POSSIBLE ROLE OF THYROTROPIN-RELEASING-HORMONE IN THE SEASONAL ADAPTATION OF SALT TRANSPORT IN THE FROG

The effect of thyrotropin-releasing hormone (TRH) on the salt transport by amphibian skin in vitro was tested. Under short circuit conditions, TRH decreased the total conductance without altering the short circuit current (representing active sodium transport) in skins obtained from warm-adapted spring frogs (Rana esculenta). TRH had no effect on either parameter in skins obtained from warm-adapted winter frogs. The asymmetric fluxes of 36Cl- and 22Na+, measured under open circuit conditions, were decreased in skins obtained from warm-adapted spring frogs (Rana pipiens). These results are interpreted to mean that TRH is capable of altering salt transport possibly by decreasing the passive chloride flux resulting in a secondary decrease in the active transport of sodium. These TRH-induced changes in the salt transport of the epithelium of the frog skin are similar to those taking place in vivo at the onset of hibernation. Our findings suggest that in frogs TRH may be involved in the hormonal control of salt and/or water balance during hibernation and, therefore, serve an osmoregulatory function. © 1979.