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Biomedical subjects

D E Clarke

Publications and source records attributed to D E Clarke.

At least 37 records · Page 2Linked to original sources
PubMed1997

N-arylpiperazinyl-N'-propylamino derivatives of heteroaryl amides as functional uroselective alpha 1-adrenoceptor antagonists.

Novel arylpiperazines were identified as alpha 1-adrenoceptor (AR) subtype-selective antagonists by functional in vitro screening. 3-[4-(ortho-Substituted phenyl)piperazin-1-yl]propylamines were derivatized with N,N-dimethyl anthranilamides, nicotinamides, as well as carboxamides of quinoline, 1,8-naphthyridine, pyrazolo[3,4-b]pyridine, isoxazolo[3,4-b]pyridine, imidazo[4,5-b]pyridine, and pyrazolo[1,5-a]pyrimidines. Strips of rabbit bladder neck were employed as a predictive assay for antagonism in the human lower tract. Rings of rat aorta were used as a "negative screen" for the test antagonists. Binding to alpha 1-ARs was relatively sensitive to size and electronic features of the arylpiperazine portion of the antagonists and permissive to these features on the heteroaryl carboxamide side. These structure-affinity findings were exploited to produce nicotinamides (e.g. 13ii and 25x) and pyrazolo[3,4-b]pyridines (e.g. 37f and 37y) ligands with nanomolar affinity at the alpha 1-AR subtype prevalent in the human lower urinary tract(pA2 values: 8.8, 10.7, 9.3, and 9.9, respectively) and displaying 2-3 orders of magnitude selectivity over the alpha 1D-AR.

Adolescent↗
PubMed1997

Drug discovery: some directional pointers.

Everybody in the pharmaceutical industry has a view on management and drug discovery. In this article, David Clarke expresses his personal views. Emphasis is placed on the role of the scientist, and the influence of the manager in programmatic scientific decision making is de-emphasized. An operational scheme for reorganization is proposed.

Career Choice↗
PubMed1997

Tetrodotoxin inhibits neuropathic ectopic activity in neuromas, dorsal root ganglia and dorsal horn neurons.

Neuropathic pain or persistent dysesthesias may be initiated by mechanical, chemical, or ischemic damage to peripheral sensory nerves. In animal models of neuropathic pain, transection or constrictive injury to peripheral nerves produces ectopic discharges originating at both injury sites and related dorsal root ganglia (DRG), and, consequently, hyperexcitability in associated dorsal horn (DH) neurons of the spinal cord. Since ectopic discharges are inhibited by agents that block voltage-sensitive Na+ channels, it has been postulated that accumulation of Na+ channels in the membrane at nerve injury sites may contribute to, or be responsible for, the development of ectopic neuronal activity (ENA). The present study therefore, tested the sensitivity of ENA to intravenously administered tetrodotoxin (TTX), an extremely potent and selective Na+ channel blocker. Comparative effects of TTX on cardiac parameters such as heart rate (HR) and diastolic blood pressure (DBP) were also studied. Experiments were performed on adult male Sprague-Dawley rats in which the common sciatic nerve had been transected 4-10 days earlier. Neuromal activity was measured in fine bundles of microfilaments teased from sciatic nerves, and extracellular microelectrode recordings were made from DRG and DH neurons. Cardiovascular parameters were recorded simultaneously. Intravenously administered TTX induced dose-dependent inhibition of ENA, with that originating from neuromas being the most sensitive; ED50 values (expressed as microg/kg, with 95% confidence limits) for neuromal, DRG and DH neuron activity were: 0.8 (0.6-1.2), 4.3 (2.2-8.4) and 36.2 (16.1-81.3), respectively. Inhibition of ENA in neuromas and DRG did not recover within 10 min after 100 or 300 microg/kg TTX. By comparison, the ED50 value for the initial decrease of HR was 17.9 (15.0-21.5) microg/kg, and partial recovery occurred within approximately 3 min. These data support the hypothesis that Na+ channel accumulation contributes to the generation of ectopic discharges in neuromas and DRG, and suggest that TTX-sensitive Na+ channels located at the nerve injury site and DRG play an important role in the genesis of neuropathic pain.

Action Potentials↗
PubMed1997

Pharmacological characterization of an alpha 1A-adrenoceptor mediating contractile responses to noradrenaline in isolated caudal artery of rat.

1. The alpha 1-adrenoceptor population mediating contraction of caudal artery of rat has been characterized by using quantitative receptor pharmacology. 2. Cumulative concentration-effect (E/[A]) curves to noradrenaline (NA) yielded a p[A]50 of 5.56 +/- 0.05 (n = 16). Prazosin caused concentration-dependent, parallel, dextral shifts of E/[A] curves to NA yielding a pKb of 8.9 (Schild regression slope = 1.0). RS-17053 (N-[2-(2-cyclopropyl methoxy phenoxy) ethyl]-5-chloro-alpha, alpha-dimethyl-1H-indole- 3-ethanamine hydrochloride; 10-100 nM), a selective alpha 1 A-adrenoceptor antagonist, produced non-parallel, biphasic, dextral shifts of E/[A] curves to NA, suggesting the involvement of more than one alpha 1-adrenoceptor subtype. Analysis of the high affinity component yielded an apparent pA2 value of 9.2 +/- 0.3. 3. A-61603, a selective agonist at alpha 1A adrenoceptors behaved as a full agonist relative to NA and yielded monophasic E/[A] curves with a p[A50] of 7.59 +/- 0.04 (n = 15). Pretreatment of tissues with chloroethylclonidine (CEC; 100 microM for 20 min, followed by 40 min washout), which preferentially alkylates alpha 1B- and alpha 1D-adrenoceptors, did not alter E/[A] curves to A-61603. Prazosin (3-300 nM) caused concentration-dependent, parallel, dextral shifts of E/[A] curves to A-61603 yielding a pA2 estimate of 9.2 +/- 0.2. 4. Experiments with alpha 1-adrenoceptor antagonists of varying subtype selectivities (RS-17053, SNAP 5089, tamsulosin, 5-methylurapidil, BMY 7378, HV 723 and REC 15/2739) revealed parallel dextral shifts of E/[A] curves to A-61603. Schild regression analyses yielded pA2 estimates of 9.2, 9.3, 11.2, 9.0, 6.3, 8.7 and 10.0 for RS-17053, SNAP 5089, tamsulosin, 5-methylurapidil, BMY 7378, HV 723 and REC 15/2739, respectively, although deviations from unit slope (possibly reflecting a secondary involvement of another alpha 1-adrenoceptor) hindered estimations of pKb for some antagonists. The antagonist affinity profile obtained reflects best that described for the alpha 1A-adrenoceptor. 5. In conclusion, caudal artery of rat contracts in response to NA via activation of at least two alpha 1-adrenoceptor subtypes. One of these subtypes displays the pharmacology of the alpha 1A-adrenoceptor, while the other remains to be defined. Use of the novel selective agonist, A-61603, allows for limited pharmacological isolation of the alpha 1A-adrenoceptor permitting characterization of the properties of selective antagonists.

Adrenergic alpha-Agonists↗
PubMed1997

Pharmacological pleiotropism of the human recombinant alpha1A-adrenoceptor: implications for alpha1-adrenoceptor classification.

1. Three fully-defined alpha1-adrenoceptors (alpha1A, alpha1B and alpha1D) have been established in pharmacological and molecular studies. A fourth alpha1-adrenoceptor, the putative alpha1L-adrenoceptor, has been defined in functional but not molecular studies, and has been proposed to mediate contraction of human lower urinary tract tissues; its relationship to the three fully characterized alpha1-adrenoceptors is not known. 2. In the present study, binding affinities were estimated by displacement of [3H]-prazosin in membrane homogenates of Chinese hamster ovary (CHO-K1) cells stably expressing the human alpha1A-, alpha1B- and alpha1D-adrenoceptors and were compared with affinity estimates obtained functionally in identical cells by measuring inhibition of noradrenaline (NA)-stimulated accumulation of [3H]-inositol phosphates. 3. For the alpha1A-adrenoceptor, binding studies revealed a pharmacological profile typical for the classically defined alpha1A-adrenoceptor, such that prazosin, RS-17053, WB 4101, 5-methylurapidil, Rec 15/2739 and S-niguldipine all displayed subnanomolar affinity. A different profile of affinity estimates was obtained in inositol phosphates accumulation studies: prazosin, WB 4101, 5-methylurapidil, RS-17053 and S-niguldipine showed 10 to 40 fold lower affinity than in membrane binding. However, affinity estimates were not 'frameshifted', as tamsulosin, indoramin and Rec 15/2739 yielded similar, high affinity estimates in binding and functional assays. 4. In contrast, results from human alpha1B- and alpha1D-adrenoceptors expressed in CHO-K1 cells gave antagonist affinity profiles in binding and functional assays that were essentially identical. 5. A concordance of affinity estimates from the functional (inositol phosphates accumulation) studies of the alpha1A-adrenoceptor in CHO-K1 cells was found with estimates published recently from contractile studies in human lower urinary tract tissues (putative alpha1L-adrenoceptor). These data show that upon functional pharmacological analysis, the cloned alpha1A-adrenoceptor displays pharmacological recognition properties consistent with those of the putative alpha1L-adrenoceptor. Why this profile differs from that obtained in membrane binding, and whether it explains the alpha1L-adrenoceptor pharmacology observed in many native tissues, requires further investigation.

Adrenergic Agents↗
PubMed1996

SDZ NVI 085, an alpha 1A-adrenoceptor agonist with 5-HT2A receptor antagonist properties.

(+/-)-SDZ NVI 085 (3,4,4a,5,10,10a-hexahydro-6-methoxy-4-methyl-9- methylthio-2H-naphth [2,3-b]-1,4-oxazine hydrochloride), an alpha 1-adrenoceptor agonist, produced a concentration-dependent relaxation (pIC50 of 7.2 +/- 0.1) in the isolated caudal artery of rat precontracted with serotonin (5-hydroxytryptamine, 5-HT, 1 microM). (+/-)- SDZ NVI 085 had no effect upon caudal arteries precontracted with vasopressin or U46619 (9,11-dideoxy-11 alpha, 9 alpha-epoxymethano-prostaglandin F2 alpha). In other studies, (+/-)-SDZ NVI 085 shifted 5-HT concentration-effect curves to the right, in a concentration-dependent manner, and Schild regression gave a pA2 estimate of 8.0 (slope of 1.0). Experiments using pharmacological resultant analysis indicated a syntopic interaction of (+/-)-SDZ NVI 085 with ketanserin (a 5-HT2 receptor antagonist) toward 5-HT-induced contractions. It is concluded that (+/-)-SDZ NVI 085 behaves as a reversible competitive 5-HT2A receptor antagonist, a property which may be of importance regarding its pharmacological effects in vivo.

Adrenergic alpha-1 Receptor Agonists↗
PubMed1996

RS-17053 (N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha, alpha-dimethyl-1H-indole-3-ethanamine hydrochloride), a selective alpha 1A-adrenoceptor antagonist, displays low affinity for functional alpha 1-adrenoceptors in human prostate: implications for adrenoceptor classification.

Norepinephrine (NE) contracts smooth muscle cells within the human lower urinary tract (LUT) (bladder neck, prostate, and urethra). Receptor distribution and pharmacological evidence have implicated activation of alpha 1A-adrenoceptors. We disclose the pharmacological properties of the novel, selective alpha 1A-adrenoceptor antagonist N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro- alpha,alpha-dimethyl-1H-indole-3-ethanamine hydrochloride (RS-17053) and examine critically the pharmacological identity of the alpha 1-adrenoceptor mediating contractions to NE in human LUT tissues. In several tissues from rat and cloned adrenoceptors, RS-17053 displayed high affinity for the alpha 1A-adrenoceptor (pKi and pA2 estimates of 9.1-9.9) and a 30-100-fold selectivity over the alpha 1B- and the alpha 1D-adrenoceptor subtypes (pK1 and pA2 estimates of 7.7-7.8). However, in isolated smooth muscle preparations from human LUT tissues, RS-17053 antagonized responses to NE only at high concentrations. Estimates of affinity (pA2) at alpha 1-adrenoceptors mediating NE-induced contractions were 7.5 in prostatic periurethral longitudinal smooth muscle (compared with 8.6 for prazosin), 6.9 in anterior fibromuscular stroma (prazosin, 8.9), and 7.1 in bladder neck (prazosin, 8.5). These findings indicate that contractile responses to NE in human LUT tissues are mediated by a receptor displaying pharmacological properties that are clearly different from those of the defined alpha 1A-adrenoceptor and raise the possibility that multiple forms of the alpha 1A-adrenoceptor may exist in human LUT that are discriminated by RS-17053. In this regard, the affinity estimates obtained with RS-17053 and other alpha 1-adrenoceptor antagonists in human LUT tissues are identical to those described for the putative alpha 1L-adrenoceptor.

Adrenergic alpha-Antagonists↗
PubMed1995

Stress fracture of the hyoid bone caused by induced vomiting.

Fracture of the hyoid bone is a well-documented but rare consequence of certain types of trauma to the neck and lower face that may result in significant complications. We report a case of hyoid bone fracture, caused by induced vomiting, that resolved without complications and discuss the mechanism of injury and its complications, as well as associated injuries.

Adult↗
PubMed1995

Characterization of alpha 1-adrenoceptors mediating vasoconstriction to noradrenaline and nerve stimulation in the isolated perfused mesentery of rat.

1. The objective of this study was to investigate the alpha 1-adrenoceptor subtype(s) mediating vasoconstrictor responses to perfused and neuronally-released noradrenaline (NA) in the isolated perfused mesentery preparation of rat. 2. Isolated mesenteric preparations (with gut attached) from male Sprague Dawley rats (250-300g) were perfused via the superior mesenteric artery with oxygenated Krebs solution at approximately 6 ml min-1. The effects of antagonists on vasoconstrictor responses to either perfused (+/-)-NA or periarterial nerve stimulation (70 V, 2 ms pulse width, 10 s train) were determined. 3. Vasoconstrictor responses to perfused NA were antagonized by prazosin (pA2 = 9.3 +/- 0.1), WB4101 (pA2 = 9.6 +/- 0.1), 5-methyl urapidil (5-MU: pA2 = 9.0 +/- 0.1), (+)-niguldipine (insurmountable) and spiperone (pA2 = 7.7 +/- 0.1). The insurmountable nature of the antagonism by (+)-niguldipine (0.1 nM) was greatly reduced by co-perfusion with prazosin (10 nM). Chloroethylclonidine (CEC: 100 microM for 20 min, followed by 40 min washout) caused an approximate twofold increase in the EC50 for (+/-)-NA and reduced the maximum response by approximately 25%. Pre-treatment of tissues with CEC (100 microM as above) did not significantly alter affinity estimates for prazosin (pA2 = 9.2 +/- 0.1), WB4101 (pA2 = 9.3 +/- 0.1) or 5-MU (pA2 = 8.7 +/- 0.2). Vasoconstrictor responses to periarterial nerve stimulation were antagonized by WB4101 > 5-MU > prazosin >> spiperone. CEC (100 microM as above) reduced nerve-stimulated responses by approximately 50%. 4. The affinity estimates for the various antagonists studied suggest that vasoconstrictor responses to both exogenous and neuronally-released NA are mediated via the same a,-adrenoceptor subtype. The pharmacological profile most resembles the 'classical' alpha l A-adrenoceptor, which, in turn, appears to be a rat homologue of the cloned bovine alpha lc-adrenoceptor.

Adrenergic alpha-1 Receptor Agonists↗
PubMed1995

Functional evidence equating the pharmacologically-defined alpha 1A- and cloned alpha 1C-adrenoceptor: studies in the isolated perfused kidney of rat.

1. The present study characterizes and classifies alpha 1-adrenoceptor-mediated vasoconstriction in the isolated perfused kidney of rat using quantitative receptor pharmacology and compares the results to radioligand binding studies (made in cloned alpha 1-adrenoceptor subtypes, native alpha 1A-adrenoceptors in submaxillary gland of rat, and alpha 1A-adrenoceptors in several other tissues of rat). 2. Concentration-effect curves to noradrenaline in the presence of 5-methyl-urapidil were biphasic, indicating alpha 1-adrenoceptor heterogeneity. The alpha 1-adrenoceptor subtype mediating the first phase (low affinity for 5-methyl-urapidil) could not be 'isolated' for detailed pharmacological characterization but was defined by a sensitivity to inhibition by chloroethylclonidine and an inability of methoxamine to activate the site. Additionally, vasoconstriction mediated by this alpha 1-adrenoceptor subtype or subtypes was abolished by nitrendipine (1 microM), thereby allowing characterization of the second, high affinity site for 5-methyl-urapidil. 3. The following antagonists interacted competitively with noradrenaline at the alpha 1-adrenoceptor for which 5-methyl-urapidil exhibits high affinity (pKB value): WB 4101 (10.3) > prazosin (9.5) approximately HV 723 (9.3) approximately 5-methyl-urapidil (9.2) > phenotolamine (8.6) > spiperone (pA2 = 8.1) approximately oxymetazoline (7.9). In contrast, insurmountable antagonism was seen with S(+)- and R(-)-niguldipine, the S(+)-isomer being approximately 30 fold more potent than the R(-)-isomer. Receptor protection experiments indicated that S(+)-niguldipine interacted directly with alpha 1-adrenoceptors. Dehydroniguldipine acted as a competitive antagonist (pKB = 9.0). Thus, the results with antagonists define the alpha 1-adrenoceptor as an alpha 1A-adrenoceptor. 4. An agonist 'fingerprint' was constructed in the presence of nitrendipine to define further the alpha 1A-adrenoceptor. The following order and relativity of agonist potency was obtained: cirazoline (1) approximately adrenaline (2) > noradrenaline (5) > phenylephrine (23) approximately amidephrine (31) > methoxamine (71) >> isoprenaline (1456) approximately dopamine (2210). 5. A high correlative association was shown between the affinity of antagonists obtained functionally in the isolated perfused kidney of rat and pKi values obtained from binding experiments with the cloned bovine alpha 1C-adrenoceptor (R2 = 0.85), native alpha 1A-adrenoceptors in submaxillary gland of rat (R2 = 0.79), and alpha 1A-adrenoceptors from several other tissues of rat (values taken from the literature, R2 = 0.89). 6. The present study demonstrates that the alpha 1A-adrenoceptor is the predominant alpha 1-adrenoceptor subtype mediating vasoconstrictor responses to exogenously administered noradrenaline in the isolated perfused kidney of rat. More importantly, alpha 1A-adrenoceptors mediating vasoconstrictor responses to noradrenaline exhibited a pharmacological equivalency to the cloned bovine alpha 1 c-adrenoceptor. Thus,definitive functional pharmacological data are provided for equating the two receptors and support results derived recently from molecular and radioligand binding studies.

Adrenergic alpha-Agonists↗
PubMed1995

Investigating the causes of fever in critically ill patients. Are you overlooking noninfectious causes?

Fever is common in the ICU because of patients' underlying chronic and critical illnesses, their tendency to receive multiple medications, and their frequent need for invasive procedures. Precise data on the etiology of fever in the ICU are lacking. However, common noninfectious causes include postoperative fever, drug fever, intramuscular injections, hemorrhage, and pulmonary atelectasis. Urinary tract infection appears to be the most common infectious cause, followed by pneumonia and sepsis. Many noninfectious conditions are potentially life-threatening; nevertheless, it is crucial to first exclude an infectious cause, since an untreated infection may cause rapid deterioration.

Critical Care↗
PubMed1995

Techniques for evaluating fever in the ICU. A stepwise approach for detecting infectious and noninfectious causes.

The initial work-up of a critically ill patient with fever begins with a hunt for an infectious cause. A positive urine culture, or the presence of dysuria or suprapubic tenderness, suggests urinary tract infection. Diagnosing pneumonia in ventilated patients is particularly difficult; CT may be helpful when chest films are hard to interpret. Blood cultures can rule out septicemia. Other common causes of fever in the ICU include abdominal abscesses and catheter-related infections; atelectasis has not been shown to cause fever. If the initial work-up fails to establish a cause of postoperative fever, and the fever resolves within 4 days, no further work-up is required.

Catheterization↗
PubMed1994

Evidence for an inhibitory 5-HT4 receptor in urinary bladder of rhesus and Cynomolgus monkeys.

1. The present study shows that 5-hydroxytryptamine (5-HT) inhibits electrically-evoked contractions of isolated urinary bladder strips from Rhesus and Cynomolgus monkeys via activation of 5-HT4 receptors. 2. 5-HT (0.1 nM-10 microM) produced concentration-dependent inhibition of the contractile response to electrical stimulation yielding a pEC50 of 7.8 (Rhesus monkey) and 7.6 (Cynomolgus monkey). This action of 5-HT was mimicked by 5-methoxytryptamine, renzapride and BIMU 8, each of which behaved as a full agonist relative to 5-HT. However, the potency estimate for BIMU 8 (pEC50 = 6.5) in Cynomolgus monkey was low, relative to 5-HT, indicating a possible heterogeneity of 5-HT4 receptors. 3. The inhibitory action of 5-HT was resistant to antagonism by methysergide (1 microM) and ondansetron (5 microM), thereby eliminating a role for 5-HT1, 5-HT2 and 5-HT3 receptors. The 5-HT4 receptor antagonists, GR 113808 (10 nM), DAU 6285 (1-10 microM) and RS 23597-190 (1 microM), produced parallel, dextral displacements of the concentration-effect curves to 5-HT and other related agonists with affinity estimates in agreement with those defined previously in other 5-HT4 receptor assay systems. 4. Experiments using direct electrical stimulation of bladder smooth muscle indicate that the 5-HT4 receptors are located post-junctionally. 5. The inhibitory action of 5-HT in isolated urinary bladder of monkey differs from the excitatory effect of 5-HT in urinary bladder of man. Species variation and its implications for the development of therapeutic agents are discussed.

Animals↗