Abstract
20-Methylcholanthrene induced the encystment of Opalina ranarum when injected into its host, Rana ridibunda. Also, urine of frogs injected with this hydrocarbon induced encystment of the parasites. It is speculated that methylcholanthrene or its metabolites reach the parasites in the recta of the frogs and stimulate the parasites to encyst. Injections of frogs with methylcholanthrene and 13-cis-retinoic acid failed to induce cyst formation in the opalinids. Moreover, encystment of the parasite was lessened when the host was injected with methylcholanthrene and retinyl palmitate. Urine of frogs injected with methylcholanthrene and 13-cis-retinoic acid failed to induce cyst formation in the parasites. Moreover, urine of frogs injected with this hydrocarbon and retinyl palmitate lessened the induction of cyst formation in the parasites in vitro. It is suggested that 13-cis-retinoic acid as well as retinyl palmitate inhibits methylcholanthrene-induced cyst formation of the opalinids.
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