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: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. 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:

Inhibitory action on rat uterine muscle contraction in vitro and acute toxicity in rats of the Thai traditional preparation Prasaplai. The activity of an aqueous extract of Prasaplai, a Thai traditional medicine, was studied on the isolated rat uterus in the oestrus stage. The results showed that the extract inhibited the contraction induced by a submaximal dose of acetylcholine (2.04×10(-4) mg mL(-1)), oxytocin (1.54×10(-4) mg mL(-1)) and prostaglandin E2 (PGE2) (6.00×10(-4) mg mL(-1)). The inhibition was concentration-dependent and reversible by tissue washing. The IC50 of Prasaplai extracts expressed as milligram of powdered preparation per millilitre of perfusion solution for acetylcholine, oxytocin and PGE2 were 11.70, 10.00 and 5.75 mg mL(-1), respectively. These data reveal that Prasaplai has an antispasmodic effect against uterine contraction by different mechanisms and corroborate the traditional use in the treatment of dysmenorrhoea. Oral administration of single dose of the water extract, calculated as powdered Prasaplai up to 20 g kg(-1) in rats, showed no sign and symptom of acute toxicity, and no rat died even at the maximum dose.
{"Chemical": ["PGE2", "acetylcholine", "oxytocin", "prostaglandin E2"]}