Influences of nifedipine on vascular conductance of portally drained viscera, liver and kidney.

Nifedipine is a potent vasodilator, which induces various dose-related hemodynamic responses in the gastrointestinal tract, liver and kidney. Blood flow was assessed in anesthetized dogs with non-cannulating electromagnetic flow sensors. Nifedipine was injected into a brachial vein at intervals of 2 min in graded doses from 1-16 micrograms.kg-1. The pulsatile flow and pressure signals were analog-digital converted and processed by a computer program to obtain mean flow (ml.min-1) and mean pressure (mm Hg) values for every 3 s. The vascular data are presented as conductance. The arterial pressure decreased 45% while vascular conductance in vessels of the stomach, duodenum, small and large bowel increased between 75 and 128%. No response was observed in the splenic and common hepatic artery. An increase of resistance in the hepatic artery proper, while portal flow increased suggests that there were changes in liver metabolism. Although the literature indicates a decrease in renal vascular resistance, we encountered a decrease in flow but no change in resistance. Neither did we find an increase in heart rate. We propose that small intravenous doses of nifedipine reduce the afterload of the left ventricle.