Bradykinin and cardiovascular system: estimation of half-life

¹ Department of Obstetrics and Gynecology, Western Reserve University School of Medicine, Cleveland, Ohio

Synthetic bradykinin in postpartal women produced a decrease in systolic and diastolic blood pressure, reduction of pulse pressure, and increased heart rate and respiration. The threshold dose for single intravenous injections was approximately 0.1 µg/kg, and that for intravenous infusions approximately 0.125 µg/kg/min. For the change in diastolic blood pressure, a linear dose-response curve was found in the semilogarithmic system in the range of 0.125– 1.25 µg/kg/min. In intravenous infusions, the maximal effect appeared, regardless of the dose, after 2–3 min. The time interval between starting the infusion and the onset of effect was distinctly dependent on the dose. These observations indicate exponential elimination or inactivation. Using a formula applicable to exponentially eliminated substances, a threshold level of 0.1 µg/kg and a half-life shorter than 0.5 min were estimated.

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