or (-)phenylephrine. Following inactivation of a portion of the alpha receptors with phenoxybenzamine, the occupancy versus response relationship for metaraminol, in contrast to the other test agonists, was biphasic. These results suggest the possibility that metaraminol interacts with different functional groups on the alpha 1 receptor than the other test agonists. In microsomes prepared from frozen aorta, metaraminol bound to two classes of sites (KH = 0.41 +/- 0.12 microM, KL = 39.1 +/- 7.1 microM) labelled by the selective alpha 1 antagonist [3H] prazosin. Similar binding characteristics were observed in microsomes prepared from aorta shipped in serum on ice or aorta from animals killed in our laboratory. Norepinephrine also bound to two sites on the alpha receptor in all three preparations tested (KH = 0.06 +/- 0.01 microM, KL = 5.09 +/- 2.4 microM; estimates from frozen aorta). The Scatchard plot of [3H]prazosin binding to microsomes prepared from frozen aorta was curvilinear. Estimates of the affinities and site densities were 49.6 +/- 15.3 pM and 44.8 +/- 11.8 pmol/gm protein and 1.0 +/- 0.2 and 43.8 +/- 17.4 pmol/gm for the high and low affinity sites, respectively. These data are consistent with the idea that there are subtypes of the alpha 1 receptor.

Analysis of neurogenic contractions induced by ML-1035 and other benzamides in the guinea-pig non-stimulated isolated ileum.

4-Amino-5-chloro-substituted benzamides have been shown to increase gastric motility in-vivo and enhance field-stimulated and peristaltic contractions in-vitro. The present experiments examined the contractile response to a series of benzamides in the guinea-pig non-stimulated ileum. Four benzamides elicited contractions in the isolated ileum which were expressed as a percentage of the contraction induced by 1 microM acetylcholine (% acetylcholine response = 12 +/- 2, 19 +/- 3, 26 +/- 2, 51 +/- 3, n = 13, 8, 17, and 21, with EC50 values of 0.85, 1.8, 5.7, and 14.2 microM for cisapride, zacopride, metoclopramide, and ML-1035 (4-amino-5-chloro-2-((2-methylsulphinyl)-ethoxy)-N- (2-(diethylamino)-ethyl)-benzamide hydrochloride), respectively). ML-1035 contractions were completely blocked by atropine and tetrodotoxin, while ganglionic blockade with hexamethonium was ineffective. Metoclopramide has been reported to sensitize postjunctional muscarinic receptors, however, ML-1035 did not enhance acetylcholine-induced contractions. Tropisetron (ICS 205-930, 1 microM), caused a parallel rightward shift in the concentration-response curve for both ML-1035 and zacopride (EC50 = 14.2 +/- 1.3 and 1.8 +/- 0.8 microM in the absence, and 26 +/- 2.7 and 6.9 +/- 2.3 microM in the presence of tropisetron for ML-1035 and zacopride, respectively) with apparent pKB values of 5.9 and 6.0 for the respective compounds. 5-Hydroxytryptaminergic receptor desensitization by 2-methyl-5-hydroxytryptamine (5-HT3) and 5-methoxytryptamine (5-HT4), attenuated the response to ML-1035.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of calcium channel activators on the response of rabbit aortic rings to alpha 1-receptor agonists: evidence for two modes of action.

The interaction between activators of the calcium channel and the alpha 1-adrenoceptor has been studied in isolated rabbit aortic rings. The data obtained in these investigations are not consistent with the idea of a homogenous population of alpha 1-receptors which trigger contraction via a single pathway. Our results suggest that calcium channel activators reveal two modes of spasmogenic action for alpha 1-adrenoceptor agonists. Furthermore, we have shown that there may be multiple drug recognition sites on the alpha 1-receptor.

Stereoselective and nonstereoselective inhibition exhibited by the enantiomers of verapamil.

The interaction of the isomers of verapamil with sites on the calcium channel and alpha 1-adrenergic receptor has been examined. The inhibitory potency of these enantiomers differ with respect to the agonist. KCl- or clonidine-induced contractions of rabbit aortic rings were inhibited in a stereoselective manner by the enantiomers of verapamil with the (-)-isomer being more potent than the (+)-isomer. Similarly, (-)-verapamil was also more potent at displacing (-)-[N-methyl-3H]desmethoxyverapamil than was the (+)-isomer. In contrast, the inhibition of norepinephrine- or phenylephrine-induced aortic contractions was not stereoselective. Differences in enantiomer potency were also observed in vivo. The ability of clonidine to increase blood pressure in the anesthetized rat was blocked in a stereoselective manner by the verapamil enantiomers, while inhibition of the pressor actions of phenylephrine was not. In summary, for agents that rely heavily on calcium channel function (KCl, clonidine), stereoselective inhibition was observed. Stereoselective inhibition was not observed against high efficacy alpha 1-agonists. This difference in stereochemistry argues that verapamil does not act at the same site when inhibiting clonidine or KCl action when compared with norepinephrine or phenylephrine.

Analysis of serotonergic mechanisms underlying benzamide-induced gastroprokinesis.

Serotonin (5-HT) receptors in the myenteric plexus mediate contractility in vitro and may regulate gastric emptying in vivo. This report examines the pharmacology of three benzamides, ML-1035 (4-amino-5-chloro-2-[2-(methylsulfinyl)-ethoxy]-N-[2- (diethylamino)ethyl]-benzamide hydrochloride), metoclopramide and cisapride, in studies which address the serotonergic mechanisms underlying benzamide-induced gastroprokinesis. All three compounds had high affinity at the 5-HT3 receptor as they displaced the 5-HT3 antagonist [3H]GR65630 from cortical membranes (Ki = 156, 232 and 1711 nM for ML-1035, metoclopramide and cisapride, respectively) and blocked the 5-HT-induced Bezold-Jarisch reflex, although cisapride was much less active in this experiment. Receptor selectivity was also compared at 5-HT1, 5-HT2, and dopamine D2 receptors in which no displacement was observed that was common to all agents. All benzamides elicited a 5-HT4-like agonist response as they enhanced field-stimulated neurogenic contractions in ileum (EC50 = 1.4, 1.6 and 0.013 microM for ML-1035, metoclopramide and cisapride, respectively). ICS 205-930, a proposed 5-HT4 antagonist, competitively antagonized this response for ML-1035 (Kb = 1.6 microM) whereas atropine blocked the twitch response and any additional responses to ML-1035. In vivo, ML-1035 and metoclopramide increased gastric emptying (IC50 = 0.87 and 3.09 mg/kg i.p., respectively). Thus, the benzamides activate a 5-HT4 receptor in the ileum which increases cholinergic contractions and may be one mechanism by which these agents increase gastric emptying.

Forensic psychiatric assessment in selected Canadian cities.

Forensic psychiatrists in six Canadian municipalities completed a single-page form following each court-ordered assessment conducted during the month of July 1978. A total of 248 cases accumulated during the study period. During the following 18 months researchers collected court dispositions on the sample. With data from all six cities pooled, 85% of patients were found fit to stand trail. Almost all, 96%, were accorded a diagnosis with 39% classified as psychotic. Overall the examining psychiatrists considered 36% to be dangerous to others in the future. When psychiatrists recommended a custodial setting, in 73% of cases the person was incarcerated. Recommendations for hospitalization were observed in 59% of cases. Although the data would seem to suggest that judges take psychiatrists' recommendations into account, the investigators were nonetheless struck by the general lack of communication between clinic and court. They offer a number a number of suggestions for improvement.

Effect of an alkylating analog of prazosin on alpha-1 adrenoceptor subtypes and arterial blood pressure.

Previous studies have shown that a chemically reactive analog of prazosin, SZL-49, reduces the alpha-1 adrenoceptor population by a maximum of 60% (Kusiak et al., 1989). These data support the idea that alpha-1 receptor subtypes exist and only one is sensitive to alkylation by SZL-49. In the present study male rats were injected (i.p.) with SZL-49 (0.5-30 mg/kg) and the effects on [3H]prazosin binding, systemic arterial blood pressure and the pressor response to phenylephrine were assessed 24 hr later. SZL-49 treatment decreased the number of [3H]prazosin sites without affecting receptor affinity. The maximal reduction in binding sites was 60% (32 fmol/mg). At doses of 0.5-, 1-, 5- and 10-mg/kg SZL-49 reduced the receptor number to the same level (83 fmol/mg control; 47-60 fmol/mg treated). Injection of SZL-49 had no effect on resting blood pressure. However, drug treatment (0.5 mg/kg and greater) shifted the phenylephrine dose-response curve to the right. The maximal 1-, 5- and 10-mg/kg SZL-49, the ED50 for phenylephrine was approximately the same. Therefore, over a 20-fold range of SZL-49 concentrations no further reduction in receptor number or phenylephrine ED50 was observed. These data support the idea that S2L-49-sensitive and resistant alpha-1 receptors exist in vivo. The alkylation resistant receptor is capable of maintaining resting blood pressure. Furthermore, both receptors appear to be involved in mediating the increase in blood pressure observed with phenylephrine.

Agonist interaction with alkylation-sensitive and -resistant alpha-1 adrenoceptor subtypes.

The interaction of agonists with alpha-1 receptor subtypes sensitive and resistant to alkylation by a prazosin analog [1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-bicyclo[2.2.2]octa-2,5- diene-z-carbonyl)-piperazine; SZL-49] has been examined. In rat aortic rings, SZL-49 (0.1-10 nM) shifted the dose-response curves for norepinephrine and phenylephrine to the right. The curves were biphasic, consisting of high and low affinity components. At greater than 10 nM, the curves became monophasic. After SZL-49 treatment, the response to norepinephrine was partially antagonized by diltiazem. Chlorethylclonidine (1-100 microM) also produced biphasic dose-response curves. Phenylephrine bound to high and low affinity sites labeled by [3H]prazosin, and the high affinity site was eliminated by SZL-49. SZL-49 (i.p.) shifted the pressor dose-response curve for phenylephrine to the right but did not decrease the maximal response. Chlorethylclonidine was much less potent than SZL-49 at shifting the pressor dose-response curve. Pertussis toxin, 50 micrograms/kg i.v., shifted the phenylephrine pressor dose-response curve in control and SZL-49-treated animals. SZL-49 inhibited norepinephrine-induced inositol phosphate formation, whereas chlorethylclonidine had no effect on inositol phosphate formation. These data show: 1) both in vitro and in vivo, alpha-1 receptor subtypes sensitive and resistant to alkylation by SZL-49 can mediate the full response of agonists; 2) these subtypes exhibit high and low affinity for agonists; 3) responses mediated by either subtype are partially dependent on calcium channel activity and a pertussis toxin-sensitive G-protein; 4) the SZL-49 sensitive site is able to enhance the formation of inositol phosphates.

Alkylation of alpha-1 receptors with a chemically reactive analog of prazosin reveals low affinity sites for norepinephrine in rabbit aorta.

The effect of a newly synthesized irreversible blocker of the alpha-1 receptor [1-(4-amino-6,7-dimethoxy-2-quinazolnyl)-4-(2-bicyclo[2,2,2] octa-2,5-dienylcarbonyl)-piperazine; SZL-49] has been evaluated in contractile studies in rabbit aorta and binding studies in aorta and brain. SZL-49 produced long lasting inhibition of norepinephrine-induced contractions which was apparent 21 hr after drug washout. The inhibition, which was dose and time dependent, was characterized by progressive shift to the right in the norepinephrine dose-response curve. The ED50 for norepinephrine was shifted from 10(-7) M to 8 X 10(-7), 3 X 10(-6), 1 X 10(-5) and 5 X 10(-4) M after incubation (30 min) and washout of increasing concentrations of SZL-49. Surprisingly, SZL-49, irrespective of the dose or incubation time, did not decrease the maximal response of aortic rings to norepinephrine. This resulted in a norepinephrine dose-response curve after SZL-treatment that is parallel to the control. SZL-49 had no effect on the spasmogenic actions of histamine, serotonin, KCl or CaCl2. In contrast to the inhibitory pattern seen with SZL-49, incubation with 10(-7) M phenoxybenzamine shifted the norepinephrine dose-response curve to the right in a nonparallel manner and significantly depressed the maximal response obtainable with norepinephrine. Incubation with 10(-6) M phenoxybenzamine for 30 min virtually abolished the response to norepinephrine. Phenoxybenzamine (10(-7) M) was without effect on aortic rings treated with a maximally effective dose of SZL-49. Prazosin weakly antagonized the contractile actions of norepinephrine observed after SZL-49 treatment, whereas yohimbine was without effect on these norepinephrine-induced contractions. In control binding studies [3H]prazosin bound to two classes of sites in both aorta and brain preparations. Affinities and densities for these sites were K1 = 67.5 pM, K2 = 309 pM; R1 = 38.2 fmol/mg, R2 = 46.47 fmol/mg in aorta and K1 = 29.6 pM, K2 = 182 pM; R1 = 6.6 fmol/mg and R2 = 30.4 fmol/mg in brain. Treatment with increasing amounts of SZL-49 (10(-10) to 10(-8) M) progressively reduced the number of [3H]prazosin sites without altering the affinity of the sites remaining. At 10(-7) M, SZL-49 eliminated completely all specific [3H]prazosin binding. Our results indicate that the site mediating norepinephrine contraction after treatment with SZL-49 does not possess the characteristics of an alpha-1 receptor and supports the hypothesis that a low affinity site for norepinephrine and prazosin exists in vascular smooth muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Planning and establishment of a high throughput screening site.

In 1996 and 1997, Glaxo Wellcome's US Research division planned and established their second generation research strategy. An important aspect of the strategy entailed development of two automated screening sites in Biochemistry in Research Triangle Park, NC. Development of the new operations required many decisions to be made very quickly, including automated process design, system selection and site preparation. Descriptions of the decision made in the development of one of the screening sites are presented in this paper.

The resolution, isolation, and pharmacological characterization of the enantiomers of a benzamide containing a chiral sulfoxide.

Rac-ML-1035 (MDL 201,035: 4-amino-5-chloro-2-[2-(methylsulfinyl)ethoxy]-N-[2-(diethylamino)ethyl] benzamide hydrochloride) is a racemic gastroprokinetic with serotonergic (5-hydroxytryptamine, 5-HT) activity and a novel chiral sulfoxide substituent. Chromatographic and chemical methods have been developed to resolve the enantiomers of rac-ML-1035, and the absolute configuration of the (R)-enantiomer has been determined. We also report pharmacological characterization of rac-ML-1035 and its respective isomers. Radioligand binding to rat cortical membranes revealed that (R)-ML-1035 (MDL 201,226) and (S)-ML-1035 (MDL 201,227) had equivalent activity at the 5-HT3 receptor. However, in isolated tissue studies including field-stimulated guinea pig ileum, field-stimulated rat fundic strip, and nonstimulated guinea pig ileum, (S)-ML-1035 was equally potent yet had greater maximal activity than (R)-ML-1035 in eliciting or facilitating cholinergic contractions. Thus, enantiomers of rac-ML-1035 can be resolved, and the relative configuration of these isomers influences their pharmacological activity.