Influence of stretch on α₁, receptor agonist phenylephrine regulated vasoconstriction in rabbit regional arteries

AIM: To investigate how to determine the optimal preloads in the study of α₁ receptor agonist phenylephrine (Phe) regulated vasoconstriction in the rabbit isolated arteries. METHODS: Vasoconstrictive responses to Phe were recorded in the rabbit renal, femoral, saphenous, mesenteric, splenic and ear arteries. RESULTS: The resting tension in various arterial rings was increased with increasing preload from 1.0 g to 5.0 g in a linear manner. The vasoconstrictive responses to KCl (120 mmol·L^-1) in the regional arteries were increased with increasing preload, however, the final plateau of the E_max of KCl was not observed in these regional arteries, with the exception of the ear artery. In the experiment with Phe (0.01 - 100 μmol·L^-1) as a vasoconstrictive agent, the EC₅₀ values of Phe (EC_50.Phe) in the rabbit mesenteric, splenic and saphenous arteries were changed largely by changing preload, however there was an optimal point where the EC_50.Phe value and its standard deviation were minimal among the five values corresponding to 1.0 g to 5.0 g preloads in each artery. CONCLUSION: The EC₅₀ values of Phe in the rabbit isolated arteries are influenced by preloads obviously. In the determination of optimal preload in isolated arterial preparations, particularly in the study of receptor regulated function, the minimal EC₅₀ value and its standard deviation of corresponding-receptor agonist should be considered as a crucial factor.