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Biomedical subjects

M D Taylor

Publications and source records attributed to M D Taylor.

At least 19 recordsLinked to original sources
PubMed1992

Effects of a unilateral 6-hydroxydopamine lesion and prolonged L-3,4-dihydroxyphenylalanine treatment on peptidergic systems in rat basal ganglia.

The effect of a unilateral 6-hydroxydopamine (6-OHDA) lesion of the medial forebrain bundle or of a sham lesion on the neuropeptide content of the striatum and substantia nigra was investigated with or without 6 months L-3,4-dihydroxyphenylalanine (L-DOPA; 200 mg/kg per day) plus carbidopa (25 mg/kg per day) treatment. [Met5]- and [Leu5]enkephalin, substance P (SP), neurotensin (NT) and cholecystokinin (CCK) were measured by a combined HPLC/RIA method. Neurotensin levels were increased in the striatum, and [Leu5]enkephalin, and SP levels were reduced in the substantia nigra as a consequence of the lesion, while the levels of other peptides were unaltered. Administration of L-DOPA to sham-operated rats bilaterally increased SP levels in striatum and substantia nigra, and [Met5]enkephalin and CCK content in substantia nigra. L-DOPA treatment of 6-OHDA-lesioned rats increased [Met5]- and [Leu5]enkephalin and CCK levels in the striatum ipsilateral to the lesion but not on the intact side. In the substantia nigra, the lesion-induced decrease in [Leu5]enkephalin and SP was reversed by L-DOPA treatment, [Met5]enkephalin and CCK levels ipsilateral to the lesion were further enhanced, and there was an increase in NT ipsilateral to the lesion. Cryptic [Met5]- and [Leu5]enkephalin increased in the ipsilateral striatum following an 6-OHDA lesion. L-DOPA treatment did not alter cryptic enkephalin levels or the lesion-induced increase in cryptic [Met5]enkephalin, while cryptic [Leu5]enkephalin was further increased in lesioned animals given L-DOPA. These results suggest that the pattern of change in basal ganglia peptides in Parkinson's disease is not due solely to the destruction of the nigrostriatal pathway, the drug treatment of the disease or a combination of these factors.

Animals↗
PubMed1992

Structure-activity relationships of a series of 2-amino-4-thiazole-containing renin inhibitors.

A series of renin inhibitors was synthesized that contained a 2-amino-4-thiazolyl moiety at the P2 position. These derivatives are potent inhibitors of monkey renin in vitro and are selective in that they only weakly inhibit the closely related aspartic proteinase, bovine cathepsin D. Four compounds exhibited oral blood pressure lowering activity in high-renin normotensive monkeys. One of these compounds, 22 (PD 134672), was selected for further evaluation in renal hypertensive monkeys, on the basis of its superior efficacy and duration of action in the in vitro assays and the normotensive primate model.

Animals↗
PubMed1992

Renin inhibitors containing alpha-heteroatom amino acids as P2 residues.

A series of renin inhibitors having alpha-heteroatom amino acids as P2 substitutions has been prepared. Examples where the heteroatom is oxygen, sulfur, or nitrogen are described. Many of the compounds exhibit subnanomolar potency when tested in vitro against monkey renin. When selected compounds were tested orally in conscious, salt-depleted, normotensive, Cynomolgus monkeys, low to moderate blood pressure lowering was observed. At an oral dose of 30 mg/kg, compound 53a lowered blood pressure by a maximum of 18 mmHg at 2.5 h post-dose.

Amino Acids↗
PubMed1992

Design and synthesis of potent, selective, and orally active fluorine-containing renin inhibitors.

A series of primate renin inhibitors containing difluorocarbinol and difluoroketone groups at the P1-P1' position have been synthesized and studied both in vitro and in vivo. In vitro, the compounds were evaluated as inhibitors of monkey renin and the closely related aspartic proteinase, cathepsin D (bovine), as a measure of enzyme selectivity. Interestingly, the difluoroketone derivatives showed greatly reduced selectivity compared with the corresponding alcohols. However, selectivity could be enhanced by judicious choice of other substituents. Sites influencing selectivity, included not only P2, which is well-known to strongly affect selectivity, but also the P4, P1-P1', and P2' sites. These results make possible the design of inhibitors with a greater selectivity for either renin versus cathepsin D. In vivo several of the compounds in the difluoroketone series have shown good oral activity in the salt depleted normotensive cynomolgus monkey model.

Administration, Oral↗
PubMed1991

Acute effects of D-1 and D-2 dopamine receptor agonist and antagonist drugs on basal ganglia [Met5]- and [Leu5]-enkephalin and neurotensin content in the rat.

The effects of acute systemic injection of the D-1 agonist SKF 38393 (2.5-20 mg/kg) or the D-1 antagonist SCH 23390 (0.25-2.0 mg/kg), and of the D-2 agonist quinpirole (0.12-1.0 mg/kg) or the D-2 antagonist sulpiride (25-100 mg/kg) on the neuropeptide content of rat basal ganglia were investigated. In striatum, the [Met5]- and [Leu5]-enkephalin content was unaffected by administration of SKF 38393 or SCH 23390. Quinpirole had no effect on [Met5]- and [Leu5]-enkephalin levels but sulpiride produced an increase in both [Met5]- and [Leu5]-enkephalin content. In the nucleus accumbens, SKF 38393 decreased and SCH 23390 increased [Met5]- and [Leu5]enkephalin levels. Quinpirole decreased [Met5]- and [Leu5]-enkephalin levels, while sulpiride decreased [Leu5]-enkephalin levels alone. The content of [Leu5]- but not [Met5]-enkephalin levels in the substantia nigra was increased by administration of SKF 38393, and decreased by SCH 23390. Quinpirole and sulpiride were without effect on the [Met5]- or [Leu5]-enkephalin content of substantia nigra. Neurotensin levels in striatum were increased by administration of SKF 38393 and decreased by SCH 23390. Similarly, quinpirole decreased the neurotensin content while sulpiride caused an increase. In the nucleus accumbens, the neurotensin content was not affected by administration of SKF 38393 but increased by SCH 23390. Neither quinpirole nor sulpiride altered neurotensin levels in the nucleus accumbens. Neurotensin levels in substantia nigra were unaffected by the administration of SKF 38393 and SCH 23390, or by quinpirole and sulpiride. These results indicate that acute administration of D-1 and D-2 agonist and antagonist drugs can alter the levels of [Met5]- and [Leu5]-enkephalin and neurotensin in basal ganglia. However, there are marked differences between brain regions in the regulation of peptide levels by acute D-1 and D-2 receptor occupation.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1991

Neuropeptide levels in the basal ganglia of aged common marmosets following prolonged treatment with MPTP.

Aged common marmosets were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 0.5-2.0 mg/kg/week i.p.) for 16 or 24 weeks, observed for a total of 30 weeks and then killed for measurement of biochemical parameters in basal ganglia. The MPTP treatment induced a marked depletion in dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid levels in the caudate nucleus and putamen. In contrast, the concentrations of five neuropeptides: [Met5]-enkephalin, [Leu5]-enkephalin, cholecystokinin, substance P and neurotensin as measured by a combined HPLC/RIA method, remained unaltered in all basal ganglia regions examined. Enkephalin precursor levels, as reflected by cryptic [Met5]-enkephalin content, were increased in the putamen, but not in the caudate nucleus, as a consequence of MPTP administration. Cryptic [Leu5]-enkephalin content remained unchanged in the striatum of MPTP treated marmosets. Overall, these results suggest an increase in striatal [Met5]-enkephalin release following chronic MPTP treatment of aged marmosets. However, the chronic treatment of aged marmosets with MPTP does not reproduce the neuropeptide alterations characteristic of Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1991

Isocratic reverse-phase HPLC separation and RIA used in the analysis of neuropeptides in brain tissue.

A reverse-phase, high-performance liquid chromatographic (HPLC) method was employed to separate and characterise five neuropeptides from complex mixtures, with important advantages over methods employed earlier using combined HPLC-RIA studies. Peptides were separated using 0.5M pyridine-0.5M formic acid buffer, pH 4, containing propan-l-ol 14% (met-enkephalin, leu-enkephalin, neurotensin) or 20% (CCK-8-S, substance P) at a flow rate of 1.0 ml/min. Isocratic conditions, and volatile solvents, resulted in a highly reproducible method, producing samples in a form designed for subsequent RIA. The application and importance of the procedure is demonstrated by comparison of the measurements of apparent peptide levels in crude brain extracts with those of authentic peptides as determined after HPLC purification.

Animals↗
PubMed1991

New inhibitors of human renin that contain novel replacements at the P2 site.

A series of renin inhibitors with novel modifications at the P2 site has been prepared. Structure-activity relationships reveal that for a particular P2 fragment the in vitro potency is highly dependent on the nature of the P2' portion in addition to the P1-P1' group. The length of the P2 side chain and choice of epsilon-N P2 substitution have been found to be important for in vitro potency although the degree of unsaturation in the P2 side chain is not particularly significant. Molecular modeling studies have shown that it is possible for the P2 side chain to interact unfavorably with the P2' binding site. It has been possible to control the specificity for renin over cathepsin D by correct modification at the P2' and P1-P1' sites. Variations at the P4 site have been utilized to lower the log P values of these renin inhibitors while maintaining high potency. Compound 42, which exhibited an IC50 of 3.70 nM, log P of 2.3, and showed high specificity for renin, was selected for further studies. It was found to be very stable under neutral, acidic, and basic conditions. In simulated intestinal juice, compound 42 had a half-life of 37 min while it was virtually unaffected by simulated gastric juice after 4 h. Compound 42 produced a significant hypotensive response upon intravenous administration to the salt-depleted normotensive cynomolgus monkey.

Animals↗
PubMed1991

Calcium channel blocking and positive inotropic activities of ethyl 5-cyano-1,4-dihydro-6-methyl-2-[(phenylsulfonyl)methyl]-4-aryl-3- pyridine-carboxylate and analogues. Synthesis and structure-activity relationships.

The synthesis and pharmacological evaluation of a series of 2-[(arylsulfonyl)methyl]-4-aryl-5-cyano-1,4-dihydropyridine-3-carboxylic acid esters and analogues are described. These compounds possess a unique profile namely, calcium channel blocking and positive inotropic activities in vitro. Compound 54 was selected as the best compound in the series and was studied in detail. The synthesis and biological profiles of enantiomers of 54 are also reported. The data indicate that although the calcium channel blocking property of 54 is stereospecific the positive inotropic activity is not. Examples of 3- and 6-cyano and other closely related 1,4-dihydropyridine derivatives are described and evaluated for comparison and were found to be devoid of dual activities mentioned above.

Animals↗
PubMed1991

Structure-activity studies of the C-terminal region of the endothelins and the sarafotoxins.

Peptides corresponding to the C-terminal 16-21 hexapeptide of the endothelins (-His-Leu-Asp-Ile-Ile-Trp) and sarafotoxins (a-c) (-His-Gln-Asp-Val-Ile-Trp) were prepared to study the role of the individual amino acids in receptor recognition and activation. Receptor binding in rabbit aorta, rabbit pulmonary artery, and rat heart ventricle is reported for all analogues. In addition, selected C-terminal hexapeptides have been evaluated functionally in two tissues (rabbit pulmonary artery and rat left atria). The C-terminal carboxylate, indole nitrogen, and nature of the aromatic residue are all important for receptor binding, but N-terminal acetylation has no effect. L-Amino acids are required in positions 19 and 21, whereas D-amino acids are tolerated in 17 and 18. D-Amino acids in positions 16 and 20 enhance the binding affinity of the hexapeptide in all three tissues. The nature of the basic residue at position 16 is important. Glu and Asn are acceptable substitutions for Asp18, although Ala leads to a substantial loss in binding. The binding of the C-terminal hexapeptide of SRTX-a, -b, and -c is less than ET[16-21] and this appears to be primarily due to the substitution of Gln for Leu17. None of the 16-21 hexapeptides showed any functional activity in the tissues studied.

Amino Acid Sequence↗
PubMed1991

Lifestyle changes in mild asthma during intermittent symptom-related use of terbutaline inhaled via 'Turbohaler'.

Beta 2-agonist therapy effectively relieves asthmatic symptoms, but an improvement in patient lifestyle has not been demonstrated. This open study in which patients acted as their own controls, assessed the efficacy and acceptability of intermittent symptom-related use of terbutaline inhaled via 'Turbohaler', and its influence on the lifestyle of 1133 inhaler-naive, mild asthmatics treated in general practice. A 1-week run-in period was followed by 4-weeks' treatment with inhaled terbutaline (500 micrograms as required). Peak expiratory flow rate (PEFR) and 'Turbohaler' technique were assessed at clinic visits. Diary cards, completed daily, assessed: the number of terbutaline inhalations, the relief obtained after use, the severity of asthma symptoms (cough, morning wheeze, nocturnal wheeze and wheeze on activity), and lifestyle indices (sleep disturbance, work/school days lost, limitation of normal activity). After terbutaline treatment, PEFR increased by 54 +/- 2 l/min (p less than 0.001), the severity of asthma symptoms was almost halved (p less than 0.001), with over two-thirds (65% to 76%) of patients reporting improvements in each variable, and the adverse effect of asthma on lifestyle was at least halved (p less than 0.001). Improvements in lung function, asthma symptoms and lifestyle were comparable for all sub-groups: adults (greater than 16 years), school-age children (6 to 16 years) and preschool children (less than or equal to 5 years). This study not only confirmed the efficacy and acceptability of intermittent symptom-related use of terbutaline inhaled via 'Turbohaler', but also demonstrated that its use enhanced patients' lifestyles.

Activities of Daily Living↗
PubMed1991

Budesonide once-daily in seasonal allergic rhinitis.

A randomized, parallel group, double-blind multi-centre study was carried out in 342 patients with symptomatic seasonal allergic rhinitis to assess the efficacy and tolerability of intranasal budesonide administered either as a single morning dose of 400 micrograms or as a 200 micrograms twice-daily dose, morning and evening, for 4 weeks. Both treatments improved the symptoms of seasonal allergic rhinitis; specific nasal symptom scores recorded daily by the patient being reduced. The proportions of patients symptom free after 4-weeks' treatment were 46% in the 400 micrograms once-daily group and 54% in the 200 micrograms twice-daily group, with total daily symptom scores recorded by diary cards reduced by 79% and 80%, respectively. The differences between the groups were not statistically significant. Sub-group analysis of patients allergic to grass pollen (n = 166) showed similar total symptom scores at each level of grass pollen exposure (no significant difference between treatment groups). Patients assessed both treatments to be effective (no significant difference between groups), with 65% of patients questioned stating a preference for a once-daily treatment given equal symptom control. Both treatments were equally well tolerated and few side-effects were reported.

Administration, Intranasal↗
PubMed1991

Intranasal budesonide once daily in seasonal allergic rhinitis.

A double-blind, parallel-group, multi-centre study was carried out in 248 patients with symptomatic seasonal allergic rhinitis to assess the effectiveness and tolerability of intranasal aqueous budesonide given as a single daily dose each morning of 400 micrograms compared with the conventional dosage regimen of 200 micrograms twice daily. After a 1-week run-in period during which only oral terfenadine was allowed for intolerable symptom relief, symptomatic patients were allocated at random to receive budesonide in one or other dosage regimen for 3 weeks. The results of assessments made by the physician at clinic visits and by patients recording daily data on diary record cards showed that specific nasal symptom incidence and severity were significantly (p less than 0.001) reduced in both treatment groups. The proportions of patients symptom-free at 3 weeks were 40% in the 400 micrograms once daily and 45% in the 200 micrograms twice daily group; in addition, mean nasal symptom scores from the daily diary cards were significantly (p less than 0.001) reduced in both groups, with a reduction in total symptom scores of 53% and 60%, respectively. The differences between the groups were not statistically significant. Total symptom scores were significantly (p less than 0.01) reduced in both dosage groups at all levels of pollen exposure. Patients rated treatment overall as being highly effective, mean scores being very similar in both groups, and tolerability was similar and good whether budesonide was given as a 400 micrograms once daily dose or as 200 micrograms twice daily. Assuming equal symptom control, 74% of patients stated they would prefer once daily to twice daily treatment.

Administration, Intranasal↗
PubMed1989

Pulmonary capillary pressures during hypoxia and hypoxemia: experimental and clinical studies.

Unlike the systemic circulation, the pulmonary vasculature constricts in response to hypoxia to divert blood flow to better-ventilated segments. The site of this response, the hypoxic pulmonary vasoconstriction, has been reported as precapillary in numerous experimental models of isolated animal lungs. In the present study, the response of intact chest dog and human lungs to hypoxia and hypoxemia, respectively, was also precapillary vasoconstriction. In dogs, hypoxia in the ipsilateral lung attenuated the normal vertical blood flow gradient. Contralateral hypoxia did not alter pulmonary regional blood flow, precapillary (Ra), postcapillary, or total pulmonary vascular resistance. In patients, an elevated alveolar-arterial oxygen pressure gradient of 50 to 150 torr resulted in significantly increased Ra. Further hypoxemia did not increase this response. In addition, the effective pulmonary capillary pressure did not bear a constant relationship to the pulmonary artery occlusion or wedge pressure (WP). Therefore, in patients in respiratory failure, WP does not reliably estimate hydrostatic pressure at the pulmonary capillaries.

Animals↗
PubMed1989

PD 122860: a novel dihydropyridine with sodium channel stimulating and calcium channel blocking properties.

The cardiac and vascular activities of ethyl 5-cyano-1,4-dihydro-6-methyl-2-[(4-pyridinyl-sulfonyl)methyl]-4-[2- (trifluoromethyl)phenyl]-3-pyridine carboxylase (PD 122860), a novel dihydropyridine, were investigated in vitro using rat heart and rabbit aorta, and compared with reference inotropic and vasodilator agents. In the rat heart, PD 122860 increased left ventricular contractility, decreased coronary resistance and altered the shape of the electrocardiogram T-wave. All three effects were observed at comparable concentrations of PD 122860. The inotropic response to PD 122860 was reversed by the Na+ channel blocker tetrodotoxin and blunted by the Na+-Ca++ exchange inhibitor dichlorobenzamil. The effects of tetrodotoxin and dichlorobenzamil on the inotropic response to the reference Na+ channel stimulant veratridine were comparable to PD 122860, whereas tetrodotoxin and dichlorobenzamil had no inhibitory effect on the inotropic responses to the adenylate cyclase stimulator forskolin or the Ca++ channel stimulant BAY K 8644. PD 122860 selectively relaxed potassium-contracted aortic rings and inhibited [3H]nitrendipine binding to rat brain membranes, suggesting that the vasodilator activity of PD 122860 is due to Ca++ channel blockade. In contrast to BAY K 8644, PD 122860 did not contract partially depolarized aortic rings, suggesting an absence of Ca++ channel stimulant activity. PD 122860 is a racemic mixture and both the vasorelaxant and [3H]nitrendipine binding inhibitory activities selectively reside in the (+)-enantiomer [(+)-PD 122860]. In contrast, the inotropic response resides with both enantiomers of PD 122860. It is therefore concluded that PD 122860 represents a unique dihydropyridine derivative which possesses both Na+ channel stimulating and Ca++ channel blocking activities.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1988

2-(2-Aryl-2-oxoethylidene)-1,2,3,4-tetrahydropyridines. Novel isomers of 1,4-dihydropyridine calcium channel blockers.

The title compounds are novel double bond isomers of 1,4-dihydropyridine-type calcium channel blockers (CCB). These derivatives were prepared by using the Hantzsch dihydropyridine synthesis. The assignment of structure was based on spectroscopic data and a regiochemically unambiguous synthesis. Several of the analogues inhibited [3H]nitrendipine binding with IC50 values as low as 25 nM. By comparison, nifedipine, a clinically useful 1,4-dihydropyridine CCB, inhibits [3H]nitrendipine binding with an IC50 of 1.6 nM. In the Langendorff rat heart preparation, treatment with the more potent derivatives produced marked dose-related increases in coronary flow with little or no effect on heart rate or contractility, except at the highest concentrations tested. The selectivity for vascular versus cardiac effects was similar to that of nifedipine, i.e., the concentration producing vasodilation was approximately 2 orders of magnitude lower than the concentration eliciting cardiodepression. These novel isomers extend the structure-activity relationships for calcium channel blockers into a series closely related to the 1,4-dihydropyridines.

Animals↗