[Comparative cardiovascular effects of nifedipine in anesthetized dogs]

"In vitro" experiments in our laboratory, using coronary conductance arteries, showed that nifedipine produced selective relaxant action. The aim of the present experiments was to demonstrate if this selective vasodilating effect was also detected on coronary resistance vessels of the whole animal. The experiments were performed in anesthetized dogs. In one of the groups a dose-response curve to nifedipine was obtained. In the other group a single dose was infused to each dog. The doses used were: 0.5, 1, 5 and 10 micrograms x kg-1 x min-1. The following parameters were measured: systolic, diastolic (DAP) and mean arterial pressure (MAP); systolic, diastolic (DCF), and mean coronary blood flow; developed tension (DT), heart rate (HR) and cardiac output (CO). Diastolic coronary resistance (DCR) was calculated as the ratio of DAP and DCF. Systemic resistance (SR) was calculated as the ratio of MAP and CO. DAP, MAP, DT and HR remained unchanged with the lowest doses used (0.5 and 1 micrograms x kg-1 x min-1). DCF increased 28 +/- 7% (P less than 0.05) with 0.5 microgram x kg-1 x min-1 and 49 +/- 11% (P less than 0.05) with 1 microgram x kg-1 x min-1. CO increased 13 +/- 3% (P less than 0.05) and 20 +/- 6% (P less than 0.05) respectively. DCR decreased 31 +/- 4% (P less than 0.05) with 0.5 microgram x kg-1 x min-1 and 36 +/- 6% (P less than 0.05) with 1 microgram x kg-1 x min-1. SR decreased 19.5 +/- 5% (P less than 0.05) and 19 +/- 7% (P less than 0.05) respectively. With 5 micrograms x kg-1 x min-1 DAP, MAP and DT decreased 31 +/- 2% (P less than 0.05), 26 +/- 4% (P less than 0.05), and 15 +/- 4% (P less than 0.05) respectively. HR remained unchanged. DCF and CO increased 39 +/- 13% (P less than 0.05) and 35 +/- 11% (P less than 0.05) respectively. DCR and SR decreased 49 +/- 5% (P less than 0.05) and 43 +/- 5% (P less than 0.05) respectively. DAP, MAP and DT decreased 34 +/- 3% (P less than 0.05), 29 +/- 1% and 31 +/- 5% (P less than 0.05) respectively, with 10 micrograms x kg-1 x min-1. HR decreased 9 +/- 3% (P less than 0.05). DCF and CO remained unchanged. DCR and SR decreased 47 +/- 9% (P less than 0.05) and 36 +/- 6% (P less than 0.05) respectively.(ABSTRACT TRUNCATED AT 400 WORDS)