Heterogeneity of [3H]-mepyramine binding sites in guinea pig cerebellum and lung

Abstract

The nature of histamine receptors in peripheral tissues is still controversial. However, evidence of heterogeneous classes of binding sites for [3H]-mepyramine are reported in the literature. The aim of our study was, therefore, to investigate the nature of this heterogeneity by comparing [3H]-mepyramine binding in a central tissue (cerebellum) and in a peripheral tissue (lung) obtained from guinea pigs and to assess its dependence upon the temperature of incubation. The results revealed that the [3H]-mepyramine interaction in both tissues is temperature-dependent. At 25 degrees C, the interaction between [3H]-mepyramine and the receptors was biphasic in the lung while only a single class of binding site was found in the cerebellum. At 0 degrees C, [3H]-mepyramine interacted with three binding sites in the lung and two in the cerebellum. The behaviour of the reference compounds (clemastine, promethazine and histamine) also supported this temperature-dependence. Moreover, two new compounds (DF 11062 and DF 11113), synthesized in our laboratories and endowed with antihistamine activity, can differentiate between the low affinity site seen at 25 degrees C in the lung and that seen in the cerebellum at 0 degrees C.

The Selective 5-HT1BReceptor Inverse Agonist 1‘-Methyl-5-[[2‘-methyl-4‘- (5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydro- spiro[furo[2,3-f]indole-3,4‘-piperidine] (SB-224289) Potently Blocks Terminal 5-HT Autoreceptor Function Both in Vitro and in Vivo

“…For dopamine D 2 and D 3 receptors the incubation buffer was 50 mM Tris (pH 7.7 at 25 °C), 120 mM NaCl, 5 mM KCl, 2 mM CaCl 2 , 1 mM MgCl 2 . Affinity for the 5-HT 4 receptor was evaluated in piglet hippocampus, by displacement of [ 125 I]SB-207710 according to the method of Brown et al Affinities for α-adrenergic, β-adrenergic, histamine H 1 and H 2 , and muscarinic M 1 and M 2 receptors were determined using literature procedures. − Briefly, the appropriate radioligand and a range of concentrations of test compound were incubated with the receptor preparation for between 30 and 45 min at 37 °C. At the end of the incubation period, samples were rapidly filtered and washed with ice-cold incubation buffer.…”

Tolterodine and its Active 5‐Hydroxymethyl Metabolite: Pure Muscarinic Receptor Antagonists

“…Binding to histamine H 1 and H 2 receptors was evaluated in the guinea pig cerebellum (versus [ 3 H]‐pyrilamine; Dini et al 1991) and in the guinea pig striatum (versus [ 125 I]‐APT; Ruat et al 1990). Tolterodine and 5‐HM (1 μM) had no affinity at H 2 receptors, since the inhibition of the specific radioligand binding amounted to <7% (no further experiments were therefore carried out).…”

Synthesis and Pharmacological Testing of 1,2,3,4,10,14b-Hexahydro-6-methoxy-2-methyldibenzo[c,f]pyrazino[1,2-a]azepin and Its Enantiomers in Comparison with the Two Antidepressants Mianserin and Mirtazapine

“…Affinities of compounds were determined using competition binding assays to determine IC 50 values at the various receptors: dopamine D2 receptors, displacement of 0.50 nM [3H]-spiperone at membranes from rat corpus striatum; h-dopamine D3 receptor, displacement of 0.30 nM [3H]-spiperone at human-cloned D3 receptors expressed in CHO-cells; h-dopamine D4.2 receptor, displacement of 0.06 nM [3H]-YM-09151-2 at human-cloned D4.2 receptors expressed in CHO-cells (method modified from NEN Life Science Products, Inc., technical data certificate PC2533-10/96); h-serotonin 5-HT1A receptor, displacement of 2 nM [3H]-5-CT at human-cloned 5-HT1A receptors expressed in HeLa cells . Additional parameters are as follows: serotonin 5-HT1D receptor, displacement of 2 nM [3H]-5-CT at membranes from bovine caudate tissue; serotonin 5-HT2A receptor, displacement of 0.50 nM [3H]-ketanserin at membranes from rat cortex tissue; serotonin 5-HT2C receptor, displacement of 0.50 nM [3H]-mesulergine from rat cloned 5-HT2C receptors expressed in NIH/3T3 cells (method available from H. Lundbeck A/S, Copenhagen); serotonin 5-HT3 receptor, displacement of [3H]-LY-278584 at membranes of rat brain tissue; α1-adrenoceptor, displacement of 0.25 nM [3H]-prazosin at membranes of rat brain tissue; α2-adrenoceptor, displacement of 0.50 nM [3H]-RX-821002 at membranes of rat brain tissue; histamine H1 receptor, displacement of 1.0 nM [3H]-pyrilamine at membranes of guinea pig lung tissue; histamine H2 receptor, displacement of 0.10 nM [3H]-APT at membranes of guinea pig striatum tissue . Inhibition of 5-HT and NA uptake into rat brain synaptasomes was described by K. P. Bøgesø .…”

“…The ability of 1 , 2 , 6 , and its enantiomers to displace the respective radioligands at the dopamine D2, D3, D4, serotonin 5-HT1A, 5-HT1D, 5-HT2A, 5-HT2C, 5-HT3, and α1- and α2-adrenergic, histamine H1 and H2 receptors, and the 5-HT and NA reuptake sites were determined. − The extracellular levels of NA, DOPAC, 5-HT, and 5-HIAA in the ventral hippocampus were measured by in vivo microdialysis after administration of 5 mg/kg sc of the racemate of 6-methoxymianserin or 2.5 mg/kg sc of either of the enantiomers. Levels were measured every 15 min for a period of 2.5 h after administration of the test compound.…”