Megalodiscus temperatus: absorption and incorporation of tritiated tyrosine, thymidine, and adenosine

Autoradiographic and liquid scintillation counting studies indicate adults of Megalodiscus temperatus can absorb large amounts of thymidine and adenosine, but use little of the thymidine in in vitro exposures of up to 72 hr. Labeling of worms exposed to ³H-adenosine in periods as short as 3 hr was achieved especially over young eggs, testes, and the ovary. Large amounts of tyrosine are found in the free amino acid pool of this worm but little is incorporated into tissues for exposure periods of up to 24 hr. Ligation experiments and autoradiograms of frozen-dried worms show thymidine and adenosine can enter via the tegument. Adenosine added to the exposure medium did not inhibit absorption of tyrosine but did markedly reduce the uptake of ³H-thymidine in 8-hr in vitro exposures. Bacteria adhering to the glycocalyx of M. temperatus were identified as Escherichia coli, but their role in uptake phenomena is unknown. The association of thymidine with the lymph vessels indicates a circulatory or excretory role for this system in M. temperatus. Adenosine was considered the best compound of the three to use for labeling cells for studies on the reproductive system.