Involvement of β(3)-adrenergic receptors in in vivo cardiovascular regulation in rainbow trout (Oncorhynchus mykiss).

Currently, we have little information concerning the involvement of β(3)-adrenergic receptors (AR) in cardiovascular regulation in fishes. The goal of this study was to investigate the effect of β(3)-AR ligands on in vivo cardiovascular function in larval and adult rainbow trout (Oncorhynchus mykiss). In adult fish, injection of BRL(37344) (β(3)-AR agonist) resulted in an increase in heart rate (f(H)) (~31%) while stroke volume (Sv) was reduced (-25.9%). Injection of SR(59230A) (β(3)-AR antagonist) and propranolol (β(1)/β(2)-AR antagonist) resulted in increases in dorsal aorta blood pressure (P(DA)) with differing effect on cardiac variables (f(H) and Sv). To confirm specificity of the results, BRL(37344) was injected following sequential injections of phentolamine (α(1)-AR antagonist), atropine (muscarinic antagonist), propranolol and SR(59230A). While phentolamine had no effect on BRL(37344), atropine completely abolished the influence of BRL(37344) on f(H), Sv and cardiac output (Q). In larval trout, BRL(37344) (10 and 100 μM) induced a significant concentration-dependent increase in f(H) while SR(59230A) (1 and 10 μM) and propranolol (1 and 10 μM) separately caused a significant concentration-dependent decrease. These data suggest that β(3)-ARs have an important role in regulation of cardiovascular function, and provide evidence for a potential interaction between muscarinic and adrenergic receptors in rainbow trout.