You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Protein", "Chemical"].

Please return the output as a JSON object of the format: {"Chemical" : ["Dexamethasone", ...], "Protein" : ["BRCA-1", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

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.
{"Chemical": ["pargyline", "DAU 6285", "mianserin", "methiothepin", "1-m-chlorophenylpiperazine", "mesulergine", "m-CPP", "LY 53857", "8-hydroxy-2-(di-n-propylamino) tetralin", "5-CT", "5-carboxamidotryptamine", "tryptamine", "phentolamine", "5-MeO-T", "rauwolscine", "Ru 24969", "5-HT", "methysergide", "2-Me-5-HT", "sumatriptan", "renzapride", "yohimbine", "alpha-Me-5-HT", "GR 127935", "ritanserin", "MK 212", "granisetron", "ketanserin", "SB 200646", "monoamine", "pirenpirone", "8-OH-DPAT", "5-methoxytryptamine", "WY 26703", "5-hydroxytryptamine", "SCH 23390", "spiperone", "SB 204070", "ICI 170809"], "Protein": ["5-hydroxytryptamine (5-HT) receptors", "5-HT2A", "alpha-adrenoceptors", "5-HT2B", "monoamine oxidase", "5-hydroxytryptamine receptors", "5-HT2C", "5-HT receptors"]}