A chemical and pharmacological study on the role of catecholamines in the dispersion reaction of Xenopus laevis

Abstract

Chemical analyses have been made of dopamine in the skin of black backgroundapted Xenopus laevis treated with α-methyl-p-tyrosine (α-MPT), an inhibitor of tyrosine hydroxylase, and without such treatment.

Based on the assumption that dopamine is involved in the dispersion reaction induced by MSH, it was expected that the amount of dopamine in treated toads was less than in untreated ones. For several reasons, which will be discussed, the expectation was not realized.

When unphysiological high doses of α-MSH were administered several times during the experiment with α-MPT, the percentage of dopamine in these animals was far less than in control animals without any treatment. In this way a direct relation proved to be present between the dispersion reaction induced by MSH and catecholamines involved in this process.

In another way, by blocking the degradation rather than the synthesis of catecholamines, a similar relation was demonstrated. Inhibition of the enzyme catechol-O-methyl transferase in MSH-treated animals resulted in an extension of the dispersion period compared with toads receiving MSH only.