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Mansour TE, Mansour JM. 
“Phosphodiesterase in the Liver Fluke. Fasciola hevatica”. 
Biochem.Pharmacol.. 1977;26,(24):2325-30.
Effects of inhibitors on the phosphodiesterase (PDase) from Fasciola hepatica are investigated. Methods Whole liver flukes were homogenized in 6 volumes 0.33 M sucrose then centrifuged at 2000 x g for 20 min to give a supernatant (SN) and a pellet (PT). These were assayed for PDase by incubation at 37¡ in 25 mM Trie.HC1 (pH 7.5) conta”ning 25 mM imidazole (pH 7.5) and 1 to 500 mcM (8-4C)-cAMP (ICN) or (8-14C) -cGMP (ICN). Reactions were stopped after 10 min by addition of Crotalus axon venom (Sigma) (5 ng/ml) which converted AMP to adenosine and, after addition of carrier, adenosine was separated from cAMP by passage through an anion exchange column then measured by scintillation counting. Endogenous cAMP in liver fluke heads was measured using the Gilson binding method (Proc. Natl. Acad. Sci. USA, 67, 305, 1970) and liver fluke motility was measured as described by Abrahams et al. (Molec. Pharmacol., iZ, 49, 1976). Results PDase activity was present mainly-in the SN and to a lesser extent in the PT from fluke homogenates. Both SN and PT PDases showed Michaelis-Menten kinetics with Km for cAMP of 8 and 12mcM, respectively. Km for cGMP were about 300mcM. SN PDase activity was inhibited competitively by isobutylmethylxanthine (IBMX, Aldrich) (KI 55 mcM), SQ20009 (Squibb) (KI 26mM), D-lysergic acid diethylamide (LSD, Sandoz) (KI 790A1M) quazodine (Mead-Johns on) (KI 75mcM), papaverine (KI 00 JIM), the ophylline (KI 550 mcM), and caffeine (KI 800mcM), but not by 5-hydroxytryptamine (5HT, Sigma) or guanosine. Exposure of liver fluke heads to 1 mM 5HT substantially increased both fluke motility and the cAMP content of heads (from 13.7+7.7 to 432+120 pmole/mg protein). All the inhibitors of PDase except caffeine also increased fluke motility. The effect of 5HT on fluke head cAMP content was prevented by SQ20009 and papaverine at 1 mM and by LSD at 1 mcM, but was enhanced by 1 mM IBMX. None of the inhibitors significantly stimulated cAMP levels when applied alone.
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