Given an abstract from a research paper, your task is to identify and label relationships between chemical compounds and genes mentioned in the abstract.

The relationship type must be one of ['DOWNREGULATOR', 'SUBSTRATE', 'INDIRECT-REGULATOR', 'PART-OF', 'MODULATOR-ACTIVATOR', 'REGULATOR', 'INHIBITOR', 'COFACTOR', 'UPREGULATOR', 'ACTIVATOR', 'ANTAGONIST', 'NOT', 'INDIRECT-DOWNREGULATOR', 'SUBSTRATE_PRODUCT-OF', 'INDIRECT-UPREGULATOR', 'AGONIST', 'PRODUCT-OF', 'MODULATOR', 'DIRECT-REGULATOR', 'UNDEFINED', 'AGONIST-INHIBITOR', 'AGONIST-ACTIVATOR', 'MODULATOR-INHIBITOR'].

Please format your output as a JSON array. Each entry in the array should express a single relation, formatted as ["<Entity_A>", "<RELATION_A_B>", "<Entity_B>"]. If no relations can be found, please output an empty JSON array [].

Abstract:

Further characterization of 5-hydroxytryptamine receptors (putative 5-HT2B) in rat stomach fundus longitudinal muscle. 1. The present study was undertaken to isolate and characterize pharmacologically homogeneous populations of 5-hydroxytryptamine (5-HT) receptors from a possible mixed receptor population mediating concentration of the longitudinal muscle of rat stomach fundus. Our aim was to extend the pharmacological characterization of the 5-HT2B receptor which is reported to be expressed in this preparation. 2. To minimize spontaneous activity and any influence of circular muscle on the contractile response, narrow (1-1.5 x 20 mm) segments of mucosa-denuded longitudinal muscle were used. Under these conditions, blockade of monoamine oxidase with pargyline (100 microM for 15 min) caused a leftward displacement of concentration-effect curves for both 5-methoxytryptamine (5-MeO-T) and tryptamine. Neither pargyline nor a number of uptake inhibitors affected responses to 5-HT. 3. In pargyline pretreated preparations, the order of potency of a number of tryptamine analogues was as follows: 5-MeO-T > or = alpha-Me-5-HT > or = 5-HT > 5-carboxamidotryptamine (5-CT) > tryptamine > 2-Me-5-HT. In addition several ligands known to act as agonists at either 5-HT2A or 5-HT2C receptors including 1-m-chlorophenylpiperazine (m-CPP), Ru 24969, MK 212 and SCH 23390 were also agonists in rat fundus whilst sumatriptan, renzapride and 8-hydroxy-2- (di-n-propylamino) tetralin (8-OH-DPAT) were very weak or inactive. With the exception of 2-Me-5-HT and m-CPP, most agonists produced monophasic concentration-effect curves consistent with an interaction at a single site. High concentrations of 2-Me-5-HT evoked relaxations which were blocked by phentolamine (1 MicroM) suggesting an interaction with alpha-adrenoceptors. m-CPP often evoked biphasic concentration-effect curves with a second contractile phase which was insensitive to yohimbine at concentrations higher than required for antagonism of responses to 5-HT.4. LY 53857, methiothepin, methysergide, ritanserin and ICI 170809 were potent but non-surmountable antagonists of 5-HT in rat fundus. In contrast, several ligands behaved as surmountable antagonists with the following order of potency: rauwolscine > yohimbine = mesulergine > mianserin = SB 204070 > WY 26703 > SB 200646 > pirenpirone > renzapride. DAU 6285, granisetron, spiperone, ketanserin, phentolamine and GR 127935 did not affect responses to 5-HT at concentrations up to 1 pM. The agonist and concentration independent profile of antagonism supported a single site interaction for both agonists and antagonists.5. We conclude that despite small differences concerning the enantiomeric selectivity and affinity of rauwolscine and yohimbine, the close pharmacological identity of 5-HT receptors in rat stomach fundus and the recently cloned 5-HT2B receptor is maintained. SB 200646, which demonstrates some selectivity for 5-HT receptors in rat stomach fundus, should provide a useful ligand for confirmation of this view and allow discrimination of 5-HT2B function both in vitro and in vivo.
[["MK 212", "AGONIST", "5-HT2A"], ["SCH 23390", "AGONIST", "5-HT2C"], ["m-CPP", "AGONIST", "5-HT2C"], ["SCH 23390", "AGONIST", "5-HT2A"], ["sumatriptan", "NOT", "5-HT2A"], ["Ru 24969", "AGONIST", "5-HT2A"], ["1-m-chlorophenylpiperazine", "AGONIST", "5-HT2C"], ["yohimbine", "REGULATOR", "5-HT2B"], ["m-CPP", "AGONIST", "5-HT2A"], ["8-hydroxy-2- (di-n-propylamino) tetralin", "NOT", "5-HT2C"], ["pargyline", "INHIBITOR", "monoamine oxidase"], ["SB 200646", "REGULATOR", "5-HT2B"], ["yohimbine", "REGULATOR", "5-HT receptors"], ["Ru 24969", "AGONIST", "5-HT2C"], ["rauwolscine", "REGULATOR", "5-HT receptors"], ["8-OH-DPAT", "NOT", "5-HT2A"], ["1-m-chlorophenylpiperazine", "AGONIST", "5-HT2A"], ["renzapride", "NOT", "5-HT2C"], ["rauwolscine", "REGULATOR", "5-HT2B"], ["8-hydroxy-2- (di-n-propylamino) tetralin", "NOT", "5-HT2A"], ["SB 200646", "REGULATOR", "5-HT receptors"], ["MK 212", "AGONIST", "5-HT2C"], ["renzapride", "NOT", "5-HT2A"]]