[Effect of nifedipine on perfusion pressure changes produced by alpha 1 adrenergic agonists and depolarizing solution...

The calcium channels blocker, nifedipine (NIF) inhibited in a partial non competitive manner the changes in perfusion pressure (delta P) caused by noradrenaline (NA) in the rat hindquarters, being the maximum inhibition of 31.0 +/- 8.3% (n = 5) for NIF 1.10(-5) M. The vasoconstrictor response of K+ 80 mM - phentolamine 3.10(-6)M was inhibited with lower concentrations of NIF than the one produced by phenylephrine (F) 1.10(-4)M. When the hindquarters were perfused with Krebs OCa-EGTA 2 mM NA developed contractile response. The administration of Ca 2.5 mM after the intracellular calcium store had been depleted, generated vasoconstriction in the presence of F 1.10(-4)M and K+ 80 mM - phentolamine 3.10(-6)M which were blocked in a 60.4 +/- 5.7 (n = 12) and 91.1 +/- 2.3% (n = 10) respectively by NIF 1.10(-5)M. The results suggest that the activation of the adrenergic receptor by NA in the perfused rat hindquarters, probably releases calcium from intracellular stores and promotes calcium influx through pathway scarcely sensitive to NIF. Both mechanisms would be responsible for the partial blockade found in our results.