Abstract
Incubation of human serum or plasma at 37°C leads to the formation of a non-dialysable vasoactive factor, which we have called active pressor principle (APP). The intravenous injection of incubated human serum into anesthetized ganglionic blocked rats causes a transient blood pressure increase similar to the response to angiotensin II. The pressure activity of incubated serum or plasma depends on temperature and time of the incubation. At 37 °C the activity reaches a maximum within 6 days. A slight decrease occurs after further incubation. At 4 °C very little APP is formed within several weeks; at 25 °C a maximum is reached after about 14 days of incubation. Incubation at 47 °C yields a maximum activity after 48 hours; further incubation induces a marked decrease in APP-concentration. During incubation of serum at 37 °C after addition of angiotensin II or noradrenaline, these substances are rapidly inactivated, whereas the APP-formation proceeds uninfluenced. After separation by means of gel filtration with
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