Amphibian prolactins: activity in the eft skin transepithelial potential bioassay

Area of Science:

• Comparative endocrinology
• Amphibian physiology
• Integumentary system function

Background:

• Prolactin (PRL) is a key hormone regulating reproduction and osmoregulation in vertebrates.
• The specific role of PRL in amphibian skin physiology, particularly in salamanders, remains incompletely understood.
• Previous studies suggest PRL influences ion transport, but direct evidence in salamanders is limited.

Purpose of the Study:

• To investigate the effects of purified amphibian prolactins (frog PRL and newt PRL) on salamander skin.
• To compare the efficacy of amphibian PRLs with ovine prolactin (oPRL) and thyrotropin-releasing hormone (TRH).
• To determine if amphibian PRLs can modulate transepithelial potential (TEP) in eft skin, reflecting sodium transport.

Main Methods:

• Purified frog prolactin (fPRL) and newt prolactin (nPRL) were isolated.
• The effects of fPRL, nPRL, oPRL, and thyrotropin-releasing hormone (TRH) were tested using an eft (Notophthalmus viridescens) skin transepithelial potential (TEP) bioassay.
• Hormone doses ranged from 0.4 to 400 micrograms/animal.

Main Results:

• Both fPRL and nPRL significantly reduced eft skin TEP at doses as low as 0.4 micrograms/animal.
• Ovine prolactin (oPRL) demonstrated a similar TEP-reducing effect.
• Thyrotropin-releasing hormone (TRH) did not alter eft skin TEP even at high doses (400 micrograms/animal).

Conclusions:

• This study provides the first direct evidence that amphibian prolactins can physiologically control salamander skin sodium transport.
• Amphibian PRLs exhibit potent effects on integumental ion transport, comparable to mammalian/ovine PRL.
• These findings highlight the conserved role of prolactin in regulating skin function across vertebrate classes.