Growth hormone is a weaker candidate than prolactin for the hormone responsible for the development of a larval-type feature in cultured bullfrog skin

SUMMARY Prolactin (PRL) has, for some years, been considered to be the `juvenile hormone9 in amphibians. Recently, growth hormone (GH) has been proposed as another candidate, because in the larval stages the expression of the mRNA GH is high but it is downregulated in the climax stages of metamorphosis or following treatment with thyroid hormone. In the present study, we investigated whether GH promotes the development of one particular larval-type feature of bullfrog tadpole skin in vitro . The amiloride-, acetylcholine- and ATP-stimulated short-circuit current (SCC) is a physiological marker of larval-type bullfrog skin. These types of ligand-stimulated SCC (1) developed when EDTA-treated tadpole skin was cultured with corticoids supplemented with PRL or GH and (2) were not significantly different between skin cultured with PRL and intact tadpole skin. However, the amiloride-induced SCC response in skin cultured with GH differed in its kinetics from that of the intact (control) tadpole. On this basis, PRL seems a better candidate than GH for the juvenile hormone, at least with regard to the development of amiloride-stimulated non-selective cation channels.