Endogenous renin-angiotensin system and drinking behavior in flounder

Area of Science:

• Comparative physiology
• Osmoregulation
• Neuroendocrinology

Background:

• Euryhaline fish, like flounder, adapt to different salinities.
• Drinking behavior is crucial for maintaining osmotic balance in fish.
• The renin-angiotensin system (RAS) plays roles in blood pressure and fluid balance.

Purpose of the Study:

• To investigate the role of the renin-angiotensin system (RAS) in regulating drinking behavior in freshwater (FW)-adapted flounder.
• To compare drinking rates between seawater- and FW-adapted flounder.
• To determine if angiotensin II is dipsogenic and vasopressor in FW-adapted fish.

Main Methods:

• Measuring plasma chloride and osmotic concentrations in seawater- and FW-adapted flounder.
• Inducing hypotension in FW-adapted flounder using papaverine.
• Administering captopril (a converting enzyme inhibitor) and exogenous angiotensin II to FW-adapted flounder.
• Observing changes in drinking rates and blood pressure.

Main Results:

• Seawater-adapted flounder exhibited higher drinking rates than FW-adapted flounder, correlating with higher plasma chloride and osmotic concentrations.
• Papaverine-induced hypotension in FW-adapted flounder significantly increased drinking rates.
• This dipsogenic response was blocked by captopril, indicating RAS activation.
• Exogenous angiotensin II induced drinking and increased blood pressure in FW-adapted flounder.

Conclusions:

• The renin-angiotensin system (RAS) is activated during hypotension in freshwater-adapted flounder and plays a significant role in stimulating drinking behavior.
• Angiotensin II acts as a dipsogen and vasopressor in this species.
• These findings highlight the physiological importance of RAS activation in controlling drinking in euryhaline fish during osmotic challenges.