The effect of spironolactone on the cardiocirculatory responses to upright tilt at sea level and at simulated high altitude.

The objective of this study was to determine if spironolactone (S) alters the cardiocirculatory responses to upright tilt at sea level (SL;50 m) and during 44 h of simulated altitude (HA;4,600 m). In a double-blind, crossover-designed study, 9 male subjects (age range: 18-25 years) received 25 mg orally, four times per day of either S or an identically-appearing placebo (P) 2 d prior to and during HA. The crossover was separated by 2 weeks. Heart rate, stroke volume, cardiac output, calf blood flow, total peripheral resistance and systemic blood pressure were obtained during supine rest and after 10 min of 60 degrees head-up tilt using an impedance monitor and an electro-sphygmomanometer. The 24-h determinations of urinary volume, sodium and potassium as well as venous plasma values for sodium, potassium and chloride were obtained daily. There were no statistically significant differences between P and S treatment periods for: caloric, electrolytes or fluid ingestion; urinary volume or electrolytes; plasma electrolytes; or any of the cardiocirculatory parameters measured in the supine or upright position at SL or during HA. It was concluded that S did not induce a significant diuresis or significantly alter vascular responsiveness to negatively effect the normal cardiocirculatory responses to upright tilt at sea level or simulated high altitude.