Interaction between phenylephrine and prostaglandins E1 and F1 alpha on the contractile responses of vascular muscle.

Prostaglandins (PGs) E1 or F1 alpha (1.4--8.4 x 10(-8) M) contracted strips of rabbit aorta and increased the contractions produced by 1--6 x 10(-7) M phenylephrine (PE). The addition of the PGs simultaneously with PE or after a low concentration of PE (2 x 10(-7) M) significantly increased the PE-induced contractions. However, when the PGs were added after a higher concentration of PE (6 x 10(-7) M) an additional increase in the PE-induced contraction was produced with PGF1 alpha but not with PGE1. Isobolic plots of the data obtained from the simultaneous addition of PE and the PGs indicate that both PGs interact with PE in a synergistic or potentiative manner, suggesting that their effects are mediated through different receptor mechanisms. Addition of the PGs after a high dose of PE indicates that there may also be either qualitative or quantitative differences between PGE1 and PGF1 alpha.