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D Hoyer

Publications and source records attributed to D Hoyer.

At least 199 records · Page 11Linked to original sources
PubMed1986

5-HT1A-receptors mediate stimulation of adenylate cyclase in rat hippocampus.

Serotonin (5-HT) stimulated adenylate cyclase activity in homogenates of rat hippocampus. This effect was pharmacologically characterised with a series of agonists and antagonists of various structural classes. These compounds where also tested in radioligand binding studies using selective ligands for the various subtypes of 5-HT1 and 5-HT2 receptors. 5-HT1A, 5-HT1B and 5-HT1C recognition sites were labelled with [3H]8-OH-DPAT([3H]8-hydroxy-2-(di-n-propylamino)-tetralin) in pig cortex membranes, [125I]CYP([125I]iodocyanopindolol) in rat cortex and [3H]mesulergine in pig choroid plexus membranes, respectively. The rank order of potency of 13 agonists stimulating adenylate cyclase activity in homogenates of rat hippocampus was in good agreement with the rank order of affinity of these agonists for the 5-HT1A binding site: N,N-dipropyl-5-carboxamidotryptamine (DP-5-CT) greater than 5-carboxamidotryptamine (5-CT) greater than 8-OH-DPAT greater than 5-HT greater than 5-methoxytryptamine (5-OCH3T) greater than d-LSD greater than 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969) greater than alpha-methylserotonin (alpha-CH3-5-HT) greater than dopamine greater than 2-methylserotonin (2-CH3-5-HT). The correlation between the respective potencies and affinities of these agonists was r = 0.934, P less than 0.001. There was no correlation between stimulation of adenylate cyclase activity by these agonists and their affinity for 5-HT1B, 5-HT1C or 5-HT2 binding sites. r = 0.381-0.108, P less than 0.20-0.73.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1986

Serotonin increases the production of inositol phosphates and mobilises calcium via the 5-HT2 receptor in A7r5 smooth muscle cells.

Serotonin (5-HT) induces inositol phosphate production and the efflux of 45Ca2+ in a smooth muscle cell line (A7r5) derived from rat aorta. These effects were pharmacologically characterised and compared to data obtained in radioligand binding studies performed with the 5-HT2 ligand [3H]ketanserin in rat brain cortex membranes. 5-HT causes in increase in the levels of inositol trisphosphate (InsP3), inositol bisphosphate (InsP2) and inositol phosphate (InsP1). InsP3 production was rapid and transient whereas InsP1 accumulated in a time and concentration dependent manner. The 5-HT stimulated InsP1 accumulation (pEC50 = 6.48) was potently and competitively inhibited by the 5-HT2 specific antagonists, pirenperone and ketanserin, whereas antagonists of other 5-HT receptors were active only at high concentrations. There was a significant correlation between inhibition of 5-HT stimulated InsP1 accumulation and 5-HT2 binding (r = 0.98, P = 0.0035). 5-HT stimulated the efflux of 45Ca2+ from preloaded cells with a pEC50 of 7.59. The rank order of potency for agonist induced Ca2+ efflux, 5-HT greater than alpha-methyl-5-HT greater than 1-methyl-5-HT greater than RU 24969 (5-methoxy-3[1,2,3,6,-tetrahydropyridin-4-yl]-1-H indole) greater than 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)-tetralin) greater than 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)-tetralin) greater than 5-CT (5-carboxamidotryptamine) is typical for a 5-HT2 receptor mediated event. The effect of 5-HT was competitively blocked by ketanserin (pA2 = 8.22).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Identity of inhibitory presynaptic 5-hydroxytryptamine (5-HT) autoreceptors in the rat brain cortex with 5-HT1B binding sites.

In rat brain cortex slices preincubated with [3H]5-HT, the potencies of 17 5-HT receptor agonists to inhibit the electrically evoked 3H overflow and the affinities of 13 antagonists (including several beta-adrenoceptor blocking agents) to antagonize competitively the inhibitory effect of unlabelled 5-HT on evoked 3H overflow were determined. The affinities of the compounds for 5-HT1B and 5-HT2 binding sites in rat brain cortex membranes (labelled by [125I]cyanopindolol = [125I]-CYP in the presence of 30 mumol/l isoprenaline and [3H]ketanserin, respectively), for 5-HT1A binding sites in pig and rat brain cortex membranes (labelled by [3H]8-hydroxy-2-(di-n-propylamino)tetralin = [3H]8-OH-DPAT) and for 5-HT1C binding sites in pig choroid plexus membranes (labelled by [3H]mesulergine) were also determined. The affinities of the drugs for the various 5-HT recognition sites ranged over 4-5 log units (the functional experiments revealed the same range of differences between the drugs). There were no significant correlations between the affinities of the drugs at 5-HT1C and 5-HT2 binding sites and their potencies or affinities, determined for the 5-HT autoreceptors. In contrast, significant correlations were found between the potencies or affinities of the drugs for the autoreceptors and their affinities at 5-HT1A or 5-HT1B binding sites; the best correlations were obtained with the 5-HT1B binding site. Some of the drugs investigated were not included in the correlation since their agonistic or antagonistic effects on the autoreceptors were weak and pEC30 or apparent pA2 values could not be determined (less than 5.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Vascular resistance, metabolism and EEG within cerebral grey and white matter during hypoxia in neonatal piglets.

To study unsolved problems of the causal chain of neonatal hypoxic brain damage in 31 hypoxic newborn non-anesthetized piglets cerebro-vascular, metabolic and EEG reactions were investigated (FiO2: 0.06-0.10, 1 h). Only in artificially ventilated newborn piglets this acute hypoxic hypoxia provoked a vital decompensation by critical depression of mean arterial blood pressure (less than or equal to 4.67 kPa [35 mmHg]) and/or a critical increase of vascular resistance (Rc) in the cerebral white matter (greater than 50%). Spontaneously breathing piglets survived always showing hyperventilation, higher pHa and an increase of cerebral O2-consumption in cerebral grey matter, partly also in white matter. This critical increase of Rc was related to a critical decrease of O2-consumption in the white matter and an insufficient decrease of Rc of the grey matter. The observed strong metabolic and hemodynamic differences between these two brain compartments can explain the evaluated special morphological vulnerability of cerebral white matter in ventilated animals.

Animals↗
PubMed1985

Characterization of the 5-HT1B recognition site in rat brain: binding studies with (-)[125I]iodocyanopindolol.

(-)[125I]Iodocyanopindolol ([125I]CYP) labels rat brain membrane sites which display high affinity for several serotonergic and beta-adrenergic compounds. The binding of [125I]CYP to these serotonergic recognition sites was evaluated in the presence of 30 microM (-)isoprenaline in order to suppress binding to beta-adrenoceptors. [125I]CYP binds in rat cortex membranes rapidly, reversibly and stereoselectively to a finite number of recognition sites: Bmax = 180 fmol/mg, KD = 230 pM. Similar affinity values of [125I]CYP were obtained in membranes from rat hippocampus and striatum. Kinetic, saturation and competition experiments suggest that under these conditions [125I]CYP binds to a single serotonergic recognition site named 5-HT1B. The pharmacological profile of 5-HT1B sites is characteristic of a 5-HT1 binding site and shows the following rank order of affinity for agonists: RU 24969, (5-methoxy-3-[1,2,3,6-tetrahydropyridin-4-yl]1H-indole) greater than 5-CT, (5-carboxamidotryptamine) greater than 5-HT, (5-hydroxytryptamine, serotonin) greater than 5-OCH3-T, (5-methoxytryptamine) much greater than 2-CH3-5-HT, (2-methylserotonin) greater than 8-OH-DPAT, (8-hydroxy-2-(di-n-pro-pylamino)-tetralin). The rank order of affinity for antagonists is: (+/-)ICYP, ((+/- )-3-I-cyano-pindolol) greater than (-)21-009, (4-[3-ter-butyl-amino-2-hydroxy-propoxy]-indol-2-carbonic acid isopropyl ester) greater than (+)21-009 greater than (-)propranolol greater than metitepin greater than (-)pindolol much greater than ketanserin greater than spiroperidol greater than mesulergine. 5-HT1B recognition sites display low affinity for selective beta 1- and beta 2-adrenoceptor antagonists, e.g. atenolol, betaxolol, ICI 89-406 and ICI 118-551. The low affinity of 5-HT1B recognition sites for some 5-HT1A, 5-HT1C and 5-HT2 selective compounds (e.g. 8-OH-DPAT, mesulergine, ketanserin) suggests that 5-HT1B recognition sites are pharmacologically different from 5-HT1A, 5-HT1C and 5-HT2 recognition sites.

Animals↗
PubMed1985

Molecular pharmacology of 5-HT1 and 5-HT2 recognition sites in rat and pig brain membranes: radioligand binding studies with [3H]5-HT, [3H]8-OH-DPAT, (-)[125I]iodocyanopindolol, [3H]mesulergine and [3H]ketanserin.

The pharmacological characteristics of the binding of [3H]8-OH-DPAT ([3H]8-hydroxy-2(di-n-propylamino)tetralin, [125I]CYP ((-)[125I]iodocyanopindolol) (in the presence of 30 microM (-)isoprenaline) and [3H]mesulergine to 5-HT1 recognition sites were studied in rat and pig brain membranes. [3H]8-OH-DPAT bound in rat and pig cortex to the 5-HT1A recognition site characterized by high affinity for 5-CT (5-carboxamido-tryptamine), 8-OH-DPAT, 5-HT (5-hydroxytryptamine, serotonin) and low affinity for pirenperone, ketanserin and mesulergine. [125I]CYP bound in rat but not in pig cortex to the 5-HT1B site which shows high affinity for (-)21-009 (4[3-ter-butyl-amino-2-hydroxy-propoxy]indol-2-carbonic acid isopropyl ester), (+/-)ICYP (3-I-cyanopindolol), 5-HT, RU 24969 (5-methoxy-3-[1,2,3,6-tetrahydropyridon-4-yl]1H-indole) and low affinity for 8-OH-DPAT, mesulergine and pirenperone. [3H]Mesulergine bound in pig choroid plexus and in rat cortex (besides binding to 5-HT2 sites in rat cortex) to the 5-HT1C recognition site characterized by high affinity for metergoline, mesulergine, 5-HT and methergine and low affinity for (-)21-009, ICYP, 8-OH-DPAT and spiroperidol. The pharmacological profile of 5-HT1A sites in rat and pig cortex appears to be identical; 5-HT1C sites in pig choroid plexus and rat cortex show no differences. In contrast, it was not possible to label 5-HT1B sites with [125I]CYP in pig brain membranes indicating that like 5-HT2 receptors, 5-HT1 recognition sites show species differences. The pharmacological profiles of the three 5-HT1 recognition sites are clearly different from one another. Furthermore, the pharmacological profile of each individual 5-HT1 recognition site is also different from that of the 5-HT2 receptors labelled with [3H]ketanserin in rat cortex membranes although some similarities exist between 5-HT2 and 5-HT1C sites. Finally, the beta-adrenoceptor antagonist (-)21-009 which has different affinities for 5-HT1A, 5-HT1B and 5-HT1C recognition sites, yielded triphasic competition curves for [3H]5-HT binding in rat cortex membranes providing evidence that [3H]5-HT labels three distinct 5-HT1 sites in these membranes.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1984

Mesulergine, a selective serotonin-2 ligand in the rat cortex, does not label these receptors in porcine and human cortex: evidence for species differences in brain serotonin-2 receptors.

The kinetic and pharmacological characteristics of the binding of [3H]ketanserin and [3H]mesulergine to frontal cortical brain membranes from rat, pig and human were studied. In the 3 species [3H]ketanserin labeled sites with the characteristics of the 5-HT2 receptors previously described in the rat. In contrast, [3H]mesulergine labeled 5-HT2 receptors in rat, but not in pig and human cortices. The characteristics of the sites labeled by [3H]mesulergine in pig cortex were similar to those of sites in the choroid plexus of rats, pigs and humans. While several reputed 5-HT2 ligands presented a similar affinity for the [3H]ketanserin binding sites in the 3 species, other such ligands, e.g. mesulergine, methysergide, cinanserin and LSD which displaced these sites with high affinity in rat brain, had lower affinities in pig and human brain. These results indicate that 5-HT2 receptors show different pharmacological profiles in different species. Caution should thus be exerted in extrapolating data from laboratory animals to humans.

Animals↗
PubMed1984

The binding of serotonergic ligands to the porcine choroid plexus: characterization of a new type of serotonin recognition site.

The kinetic and pharmacological characteristics of the binding of [3H]5-HT (serotonin), [3H]8-OH-DPAT (8-OH-2-di-n-propylaminotetraline), [3H]LSD, [3H]ketanserin and [3H]mesulergine to membranes from frontal cortex, hippocampus and choroid plexus of pig brain were studied. The binding of these ligands to frontal cortex and hippocampus demonstrated the presence of 5-HT1 and 5-HT2 sites in both tissues, although hippocampus was richer in 5-HT1 (subtype 5-HT1A) sites. [3H]5-HT, [3H]mesulergine and [3H]LSD labeled the pig choroid plexus with high affinity. The pharmacological profiles of [3H]5-HT and [3H]mesulergine binding to this tissue were closely comparable. Ligands reported as selective for 5-HT1A, 5-HT1B or 5-HT2 subtypes did not show high affinity for these binding sites. Therefore, these 5-HT binding sites in pig choroid plexus could be named 5-HT1C. Other drugs with a high affinity for these sites were methysergide and mianserine. In pig frontal cortex, [3H]5-HT labeled the different subtypes of 5-HT1 sites. In contrast, [3H]mesulergine bound in pig frontal cortex to a small population of sites with pharmacological properties similar to those of the choroid plexus 5-HT1C sites. Possible physiological functions in which these sites might be involved are discussed.

Animals↗
PubMed1984

Characterization of IBE 2254 binding to alpha 1-adrenergic receptors on intact DDT1 smooth muscle cells: comparison with membrane binding and correlation with phosphoinositides breakdown.

The binding of the antagonist IBE 2254 (IBE) to alpha 1-adrenergic receptors was characterized on intact DDT1 smooth muscle cells. IBE binding was rapid, reversible, stable and saturable: Bmax = 113000 +/- 13000 receptors/cell, KD = 110 +/- 13 pM (n = 25). Saturation and competition experiments analysed by non linear curve fitting indicated a single population of binding sites with a pharmacological profile typical for alpha 1-adrenergic receptors. Antagonists competed for IBE binding sites in the following order: prazosin greater than phentolamine = phenoxybenzamine greater than yohimbine. The rank order for agonists was clonidine greater than epinephrine greater than norepinephrine greater than phenylephrine. There was a significant correlation between IBE binding to intact cells, DDT1 membranes and rat cortex membranes. Neither agonists nor antagonists showed noticeable changes in their affinity for IBE binding on either system. There was also a good correlation between IBE binding and breakdown of phosphoinositides (PI) measured in intact cells.

Animals↗
PubMed1984

Identification of 5HT2-receptors on longitudinal muscle of the guinea pig ileum.

In binding experiments with the radioligands [3H]Ketanserin (HKet) and [125I]LSD (ILSD) 21 compounds were investigated using rat brain cortex membranes. The pKD-values of the compounds were virtually independent of the radioligand used and their rank order was consistent with classification of the binding sites as being of the 5-HT2-type. In contrast, in the longitudinal muscle of the guinea pig ileum in the presence of 0.3 microM cinanserin, ILSD labelled sites which were quite different to those in the cortex. In a functional test antagonism of the 5HT induced contraction of the guinea-pig ileum was measured in the presence of 1 microM atropine. The pharmacological inhibition constants (IC50-values) of 8 compounds correlated well with the dissociation constants for HKet binding in the cortex and did not correlate with the data from ILSD binding in the guinea pig ileum. It is concluded that the ileum contains postjunctional 5HT2-receptors which mediate contraction. The nature of the ILSD binding sites in the ileum remains to be elucidated.

Animals↗
PubMed1984

Agonist-induced changes in the properties of beta-adrenergic receptors on intact S49 lymphoma cells. Time-dependent changes in the affinity of the receptor for agonists.

The binding of the antagonist [125I]iodopindolol to beta-adrenergic receptors on intact wild-type S49 mouse lymphoma cells and mutants that have impaired abilities to generate cyclic AMP in response to catecholamines was studied. The binding of [125I]iodopindolol is of high affinity (KD = 35 pM), rapid, stable over 90 min, and rapidly reversible (t1/2 = 8 to 11 min). Nonspecific binding was very low (less than 5% of total binding at the KD). Kinetic and competition experiments performed under steady-state and non-equilibrium conditions revealed that the binding characteristics for agonists were very different in intact cells and in membranes. The interactions of antagonists, on the other hand, appeared to be identical in studies carried out with intact cells and membranes. In intact cells, the affinity of the receptor for agonists was observed to decrease rapidly within the first 5 min of exposure of the cells to an agonist. Competition experiments revealed that at least 80% of the receptor-agonist complex was in a high-affinity state when studies were carried out using short incubation times (0.5-1 min). Under equilibrium conditions, about 80% of the complex in wild-type, uncoupled, and kinase-deficient cells was of a low affinity. At equilibrium, only low-affinity binding was seen with coupling protein-deficient cells. This rapid, time-dependent decrease in the affinity of receptors for agonists was seen with most agonists although not with zinterol. The phenomenon was not due to differences in the kinetics of the interactions of agonists and [125I]iodopindolol with the receptor, and it is likely that the receptor undergoes a conformational change upon exposure to agonists. This effect was not observed in membranes and was not related to the presence of a functional guanine nucleotide-binding protein or to the production of cyclic AMP. Furthermore, hydrophilic agonists and antagonists, under short-term incubation conditions, did not fully compete for the binding sites labeled with the lipophilic radioligand [125I]iodopindolol, although this binding was fully and stereospecifically competed for by lipophilic antagonists. This suggests that in untreated cells a small but significant fraction of the receptors is sequestered in an environment not accessible to hydrophilic ligands.

Adenylyl Cyclases↗
PubMed1984

Three distinct subtypes of serotonergic receptors mediate the triphasic blood pressure response to serotonin in rats.

In pentobarbitone- or urethane-anaesthetized normotensive rats the triphasic pressure response to serotonin (5-HT): a short-lasting depressor phase with an intense bradycardia, a pressor phase and a prolonged hypotension, was investigated. The highly selective 5-HTM antagonist ICS 205-930 (1 microgram/kg) inhibited the first but not the second or third phase. The 5-HT2 antagonist ketanserin (0.1 mg/kg) inhibited the second but not the first or third phase. Following selective blockade of the pressor component with ketanserin (0.1 mg/kg), the hypotensive potency of eight serotonin receptor agonists was quantified (-log ED50). A correlation (r = 0.75, P less than 0.05) was observed between this parameter and the displacement of the 5-HT1 ligand [3H]-5-HT. It is suggested that the three phases are due to 5-HTM-, 5-HT2- and 5-HT1-receptor activation, respectively.

Animals↗
PubMed1983

Binding of 125I-cyanopindolol to beta-1-adrenoceptors in a high and low affinity state.

Investigation of binding properties of (+), (-) and (+/-) 125Iodocyanopindolol (ICYP) to beta 1-adrenoceptors of guinea pig left ventricle membranes revealed that these radioligands bind to receptors in a high and low affinity state which is not influenced by guanylnucleotides. The contribution of the (+)enantiomer to the binding of the racemic ligand at low receptor concentrations can be neglected since the dissociation time courses of (+/-) and (-) ICYP are identical. The existence of two affinity states of beta-adrenoceptors interacting with the antagonist ICYP was evident from 1: biphasic dissociation kinetics and 2: from curvilinear Scatchard plots.

Animals↗
PubMed1982

Non-specific uptake of the radioligand 125I-IHYP by intact human lymphocytes: reversal of the uptake process.

Binding of (+/-)[125I]iodohydroxybenzylpindolol (IHYP) to beta-adrenoceptors on intact human peripheral blood lymphocytes was found to be associated with a high degree of non-specific intracellular uptake of the radioligand. Non-specific binding on cellular surfaces was identified by displacing IHYP from its specific binding sites with the cold competing antagonist (+/-)-propranolol. Another methodological approach, however, was necessary to eliminate the uptake problem: release of intracellularly accumulated IHYP was achieved by sedimentation of the IHYP-loaded cells and resuspension in hypotonic buffer (HME buffer) for 10 min at +4 degrees C. The true value of maximal IHYP binding measured after IHYP release was 970 binding sites/cell as compared with 2300 receptors/cell found under standard binding conditions. This difference in maximal IHYP binding obtained by the 2 methods is attributed to the strong interference of the uptake process with the measurement of specific IHYP binding. Further evidence for the efficiency of the procedure to reverse the uptake process was obtained with the very slowly dissociable beta-adrenoceptor antagonist FM 24. Pre-incubation of the cells with 5 x 10(-5) M FM 24 totally prevented specific IHYP binding. Any IHYP measured on cells in the presence of FM 24, therefore, must have been due to mere non-specific binding and cellular uptake of the radioligand. Even though the uptake of IHYP was enhanced in FM-24-treated cells, this influx could be completely reversed by exposing the IHYP-loaded cells to HME buffer for 10 min at +4 degrees C. Our findings indicate that our experimental conditions are suitable for beta-receptor binding studies on intact cells with IHYP, because the uptake of the labeled ligand is eliminated.

Humans↗
PubMed1982

[125Iodo]BE 2254, a new radioligand for alpha 1-adrenoceptors.

[125Iodo]2-[beta-(14-hydroxyphenyl)-ethyl-aminomethyl]-tetralone([125Iodo]BE 2254 or IBE 2254), a new iodinated radioligand of high specific radioactivity (2175 Ci/mmol), was synthesized and used to characterize alpha 1-adrenoceptors in rat lung and cerebral cortex membranes. The binding constants of IBE 2254, using rat lung and cortex membranes, were Kd = 53 +/- 10 pM, Bmax = 53 +/- 8 fmol/mg; and Kd = 78 +/- 14 pM, Bmas = 210 +/- 26 fmol/mg, respectively (Kd = dissociation constant of IBE 2254 determined in saturation experiments). In equilibrium binding experiments with IBE 2254, at concentrations of the free ligand up to 1.2 nM, only one class of binding sites could be detected. In kinetic experiments, the association and dissociation rate constants were 2.3 X 10(9) M-1 min-1 and 0.10 min-1, respectively. In rat cerebral cortex membranes, alpha-adrenoceptor antagonists competed for IBE 2254 binding in the following order: prazosin greater than BE 2254 greater than WB 4101 greater than phentolamine greater than corynanthine greater than yohimbine greater than rauwolscine, indicating strongly that IBE 2254 binds to alpha 1-adrenoceptors. The calculated affinities of different alpha-adrenoceptor blocking agents from inhibition of IBE 2254 binding were nearly identical in rat lung and cerebral cortex. The low dissociation constant of the ligand together with its high specific radioactivity allows binding studies to be carried out with tissue samples where only small densities of alpha 1-adrenoceptors are present.

Adrenergic alpha-Antagonists↗