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The PDE6 preparation is bovine retina rather than human.\nexposure: Sildenafil against PDE1 to PDE5 prepared from human tissues and PDE6 from bovine retina, with zaprinast as comparator\nevidence_span: {\"source_cache\": \"artifacts/sildenafil-research/9598563.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"860e09237bbae4ec5bb65a640186902908ccb9c6ec502b504a1ecddbb33810a2\", \"start_char\": 0, \"end_char\": 1755, \"text_sha256\": \"860e09237bbae4ec5bb65a640186902908ccb9c6ec502b504a1ecddbb33810a2\"}\n[sil-p9598563] Effects of sildenafil on the relaxation of human corpus cavernosum tissue in vitro and on the activities of cyclic nucleotide phosphodiesterase isozymes. 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