To investigate how the response to a bolus and an infusion of
furosemide is modulated by the rate of fluid replacement and by
hypoalbuminemia, rabbits received 5 mg/kg of
furosemide as a bolus or infused over 60 min, whereas diuresis was replaced with 13, 121, or 238 ml/h NaCl 0.9%/
glucose 5% (50:50). Natriuretic and
diuretic efficiencies were greater with the infusion than with the bolus of
furosemide. Fluid replacement increased natriuretic and
diuretic efficiency of
furosemide bolus but only
diuretic efficiency of
furosemide infusion.
Furosemide net fluid depletion reached a plateau when fluid replacement increased beyond 121 ml/h. Repeated
plasmapheresis decreased
plasma albumin by 30% (P <.05) and increased
furosemide unbound fraction (P <.05). Compared with control rabbits,
hypoalbuminemia decreased the natriuresis of the bolus (22.7 +/- 1.5-16.6 +/- 1.3 mmol, P <.05) but not that elicited by
furosemide infusion (26.2 +/- 1.8 mmol). Given as a bolus,
furosemide natriuretic and
diuretic response as a function of its urinary rate of excretion exhibited an hyperbolic relationship, and after its infusion a clockwise hysteresis, denoting tolerance. Plasma
renin activity was increased by the bolus and the infusion of
furosemide, even in the presence of 121 ml/h of fluid replacement. It is concluded that: 1) the increase in natriuretic/
diuretic efficiency of the bolus induced by fluid replacement is greater than when
furosemide is infused, 2)
furosemide net effect does not increase proportionally to fluid replacement, and 3) the infusion of
furosemide prevents the
hypoalbuminemia-induced decrease in response of
furosemide given as a bolus.