LOCALIZATION OF ANGIOTENSIN II RESPONSES IN THE TROUT CARDIOVASCULAR SYSTEM

Area of Science:

• Physiology
• Comparative Physiology
• Cardiovascular Research

Background:

• The renin-angiotensin system (RAS) regulates arterial blood pressure in many fish.
• In trout, the specific cardiovascular targets of angiotensin II (ANG II) remain unidentified.
• Previous studies indicate ANG II lacks direct constrictor effects on large trout arteries and veins.

Purpose of the Study:

• To investigate the cardiovascular pressor effectors of the RAS in rainbow trout (Oncorhynchus mykiss).
• To identify specific vascular beds and tissues responsive to angiotensin activation in trout.
• To elucidate the role of ANG II in trout cardiovascular regulation.

Main Methods:

• Utilized perfused organs and isolated tissues from rainbow trout.
• Examined dose-dependent responses to salmonid ANG II and ANG I in perfused gill, skeletal muscle-kidney (PDA), and splanchnic (PCM) circulations.
• Assessed the activity of angiotensin-converting enzyme (ACE) and the effects of adrenergic inhibitors.

Main Results:

• Salmonid ANG II induced dose-dependent vasoconstriction in perfused PCM, PDA, and gills.
• ANG II was more potent in the PCM compared to the PDA and gills.
• Angiotensin converting enzyme (ACE) efficiently converted ANG I to ANG II in the PDA but not the PCM.
• ANG II did not affect cardiac function, red blood cells, or non-vascular smooth muscles.

Conclusions:

• The systemic microcirculation is the primary site of angiotensin-mediated pressor responses in trout.
• The RAS in trout has minimal direct effects on the heart or non-vascular smooth muscle.
• The vascular microcirculation represents an early site of direct systemic RAS action from an evolutionary perspective.