Effect of lithium chloride and theophylline on hexosaminidase activity in tadpole tail discs

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Tail fin discs from Rana catesbeiana were cultured for up to 5 days in the presence of triiodothyronine, cyclic AMP, theophylline, LiCl, or combinations of them, and metamorphic changes were measured by changes in the specific activity of hexosaminidase, a lysosomal marker enzyme. Triiodothyronine (154 n M) and cyclic AMP (100 μ M) induce comparable metamorphic changes. Triiodothyronine causes a 30% decrease in cyclic AMP in the first 5 hr, more than a 100% increase in the next day, and a gradual decrease during subsequent days. Theophylline, an inhibitor of phosphodiesterase, does not of itself induce normal metamorphic changes, but it potentiates the action of triiodothyronine. Lithium chloride, an inhibitor of adenylate cyclase, blocks all the hormone-stimulated increase in hexosaminidase activity only if presented in the first hour of hormone treatment. These results indicate that an early increase in the level of cyclic AMP may mediate triiodothyronine-induced metamorphic change and that triiodothyronine stimulates the adenylate cyclase system.