355 EFFECTS OF INTRAVENOUS DILTIAZEM ON HEMODYNAMICS AND REGIONAL BLOOD FLOWS IN THE NEWBORN PIGLET

Abstract

Calcium antagonists are a new class of drugs which may be useful during the neonatal period. Since their effects on regional blood flows (RBF) had not been studied, we assessed the effects of IV diltiazem (DTZ) on hemodynamics and RBF measured with radioactive microspheres in urethan- anesthetized piglets (age = 5.4 ± 0.6 d). Six piglets received DTZ (0.5 and 1 mg/kg, leading to plasma concentrations of 0.52 ± 0.03 and 1.14 ± 0.07 ug/ml respectively, as measured by high pressure liquid chromatography). Six other piglets received saline (control group). All the parameters studied were stable in the control group. With both doses, DTZ decreased mean arterial blood pressure (28 and 24%, p < 0.001) and heart rate (9 and 13%), p < 0.001). Cardiac index and systemic vascular resistance were not modified. DTZ markedly increased the coronary blood flow (54% and 55% after 0.5 and 1 mg/kg respectively, p < 0.01) with no change in the endocardium/epicardium ratio. Coronary resistance was decreased. To a lesser extent, DTZ (0.5 mg/kg) increased significantly (p < 0.05) the blood flow to the brain (27%), liver (7%), ileum (6%) and diaphragm (26%). In contrast, DTZ at a dose of 1 mg/kg induced a significant decrease in renal blood flow (37%, p < 0.05). We conclude that in the newborn piglet, blockade of the slow calcium channels by DTZ induces a coronary vasodilatation. The decrease in renal blood flow after high doses requires further investigation.