Angiotensin and drinking rates in the euryhaline killifish

Area of Science:

• Physiology
• Endocrinology
• Comparative Biology

Background:

• Osmoregulation is crucial for fish survival, especially in euryhaline species like Fundulus heteroclitus that tolerate varying salinity.
• The renin-angiotensin system (RAS) plays a key role in fluid and electrolyte balance in vertebrates.

Purpose of the Study:

• To investigate the role of angiotensin II in regulating drinking behavior in the euryhaline fish Fundulus heteroclitus.
• To determine if endogenous angiotensin II acts as a physiological stimulus for drinking in fish.

Main Methods:

• Drinking rates of Fundulus heteroclitus were measured under different conditions.
• Fish were exposed to angiotensin II, a competitive inhibitor of angiotensin II (P-113), and a converting enzyme inhibitor (SQ20881).
• Experiments were conducted on fish adapted to saltwater and freshwater, as well as those acutely exposed to saltwater.

Main Results:

• Angiotensin II significantly stimulated drinking in Fundulus heteroclitus adapted to both salt- and freshwater.
• The angiotensin II inhibitor P-113 markedly decreased drinking rates in saltwater-adapted and acutely saltwater-exposed fish.
• The converting enzyme inhibitor SQ20881 also effectively inhibited drinking behavior.

Conclusions:

• The findings support the hypothesis that endogenously produced angiotensin is a physiological stimulus for drinking in fish.
• Angiotensin II is implicated in the osmoregulatory control of drinking in euryhaline teleosts.
• Pharmacological inhibition of the renin-angiotensin system affects water intake in fish.