The progressive pressor response to angiotensin in the rabbit.

1. The threshold for any detectable rise of systemic arterial pressure during the prolonged intravenous administration of angiotensin to conscious rabbits was observed to be an infusion rate of 0.003-0.006 mug.kg(-1).min(-1).2. At infusion rates between threshold and 0.04 mug.kg(-1).min(-1) the systemic arterial pressure rose progressively over a 3- to 7-day period to a plateau.3. On stopping the angiotensin infusion the blood pressure fell rapidly back to its base line much faster than it rose during the infusion. The time taken to reach control values was approximately related to the duration of the infusion.4. At infusion rates of about 0.05 mug.kg(-1).min(-1) the full rise of blood pressure developed within a few minutes, and could be sustained without change for many days. At higher rates the blood pressure diminished with time.5. Diurnal fluctuations of blood pressure were often seen during prolonged infusions of angiotensin at low rates; and more rapid fluctuations of blood pressure over an hour or two were frequently encountered immediately after an infusion was turned off.6. The possible role of angiotensin in producing chronic renal hypertension is discussed in the light of these observations.