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Biomedical subjects

O E Brodde

Publications and source records attributed to O E Brodde.

At least 181 records · Page 10Linked to original sources
PubMed1983

No evidence for temperature-dependent changes in the pharmacological specificity of beta 1- and beta 2-adrenoceptors in rabbit lung membranes.

In rabbit lung membranes known to contain both beta 1- and beta 2-adrenoceptors it was studied whether changes in incubation temperature may affect binding characteristics and/or selectivity of beta 1- and beta 2-adrenoceptor drugs. For this purpose inhibition of binding of the highly specific beta-adrenoceptor radioligand (+/-)-125iodocyanopindolol (ICYP) by beta 1-and beta 2-selective as well as non-selective drugs was determined at incubation temperatures of 37 degrees C and 18 degrees C and analyzed by Hofstee-plots. 1. The density of beta-adrenoceptors in rabbit lung membranes was identical independently of the incubation temperature. 2. At both incubation temperatures beta 1- and beta 2-selective drugs showed biphasic displacement curves and non-linear Hofstee-plots, while inhibition of binding by the non-selective drugs resulted in monophasic displacement curves with linear Hofstee-plots. With decreasing temperature affinity of antagonists to beta-adrenoceptors increased only slightly, while affinity of agonists increased markedly. 3. For all beta 1- and beta 2-selective drugs the same ratio beta 1/beta 2-adrenoceptors was calculated from the Hofstee-plots independently of the incubation temperature: It amounted to about 80% beta 1- and 20% beta 2-adrenoceptors in rabbit lung. 4. At an incubation temperature of 37 degrees C the displacement curve of the agonist isoprenaline was biphasic in the absence of GTP with a non-linear Hofstee-plot indicating that at 37 degrees C isoprenaline binds to high and low affinity states of the beta-adrenoceptors in rabbit lung. At 18 degrees C, however, beta-adrenoceptors do not form the high affinity GTP-sensitive complex with agonists, since GTP had no influence on isoprenaline displacement curves. 5. It is concluded that a decrease in the incubation temperature of ICYP binding assay from 37 degrees C to 18 degrees C does neither alter the relative amount of beta 1- and beta 2-adrenoceptors in rabbit lung membranes nor the selectivity of beta 1- and beta 2-selective adrenoceptor drugs.

Adrenergic beta-Antagonists↗
PubMed1983

Coexistence of beta 1- and beta 2-adrenoceptors in human right atrium. Direct identification by (+/-)-[125I]iodocyanopindolol binding.

The highly specific beta-adrenoceptor radioligand, (+/-)-[125I]iodocyanopindolol, has been used to subclassify beta-adrenoceptors in membranes from human right atrial appendage obtained during open heart surgery. Binding of (+/-)-[125I]iodocyanopindolol was saturable (Bmax = 86.4 +/- 7.4 fmol (+/-)-[125I]iodocyanopindolol bound/mg protein, n = 4), of high affinity (KD = 53 +/- 6 pM, n = 4), rapid, reversible, and stereospecific. The relative potencies of isoprenaline, adrenaline, and noradrenaline for inhibition of (+/-)-[125I]iodocyanopindolol binding and activation of adenylate cyclase were 1:10:10, indicating a population composed mainly of beta 1-adrenoceptors. Inhibition of (+/-)-[125I]iodocyanopindolol binding by beta 1- (practolol, metoprolol, betaxolol) and beta 2- (IPS 339, ICI 118,551, zinterol, procaterol) selective drugs, however, resulted in biphasic displacement curves with slope factors (nH, pseudo Hill coefficients) significantly less than 1.0. Nonlinear regression analysis of these curves revealed a beta 1: beta 2 ratio of 80:20 in human right atrial appendage. Nonselective beta-adrenergic drugs (propranolol, isoprenaline, and adrenaline), on the contrary, inhibited binding with monophasic displacement curves and nH = 1.0. Binding of agonists to the beta-adrenoceptors in human right atrial appendage seems to be regulated by guanyl nucleotides. In the absence of GTP, isoprenaline binds to high and low affinity state of the beta-adrenoceptors. GTP (10(-4) M) converts this heterogeneous binding into a homogeneous one of low affinity. It is concluded that, in human right atria, beta 1- and beta 2-adrenoceptors coexist; however, beta 1-adrenoceptors predominate. The physiological function of beta 2-adrenoceptors in human right atrium remains to be elucidated.

Adenylyl Cyclases↗
PubMed1983

Subclassification of human beta-adrenergic receptors mediating renin release.

To determine the beta-adrenoceptor subtype controlling renin release from the kidneys, several beta-adrenoceptor subtype selective agonists and antagonists were administered to 15 healthy volunteers. While isoprenaline infusion (1, 2 and 4 micrograms/min for 5 min each) markedly increased plasma renin activity (PRA), the beta 2-selective agonist fenoterol failed to change PRA. The isoprenaline induced rise in PRA could be completely prevented by the beta 1-selective antagonists metoprolol (10 mg i.v. 45 min prior to isoprenaline infusion) and betaxolol (5 mg i.v. 45 min prior to infusion) indicating that renin release is mediated by beta 1-adrenoceptors. Binding studies with the highly specific beta-adrenoceptor radioligand (+/-)-125iodocyanopindolol demonstrated that membranes from human kidney cortical slices contain predominantly, if not exclusively, beta 1-adrenoceptors. These in vivo and in vitro results support the view that the beta-adrenoceptor mediating renin release from the human kidney is of the beta 1-subtype.

Adrenergic beta-Agonists↗
PubMed1983

Endogenous and exogenous regulation of human alpha- and beta-adrenergic receptors.

Regulation of human beta 2-adrenergic receptors in lymphocytes (determined by (+/-)-125iodocyanopindolol (ICYP) binding) and alpha 2-adrenergic receptors in platelets (determined by 3H-yohimbine binding) was studied. While beta 2-adrenergic receptor number did not change with age, a significant negative correlation between the number of alpha 2-adrenergic receptors and age was found; plasma catecholamines, on the contrary, were elevated in the elderly. In healthy women during normal menstrual cycle the number of alpha 2-adrenergic receptors decreased with increasing plasma estradiol levels. Incubation of lymphocyte membranes with isoprenaline (100 microM) and of platelet membranes with clonidine (1-100 microM) led to a reduction of the number of beta 2- and alpha 2-receptors, respectively, without changes in the KD-values. Treatment of hypertensive patients with clonidine (3x150 micrograms/die) for 7 days reduced the number of alpha 2-adrenergic receptors in platelets. In platelet membranes from such treated patients inhibition of 3H-yohimbine binding by clonidine and adrenaline was not affected by 10(-4)M GTP. It is concluded, that human alpha- and beta-adrenergic receptors undergo regulatory mechanisms similar to those recently described for adrenergic receptors in a variety of animal models.

Adolescent↗
PubMed1983

Decreased number of alpha-adrenergic receptors in platelets of patients on maintenance haemodialysis.

In patients on maintenance haemodialysis the number of platelet alpha 2-adrenergic receptors, as assessed by 3H-yohimbine binding, was significantly lower than that in healthy volunteers. Responses to alpha 1-adrenergic receptor stimulation, determined by increases in systolic blood pressure produced by intravenous injections of phenylephrine, were also diminished in chronic haemodialysis patients. Thus, reduced sympathetic activity often observed during chronic haemodialysis treatment may be due to reduced number and/or sensitivity of alpha 1- and alpha 2-adrenergic receptors.

Adult↗
PubMed1983

3H-yohimbine binding to guinea-pig kidney and calf cerebral cortex membranes: comparison with human platelets.

The highly specific alpha 2-adrenoceptor antagonist 3H-yohimbine was used to label in guinea-pig kidney and calf cerebral cortex membranes alpha 2-adrenoceptors. In both tissues binding was saturable, of high affinity (KD = 3-5 nM), rapid and readily reversible. alpha-Adrenergic antagonists inhibited binding with rank order of potency: rauwolscine greater than or equal to yohimbine greater than phentolamine much greater than prazosin greater than or equal to corynanthine, which is the typical one for alpha 2-adrenoceptors. Displacement curves of alpha-adrenergic agonists (clonidine greater than guanfacine greater than adrenaline greater than or equal to noradrenaline) were in the absence of GTP shallow with pseudo-Hill coefficients (nH) significantly less than 1.0. In the presence of GTP (10(-4) M) the curves were shifted to the right to lower affinities. However, only in guinea-pig kidney membranes nH increased up to 1.0, while in calf cerebral cortex membranes nH was not significantly influenced by GTP. The properties of alpha 2-adrenoceptors--as assessed by 3H-yohimbine binding--in guinea-pig kidney and calf cerebral cortex are, therefore, very similar to those recently determined under identical experimental conditions in human platelet membranes (Brodde et al., 1982). Although some tissue and/or species differences exist--especially the 5-6 times higher affinity of prazosin at renal and brain than at platelet alpha 2-adrenoceptors--it is concluded that alterations of human platelet alpha 2-adrenoceptors under various (patho) physiological conditions can be taken as representative for changes of other peripheral and/or central alpha 2-adrenoceptors.

Animals↗
PubMed1982

Vascular dopamine receptors: Demonstration and characterization by in vitro studies.

Substantial evidence has accumulated that in certain vascular beds dopamine produces its relaxant effect through stimulation of specific dopamine receptors. The goal of this review is to describe several in vitro models (perfused mesenteric vessels of the dog; renal, mesenteric, splenic, coronary and cerebral arterial strips of rabbits, dogs and cats; perfused kidney of the rat) recently developed to demonstrate such specific relaxations induced by dopamine and dopaminomimetics. On these models studies on structure-activity relationship for activation of the dopamine receptor resulted in the following order of potency for agonists: SK&F 38393 (partial agonist) greater than epinine greater than A-6, 7-DTN greater than or equal to dopamine greater than N, N-di-n-propyl-dopamine (partial agonist) greater than apomorphine (partial agonist). The dopamine receptor antagonists (+)-butaclamol, cis-alpha-flupenthixol, metoclopramide, droperidol and bulbocapnine were found to competitively antagonize dopamine induced relaxation. In addition, in two isolated organ systems (rabbit mesenteric artery, rat perfused kidney) stereospecificity of the vascular dopamine receptor was demonstrated with the isomers of butaclamol. With the development of several in vitro models demonstrating a specific antagonism against dopamine induced relaxation an important requirement for definition of a specific dopamine receptor if fulfilled according to classical pharmacological criteria. Thus, there can be do doubt on the existence of post-synaptic dopamine receptors mediating vasodilation in certain vascular tissues.

Animals↗
PubMed1982

Age-dependent decrease of alpha 2-adrenergic receptor number in human platelets.

In 36 healthy subjects of various ages (14-76 years) the number of alpha 2-adrenergic receptors in platelets - as determined by [3H]yohimbine binding - and plasma catecholamine levels were measured. A highly significant negative correlation (r = -0.666, P less than 0.001) between the number of alpha 2-adrenergic receptors and age was found; on the contrary, plasma catecholamine concentrations increased with increasing age. Thus, reduced responses in the elderly to adrenergic stimuli may be due to reduced number of adrenergic receptors.

Adolescent↗
PubMed1982

Homogeneous class of beta-1 adrenergic receptors in rat kidney. Identification by (+/-)-125 iodocyanopindolol binding.

The highly specific beta-adrenergic radio-ligand (+/-)-125 iodocyanopindolol (ICYP) was used to characterize the beta-adrenergic receptor subtype present in rat kidney. Binding of ICYP to membranes from rat kidney was of high affinity (KD = 68.9 pM) and saturable with 1.06 pmoles ICYP bound/g tissue wet wt at maximal occupancy of the sites. Analysis of inhibition of ICYP binding by beta 1- and beta 2-selective adrenergic drugs via pseudo-Scatchard ("Hoifstee') plots resulted in linear plots indicating the existence of a homogeneous population of beta-adrenergic receptors. From the resulting KD-values for practolol (2.2 microM), metoprolol (0.21 microM), zinterol (0.4 microM) and IPS 339 (0.046 microM) it is concluded that the beta-adrenergic receptor in rat kidney is of the beta 1-subtype. This subclassification is further supported by the fact that (-)-noradrenaline and (-)-adrenaline were equipotent in inhibiting ICYP binding. The beta-adrenergic agonists (-)-isoprenaline and zinterol bind to two distinct states of this beta 1-receptor, a high and low affinity state. GTP (10(-4) M) converts this heterogeneous binding into a homogeneous low affinity binding.

Animals↗
PubMed1982

GTP regulates binding of agonists to alpha 2-adrenergic receptors in human platelets.

The potent alpha 2-adrenergic receptor antagonist 3H-yohimbine was used to characterize alpha-adrenergic receptors in human platelet membranes. Binding of 3H-yohimbine was at 25 degrees rapid (t 1/2 = 3 min) readily reversible (t 1/2 = 5.5 min), saturable with 221 +/- 38.9 fmoles bound/mg protein (N = 10) and of high affinity (KD = 1.97 nM). Inhibition of binding by alpha-adrenergic antagonists showed monophasic displacement curves with Hill-coefficients of approximately 1.0. The rank order of potency was: rauwolscine greater than or equal to yohimbine greater than phentolamine greater than phenoxybenzamine greater than AR-C 239 greater than or equal to corynanthine greater than prazosin, indicating that the alpha-adrenergic receptor in human platelets is of the alpha 2-subtype. On the contrary, agonist (clonidine, guanfacine, alpha-methyl-noradrenaline, noradrenaline and adrenaline) displacement curves were shallow with Hill-coefficients of approximately 0.7. Non-linear regression analysis showed that agonists bind to two affinity states of the alpha 2-adrenergic receptor, a high and a low affinity state. In the presence of GTP (10(-4) M) agonist concentration-inhibition curves were shifted to the right to lower affinities and Hill-coefficients increased up to 1.0 K1-values for inhibition of binding in the presence of GTP were in the same range as those for low affinity state in the absence of GTP. It is concluded that GTP regulates binding of alpha 2-adrenergic agonists at the human alpha 2-adrenergic receptor.

Adrenergic alpha-Agonists↗
PubMed1981

Regulation of alpha 1-adrenoceptors in the cerebral cortex of the rat by thyroid hormones.

The influence of thyroid hormones on the concentration and properties of alpha 1-adrenoceptors in a crude membrane fraction obtained from the rat cerebral cortex was investigated using the [3H]-WB 4101 binding assay. Animals were made hypothyroid by feeding 6-propyl-2-thiouracil for 8 weeks. Hyperthyroidism was induced by triiodothyronine injections (50 microgram/100 g body weight) for 9 days. 1. The binding of [3H]-WB 4101 was saturable and of high affinity in controls as well as in hyper- and hypothyroid animals. The maximal number of binding sites (Bmax), which amounted to 95 fmol/mg protein in control animals, was increased by 27% in cortical membranes from hyperthyroid rats and reduced by 23% in the hypothyroid group. 2. The reduction in [3H]-WB 4101 binding due to 6-propyl-2-thiouracil feeding was reversible by triiodothyronine treatment. 3. Dissociation constants (KD) calculated from saturation experiments (0.25 nM) or kinetic data (0.21 nM) remained unchanged in altered thyroid states. 4. Inhibition of [3H]-WB 4101 binding by adrenergic agonists and antagonists revealed no differences between euthyroid and hypothyroid animals. The higher affinity of prazosin to the binding sites compared with yohimbine indicated that [3H]-WB 4101 predominantly labeled alpha 1-adrenoceptors. It is concluded that thyroid hormones regulate the number of alpha 1-adrenoceptors in membranes of the rat cerebral cortex, leaving their affinities unchanged.

Animals↗
PubMed1980

Decreased number of beta-adrenoceptors in cerebral cortex of hypothyroid rats.

The influence of thyroid hormone deficiency on beta-adrenoceptors in the rat cerebral cortex was investigated using the 3H-dihydroalprenolol binding assay. The maximal number of binding sites (Bmax) and the dissociation constants (KD) were determined in the brain tissue from euthyroid animals and from rats made hypothyroid by feeding 6-propyl-2-thiouracil. Hypothyroidism resulted in a 37% decrease in beta-adrenoceptor density (Bmax). The dissociation constants (KD) of both groups were not significantly different.

Animals↗