Search results for "Clonidine"

A possible structural determinant of selectivity of boldine and derivatives for the alpha 1A-adrenoceptor subtype.

1996

1. The selectivity of action of boldine and the related aporphine alkaloids, predicentrine (9-O-methylboldine) and glaucine (2,9-O-dimethylboldine) and alpha 1-adrenoceptor subtypes was studied by examining [3H]-prazosin competition binding in rat cerebral cortex. WB 4101 and benoxathian were used as selective alpha 1A-adrenoceptor antagonists. 2. In the competition experiments [3H]-prazosin (0.2 nM) binding was inhibited by WB 4101 and benoxathian. The inhibition curves displayed shallow slopes which could be subdivided into high and low affinity components (pKi = 9.92 and 8.29 for WB 4101, 9.35 and 7.94 for benoxathian). The two antagonists recognized approximately 37% of the sites with h…

Clonidine increases membrane-associated phospholipase A2

2005

Background and objective: An anti-inflammatory effect of α 2 -adrenoreceptor agonists has been suggested. Phospholipase A 2 is a key enzyme in the production of precursors of inflammatory lipid mediators. The aim of the present study was to investigate the effect of clonidine on phospholipase A 2 activity in an established in vitro model. Methods: Human being platelet membranes containing active phospholipase A 2 were exposed to buffer control or to three increasing concentrations of clonidine. Phospholipase A 2 was measured by a radioisotope technique. Results: A massive increase in phospholipase A 2 activity was measured after clonidine exposure leading to final values of 92.5 ′ 3.1 pmol …

Determination of alinidine in human plasma by high-performance liquid chromatography.

1981

Study on the histamine-like activity of guanfacine

1990

Abstract The effects of guanfacine have been studied on guinea-pig isolated atria and diethylstilboestrol-treated rat isolated uterus to determine whether it possesses histamine-like activity. Guanfacine produced a concentration-dependent negative chronotropic effect which was not modified by ranitidine (0.1 μM). In rat isolated uterus contracted by KCl, clonidine (5–5000 μM) produced concentration-dependent relaxation which was blocked by ranitidine (0.1 μM), but guanfacine only produced relaxation at high concentrations (100–1000 μM), and this was not affected by ranitidine (0.1 μM). It is concluded that guanfacine, unlike clonidine, does not produce effects due to activation of H2-recept…

A fifth class of antiarrhythmic action?

1981

Alpha 1 adrenoceptor expression in skin, nerves and blood vessels of patients with painful diabetic neuropathy

2021

Abstract Diabetic neuropathy (dNP) patients often suffer from severe neuropathic pain. It was suggested that alpha-1 adrenoceptor (α1-AR) hyperresponsiveness contributes to pain in dNP. The aim of our study was to quantify α1-AR expression using immunohistochemistry in skin biopsies of nine patients with painful diabetic neuropathy compared to 10 healthy controls. Additionally, the association between α1-AR expression and activation with spontaneous and sympathetically maintained pain (SMP) induced by intradermal injection of the α1-agonist phenylephrine was investigated. For control purposes the α2-agonist clonidine was injected in a different session. We found that dermal nerve density wa…

CLONIDINE, A PARTIAL AGONIST OF THE HISTAMINERGIC H2 RECEPTORS?

1978

Adrenergic modulation of the release of 5-hydroxytryptamine from the vascularly perfused ileum of the guinea-pig

1988

1. Isolated segments of the guinea-pig ileum were vascularly perfused and the release of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) into the portal venous effluent was determined by h.p.l.c. with electrochemical detection. Test substances were applied via the arterial perfusion medium. 2. Isoprenaline (0.1 microM) increased the outflow of 5-HT and 5-HIAA maximally by about 75% and this was antagonized by propranolol (0.1 microM). Forskolin (1-10 microM) increased the outflow of 5-HT by approximately 105% and that of 5-HIAA by approximately 55%. The phosphodiesterase inhibitor AH 21-132 (0.1-1 microM) increased the outflow of 5-HT and 5-HIAA by about 70%. Isoprenaline…

Drug induced variations of the renin-angiotensin-aldosterone system in rats. II. Antihypertensives

1977

Summary Groups of male rats were treated with antihypertensive drugs (alpha-methyl-dopa, clonidine, propranolol, reserpine, diazoxide) which were administered under conditions causing the onset of high plasma renin activity (PRA) and high plasma and urine aldosterone levels, i.e. together with distilled water load (5% of body weight). Alpha-methyl-dopa and propranolol, which fail to significantly alter PRA and plasma aldosterone levels when administered without distilled water load, cause a marked decrease of plasma and urine aldosterone levels and of PRA when administered together with distilled water load, while diazoxide, and reserpine cause a marked increase of these values. Clonidine c…

The inhibition by dopamine of cholinergic transmission in the isolated guinea-pig ileum. Mediation through alpha-adrenoceptors.

1982

1. Segments of the guinea-pig ileum were incubated in Tyrode's solution containing 3 μM propranolol. Dopamine, like noradrenaline and clonidine, inhibited the twitch response to field stimulation. The inhibitory action of dopamine remained unchanged in the presence of the dopamine uptake inhibitor nomifensine (1 μM). Tissue from reserpine-pretreated amimals was insensitive to tyramine but the response to dopamine was not affected. It is, therefore, assumed that the effect of dopamine is due to a direct receptor stimulation and not to the release of noradrenaline. 2. The inhibitory action of dopamine was not antagonized by the dopamine receptor antagonists cis-flupenthixol, pimozide or dompe…