Amphibian prolactins: activity in the eft skin transepithelial potential bioassay.

The effects of purified prolactins isolated from frogs (fPRL; Rana catesbeiana) and newts (nPRL; Cynops pyrrhogaster) were compared with those of ovine prolactin (oPRL) and thyrotropin releasing hormone (TRH) in the eft (Notophthalmus viridescens) skin transepithelial potential (TEP) bioassay. At total doses as low as 0.4 micrograms/animal, both fPRL and nPRL were as effective as oPRL in reducing eft skin TEP. By contrast, TRH at total doses as high as 400 micrograms/animal was ineffective in altering eft skin TEP. These data provide the first direct evidence that amphibian PRLs can exert significant physiological control over salamandrid integumental sodium transport.