I. Matot et Cf. Neely, PULMONARY VASODILATOR RESPONSES TO NICARDIPINE - COMPARISON WITH OTHER VASODILATORS, Critical care medicine, 23(11), 1995, pp. 1851-1857
Objectives: To determine the direct effect of nicardipine on the pulmo
nary vascular bed of the intact-chest, spontaneously breathing cat, an
d to compare its effectiveness as a pulmonary vasodilator with the eff
ectiveness of isoproterenol, nitroglycerin, and sodium nitroprusside.
Design: Prospective, controlled animal study. Each animal received all
drugs in random order. Setting: Animal laboratory at a university. Su
bjects: Experiments were performed in vivo in ten intact-chest, sponta
neously breathing cats with controlled pulmonary blood flow and consta
nt left atrial pressure, during conditions of increased pulmonary vasc
ular tone. Interventions: Five animals received intralobar injections
of nicardipine (0.1 to 100 mu g), nitroglycerin (0.1 to 10 mu g), sodi
um nitroprusside (0.1 to 100 mu g), and isoproterenol (0.01 to 1 mu g)
. Injections were made only when lobar arterial pressure had returned
to baseline value. In another five animals, nicardipine, nitroglycerin
, and sodium nitroprusside were administered intravenously as a contin
uous drug infusion in incremental doses titrated to produce a 20% redu
ction in mean systemic arterial pressure. Each dose was infused until
lobar and systemic arterial pressures stabilized. A minimum, 30-min in
terval was allowed between the infusions of these drugs. Measurements
and Main Results: When pulmonary vascular tone was increased with a th
romboxane A, mimetic (analog), U46619 (a stable prostaglandin endopero
xide analog), intralobar injections of nicardipine caused dose-related
decreases in lobar arterial pressure without affecting left atrial pr
essure. When compared with the other vasodilator agents, the order of
potency was isoproterenol much greater than nitroglycerin > nicardipin
e = sodium nitroprusside. Isoproterenol reduced mean systemic arterial
pressure 10 to 100 times greater than nitroglycerin, nicardipine, or
sodium nitroprusside. However, there were no significant differences b
etween the latter three drugs in producing a decrease in mean systemic
arterial pressure. When infused intravenously, nitroglycerin caused t
he largest amount of pulmonary vasodilation for a given amount of syst
emic vasodilation. There were no significant differences between the p
ulmonary vasodilator responses of nicardipine and sodium nitroprusside
. Conclusions: In this feline model of increased pulmonary vascular re
sistance, nicardipine exerts a direct vasodilator effect in vivo on th
e pulmonary vascular bed. Nicardipine, nitroglycerin, and sodium nitro
prusside caused similar decreases in systemic arterial pressure. Howev
er, the pulmonary vasodilator effect was greater with nitroglycerin, w
hich suggests that nitroglycerin is more vasoselective for the pulmona
ry vascular bed than nicardipine or sodium nitroprusside.