The role of circulating bradykinin in the regulation of cardiovascular homeostasis was studied in the normotensive conscious rat using a competitive antagonist of bradykinin at the receptor level. This antagonist (B4162) was administered intravenously as a bolus dose of 400 micrograms. This dose was shown to effectively block the hypotensive effect of exogenous bradykinin (2.5 micrograms) for at least 5 min. The bradykinin antagonist was administered at the end of an infusion of angiotensin II (1 ng/min, n = 5, or 12.5 ng/min, n = 6), of methoxamine (0.5 micrograms/min, n = 5, or 4 micrograms/min, n = 6), of lysine vasopressin (0.25 mUI/min, n = 11) or of saline (10 microliter/min, n = 7). The bradykinin antagonist did not change the mean arterial pressure of the control rats. The low doses of angiotensin II and of methoxamine did not have an effect on mean blood pressure. The bradykinin antagonist however increased mean blood pressure of these rats within 1 min by 10 +/- 2 (p less than 0.01, mean +/- SEM) and by 12 +/- 3 (p less than 0.01) mmHg, respectively. The large dose of angiotensin II raised mean blood pressure from 127 +/- 3.6 to 142 +/- 4.9 mmHg and that of methoxamine from 130 +/- 2 to 146 +/- 5 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)