RESUMO
In functional pharmacological assays, talsaclidine has been described as a functionally preferential M1 agonist with full intrinsic activity, and less pronounced effects at M2- and M3 receptors. In accordance with this, cholinomimetic central activation measured in rabbits by EEG recordings occurred at a 10 fold lower dose than that inducing predominantly M3-mediated side effects. This pharmacological profile is also reflected in the clinical situation: Both in healthy volunteers and in Alzheimer patients--unlike after unspecific receptor stimulation through cholinesterase inhibitors--the mainly M3-mediated gastrointestinal effects (like nausea and vomiting) were not dose-limiting. Rather, sweating and hypersalivation, mediated through muscarinic receptors, occurred dose-dependently and were finally dose-limiting. In contrast to talsaclidine, sabcomeline had a less pronounced functional M1 selectivity in pharmacological assays. This was also shown in anaesthetized guinea pigs where sabcomeline alone induced bronchoconstriction, and in the rabbit EEG where central activation and cholinergic side effects occurred in the same dose range. Neither drug, however, showed convincing improvement of cognitive functions in patients with mild-to-moderate Alzheimer's disease. This asks for a reassessment of the muscarinic hypothesis for the treatment of this disease.
Assuntos
Doença de Alzheimer/tratamento farmacológico , Iminas/farmacologia , Agonistas Muscarínicos/farmacologia , Quinuclidinas/farmacologia , Receptores Muscarínicos/metabolismo , Antagonistas Adrenérgicos beta/farmacologia , Adulto , Animais , Espasmo Brônquico/induzido quimicamente , Relação Dose-Resposta a Droga , Eletroencefalografia/efeitos dos fármacos , Feminino , Cobaias , Coração/efeitos dos fármacos , Humanos , Iminas/administração & dosagem , Iminas/efeitos adversos , Iminas/uso terapêutico , Técnicas In Vitro , Masculino , Pessoa de Meia-Idade , Agonistas Muscarínicos/administração & dosagem , Agonistas Muscarínicos/efeitos adversos , Agonistas Muscarínicos/uso terapêutico , Músculo Liso/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Propanolaminas/farmacologia , Quinuclidinas/administração & dosagem , Quinuclidinas/efeitos adversos , Quinuclidinas/uso terapêutico , Coelhos , RatosRESUMO
The in vitro biological characterisation of the first potent and selective non-peptide neuropeptide Y Y(2) receptor antagonist, (S)-N(2)-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6h)-oxodibenz[b, e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl] cylopentyl] acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2, 4-triazol-4-yl]ethyl]-argininamid (BIIE0246) is reported. BIIE0246 displaced [125I]neuropeptide Y with high affinity (IC(50)=3.3 nM) from the human neuropeptide Y Y(2) receptor and proved to be highly selective. BIIE0246 displayed antagonistic properties and thus represents the first selective non-peptide neuropeptide Y Y(2) receptor antagonist.
Assuntos
Arginina/análogos & derivados , Benzazepinas/farmacologia , Receptores de Neuropeptídeo Y/antagonistas & inibidores , Animais , Arginina/metabolismo , Arginina/farmacologia , Benzazepinas/metabolismo , Ligação Competitiva/efeitos dos fármacos , Células CHO , Linhagem Celular , Cricetinae , Relação Dose-Resposta a Droga , Humanos , Radioisótopos do Iodo , Masculino , Contração Muscular/efeitos dos fármacos , Neuropeptídeo Y/metabolismo , Neuropeptídeo Y/farmacologia , Ensaio Radioligante , Ratos , Receptores de Neuropeptídeo Y/metabolismo , Células Tumorais Cultivadas , Ducto Deferente/efeitos dos fármacos , Ducto Deferente/fisiologiaRESUMO
Several attempts to investigate the bioactive conformation of neuropeptide Y have been made so far. As cyclic peptides are much more rigid than linear ones, we decided to synthesise cyclic analogues of the C-terminal dodekapeptide amide neuropeptide Y Ac-25-36. Cyclisation was performed by side chain lactamisation of ornithine or lysine and glutamic or aspartic acid. The affinity of the 19 peptides ranged from Ki 0.6 nM to greater than 10,000 nM. We found that the size, position, orientation, configuration. and the location of the cycle plays an important role for receptor recognition. Circular dichroic studies have been performed to characterise the secondary structure of each peptide. Receptor binding studies were carried out on human neuroblastoma cell lines SK-N-MC (Y1) and SMS-KAN (Y2), and on rabbit kidney membranes (Y2). The pharmacological and spectral data showed that the alpha-helix content was not the predominant factor for high Y2-receptor affinity. Instead, the location and the size of the hydrophobic lactam bridge, and the conserved C-terminal tetrapeptide (Arg-Glu-Arg-Tyr) seemed to be the main parameters. Using molecular dynamics, the structures of four cyclic peptides (i,i+4) have been investigated and compared with the previously published NMR structure of one of the cyclic peptide analogues. Significant differences have been found in the overall three-dimensional fold of the peptides. The distances between the N- and the C-terminus allow discrimination between peptides with high binding affinity and those with low binding affinity, because of the correlation that was found with the measured affinity. Thus, this study suggests that a turn-like structure and the orientation of the C-terminus towards the N-terminus play major roles for high affinity binding of cyclic dodecapeptides to the Y2-receptor. None of the cyclic segments exhibits significant affinity to the Y1-receptor. Thus, these results support the hypothesis of a discontinuous binding site of neuropeptide Y at the Y1-receptor.
Assuntos
Receptores de Neuropeptídeo Y/química , Animais , Dicroísmo Circular , Humanos , Espectroscopia de Ressonância Magnética , Masculino , Neuropeptídeo Y/metabolismo , Peptídeos Cíclicos/síntese química , Estrutura Secundária de Proteína , Coelhos , Receptores de Neuropeptídeo Y/metabolismo , Relação Estrutura-Atividade , Células Tumorais CultivadasRESUMO
1. Neuropeptide-induced histamine release is thought to occur via receptor-independent mechanisms, with net charge and lipophilicity being important factors. 2. In this study, the histamine releasing ability of neuropeptide Y (NPY), two C-terminal segments of NPY and 13 centrally truncated NPY analogues was examined. These results were compared with the ability of the peptides to bind to the Y2 receptor in the rabbit kidney membrane model and with their hypotensive actions in the anaesthetized-rat model. 3. All analogues tested, with the exception of [Glu4,25,33,35]-NPY(1-4)-Ahx-(25-36) and [Asp4,25,33,35]NPY(1-4)-Ahx-(25-36) which were devoid of histamine releasing activity, evoked a dose-dependent histamine release but there were marked differences between the peptides. The native peptide was the least active. 4. Histamine release was not linked to the ability of the peptides to displace NPY from Y2 receptors. There was a statistical correlation between the hypotensive effects expressed as ED10 values (mumol kg-1, which induced a blood pressure decrease of 10 mmHg) and the EC25 for histamine release (r = 0.62, P = 0.04), although histamine release may not be the sole determinant of the alterations in blood pressure. 5. There was a strong negative correlation between EC25 for histamine release and net positive charge (r = -0.93, P = 5.7 x 10(-7), i.e. increasing the net positive charge caused greater histamine release. However, there was a 12 fold difference in activity amongst the most positively charged analogues (+5). Helicity did not correlate with histamine releasing ability. 6. In the development of NPY-related drugs the avoidance of compounds with net positive charge is recommended.
Assuntos
Pressão Sanguínea/efeitos dos fármacos , Liberação de Histamina/efeitos dos fármacos , Mastócitos/efeitos dos fármacos , Neuropeptídeo Y/análogos & derivados , Neuropeptídeo Y/farmacologia , Animais , Fenômenos Químicos , Físico-Química , Dicroísmo Circular , Técnicas In Vitro , Rim/efeitos dos fármacos , Rim/metabolismo , Masculino , Mastócitos/metabolismo , Coelhos , Ratos , Receptores de Neuropeptídeo Y/efeitos dos fármacos , Relação Estrutura-AtividadeRESUMO
Alzheimer disease (AD) is a neurodegenerative disorder lacking an effective therapy. The etiology is controversial and among different drug strategies, the cholinergic approach has gained great interest owing to biochemical and pharmacological evidence of the crucial role of acetylcholine in cognitive functions. Several attempts exploiting the boosting of the cholinergic system are currently under way. Inhibitors of the acetylcholinesterase enzyme sustain the availability of the natural transmitter by limiting its removal from the synapse. In a different approach, exogenous agonists may substitute acetylcholine itself. In this way the issue of the extensive cholinergic cell loss occurring in AD and leading to a reduction of cholinergic functions, could be advantageously bypassed. Moreover the discovery of different muscarinic receptor subtypes, most notably the M1 subtype as that involved in the postsynaptic transmission, has offered new opportunities to face the problem in a very specific way. In this line of research, we have now identified BIMC 182 as a new functionally selective M1 agonist. Whereas its affinity for the different receptor subtypes is almost similar (radioreceptor binding), its functional selectivity is pointed out by specific "in vitro" models. BIMC 182 behaves as a full agonist at M1 (rat superior cervical ganglion, pD2 4.8) and as a partial agonist at M2 and M3 sites (g.p. heart pD2 = 5.4 and g.p. ileum pD2 = 4.5). The agonist profile is further confirmed in hm1 transfected CHO cells where the compound stimulates PI turnover. BIMC 182 penetrates well the brain as shown by the increase in the energy of the low frequency band (theta waves) in the cortical EEG of rabbits (3 mg/kg i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Doença de Alzheimer/tratamento farmacológico , Agonistas Muscarínicos/farmacologia , Animais , Encéfalo/efeitos dos fármacos , Células CHO , Cricetinae , Feminino , Aprendizagem/efeitos dos fármacos , Masculino , Agonistas Muscarínicos/metabolismo , Agonistas Muscarínicos/uso terapêutico , Coelhos , Ratos , Receptores Muscarínicos/metabolismoRESUMO
A discontinuous 17-amino acid peptide analog of neuropeptide Y (NPY), NPY 1-4-Ahx-25-36 containing 6-aminohexanoic acid instead of the residues 5 to 24, was found to bind preferentially to Y2 subtypes of NPY receptors. In order to further characterize the binding site, three different types of cyclic analogs were synthesized. Firstly lactamisation between residues 2 and 30 led to the most selective Y2-agonist, secondly lactamisation between the N-terminus and residue 31 reduced binding significantly. Thirdly, any cyclization including the C-terminus led to an inactive compound. Circular dichroism revealed different conformations for the three analogs with reduced alpha-helical content in comparison to the linear ana-log. The different conformation of the peptides has been confirmed by molecular dynamics simulations. A model for peptide-receptor interaction is suggested.
Assuntos
Neuropeptídeo Y/análogos & derivados , Peptídeos Cíclicos/metabolismo , Receptores de Neuropeptídeo Y/metabolismo , Sequência de Aminoácidos , Animais , Dicroísmo Circular , Simulação por Computador , Técnicas In Vitro , Rim/metabolismo , Dados de Sequência Molecular , Neuropeptídeo Y/síntese química , Neuropeptídeo Y/metabolismo , Peptídeos Cíclicos/síntese química , Conformação Proteica , CoelhosAssuntos
Rim/metabolismo , Neuropeptídeo Y/metabolismo , Receptores de Neuropeptídeo Y/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Dados de Sequência Molecular , Neuropeptídeo Y/síntese química , Neuropeptídeo Y/química , Neuropeptídeo Y/farmacologia , Coelhos , Receptores de Neuropeptídeo Y/química , Receptores de Neuropeptídeo Y/efeitos dos fármacos , Receptores de Neuropeptídeo Y/imunologia , Relação Estrutura-AtividadeRESUMO
Previous attempts to classify neuropeptide Y receptor subtypes suffered from relying only on carboxyl-terminal analogs and fragments of neuropeptide Y. We have tested the potency and affinity of chemically different compounds, i.e., centrally truncated analogs of neuropeptide Y, in three Y1-like (Ca2+ mobilization in HEL cells, blood pressure increases in pithed rats, and 125I-neuropeptide Y binding in SK-N-MC cells) and two Y2-like (125I-neuropeptide Y binding to rabbit kidney membranes and presynaptic inhibition in rat vas deferens) model systems of neuropeptide Y receptors. Our data confirm the concept of two major subclasses of neuropeptide Y receptors, with some centrally truncated neuropeptide Y analogs having high affinity for Y2-like and low affinity for Y1-like neuropeptide Y receptors. Some of the truncated neuropeptide Y analogs are antagonists at Y1-like receptors and (possibly partial) agonists at Y2-like receptors. Our data also indicate that amino acid residues distal from the amino- and carboxyl-terminal ends of the peptide may subtype-selectively affect affinity and intrinsic efficacy of peptide agonists at neuropeptide Y receptors.
Assuntos
Neuropeptídeo Y/metabolismo , Receptores de Neuropeptídeo Y/metabolismo , Sequência de Aminoácidos , Animais , Pressão Sanguínea/efeitos dos fármacos , Cálcio/metabolismo , Células Cultivadas , Humanos , Técnicas In Vitro , Dados de Sequência Molecular , Neuropeptídeo Y/química , Neuropeptídeo Y/farmacologia , Coelhos , Ratos , Relação Estrutura-Atividade , Transmissão Sináptica/efeitos dos fármacosRESUMO
The low-molecular-mass, cyclic analog of neuropeptide Y, [Ahx5-24, gamma-Glu2-epsilon-Lys30] NPY (YESK-Ahx-RHYINKITRQRY; Ahx, 6-aminohexanoic acid; NPY, neuropeptide Y), was synthesized and investigated for receptor binding, inhibition of forskolin-stimulated cAMP accumulation, inhibition of electrically stimulated rat vas deferens contractions and ability to increase blood pressure. Like the linear peptide [Ahx5-24] NPY (YPSK-Ahx-RHYINLITRQRY), the more rigid, cyclic analog showed good correlation between receptor binding to rabbit kidney membranes and biological activity in the vas deferens assay. Binding of this peptide to a new Y2-receptor-expressing cell line was slightly reduced, compared to the linear peptide [Ahx5-24] NPY, however inhibition of cAMP accumulation was even more efficient. Unlike the linear peptide [Ahx5-24] NPY, the cyclic analog did not induce a blood pressure increase in rats. Reduced binding to Y1 receptor-expressing SK-N-MC cells, as well as the loss of capability of signal transduction, suggest that only Y2-mediated activity is preserved after cyclization. The selectivity of the cyclic compound for Y2 subtypes of NPY receptors with respect to inhibition of cAMP accumulation is more than fortyfold increased, as compared to the linear NPY-(13-36) peptide, which has been used to determine Y2 selectivity so far.
Assuntos
Neuropeptídeo Y/análogos & derivados , Fragmentos de Peptídeos/química , Peptídeos Cíclicos/química , Receptores de Neurotransmissores/metabolismo , Sequência de Aminoácidos , Animais , Pressão Sanguínea/efeitos dos fármacos , Membrana Celular/metabolismo , Colforsina/farmacologia , AMP Cíclico/metabolismo , Estimulação Elétrica , Humanos , Córtex Renal/metabolismo , Masculino , Dados de Sequência Molecular , Contração Muscular/efeitos dos fármacos , Neuropeptídeo Y/química , Neuropeptídeo Y/metabolismo , Neuropeptídeo Y/farmacologia , Fragmentos de Peptídeos/metabolismo , Fragmentos de Peptídeos/farmacologia , Peptídeos Cíclicos/metabolismo , Peptídeos Cíclicos/farmacologia , Coelhos , Ratos , Receptores de Neuropeptídeo Y , Sinapses/fisiologia , Células Tumorais Cultivadas , Ducto Deferente/efeitos dos fármacos , Ducto Deferente/fisiologiaRESUMO
C-terminal analogues of neuropeptide Y (NPY) of small molecular size have been synthesized. The influence of chain length, single or multiple amino acid substitution, and segment substitutions on receptor binding, pre- and postsynaptic biological activity, and conformational properties have been investigated. Receptor binding and in vivo assays revealed biological activity for NPY Ac-25-36 that increased with increasing alpha-helicity. In attempts to stabilize the alpha-helical content, three independent types of modified NPY Ac-25-36 analogues were synthesized. Strong agonistic activities could be detected in a series of discontinuous analogues, which are constructs of N-terminal parts linked via different spacer molecules to C-terminal segments. One of the most active molecules was NPY 1-4-Aca-25-36 (Aca, epsilon-aminocaproic acid). For the first time conformational properties of a series of small NPY analogues have been investigated by CD, and correlated with biological activity and receptor binding. A C-terminal dodecapeptide segment of NPY with an amount of 50% substitution to the native C-terminal sequence of NPY was found to exhibit significant receptor binding.
Assuntos
Neuropeptídeo Y/química , Sequência de Aminoácidos , Animais , Pressão Sanguínea/efeitos dos fármacos , Dicroísmo Circular , Dados de Sequência Molecular , Neuropeptídeo Y/análogos & derivados , Neuropeptídeo Y/metabolismo , Neuropeptídeo Y/farmacologia , Conformação Proteica , Ratos , Receptores de Neuropeptídeo Y , Receptores de Neurotransmissores/metabolismo , Relação Estrutura-AtividadeRESUMO
C-terminal analogues of neuropeptide Y have been synthesized. The influence of chain length, single-amino-acid substitutions and segment substitutions on receptor binding, biological activity and conformational properties has been investigated. Receptor binding and in vivo assays revealed biological activity already for amino acids 28-36 of neuropeptide Y [neuropeptide Y-(Ac-28-36)-peptide] which increased with increasing chain length. Replacement of Arg25 in neuropeptide Y-(Ac-25-36)-peptide had no influence on binding, whereas Arg33 and Arg35 cannot be replaced by lysine or ornithine without considerable decrease in receptor binding. The introduction of conformational constraints by the 2-aminoisobutyric acid residue (Aib) in position 30 and replacing the amino acids 28-32 by Ala-Aib-Ala-Aib-Ala decreased receptor binding. However, the corresponding Aib-Ala-Aib-Ala-Aib-substituted analogue and a more flexible analogue with Gly5 at position 28-32 exhibited considerable affinity for the receptor. All these substitutions led to a decrease in postsynaptic activity. Strong agonistic activities could be detected in a series of 10 discontinuous analogues, which are constructs of N-terminal parts linked via different spacer molecules to C-terminal segments. One of the most active molecules was neuropeptide Y amino acids 1-4 linked to amino acids 25-36 through aminohexanoic acid (Ahx) [neuropeptide Y-(1-4-Ahx-25-36)-peptide].
Assuntos
Neuropeptídeo Y/química , Sequência de Aminoácidos , Animais , Pressão Sanguínea/efeitos dos fármacos , Cromatografia em Camada Fina , Dados de Sequência Molecular , Neuropeptídeo Y/metabolismo , Neuropeptídeo Y/farmacologia , Conformação Proteica , Coelhos , Ratos , Receptores de Neuropeptídeo Y , Receptores de Neurotransmissores/metabolismo , Espectrofotometria Ultravioleta , Relação Estrutura-Atividade , Sinapses/efeitos dos fármacosRESUMO
Based on the hypothetical 3D structure of neuropeptide Y (NPY), NPY 1-4-Aca-25-36, a 17 amino acid analogue, has been synthesized replacing the sequence NPY 5-24 by epsilon-aminocaproic acid (Aca). This low-molecular weight deletion analogue showed nearly comparable receptor affinity to NPY. In order to elucidate the structural requirements for receptor recognition each amino acid of 1-4-Aca-25-36 was exchanged by its D-enantiomer, glycine and L-alanine. In addition distinct amino acids were replaced by closely related residues. Multiple peptide synthesis was applied using Fmoc-strategy and BOP activation. Binding assay was performed on rabbit kidney membrane preparations. The results of structure affinity studies suggest that the C-terminal tetrapeptide NPY 33-36 is essential for receptor recognition.
Assuntos
Neuropeptídeo Y/metabolismo , Alanina/metabolismo , Sequência de Aminoácidos , Sítios de Ligação , Variação Genética , Glicina/metabolismo , Dados de Sequência Molecular , Neuropeptídeo Y/análogos & derivados , Neuropeptídeo Y/química , Conformação Proteica , EstereoisomerismoRESUMO
Analogues of neuropeptide Y (NPY) containing small N- and C-terminal segments linked via flexible spacer arms were found to exhibit receptor binding affinity constants almost as high as NPY as well as post- and presynaptic NPY-agonistic activities. One of the most active analogues contains N-terminal NPY segment 1-4 linked via epsilon-aminocaproic acid (Aca) to the C-terminal partially alpha-helical peptide amide segment 25-36. NPY 1-4-Aca-25-36 is the first highly potent NPY agonist, which is of considerably reduced size in comparison to the native hormone. The analogues are accessible by solid-phase synthesis using Fmoc strategy.
Assuntos
Neuropeptídeo Y/metabolismo , Fragmentos de Peptídeos/metabolismo , Ácido Aminocaproico , Estrutura Molecular , Neuropeptídeo Y/análogos & derivados , Conformação Proteica , Receptores de Neuropeptídeo Y , Receptores de Neurotransmissores/metabolismoRESUMO
MEN 935 [1-(3-[3-(1-naphthoxy)-2-hydroxypropyl) amino)-3,3-dimethylpropyl)-2-benzimidazolinone-hydrochloride monohydrate, adimolol] is a long acting antihypertensive agent with beta- and alpha-adrenolytic properties. Preliminary experiments in pithed rats had led to the suggestion that the alpha-adrenolytic activity was of the alpha 2-subtype. The alpha-adrenolytic properties of MEN 935 were now tested in isolated vascular preparations of rat aorta, rabbit vena ischiadica and rabbit vena cava inferior against the selective alpha 1-adrenergic agonist phenylephrine (PE) and the selective alpha 2-adrenergic agonist B-HT 920 [2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-(4,5-d)azepine]. The experiments were performed in absence and in presence of 5 X 10(-9) mol/l angiotensin II (A II). MEN 935 antagonized contractions to phenylephrine as well as those to B-HT 920 in each vessel. A twofold shift to the right of the concentration-response curves to both agonists was obtained with concentrations between 1.9 X 10(-8) and 1.4 X 10(-5) mol/l, depending on the vessel under investigation. A II modulated the adrenolytic properties of MEN 935 in each vessel. However, irrespective of the presence or absence of A II, no pharmacologically relevant difference between antagonism against PE or B-HT 920 could be seen. In isolated vessels, MEN 935 exerts a nonselective alpha-adrenergic antagonism. In receptor binding studies in rat cerebellar cortex, MEN 935 showed a Ki of 5.2 X 10(-7) mol/l at alpha 1-adrenoceptors and a Ki of 1.3 X 10(-5) mol/l at alpha 2-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Angiotensina II/farmacologia , Vasos Sanguíneos/metabolismo , Propanolaminas/farmacologia , Receptores Adrenérgicos alfa/efeitos dos fármacos , Animais , Azepinas/farmacologia , Feminino , Técnicas In Vitro , Masculino , Fenilefrina/farmacologia , Coelhos , Ratos , Receptores Adrenérgicos alfa/metabolismo , Vasoconstrição/efeitos dos fármacosRESUMO
Mammalian atria contain different peptides with potent diuretic, natriuretic, smooth muscle relaxing and blood pressure lowering properties. A preprohormone of these peptides is synthetized and stored in specific granules in atrial myocytes. Different peptides have been isolated, analyzed and in vitro synthetized. Their biological activity indicates a potential role in the regulation of volume and sodium homeostasis as well as in blood pressure regulation.
Assuntos
Proteínas Musculares , Sequência de Aminoácidos , Animais , Fator Natriurético Atrial , Diuréticos , Hemodinâmica/efeitos dos fármacos , Humanos , Rim/irrigação sanguínea , Rim/efeitos dos fármacos , Proteínas Musculares/metabolismo , Proteínas Musculares/farmacologia , Proteínas Musculares/fisiologia , Natriurese/efeitos dos fármacos , Conformação Proteica , Precursores de Proteínas , Sistema Renina-Angiotensina/efeitos dos fármacosRESUMO
In rabbits, clonidine (200 micrograms/kg) exerted no blood pressure lowering effect after oral administration contrary to the strong decrease in blood pressure after i.v. injection. This surprising effect induced experiments on metabolic degradation of clonidine in the rabbit. After oral administration 14C-clonidine was rapidly almost totally metabolised and only minimal concentrations could be detected in the brain. In the urine (24-h collection) no clonidine was detected after oral dosing. In contrast, 15 min after i.v. injection 30% of radioactivity was unchanged clonidine in the plasma. In the brain 70% of the radioactivity during the first 2 h was clonidine. In accord with this, in the urine 22% of the dose administered was excreted as clonidine. From these experiments it is concluded that predominantly unchanged clonidine penetrates the blood-brain barrier. So the lack of effect after oral clonidine depends on the too low concentration of clonidine in the brain. To assess the pharmacological activity of clonidine metabolites identified in rabbit and other species including man, seven different compounds were injected to rabbits either systemically (i.v.) or intracisternally (i.c.i). Only p-hydroxy-clonidine-hydrobromide (St 666) induced weak blood pressure decreases after i.v. and strong ones after i.ci. injection, but to a lesser extent than clonidine itself.
Assuntos
Pressão Sanguínea/efeitos dos fármacos , Clonidina/farmacologia , Administração Oral , Animais , Biotransformação , Encéfalo/metabolismo , Cromatografia em Camada Fina/métodos , Cisterna Magna , Clonidina/administração & dosagem , Clonidina/metabolismo , Cães , Fezes/análise , Feminino , Frequência Cardíaca/efeitos dos fármacos , Injeções , Injeções Intravenosas , Masculino , CoelhosRESUMO
In anaesthetized rabbits the hypotensive activity of a group of 2,3-disubstituted 2-aryl-imino-imidazolidines was estimated. Compounds with 3-bromo substituents at the phenyl moiety of the molecule are more than or as active as clonidine. Correlations between blood pressure lowering effect and lipophilicity, maximum alpha-adrenergic effects (alpha E') and -log ED50 (pD2') of blood pressure increase in spinalized rats and pKA were calculated. The results show a positive linear correlation between as well partition coefficient as alpha E' and hypotension. The relationship between pD2' and hypotensive. effect is less prominent. pKA seems to have no influence on the blood pressure effects of these compounds.
Assuntos
Imidazóis/farmacologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Cisterna Magna , Clonidina/farmacologia , Feminino , Imidazóis/síntese química , Injeções , Injeções Intravenosas , Masculino , Coelhos , Relação Estrutura-AtividadeRESUMO
Changes in brain neuropeptide content in spontaneously hypertensive rats may be primarily related to the development of hypertension or may be secondary consequences of it. We have measured brain concentrations of beta-endorphin, Leu-enkephalin, arginine vasopressin (AVP) and oxytocin (OXT) in stroke-prone spontaneously hypertensive rats (SHRSP) and in age-matched normotensive Wistar Kyoto (WKY) controls, as well as in SHRSP with normalized blood pressure by chronic treatment with clonidine. Opioid peptide contents were measured in 12-, 18- and 24-week-old rats. beta-Endorphin was measured in the neuro-intermediate and anterior lobes of the pituitary, the hypothalamus, mid-brain and brain stem; Leu-enkephalin in the neuro-intermediate lobe of the pituitary, hypothalamus, mid-brain, brain stem, as well as in the spinal cord and adrenal glands. AVP and OXT were measured in the neuro-intermediate lobe of the pituitary, hypothalamus, brain stem and spinal cord. beta-Endorphin in the neuro-intermediate lobe of the pituitary was significantly higher in 12- and 18-week-old SHRSP. Adrenal gland Leu-enkephalin was lower in SHRSP as compared with the WKY. OXT and AVP contents were markedly reduced in all brain regions of SHRSP except the neuro-intermediate lobe of the pituitary, where no significant changes were found. In no case did long-term antihypertensive treatment with clonidine reverse the altered peptide content in the SHRSP. We conclude that alterations in brain neuropeptide content in SHRSP are not secondary to hypertension. The blood pressure lowering activity of clonidine appears not to depend on major alterations of peptide concentrations. A genetic defect in the synthesis of adrenal enkephalins and hypothalamic OXT and AVP seems likely from these studies.
Assuntos
Encéfalo/metabolismo , Hipertensão/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Animais , Arginina Vasopressina/metabolismo , Clonidina/uso terapêutico , Endorfinas/metabolismo , Encefalina Leucina/metabolismo , Hipertensão/tratamento farmacológico , Masculino , Ocitocina/metabolismo , Ratos , Ratos Endogâmicos SHR , Ratos Endogâmicos WKY , beta-EndorfinaRESUMO
The effects of the selective alpha 1-and alpha 2-adrenergic agonists phenylephrine and B-HT 920 (2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepine) and the respective antagonists prazosin and yohimbine on smooth muscle activity of isolated rat aorta, rabbit vena cava inferior and rabbit vena ischiadica have been investigated. In addition, the influence of angiotensin II on the effects of these agonists and antagonists was evaluated. Among the two agonists phenylephrine was the most potent in the rat aorta and B-HT 920 in the two venous vessels. Prazosin and yohimbine revealed a competitive antagonism against both agonists in all three vessels. No differentiation between alpha 1- and alpha 2-adrenoceptor mediated responses was seen in rat aorta and rabbit vena ischiadica. In the rabbit vena cava, prazosin was more potent against phenylephrine than against B-HT 920 whilst yohimbine was more potent against B-HT 920 than against phenylephrine, thus pointing to the existence of functional alpha 1- and alpha 2-adrenoceptors. Angiotensin II (5 X 10(-9) mol/l) induced sustained contractions in rat aorta and transient contractions of different relative magnitude in the veins. Angiotensin II pretreatment increased the potency of phenylephrine in all vessels with no influence on maximum contraction. B-HT 920 potency was increased in the vein preparations; maximum contractions were increased in rat aorta, decreased in rabbit vena cava and not influenced in rabbit vena ischiadica.(ABSTRACT TRUNCATED AT 250 WORDS)